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Visual observations of social behavior and dominance relationships in cattle have been used to examine associations with productivity and well-being. This method is time consuming limiting the number of animals that can be evaluated. The objective of this study was to validate an algorithm to quantify feedbunk replacement events using data from an electronic feeding system. Crossbred beef steers (n = 20) fed a grower diet were housed in 1 of 2 pens each equipped with 3 electronic feedbunks (GrowSafe Systems) and video recorders. A trained video observer recorded all feedbunk replacement events and other agonistic activities at the feedbunk over a 4-d period (24 h/d). The electronic feeding system recorded the start and end timestamps of bunk visit (BV) events for each animal. An algorithm was developed to determine BV events deemed to be replacement events, defined as a BV event when an actor animal displaced a reactor animal from the feedbunk and occupied the same feeder within a specified period of time (replacement criterion). We calculated the recall and precision corresponding to replacement criterions from 1 to 60 s, and the optimum replacement criterion was determined to be between 18 and 20 s. The recall, precision and F-score of the algorithm using this replacement criterion were high (on average > 0.75). Furthermore, a replacement competition index was computed as a proxy for competitive feedbunk behavior, calculated as the number of actor-initiated replacement events divided by the total number of replacement events for each steer. Using Spearmans rank correlation we found high correlations (r > 0.7; P < 0.05) between the electronic and observed indices. These preliminary results demonstrate the potential of the GrowSafe system to quantify feedbunk replacement events for confined beef cattle, providing opportunities to evaluate associations between competitive feedbunk behavior and economically relevant traits.

This study examined the effects of multivalent respiratory vaccine treatment (VT) and animal temperament classification on feeding behavior traits, feed intake and animal performance in response to a bovine viral diarrhea virus (BVDV) challenge. Nellore–Angus crossbred steers (n = 360, initial body weight (BW) 330 ± 48 kg) were assigned to one of three vaccine treatments: non-vaccinated (NON), modified live (MLV) and killed (KV) regarding respiratory viral pathogens, and inoculated intranasally with the same BVDV1b strain. Cattle temperament categories were based on exit velocity. Overt clinical signs of respiratory disease were not observed, yet the frequency and duration of bunk visit events as well as traditional performance traits decreased (p &lt, 0.01) following BVDV challenge and then rebounded in compensatory fashion. The reduction in dry matter intake (DMI) was less (p &lt, 0.05) for MLV-vaccinated steers, and MLV-vaccinated steers had longer (p &lt, 0.01) durations of bunk visit and meal events and slower (p &lt, 0.01) eating rates compared with KV- and non-vaccinated steers following BVDV challenge. Greater differences in most feeding behavior traits due to VT existed within calm vs. excitable steers. Respiratory vaccination can reduce the sub-clinical feeding behavior and performance effects of BVDV in cattle, and the same impacts may not occur across all temperament categories.

The objectives of this study were to examine the relationship between residual feed intake (RFI) and DM and nutrient digestibility, in vitro methane production, and volatile fatty acid (VFA) concentrations in growing beef cattle. Residual feed intake was measured in growing Santa Gertrudis steers (Study 1; n = 57; initial BW = 291.1 ± 33.8 kg) and Brangus heifers (Study 2; n = 468; initial BW = 271.4 ± 26.1 kg) fed a high-roughage-based diet (ME = 2.1 Mcal/kg DM) for 70 d in a Calan-gate feeding barn. Animals were ranked by RFI based on performance and feed intake measured from day 0 to 70 (Study 1) or day 56 (Study 2) of the trial, and 20 animals with the lowest and highest RFI were identified for subsequent collections of fecal and feed refusal samples for DM and nutrient digestibility analysis. In Study 2, rumen fluid and feces were collected for in vitro methane-producing activity (MPA) and VFA analysis in trials 2, 3, and 4. Residual feed intake classification did not affect BW or BW gain (P > 0.05), but low-RFI steers and heifers both consumed 19% less (P < 0.01) DMI compared with high-RFI animals. Steers with low RFI tended (P < 0.1) to have higher DM digestibility (DMD) compared with high-RFI steers (70.3 vs. 66.5 ± 1.6% DM). Heifers with low RFI had 4% higher DMD (76.3 vs. 73.3 ± 1.0% DM) and 4 to 5% higher (P < 0.01) CP, NDF, and ADF digestibility compared with heifers with high RFI. Low-RFI heifers emitted 14% less (P < 0.01) methane (% GE intake; GEI) calculated according to Blaxter and Clapperton (1965) as modified by Wilkerson et al. (1995), and tended (P = 0.09) to have a higher rumen acetate:propionate ratio than heifers with high RFI (GEI = 5.58 vs. 6.51 ± 0.08%; A:P ratio = 5.02 vs. 4.82 ± 0.14%). Stepwise regression analysis revealed that apparent nutrient digestibilities (DMD and NDF digestibility) for Study 1 and Study 2 accounted for an additional 8 and 6%, respectively, of the variation in intake unaccounted for by ADG and mid-test BW0.75. When DMD, NDF digestibility, and total ruminal VFA were added to the base model for Study 2, trials 2, 3, and 4, the R2 increased from 0.33 to 0.47, explaining an additional 15% of the variation in DMI unrelated to growth and body size. On the basis of the results of these studies, differences in observed phenotypic RFI in growing beef animals may be a result of inter-animal variation in apparent nutrient digestibility and ruminal VFA concentrations.

Objectives were to evaluate the effects of temperament at feedlot arrival and breed type on productivity, feed efficiency, feeding behavior, and carcass quality traits in finishing beef heifers, and to examine interactions between temperament and breed type. Heifers (Angus, Braford, Brangus, and Simbrah, N = 411, BW = 280 kg) were fed a high-grain diet (ME = 3.0 Mcal/kg DM) in pens equipped with electronic feed bunks. Quality grade (QG), yield grade (YG), and Warner-Bratzler shear (WBS) force values (day 1 and 14 postmortem) were evaluated. Relative exit velocity (REV) at feedlot arrival was used as a covariate in mixed models to assess the effects of temperament and interactions with breed type, with means compared at ±1 SD from the mean initial REV. Calm heifers (mean REV minus 1 SD) had 4% greater (P < 0.001) initial BW, 12% greater (P < 0.001) ADG, 8% greater (P < 0.001) DMI, and 4% greater (P < 0.02) G:F than heifers with excitable temperaments (mean REV plus 1 SD). A temperament × breed interaction was detected (P < 0.01) for residual feed intake (RFI). Braford heifers had a more (P < 0.05) negative REV covariate slope (−1.49 ± 0.65) than the other breeds, such that excitable Braford heifers had lower (P < 0.05) RFI than the other breeds with excitable temperaments. Temperament × breed interactions were observed (P < 0.001) for DMI per BW(0.75) and bunk visit (BV) duration. Braford heifers had more (P < 0.05) negative REV covariate slopes for both traits than Angus, Brangus, and Simbrah heifers such that excitable Braford heifers consumed less (P < 0.05) DMI per BW(0.75) and had less BV duration compared to excitable Angus and Brangus heifers. Calm heifers had 9% greater (P < 0.01) meal duration, and consumed meals that were 22% longer (P < 0.001) and 17% larger (P < 0.001) compared to excitable heifers. Calm heifers had 12% more (P < 0.001) BV events per meal then excitable heifers. Carcasses from calm heifers were 4% heavier (P < 0.05) and had 7% greater (P = 0.05) backfat (BF) depth and tended to have 4% greater (P = 0.07) USDA YG than carcasses from excitable heifers. Additionally, loin steaks from calm heifers had 8% lower (P < 0.05) WBS force than steaks from excitable heifers. Based on a carcass grid with discounts and premiums for HCW, QG, YG, and tenderness, calm heifers returned $62 more (P < 0.01) revenue per animal than excitable heifers. These results demonstrate that heifers with divergent phenotypes for temperament on feedlot arrival differ in their performance, feed efficiency, and feeding behavior patterns, as well as carcass quality and revenue.

Objectives were to determine whether live yeast (LY) supplementation would affect daily dry matter feed intake, body weight (BW), immune, and febrile responses to a viral-bacterial (VB) respiratory challenge. Crossbred heifers (N = 38, BW = 230 ± 16.4 kg) were allocated into a 2 × 2 factorial treatment arrangement: Factor 1 = roughage-based diet with or without LY (Saccharomyces cerevisiae boulardii CNCM I-1079, 62.5 g/hd/d), Factor 2 = VB, intranasal administration of bovine herpesvirus-1 (BHV-1, 2 ×10(8), PFU) on day 0 and endobronchial inoculation with Mannheimia haemolytica (5.4 × 10(10), CFU) on day 3, or intranasal saline administration followed by inoculation with phosphate buffer solution (PBS). Heifers were fed their respective diets for 27 d prior to VB challenge on day 0. Heifers were housed by treatment and group-fed using electronic feedbunks. Thermo-boluses (Medria; Châteaubourg, FR) measured rumen temperature (RUT) at 5-min intervals and rectal temperature and whole blood samples were collected on days 0, 3 to 8, 10, 13, and 15. Data were analyzed using repeated measures in the mixed procedure of SAS with fixed effects of day, diet, inoculation, and their interactions. Animals fed LY exhibited a 16% increase (P = 0.02) in neutrophils relative to CON. Diet × inoculation × day interactions were detected for monocytes and haptoglobin. The VB-LY had the greatest (P < 0.05) concentration of monocytes on day 4, followed by VB-CON which was greater (P < 0.05) than PBS treatments. Haptoglobin concentration was greatest (P < 0.02) for VB-CON on day 5, followed by VB-LY which was greater (P < 0.05) than PBS. Heifers supplemented with LY had less (P < 0.05) haptoglobin production than CON. The VB challenge produced nasal lesions that increased (P < 0.01) with day, reaching a zenith on day 6 with 70% of the nares covered with plaques, and increased (P < 0.05) neutrophils on days 3 to 5. The VB challenge increased RUT (P < 0.05) days 2 to 7 and rectal temperature (P < 0.05) on days 0 and 3 to 6. The increased rectal temperature on day 0 was likely due to increased ambient temperature at time of challenge, as VB heifers were processed after the PBS heifers to avoid contamination. The VB challenge was effective at stimulating immune responses, and RUT was effective for measuring febrile responses. These results indicate that prior LY supplementation altered the leukogram in response to VB challenge, suggestive of increased innate immune response.

The objectives of this study were to evaluate the effectiveness and accuracy of monitoring feeding behavior patterns using cumulative summation (CUSUM) procedures to predict the onset of bovine respiratory disease (BRD) in beef cattle. Growing bulls (N = 231) on a 70-d growth and efficiency trial were used in this study. Between days 28 and 38 of the study, 30 bulls were treated for BRD based on observed clinical signs and elevated rectal temperature (>39.5 °C); remaining bulls (n = 201) were considered healthy. Clinically-ill and healthy bulls were used to evaluate sensitivity and specificity of CUSUM models, with accuracy calculated as the average of sensitivity and specificity. All data were standardized prior to generating CUSUM charts in a daily accumulative manner. Eight univariate CUSUM models were evaluated including DMI, bunk visit (BV) frequency, BV duration, head down (HD) duration, eating rate, maximal nonfeeding interval (NFI Max), SD of nonfeeding interval (NFI SD), and time to bunk (TTB). Accuracies for detection of BRD were 80.1, 69.4, 72.4, 79.1, 63.7, 64.6, 73.2, and 48.7%, respectively, and average day of detection prior to observed symptoms of BRD were 1.0, 3.2, 3.2, 4.8, 10.2, 2.7, 1.5, and 0.6 d, respectively. Principal component analysis (PCA) of all 8 univariate traits (full model) was used to construct multivariate factors that were similarly monitored with CUSUM. Two reduced multivariate models were also constructed that included the 3 best performing feeding behavior traits (BV duration, HD duration, NFI SD) with (RBD) and without DMI (RB). Accuracy of the full multivariate model was similar to the best of the univariate models (75.0%). However, both of the reduced multivariate models (RB and RBD) were more accurate (84.0%) than the full multivariate model. All 3 of the multivariate models signaled (P < 0.05) 2.0 to 2.1 d prior to clinical observation. These results demonstrate that the use of PCA-derived multivariate factors in CUSUM charts was more accurate compared with univariate CUSUM charts, for pre-clinical detection of BRD. Furthermore, adding DMI to the RB model did not further improve accuracy or signal day of BRD detection. The use of PCA-based multivariate models to monitor feeding behavior traits should be more robust than relying on univariate trait models for preclinical detection of BRD. Results from this study demonstrate the value of using CUSUM procedures to monitor feeding behavior patterns to more accurately detect BRD prior to clinical symptoms in feedlot cattle.

The objective of this experiment was to determine if statistical process control (SPC) procedures coupled with remote continuous data collection could accurately differentiate between animals experimentally inoculated with a viral–bacterial (VB) challenge or phosphate buffer solution (PBS). Crossbred heifers (N = 38; BW = 230 ± 16.4 kg) were randomly assigned to treatments by initial weight, average daily gain (ADG), bovine herpes virus 1, and Mannheimia haemolytica serum titers. Feeding behavior, dry matter intake (DMI), animal activity, and rumen temperature were continuously monitored remotely prior to and following VB challenge. VB-challenged heifers exhibited decreased (P < 0.01) ADG and DMI, as well as increased (P < 0.01) neutrophils and rumen temperature consistent with a bovine respiratory disease (BRD) infection. However, none of the heifers displayed overt clinical signs of disease. Shewhart and cumulative summation (CUSUM) charts were evaluated, with sensitivity and specificity computed on the VB-challenged heifers (n = 19) and PBS-challenged heifers (n = 19), respectively, and the accuracy was determined as the average of sensitivity and specificity. To address the diurnal nature of rumen temperature responses, summary statistics (mean, minimum, and maximum) were computed for daily quartiles (6-h intervals), and these quartile temperature models were evaluated separately. In the Shewhart analysis, DMI was the most accurate (95%) at deciphering between PBS- and VB-challenged heifers, followed by rumen temperature (94%) collected in the 2nd and 3rd quartiles. Rest was most the accurate accelerometer-based traits (89%), and meal duration (87%) and bunk visit (BV) frequency (82%) were the most accurate feeding behavior traits. Rumen temperature collected in the 3rd quartile signaled the earliest (2.5 d) of all the variables monitored with the Shewhart, followed by BV frequency (2.8 d), meal duration (2.8 d), DMI (3.0 d), and rest (4.0 d). Rumen temperature and DMI remained the most accurate variables in the CUSUM at 80% and 79%, respectively. Meal duration (58%), BV frequency (71%), and rest (74%) were less accurate when monitored with the CUSUM analysis. Furthermore, signal day was greater for DMI, rumen temperature, and meal duration (4.4, 5.0, and 3.7 d, respectively) in the CUSUM compared to Shewhart analysis. These results indicate that Shewhart and CUSUM charts can effectively identify deviations in feeding behavior, activity, and rumen temperature patterns for the purpose of detecting sub-clinical BRD in beef cattle.

Objectives of this study were to evaluate the effects of DFM with and without Monensin plus Tylan on feed efficiency and feeding behavior patterns in steers. Crossbred steers (n = 125; BW = 303 kg) were randomly assigned to 1 of 4 treatments in a 2 x 2 factorial design: (1) control (no feed additives), (2) DFM only (25 g/d; Natur’s Way), (3) Monensin (40 g/ton) plus Tylan only (MON) and (4) DFM and MON. In pens with GrowSafe feedbunks, steers were fed the grower diet for 14 d and transitioned to a finisher diet on 16 d. During the grower/transition phase, MON-fed steers had 9.5% higher (P < 0.05) ADG and improved F:G (7.8 vs 8.94; P = 0.06) and RFI (-0.28 vs 0.27 kg/d; P < 0.01) vs CON-fed steers. DFM-fed steers had lower (P < 0.01) ADG, but similar F:G and RFI than CON-fed steers. Daily variances of bunk-visit event frequencies were reduced (P < 0.01) in MON- vs CON-fed steers. During the finisher period, MON x DFM interactions (P < 0.10) were observed for ADG and F:G. MON-fed steers had numerically improved F:G (5%) when DFM was excluded, but not when DFM was included. MON-fed steers had lower RFI (P < 0.01; -0.23 vs 0.23 kg/d), whereas DFM-fed steers had higher RFI (P < 0.01) compared to respective controls. MON-fed steers ate less (P < 0.01) DMI, spent 9% more (P < 0.05) time consuming meals and had 14% slower (P < 0.01) meal eating rate then CON-fed steers. The DFM did not positively affect feed efficiency. Although the magnitude of improvement in feed efficiency due to MON was small, results demonstrated that MON may minimize digestive upsets by reducing daily variation in feeding behavior during diet transition and slow meal-eating rate on high-grain diets.

Animal variation in social dominance within a herd has been shown to be associated with performance, feed efficiency and animal well-being. The objective of this study was to quantify disruptive feeding events in cattle fed a high-grain diet. Crossbred steers (n = 85) housed in a pen with GrowSafe bunks were used in this study. An algorithm was developed to quantify displacement events defined as an animal being displaced by another within 5 sec. These feed bunk displacement events were further separated into either displacer events or displacee events. A displacer event was defined as an animal displacing another (aggressive). A displacee event was defined as an animal being displaced (submissive). The displacer events as a proportion of total displacement events were used to classify animals as aggressive versus submissive (±0.5 SD). Animals with fewer displacer events as a proportion of total displacement events (submissive < 0.5 SD) had greater (P < 0.05) frequency and duration of bunk visit events and head down duration than the animals who initiated more displacer events as a total of displacement events (aggressive > 0.5 SD). Additionally, submissive animals also had a slower (P < 0.05) bunk visit eating rate than aggressive animals. The results of this initial analysis found that due to the associations between feed bunk displacements and feeding behavior, there may be potential to correlate this trait with temperament and performance traits as well as be a potential indicator of feed efficiency in confined cattle.

Immunologic, physiologic, and behavioral responses to a combined viral-bacterial respiratory challenge were explored in beef steers (initial BW 293 kg). Steers (n = 24) were inoculated intranasally with bovine herpes virus-1 (2×108 PFU) and intratracheally with Mannheimia haemolytica (MH, 2.15×1010 CFU) on days -3 and 0, respectively, (n = 16; VB), or similarly inoculated with phosphate-buffered saline (n = 8; PBS). Venous and arterial blood were collected on -3, -1, 0, 2, 3, 5, 7, 10, and 14 relative to MH challenge for CBC, haptoglobin, and arterial blood oxygen saturation analysis. Continuously recorded variables included rumen temperature, activity, rumination, DMI, and feeding behavior. Data were analyzed with a repeated-measures mixed model (SAS 9.4) with fixed effects of day, inoculation, and the interaction. Bunk visit frequency and DMI were reduced (P < 0.01) in VB steers throughout the 14 d post-MH period compared to PBS steers. Rumination (days 1, 7) and activity (days 1, 2, 4–8, and 11–13) were reduced (P < 0.03) in VB steers vs PBS steers. Rumen temperature was elevated (P < 0.04) in VB steers until day 6 post MH inoculation. Neutrophil concentrations (days 2 and 3), platelets (days 7–14), fibrinogen (days 2–10), and haptoglobin (days 2–7) were elevated (P < 0.05) in VB vs PBS steers. Hematocrit was depressed (P < 0.05) in VB steers on days 3–10. The VB steers had decreased (P < 0.05) arterial SO2% and pO2 than PBS steers; however, the inoculation × day interaction was not significant. Results indicate that the experimental VB challenge substantially altered rumen temperature, DMI, feeding behavior, rumination and immunological response as expected. Arterial sO2% and pO2 concentrations were reduced minimally by VB challenge, indicating challenges in using blood gas to detect BRD in beef cattle.

A retrospective analysis of data from a previous study (Kayser et al., J. Anim. Sci. 97:596; 2019) revealed that steers challenged with Mannheimia haemolytica (MH) had divergent serum haptoglobin (HPT) despite having similar leukocyte and temperature responses. In that study, 36 steers (BW 352 ± 23 kg) were fitted with rumen boluses and were fed from electronic bunks to measure DMI and feeding behavior prior to inoculation with saline or MH. Whole blood was collected on days -4, 0, 1, 2, 3, 5, 7, 10 and 14 relative to MH inoculation. The MH steers were retrospectively classified as HPT responsive (RES; n = 9; mean AUC = 62.6 mg/dL/d) or HPT non-responsive (NON; n = 9; mean AUC = 4.5 mg/dL/d). The current objective was to determine if the HPT responsive phenotype altered other immunologic, physiologic, or behavioral responses, compared with saline controls (CON; n = 18). The magnitude of increase in neutrophils (P< 0.01) and total leukocytes (P< 0.05) was greater in RES than NON or CON on d1. All MH-challenged steers experienced a transient febrile response, but temperature was greater (P< 0.01) in RES on days 0 and 4 compared to NON and CON. Intake was depressed in all three groups d0, but magnitude of depression in RES was greater (P< 0.01) than NON or CON, and remained lower (P < 0.01) d 1, 2, 3, 6, and 8. Bunk-visit duration was decreased (P < 0.01) in all MH-challenged steers on day 0, but RES were greater (P < 0.02) than NON and CON d 11 and 12. Correspondingly, bunk-visit eating rate of RES was decreased (P < 0.01) from day 2 - 14. Had this not been a sub-clinical challenge model, the greater reduction in intake and increased leukocyte recruitment may have resulted in performance differences between RES and NON steers. These results suggest that differences in HPT responsiveness may be associated with differences in innate immunocompetence.

Indicator traits associated with disease resiliency would be useful to improve the health and welfare of feedlot cattle. A post hoc analysis of data collected previously (Kayser et al., 2019a) was conducted to investigate differences in immunologic, physiologic, and behavioral responses of steers (N = 36, initial BW = 386 ± 24 kg) that had differential haptoglobin (HPT) responses to an experimentally induced challenge with Mannheimia haemolytica (MH). Rumen temperature, DMI, and feeding behavior data were collected continuously, and serial blood samples were collected following the MH challenge. Retrospectively, it was determined that 9 of the 18 MH-challenged steers mounted a minimal HPT response, despite having similar leukocyte and temperature responses to other MH-challenged steers with a greater HPT response. Our objective was to examine differences in behavioral and physiological responses between MH-challenged HPT responsive (RES; n = 9), MH-challenged HPT nonresponsive (NON; n = 9), and phosphate-buffered saline-inoculated controls (CON; n = 18). Additionally, 1H NMR analysis was conducted to determine whether the HPT-responsive phenotype affected serum metabolite profiles. The RES steers had lesser (P < 0.05) cortisol concentrations than NON and CON steers. The magnitude of the increases in neutrophil concentrations and rumen temperature, and the reduction in DMI following the MH challenge were greatest (P < 0.05) in RES steers. Univariate analysis of serum metabolites indicated differences between RES, NON, and CON steers following the MH challenge; however, multivariate analysis revealed no difference between HPT-responsive phenotypes. Prior to the MH challenge, RES steers had longer (P < 0.05) head down and bunk visit durations, slower eating rates (P < 0.01) and greater (P < 0.05) daily variances in bunk visit frequency and head down duration compared with NON steers, suggesting that feeding behavior patterns were associated with the HPT-responsive phenotype. During the 28-d postchallenge period, RES steers had decreased (P < 0.05) final BW, tended (P = 0.06) to have lesser DMI, and had greater (P < 0.05) daily variances in head down and bunk visit durations compared with NON steers, which may have been attributed to their greater acute-phase protein response to the MH challenge. These results indicate that the HPT-responsive phenotype affected feeding behavior patterns and may be associated with disease resiliency in beef cattle.

The objective of this study was to examine the differences in feeding behavior patterns of steers with divergent phenotypes for residual feed intake (RFI). Three trials were conducted with 508 Angus-based composite crossbred steers (body weight [BW] = 309 ± 57 kg) fed a high-concentrate diet in pens equipped with electronic feed bunks (GrowSafe System). Initial and final carcass ultrasound measurements (intra-muscular fat, backfat depth, and rib-eye area) were collected on days 0 and 70, and BW measured at 14-d intervals. Individual dry matter intake (DMI) and feeding behavior traits were collected for 70 d, and RFI calculated as the residual from the regression of DMI on average daily gain (ADG) and mid-test BW0.75. Steers were ranked by RFI and assigned to low-, medium-, and high-RFI classes based on ± 0.5 SD from the mean RFI within the trial. The feeding behavior traits evaluated in this study included frequency and duration of bunk visit (BV) and meal events, head-down (HD) duration, mean meal length, time-to-bunk interval, the maximum nonfeeding interval, and the day-to-day variation of these traits, defined as the root mean squared error (RMSE) from linear regression of each trait on the day of trial. Additionally, three ratio traits were evaluated: BV events per meal, HD duration per BV event, and HD duration per meal event. Low-RFI (feed-efficient) steers consumed 16% less (P < 0.01) DMI, while BW and ADG were not different compared with high-RFI steers. Low-RFI steers had 18% fewer and 21% shorter (P < 0.01) BV events, and 11% fewer and 13% shorter (P < 0.01) meal events per day compared with high-RFI steers. Furthermore, low-RFI steers exhibited less (P < 0.05) day-to-day variance in DMI, as well as in frequency and duration of BV and meal events and HD duration compared with high-RFI steers. Differences in feeding behavior traits due to RFI were minimally affected by covariate adjustment for DMI, indicating that steers with divergent RFI have distinct feeding behavior patterns that are largely independent of differences in DMI. These results suggest that feeding behavior traits may be useful biomarkers for the prediction of feed efficiency in beef cattle.

The objective of this experiment was to determine if statistical process control (SPC) procedures coupled with the remote continuous collection of feeding behavior patterns, accelerometer-based behaviors, and rumen temperature can accurately differentiate between animals experimentally inoculated with Mannheimia haemolytica (MH) or PBS. Thirty-six crossbred steers (BW = 352 ± 23 kg) seronegative for MH were randomly assigned to bronchoselective endoscopic inoculation with MH (n = 18) or PBS (n = 18). Electronic feed bunks were used to measure DMI and feeding behavior traits, accelerometer-based neck collars measured feeding- and activity-behavior traits, and ruminal thermo-boluses measured rumen temperature. Data were collected for 28 d prior to and following inoculation. Steers inoculated with MH exhibited elevated (P < 0.02) levels of neutrophils and rumen temperature indicating that MH challenge effectively stimulated immunologic responses. However, only nine of the MH steers exhibited increased serum haptoglobin concentrations indicative of an acute-phase protein response and one displayed clinical signs of disease. Shewhart charts (SPC procedure) were used for two analyses, and sensitivity was computed using all MH-challenged steers (n = 18), and a subset that included only MH-challenged haptoglobin-responsive steers (n = 9). Specificity was calculated using all PBS steers in both analyses. In the haptoglobin-responsive only analysis, DMI and bunk visit (BV) duration had the greatest accuracy (89%), with accuracies for head-down (HD) duration, BV frequency, time to bunk, and eating rate being less (83%, 69%, 53%, and 61%, respectively). To address the diurnal nature of rumen temperature, data were averaged over 6-h intervals, and quarterly temperature models were evaluated separately. Accuracy for the fourth quarter rumen temperature was higher (78%) than the other quarterly temperature periods (first = 56%, second = 50%, and third = 67%). In general, the accelerometer-based behavior traits were highly specific ranging from 82% for ingestion to 100% for rest, rumination, and standing. However, the sensitivity of these traits was low (0% to 50%), such that the accuracies were moderate compared with feeding behavior and rumen temperature response variables. These results indicate that Shewhart procedures can effectively identify deviations in feeding behavior and rumen temperature patterns to enable subclinical detection of BRD in beef cattle.

Objectives of this experiment were to examine the effects of live yeast (LY) supplementation on immunological, physiological, and behavioral responses in steers experimentally challenged with Mannheimia haemolytica (MH). Thirty-six crossbred Angus steers (BW = 352 ± 23 kg) seronegative for MH were allocated within a 2 × 2 factorial arrangement: Factor 1 = roughage-based diet with LY (Saccharomyces cerevisiae boulardii CNCM I-1079, 25 g·per steer daily) or negative control (CON). Factor 2 = bronchoselective endoscopic inoculation with MH or phosphate buffer solution (PBS). Steers were fed their respective diets for 28 d prior to MH challenge on day 0. Reticulo-rumen temperature (RUT; ThermoBolus, Medria) was measured continuously at 5-min intervals and rectal temperature on days -4, 0, 1, 2, 3, 5, 7, 10, and 14 relative to MH inoculation. Compared with PBS-treated steers, the steers inoculated with MH had increased (P 41 °C) 9 to 11 h post-MH challenge, whereas rectal temperature was increased (P < 0.04) in MH-inoculated steers on day 1 post-MH challenge. Supplementation with LY increased (P < 0.05) rectal temperature on days 0, 7, and 10, relative to CON steers. There were inoculation x day interactions (P < 0.01) for lymphocyte, neutrophil, leukocyte, and haptoglobin concentrations. Steers challenged with MH had increased (P < 0.05) neutrophil concentration from days 1 to 3, leukocyte concentration on days 1 and 2 and haptoglobin concentration on days 1 to 5 post-MH challenge compared with PBS-treated steers. Steers supplemented with LY exhibited increased (P < 0.02) cortisol throughout the study compared with the CON treatment. Following inoculation, MH-challenged steers exhibited reduced (P < 0.05) DMI, eating rate, frequency, and duration of bunk visit (BV) events compared with PBS-treated steers. Results from this study demonstrate that the experimental challenge model effectively stimulated acute-immune responses and behavioral changes that are synonymous with naturally occurring bovine respiratory disease (BRD). However, supplementation with LY minimally altered the impact of the MH challenge on physiological and behavioral responses in this study. Continuously measured RUT was more sensitive at detecting febrile responses to MH challenge than rectal temperature. These results serve to guide future research on behavioral and physiological alterations exhibited during a BRD infection.

The objective of this study was to evaluate the effects of Levucell SC (LY; Saccharomyces cerevisiae CNCM I-1077) supplementation on performance, feed efficiency, ruminal temperature, feeding behavior, and carcass quality traits in yearling steers. Forty-eight crossbred steers were randomly allocated into two treatments: (1) Control and (2) LY with two pen replicates per treatment (12 steers per pen). Steers were housed in pens equipped with GrowSafe and fitted with reticulo-rumen boluses. All steers were maintained on their respective dietary treatments until harvest to assess carcass traits. There were no differences amongst treatments in DMI, ADG, morbidity or mortality rates, ruminal temperature or F:G. Live-yeast supplemented steers had 17% greater (P = 0.05) backfat thickness than control steers, which resulted in a 13% increase in yield grade, with no differences in all other carcass traits. Live-yeast steers exhibited different feeding behavior patterns than control steers, such that LY steers approached the bunk 25 minutes earlier (P = 0.01) than control steers, had 22% greater (P < 0.05) bunk visit (BV) duration, 41% increased (P < 0.05) head down duration, 18% slower (P < 0.05) BV eating rates, and a tendency for 9% lower BV frequency. Meal criterion was 47% longer (P = 0.01) for LY steers resulting in a reduction (P = 0.07) in meal frequency. Additionally, LY steers consumed 27% longer meals (P < 0.05) that tended to be larger in size (P = 0.09). Although DMI was not different throughout the trial, LY displayed 10% decreased (P < 0.05) meal-eating rates due to longer meal lengths. Overall, LY steers approached the feed bunk sooner following feed delivery, ate fewer, but larger meals at a slower rate, and spent more time eating compared to control steers. Live-yeast supplementation clearly altered feeding behavior patterns, suggesting more favorable fermentation and the capability to mitigate metabolic stress in steers fed high-grain diets by altering meal patterns.

The objective of this study was to determine if the magnitude of interactive feeding activity at the feedbunk affects feed efficiency and feeding behavior patterns in beef cattle. This study used data from 498 crossbred steers (3 trials) fed high-concentrate diets in pens with electronic feed bunks (GrowSafe Systems). Timestamp data for bunk visit (BV) events were used to develop an algorithm to quantify those BV events deemed to be replacement events; Defined as those that occur when an animal displaces and replaces another animal from the feedbunk within a specified period of time (replacement criterion). For this study, a replacement criterion of ≤ 18 s was used. A replacement activity index (RAI) was computed for each steer as the number of replacement events divided by total BV events. Within pen, steers were classified into 1 of 3 phenotypes based on ± 0.5 SD from mean RAI. Steers with high RAI (> 0.5 SD from mean RAI) were hypothesized to be more interactive at the feedbunk, whereas steers with low RAI were less interactive at the feedbunk. A mixed model with RAI class as fixed effect, and trial and pen within trial as random effects was used for data analysis. The low RAI steers had 6% fewer BV events that were 12% longer (P < 0.001) in duration than high RAI steers. Additionally, eating rate (g/min) was 14% slower (P < 0.001) and time to approach the feedbunk following feed delivery 6 min longer (P < 0.001) in low vs high RAI steers. The low-RAI steers had substantially less (P < 0.01) feeding activity during peak feeding time than high RAI. Further research is warranted to evaluate interactive feeding activity at the feedbunk as a potential indicator of performance and feed efficiency in feedlot cattle.

Opportunities exist to improve the efficacy of antimicrobial treatment and animal welfare standards through use of remote sensor technologies for early detection of bovine respiratory disease (BRD). A post-hoc analysis using statistical process control (SPC) procedures was performed on continuously-recorded physical activity data collected from BRD-diagnosed and healthy calves from Pillen et al. (2016). We hypothesized that SPC models that monitor physical activity traits (step count, motion index, standing time, lying bouts) would yield higher diagnostic accuracies compared to methods based on visual observation of clinical signs of illness for detecting the onset of BRD. Crossbred steers and bulls (n = 266; initial BW = 180 kg) at high risk for BRD were fitted with leg-attached accelerometers (IceQube, IceRobotics, Ltd.) upon arrival at a commercial feedlot and evaluated for 56 d Overall, calves experienced 48% morbidity, with the average day of first treatment occurring 16 d post-feedlot arrival. Shewhart charts were used to evaluate daily changes in each trait as univariate models and combined traits in principal component analysis (PCA)–constructed multivariate models, relative to the day of BRD diagnosis. Diagnostic test sensitivity and specificity were calculated for each model and compared. The univariate models had relatively low sensitivities (

Objectives of this study were to evaluate the use of feeding behavior traits to predict individual-animal RFI and DMI of growing cattle fed high-grain finishing diets. Performance, DMI, and feeding behavior data were collected from 1 study utilizing 498 Angus-based composite steers (Study 1), and 2 studies utilizing 408 heifers (Study 2) and 321 steers (Study 3) composed of Brangus, Braford, Simbrah, and Angus breeds. DMI and feeding behavior traits were measured using a GrowSafe system, and RFI calculated within trial. Seventeen feeding behavior traits were evaluated: Frequency and duration of bunk visit (BV) and meal events, head-down duration (HDD), average meal length, maximum non-feeding interval, corresponding day-to-day variation (SD) of these traits, and ratios of HDD per BV duration, HDD per meal duration, and BV events per meal event. Partial least squares regression (PLSR) models for DMI and RFI were calibrated using data from Study 1 and 2, and independently validated using Study 3. Independent variables for the DMI models included mid-test BW0.75, ADG, frame size, and ultrasound traits, with and without feeding behavior traits, and for the RFI model included frame size, ultrasound, and feeding behavior traits. For prediction of DMI, validation R2 (R2v) of the base model (Mid-test BW0.75, ADG, frame size, and ultrasound) was 0.46. Inclusion of feeding behavior traits to the base model increased R2v to 0.66. For prediction of RFI, R2v was low (0.37), but the model classified 51% of calves into the correct RFI group (± 0.50 SD), with only 7% incorrectly classified across 2 RFI groups. Ongoing development of biosensor-based technologies to quantify feeding behavior patterns provides opportunities to predict DMI in support of precision nutrition, and reduce costs of identifying feed-efficient cattle. Further research is warranted to evaluate the robustness of PLSR-based models to predict RFI and DMI in cattle.

Arterial oxyhemoglobin saturation (SaO2) is considered to be the reference method for evaluating lung function. There is current interest in development of biosensors to measure SpO2 (peripheral oxygen saturation) using infrared technology as a non-invasive alternative for pre-clinical respiratory detection of disease in animals. Objectives of this study were to investigate effects of experimentally-induced hypoxemia on hemodynamics (heart rate, HR and blood pressure, BP) and SaO2, and to evaluate the ability of 2 SpO2 pulse oximeters (PowerLab, AD Instruments; Passport2, Datascope) to predict SaO2 in cattle. Further, arterial lactate concentrations were measured as an indicator of oxygen delivery to tissues. Graded levels of hypoxia in seven anesthetized Holstein steers (BW = 127 ± 7 kg) were achieved by step-wise reductions in inspired oxygen fraction (FiO2) from baseline (20–35%) to target levels of 14–15%, 16–17%, and 18–19%. When the desired FiO2 levels were sustained for at least 3 min, arterial blood samples (n = 56) were collected and analyzed using a co-oximeter (pHOx-Ultra, Nova Biomedical) to determine SaO2 and lactate. Simultaneously, BP, HR and SpO2 data from the 2 pulse oximeters were recorded. Data were analyzed with a mixed model that included level of FiO2 as fixed effect. As expected, SaO2 decreased (P < 0.001) as FiO2 was reduced. Heart rate increased (P < 0.001) as FiO2 was reduced, although BP was unaffected by hypoxia. While not significantly different (P = 0.15), arterial lactate concentrations were reduced with declining FiO2. Likewise, the SpO2 values recorded by both pulse oximeters decreased (P < 0.001) incrementally as FiO2 declined, although values were only moderately correlated (P < 0.01; r = 0.35 to 0.41) with SaO2. These results demonstrate that future efforts to develop biosensors to monitor SpO2 and HR may have utility for preclinical detection of respiratory disease in livestock.

Objectives of this study were to characterize feeding-behavior (FB) patterns in growing dairy heifers with divergent RFI phenotypes (±0.50 SD) and to evaluate the accuracy of partial least squares regression (PLSR) models to predict RFI based on FB traits. Performance, DMI, and FB traits were measured for 70 to 100 d in 15 trials with Holstein heifers (n = 611) fed a corn-silage based ration. Seventeen FB traits were evaluated: frequency and duration of bunk visit (BV) and meal events, head-down duration (HDD), meal length, maximum non-feeding interval, corresponding day-today variation (SD) of these traits, and ratios of HDD per BV duration and meal duration, HDD per meal duration, and BV events per meal event. Data was analyzed using a mixed model that included RFI group and trial. The PLSR model for RFI was developed using cross-validation procedures (Leave-One-Out) in JMP (SAS), with FB traits as independent variables. LowRFI heifers consumed 24% less (P < 0.01) DMI and had lower (P < 0.01) day-to-day DMI variation than high-RFI heifers. Distinct differences were observed in FB patterns between low- and high-RFI heifers (Table 1). Eight of 17 FB traits were included [selected based on variable of importance (VIP) score > 0.80] in the PLSR model that explained 33% of the variation in RFI. Head-down duration had the highest VIP score; accordingly, low-RFI animals had 44% lower HDD and 30 and 40% lower ratios of HDD per BV duration and meal duration, respectively. Additionally, low-RFI animals had 20 and 18% fewer BV and meal events per day, spent 21% less time eating during BV events, and had reduced day-to-day variation in HDD and meal frequency. For this study, distinctive differences were observed in the FB patterns of Holstein heifers with divergent RFI, which explained 33% of the between-animal variation in RFI.

Epub ahead of print Conference: 10th International Symposium on the Nutrition of Herbivores - Herbivore Nutrition Supporting Sustainable Intensification and Agro-Ecological Approaches Location: Clermont Ferrand, FRANCE Date: SEP 02-06, 2018; International audience; Animal's feed efficiency in growing cattle (i.e. the animal ability to reach a market or adult BW with the least amount of feed intake), is a key factor in the beef cattle industry. Feeding systems have made huge progress to understand dietary factors influencing the average animal feed efficiency. However, there exists a considerable amount of animal-to-animal variation around the average feed efficiency observed in beef cattle reared in similar conditions, which is still far from being understood. This review aims to identify biological determinants and molecular pathways involved in the between-animal variation in feed efficiency with particular reference to growing beef cattle phenotyped for residual feed intake (RFI). Moreover, the review attempts to distinguish true potential determinants from those revealed through simple associations or indirectly linked to RFI through their association with feed intake. Most representative and studied biological processes which seem to be connected to feed efficiency were reviewed, such as feeding behaviour, digestion and methane production, rumen microbiome structure and functioning, energy metabolism at the whole body and cellular levels, protein turnover, hormone regulation and body composition. In addition, an overall molecular network analysis was conducted for unravelling networks and their linked functions involved in between-animal variation in feed efficiency. The results from this review suggest that feeding and digestive-related mechanisms could be associated with RFI mainly because they co-vary with feed intake. Although much more research is warranted, especially with high-forage diets, the role of feeding and digestive related mechanisms as true determinants of animal variability in feed efficiency could be minor. Concerning the metabolic-related mechanisms, despite the scarcity of studies using reference methods it seems that feed efficient animals have a significantly lower energy metabolic rate independent of the associated intake reduction. This lower heat production in feed efficient animals may result from a decreased protein turnover and a higher efficiency of ATP production in mitochondria, both mechanisms also identified in the molecular network analysis. In contrast, hormones and body composition could not be conclusively related to animal-to-animal variation in feed efficiency. The analysis of potential biological networks underlying RFI variations highlighted other significant pathways such as lipid metabolism and immunity and stress response. Finally, emerging knowledge suggests that metabolic functions underlying genetic variation in feed efficiency could be associated with other important traits in animal production. This emphasizes the relevance of understanding the biological basis of relevant animal traits to better define future balanced breeding programmes.

Objectives of this experiment were to examine the effects of live yeast (LY) supplementation on immunological, physiological, and behavioral responses in steers experimentally challenged with Mannheimia haemolytica (MH). Thirty-six crossbred Angus steers (BW = 352 ± 23 kg) seronegative for MH were allocated within a 2 × 2 factorial arrangement: Factor 1 = roughage-based diet with LY (Saccharomyces cerevisiae boulardii CNCM I-1079, 25 g·per steer daily) or negative control (CON). Factor 2 = bronchoselective endoscopic inoculation with MH or phosphate buffer solution (PBS). Steers were fed their respective diets for 28 d prior to MH challenge on day 0. Reticulo-rumen temperature (RUT; ThermoBolus, Medria) was measured continuously at 5-min intervals and rectal temperature on days −4, 0, 1, 2, 3, 5, 7, 10, and 14 relative to MH inoculation. Compared with PBS-treated steers, the steers inoculated with MH had increased (P < 0.05) RUT from 2 to 24 h, reaching a zenith (>41 °C) 9 to 11 h post-MH challenge, whereas rectal temperature was increased (P < 0.04) in MH-inoculated steers on day 1 post-MH challenge. Supplementation with LY increased (P < 0.05) rectal temperature on days 0, 7, and 10, relative to CON steers. There were inoculation x day interactions (P < 0.01) for lymphocyte, neutrophil, leukocyte, and haptoglobin concentrations. Steers challenged with MH had increased (P < 0.05) neutrophil concentration from days 1 to 3, leukocyte concentration on days 1 and 2 and haptoglobin concentration on days 1 to 5 post-MH challenge compared with PBS-treated steers. Steers supplemented with LY exhibited increased (P < 0.02) cortisol throughout the study compared with the CON treatment. Following inoculation, MH-challenged steers exhibited reduced (P < 0.05) DMI, eating rate, frequency, and duration of bunk visit (BV) events compared with PBS-treated steers. Results from this study demonstrate that the experimental challenge model effectively stimulated acute-immune responses and behavioral changes that are synonymous with naturally occurring bovine respiratory disease (BRD). However, supplementation with LY minimally altered the impact of the MH challenge on physiological and behavioral responses in this study. Continuously measured RUT was more sensitive at detecting febrile responses to MH challenge than rectal temperature. These results serve to guide future research on behavioral and physiological alterations exhibited during a BRD infection.

This study investigated the possible mechanisms for explaining interanimal variation in efficiency of feed utilization in intact male Holstein calves. Additionally, we examined whether the feed efficiency (FE) ranking of calves (n = 26) changed due to age and/or diet quality. Calves were evaluated during three periods (P1, P2, and P3) while fed a high-quality diet (calculated mobilizable energy [ME] of 11.8 MJ/kg DM) during P1 and P3, and a low-quality diet (calculated ME of 7.7 MJ/kg DM) during P2. The study periods were 84, 119, and 127 d, respectively. Initial ages of the calves in P1, P2, and P3 were 7, 11, and 15 mo, respectively, and initial body weight (BW) were 245, 367, and 458 kg, respectively. Individual dry matter intake (DMI), average daily gain (ADG), diet digestibility, and heat production (HP) were measured in all periods. The measured FE indexes were: residual feed intake (RFI), the gain-to-feed ratio (G:F), residual gain (RG), residual gain and intake (RIG), the ratio of HP-to-ME intake (HP/MEI), and residual heat production (RHP). For statistical analysis, animals' performance data in each period, were ranked by RFI, and categorized into high-, medium-, and low-RFI groups (H-RFI, M-RFI, and L-RFI). RFI was not correlated with in vivo digestibility, age, BW, BCS, or ADG in all three periods. The L-RFI group had lowest DMI, MEI, HP, retained energy (RE), and RE/ADG. Chemical analysis of the longissimus dorsi muscle shows that the L-RFI group had a higher percentage of protein and a lower percentage of fat compared to the H-RFI group. We suggested that the main mechanism separating L- from H-RFI calves is the protein-to-fat ratio in the deposited tissues. When efficiency was related to kg/day (DMI and ADG) and not to daily retained energy, the selected efficient L-RFI calves deposited more protein and less fat per daily gain than less efficient H-RFI calves. However, when the significant greater heat increment and maintenance energy requirement of protein compared to fat deposition in tissue were considered, we could not exclude the hypothesis that variation in efficiency is partly explained by efficient energy utilization. The ranking classification of calves to groups according to their RFI efficiency was independent of diet quality and age.

Despite tremendous advancements in the livestock sector, additional opportunities exist to improve even further livestock production around the globe. Forecasting is not an exact science and it relies heavily on past and current knowledge. Improvements in the nutritional sciences (both human and animal) include a better understanding of agents that cause deterioration of human health, improving the quality of animal products, applying effective fetal programming, developing new feeds and feeding strategies, and revisiting longstanding technologies. Improvements in the understanding of the rumen microbiome will enable scientists to increase the fermentation efficiency and, hopefully, select microbial species of greater interest. Improvements in remote sensing and ground-based instrumentation, telecommunications, and weather forecasting technologies will aid in the continued improvements of early warning systems to assist livestock producers in reducing risk and adapting to the changing environment. Broad utilization of sensor technologies will allow scientists to collect real-time data and, when combined with mathematical modeling, decision support systems will become an indispensable managerial tool for livestock production with the possibility to automate low-level decisions on the farm, such as supplementation schedules, sorting of animals, and early detection of disease and outbreaks. The identification of feed efficient animals may be the single most impactful advancement towards long-term livestock sustainability and the promise of feeding the world animal products. We contend that education across societal levels is the first step to solve current and future challenges of the livestock industry. The dilemma has been who will take the first step forward.

The objective of this study was to evaluate the use of fecal near-infrared reflectance spectroscopy (NIRS) profiling to predict diet nutritional characteristics and voluntary DMI in beef cattle. Fecal samples were collected for growing cattle across 11 experiments in which individual animal performance and DMI was measured. Dried and ground fecal composite samples collected from each animal were subjected to fecal NIRS analysis by a Foss NIRS 6500 scanning monochromator (Foss, Eden Prairie, MN) at the Grazingland Animal Nutrition Laboratory (Temple, TX). Fecal spectra were then used to develop equations to predict diet composition (trials 1 to 11; = 408), digestibility (trials 1 to 5; = 155), and DMI (trials 1 to 11; = 408). Coefficients of determination for calibration () and cross-validation () for prediction of diet nutritional characteristics were lower for NDF ( = 0.85; = 0.82) than for CP ( = 0.90; = 0.88). For the prediction of DMI, and ranged from 0.69 and 0.67 for the prediction of trial-average DMI to 0.76 and 0.73 for the prediction of fecal-collection-period DMI. While the and obtained for the prediction of DMI were lower than those obtained for the prediction of diet composition or digestibility, fecal NIRS prediction equations for DMI were successful in predicting the mean DMI of groups, as no differences were found for the prediction of fecal-collection-period DMI (Diff. = 1.10; = 0.72) or trial DMI (Diff. = -0.47; = 0.86).

Feeding behavior has the potential to enhance prediction of feed intake and to improve understanding of the relationships between behavior, DMI, ADG, and residual feed intake (RFI) in beef cattle. Two cohorts, born in 2009 and 2010, the progeny of Red Angus bulls (n = 58 heifers and n = 53 steers), were evaluated during the growing phase, and the latter group of steers was also evaluated during the finishing phase. All behavior analyses were based on 7 feeding behavior traits (bunk visit frequency, bunk visit duration [BVDUR], feed bout frequency, feed bout duration, meal frequency, meal duration, and average meal intake) and their relationships with ADG, DMI, and RFI. During the growing phase, feeding duration traits were most indicative of DMI with positive correlations between BVDUR and DMI for cohort 1 steers, growing phase (n = 28, r = 0.52, P = 0.00); cohort 2 steers, growing phase (n = 25, r = 0.44, P = 0.01); and cohort 2 heifers, growing phase (n = 29, r = 0.28 P = 0.05). There were similar trends toward correlation of BVDUR and RFI for both steer groups and cohort 1 heifers, growing phase (C1HG; n = 29; r = 0.27, P = 0.06; r = 0.30, P = 0.07; and r = 0.26, P = 0.08, respectively). Feed bout frequency was correlated with ADG in C1HG and in cohort 2 steers, finishing phase (r = -0.31, P = 0.04, and r = 0.43, P = 0.01, respectively). Feed bout duration was correlated with ADG in heifer groups (r = 0.29 and r = 0.28, P = 0.05 for both groups) and DMI for all growing phase animals (r = 0.29 to 0.55, P ≤ 0.05 for all groups). Evaluation of growing vs. finishing phase steer groups suggests that all behaviors, RFI, and DMI, but not ADG, are correlated through the growing and finishing phases (P ≤ 0.01 for all variables excluding ADG), implying that feeding behaviors determined during the growing phase are strong predictors of DMI in either life stage. Sire maintenance energy EPD effects (measured as high or low groups) on progeny feeding behaviors revealed a difference in meal duration with a tendency to differ in average meal intake (P = 0.01 and P = 0.07, respectively). Feeding behavior duration traits may be useful predictors of DMI in Red Angus cattle.

New approaches to limit expenses associated with input, without compromising profit, are needed in the beef industry. Residual feed intake (RFI) is an efficiency trait that measures variation in feed intake beyond maintenance, growth, and body composition. The addition of feeding behavior analysis to standard RFI tests may provide an approach to more readily identify feed-efficient cattle. The current study analyzes 7 feeding behaviors (BVFREQ: bunk visit frequency, BVDUR: bunk visit duration, FBFREQ: feed bout frequency, FBDUR: feed bout duration, MFREQ: meal frequency, MDUR: meal duration, and AMINT: average meal intake) and their relationships with RFI, ADG, and DMI in Japanese Black (Wagyu) cattle. Three cohorts of yearling Wagyu animals were studied using a standard 70-d RFI test, and data from divergent ( ± 0.5 SD from population RFI mean) subsets of animals were analyzed for feeding behaviors [n = 58, bulls on high-concentrate diet (C1); n = 36, bulls on a lower-concentrate diet (C2); n = 34, heifers on a lower-concentrate diet (C3)]. The following behaviors were correlated with ADG: BVFREQ (r = 0.32, P = 0.01; C1 bulls), BVDUR (r = 0.42, P = 0.01, C2 bulls), FBFREQ (r = 0.37, P < 0.01; C1 bulls), FBDUR (r = 0.46, P < 0.01, C1 bulls), and MFREQ (r = 0.42, P < 0.01, C2 bulls). Behaviors were trending or significantly correlated with DMI for all cases except for MFREQ for C3 and AMINT for C2. Residual feed intake was positively correlated with MDUR across all cohorts (r = 0.31, P = 0.02; r = 0.38, P = 0.02; r = 0.54, P ≥ 0.01, respectively). For C2 bulls and C3 heifers, RFI was positively correlated with behavior frequency categories (BVFREQ; r = 0.44, P = 0.01; r = 0.60, P ≤ 0.01, respectively, and FBFREQ r = 0.46, P ≤ 0.01; r = 0.60, P ≤ 0.01, respectively). Bunk visit frequency and FBFREQ were highly correlated with RFI status (high or low) in C2 bulls and C3 heifers. Behavior duration categories (BVDUR, FBDUR, and MDUR) were most correlated with efficiency status in C1 bulls. However, behavior frequency categories (BVFREQ and FBFREQ), as well as MDUR, were most correlated with efficiency status in C2 bulls and C3 heifers. Inclusion of meal duration measurements when evaluating RFI provides an additional tool in understanding the drivers of variation in this important trait in Wagyu cattle. The present study provides new insights into feed intake patterns of a beef breed for which there are few reports of feeding behavior.

The objective of this study was to evaluate the relationship between hepatic mitochondrial function and residual feed intake (RFI) in growing beef cattle. In Trial 1, RFI was measured in 29 Angus heifers (initial BW = 258.0 ± 24.9 kg) from divergent IGF-I selection lines created at the Eastern Agricultural Research Station (The Ohio State University) fed a grain-based diet (calculated ME = 2.85 Mcal/kg DM). In Trial 2, RFI was measured in 119 Santa Gertrudis steers (initial BW = 308.4 ± 28.1 kg) fed a roughage-based diet (calculated ME = 2.21 Mcal/kg DM). At the end of the RFI measurement period, cattle in Trial 1 (n = 7 low RFI and n = 7 high RFI) and in Trial 2 (n = 6 low RFI and n = 8 high RFI) with measures of RFI exceeding 0.5 (Trial 1) or 1.0 (Trial 2) SD from the mean RFI were selected to measure mitochondrial function. Overall ADG, DMI, and RFI were 1.19 ± 0.15, 9.31 ± 1.12, and 0.00 ± 0.63 kg/d and 0.83 ± 0.16, 9.48 ± 1.00, and 0.00 ± 0.86 kg/d in Trial 1 and 2, respectively. Cattle with low RFI consumed 13 and 24% less (P 0.10). In Trial 1, cattle with low RFI tended (P = 0.06) to have greater state 3 respiration rates than cattle with high RFI, but state 3 respiration rates were similar (P > 0.10) between cattle with low and high RFI in Trial 2. In both trials, cattle with low RFI had greater (P 0.10) was observed in Trial 2. Proton-leak kinetics were similar (P > 0.05) between cattle with low and high RFI in both trials. These data suggest that ADP has greater control of oxidative phosphorylation in liver mitochondrial of cattle with low RFI compared to their high RFI counterparts.

Effective tick management on grazing animals is facilitated by accurate noninvasive detection methods. Fecal analysis provides information about animal health and nutrition. Diet affects fecal composition; stress may do likewise. The constituents in feces that may be affected by tick burdens and in turn affect near-infrared spectra have not been reported. Our objective was to examine the interaction between plane of nutrition and tick burden on fecal composition in cattle. Angus cross steers (n = 28; 194 ± 3.0 kg) were assigned to 1 of 4 treatments (n = 7 per group) in a 2 × 2 factorial arrangement: moderate (14.0 ± 1.0% CP and 60 ± 1.5% TDN) vs. low (9.0 ± 1.0% CP and 58 ± 1.5% TDN) plane of nutrition and control (no tick) vs. tick treatment [infestation of 300 pair of adult Lone Star ticks (Amblyomma americanum) per treated animal]. Fecal samples were collected at approximately 0700 h on d -7, 0, 7, 10, 14, 17, and 21 relative to tick infestation. Fecal constituents measured were DM, OM, pH, Lactobacillus spp., Escherchia coli, acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, IgA, and cortisol. Experimental day affected (P < 0.05) all constituents measured. Plane of nutrition affected (P < 0.05) DM, OM, VFA, and IgA. Tick treatment numerically (P = 0.13) reduced cortisol. A multivariate stepwise selection model containing cortisol and E. coli values on d 10 and d 14 accounted for 33% of the variation in daily adult female tick feeding counts across both planes of nutrition (P < 0.07). Within the moderate plane of nutrition, a model containing only cortisol on d 10 and d 14 described 59% of the variation in the number of feeding ticks (P < 0.02). Similarly, a model including cortisol, propionate, isovalerate, and DM at d 10 and d 14 d described 95% of the variation in total feeding ticks in the low plane of nutrition. Of the constituents measured, fecal cortisol offers the best possibility of noninvasively assessing stress by way of a single assay but the presence of ticks would still need to be confirmed visually. Although several constituents measured in this study should exist in sufficient quantity to directly affect near-infrared spectra, none stood out as a clear descriptor of prior observed differences in fecal spectra between tick-treated versus non-tick-treated animals. There were, however, groups of fecal constituents related to daily adult female tick feeding numbers (as a visual estimation of tick stress).

Methods to improve accuracy of preclinical detection of bovine respiratory disease (BRD) are needed to reduce the economic impact of this disease, improve animal welfare, and promote more judicious use of antimicrobials in beef cattle. The objectives of this study were to retrospectively characterize time-series deviations in DMI and feeding behavior patterns preceding the display of observed clinical symptoms associated with BRD and to identify those feeding behavior traits that would be most predictive of BRD. The study was conducted with 231 seed stock bulls (391 ± 55 kg initial BW) representing 5 breeds that were housed in a facility equipped with GrowSafe feed bunks at a commercial bull-test facility. All bulls were vaccinated against standard viral and bacterial pathogens before and on arrival at the facility. Daily DMI and feeding behavior traits (frequency and duration of bunk visit events, head-down duration, variance of nonfeeding intervals, and time to approach feed bunk following feed-truck delivery) were measured for 70 d with a GrowSafe system. During a 10-d period from Day 28 to 37 of the trial, 30 bulls were administered antimicrobial therapy for clinical symptoms of BRD (rectal temperatures > 39.5°C). All remaining bulls ( = 201) were administered metaphylactic therapy on Day 38 of the trial in response to an acute decrease in feed intake. A retrospective analysis was conducted using a 2-slope broken-line regression model to identify inflection points in DMI and feeding behavior traits relative to onset of illness. The bulls were separated into 2 cohort groups based on observed clinical illness ( = 30) or those metaphylactically treated ( = 201), with the 2-slope broken-line regression model applied separately to each cohort. The model-detected inflection points for DMI were 6.8 and 3.8 d before observed clinical illness and metaphylactic treatment, respectively, and the reductions in DMI from detected inflection points to the day of observed clinical illness and day of metaphylactic treatment were 39.3 and 49.8%, respectively. Furthermore, the model-detected inflection points for individual feeding behavior traits ranged from 1.3 to 14.2 d before observed clinical illness and from 3.8 to 12.6 d before metaphylactic treatment. Results from this study demonstrate the potential value of electronic behavior-monitoring systems to improve the sensitivity and specificity of preclinical detection of BRD in feedlot cattle.

A meta-analysis was conducted to examine phenotypic relationships between feed efficiency, scrotal circumference, and semen quality traits in yearling bulls. Data evaluated were obtained from 5 postweaning trials involving Angus (n = 92), Bonsmara (n = 62), and Santa Gertrudis (n = 50) bulls fed diets that ranged from 1.70 to 2.85 Mcal ME/kg DM. After an adaptation period of 24 to 28 d, feed intake was measured daily, and BW was measured at 7- or 14-d intervals during the 70- to 77-d trials. Ultrasound carcass traits (12th-rib back fat thickness, BF; LM area, LMA) and scrotal circumference (SC) were measured at the start and end of each trial. Semen samples were collected by electroejaculation within 51 d of the end of the trials when the age of bulls averaged from 365 to 444 d and were evaluated for progressive sperm motility and morphology. Residual feed intake (RFI) was calculated as the difference between actual DMI and expected DMI from linear regression of DMI on ADG and midtest BW(0.75), with trial, trial by ADG, and trial by midtest BW(0.75) as random effects. Across all studies, bulls with low RFI phenotypes (0.5 SD below the mean RFI of 0) consumed 20% less DM and had 10% less BF but had similar ADG, SC, and semen quality traits compared with high-RFI bulls (0.5 SD above the mean RFI of 0). Gain to feed ratio was strongly correlated with ADG (0.60) and weakly correlated with initial BW (-0.17) and DMI (-0.26). Residual feed intake was not correlated with ADG, initial age, or BW but was correlated with DMI (0.71), G:F (-0.70), and BF (0.20). Initial SC (-0.20), gain in SC (-0.28), and percent normal sperm (-0.17) were correlated with G:F, but only sperm morphology was found to be weakly associated with RFI (0.13). These data suggest that RFI is not phenotypically associated with SC or sperm motility but is weakly associated with sperm morphology.

Meals are clusters of feedbunk visit (BV) events that are differentiated from the next meal by a nonfeeding interval that is longer compared with the nonfeeding intervals within a meal. The longest nonfeeding interval considered to be part of a meal is defi ned as the meal criterion. The objective of this study was to determine which combination of 2 probability density functions ((PDF): Gaussian normal (G), Weibull (W), Log-Normal, Gamma, and Gumbel) used in a bimodal distribution model had the best fi t of nonfeeding interval data collected in beef heifers. Feeding behavior traits (572,627 total BV events) were measured in 119 heifers fed a high-grain diet (3.08 Mcal ME/kg DM), using a GrowSafe system for 66 d. The frequency and duration of BV events averaged 75 ± 15 events/d and 73.0 ± 22.3 min/d, respectively. The bimodal PDF combinations were fi tted to the log 10 -transformed interval lengths between BV events for each animal, using R mixdist package (2.13). The Akaike Information Criterion (AIC) was used to assess goodness of fi t of the 25 bimodal PDF combinations. The PDF model with the least AIC value was selected as the best fi t for each individual. A χ 2 analysis of the selected best PDF distribution across individuals revealed that 78.2% of the heifers best fi t were G-W or W-W PDF models. The likelihood probability estimates were calculated from the average AIC deviation of each model from the standard G-G model. The G-W likelihood probability estimate was greater (P = 0.001) than the W-W combination (0.997 vs. 0.727). Our analysis indicated the G-W model had a statistically better fi t and is most likely the best approach to defi ne meal criterion in beef heifers fed high-grain diets.

The objective of this study was to evaluate the use of an electronic radio-frequency-identification-based system (GrowSafe System Ltd., Airdrie, Alberta, Canada) to measure feeding behavior traits in beef cattle fed a high-grain diet. Feeding behavior data were recorded by the GrowSafe system and time-lapse video using 10 heifers over a 6-d period. Observed bunk visit (BV) and meal event data (frequency and duration) were compared with electronic feeding behavior data generated by the GrowSafe system at 5 parameter settings (MPS; 30, 60, 100, 150, and 300 s), which are used to define the maximum duration between consecutive electronic identification recordings to initiate a subsequent BV event. A random coefficient model was used to compare video and electronic data using orthogonal contrasts. Video data were regressed on the electronic feeding behavior data to obtain an estimate of precision (r(2)) and other statistical estimates, including mean square error of prediction and concordance correlation coefficient, to access the adequacy of the electronic system predictions. The variation in MPS values affected BV data, but not meal event data. Electronic meal frequency and duration data were not different (P > 0.50) from observed values, and were not affected by electronic MPS values. The optimal MPS value for prediction of BV and meal event frequency and duration traits was 100 s. Our evaluation indicated the GrowSafe system 4000E was able to predict BV and meal event data when the 100-s MPS was used to analyze the feeding behavior data.

Methane is a potent greenhouse gas and its release to the atmosphere is widely believed to contribute to global warming. Ruminal enteric CH4 production represents a loss of 2–15% of the animal's gross energy (GE) intake and contributes nearly 20% of US CH4 emissions. Studies have evaluated the CH4 inhibiting potential of select short chain nitrocompounds, such as nitroethane, but results demonstrating their effects on ruminant exhaled CH4 emissions are lacking. Our study determined effects of oral nitroethane administration on CH4 emissions, accumulations of volatile fatty acids (VFA) and on ruminal CH4 producing activity in steers fed a forage based diet containing 8.8 MJ/kg of metabolizable energy on a dry matter (DM) basis. Effects of nitroethane administration on ruminal nitroethane reducing activity were also determined. Holstein steers (n = 24) of 317 ± 6.5 kg body weight (BW) were assigned to 4 treatments that included: 0, 30, 60 and 120 mg nitroethane/kg BW/d. Treatments were administered via oral gavage twice daily at 08:00 and 16:00 h for 8 d. DM intake decreased quadratically as level of nitroethane increased with steers administered 60 and 120 mg nitroethane/kg BW consuming 14 and 7% lower DM, respectively, than steers administered 0 or 30 mg nitroethane/kg BW. Methane emissions as a proportion of GE intake and ruminal CH4 producing activity both decreased linearly (P This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

The objective of this study, which was part of an integrated project to investigate the antimicrobial effects of dietary tannins on native food borne pathogens in beef cattle, was to examine the effects of source of tannin (condensed, CT, vs. hydrolysable, HT) on performance, feed efficiency, ruminal fermentation parameters, and carcass and non-carcass traits in finishing beef steers. Thirty-six crossbred steers averaging 414 ± 40 kg BW were stratified by initial BW and randomly assigned to one of three treatments: control (CN), CT, or HT tannins. Commercially available tannin extracts were added to a high-grain diet (ME = 11.9 MJ/kg DM) at 14.9 g/kg DM. Mimosa and chestnut extracts provided condensed tannin and hydrolysable tannin, respectively. Steers were individually fed using Calan gate feeders a high-grain diet. Rumen fluid was collected on days 0, 21, and 42 via stomach tube and analyzed for VFA and in vitro methane producing activity. Cattle were harvested at the end of the study and carcass data collected 24-h postharvest. There was no effect ( P >0.05) of tannin supplementation on animal performance, ruminal fermentation parameters, in vitro methane producing activity, or carcass and non-carcass traits, except for HCW, EBW, and rumen mass and empty GIT (g/kg EBW). Condensed tannin steers had 3.7% lower ( P P P P

The objective of this study was to characterize residual feed intake (RFI) and to estimate phenotypic and genetic correlations with performance and ultrasound carcass traits in growing heifers. Four postweaning feed efficiency trials were conducted using 468 Brangus heifers. The complete Brangus pedigree file from Camp Cooley Ranch (Franklin, TX), which included 31,215 animals, was used to generate genetic parameter estimates. The heifer progeny from 223 dams were sired by 36 bulls, whereas the complete pedigree file contained 1,710 sires and 8,191 dams. Heifers were individually fed a roughage-based diet (ME = 1.98 Mcal/kg of DM) using Calan gate feeders for 70 d. Heifer BW was recorded weekly and ultrasound measures of 12th- to 13th-rib fat thickness (BF) and LM area (LMA) obtained at d 0 and 70. Residual feed intake (RFIp) was computed as actual minus predicted DMI, with predicted DMI determined by linear regression of DMI on mid-test BW(0.75) (MBW) and ADG with trial, trial x MBW, and trial x ADG as random effects. Overall means for ADG, DMI, and RFI were 1.01 (SD = 0.15), 9.51 (SD = 1.02), and 0.00 (SD = 0.71) kg/d, respectively. Stepwise regression analysis revealed that inclusion of gain in BF and final LMA into the base model increased the R(2) (0.578 vs. 0.534) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted RFI (RFIc) were strongly correlated phenotypically and genetically with DMI and FCR, but not with ADG or MBW. Gain in BF was phenotypically correlated (P < 0.05) with RFIp (0.22), but not with FCR or RFIc; however, final BF was genetically correlated (P < 0.05) with RFIp (0.36) and RFIc (0.39). Gain in LMA was weakly phenotypically correlated with FCR, but not with RFIp or RFIc; however, gain in LMA was strongly genetically correlated with RFIp (0.55) and RFIc (0.77). The Spearman rank correlation between RFIp and RFIc was high (0.96). These results suggest that adjusting RFI for ultrasound carcass composition traits will facilitate selection phenotypically independent of growth, body size, and carcass composition; however, genetic relationships may still exist between RFI and carcass composition.

As grain prices have increased dramatically in the past year, understanding the fundamental genetic, cellular, and biochemical mechanisms responsible for feed efficiency (FE; g of gain/g of feed) or residual feed intake (RFI; an alternative feed efficiency trait that quantifies interanimal variation in DMI that is unexplained by differences in BW and growth rate) in livestock and poultry is extremely important with respect to maintaining viable meat production practices in the United States. Although breed and diet have long been known to affect mitochondrial function, few studies have investigated differences in mitochondrial function and biochemistry due to interanimal phenotypic differences in FE or RFI (i.e., variation among animals of the same breed and fed the same diet). This paper reviews existing literature on relationships of mitochondrial function and biochemistry with FE and RFI in poultry and livestock. The overall goal of all of this paper is to assist the development of tools (e.g., genetic markers or biomarkers) to aid commercial breeding companies in genetic selection that, in turn, will help maintain viable livestock and poultry industries in the United States and around the world.

The objectives of this study were to characterize feed efficiency traits and to examine phe- notypic correlations between performance and feeding behavior traits, and ultrasound measurements of car- cass composition in growing bulls. Individual DMI and feeding behavior traits were measured in Angus bulls (n = 341; initial BW = 371.1 ± 50.8 kg) fed a corn silage-based diet (ME = 2.77 Mcal/kg of DM) for 84 d in trials 1 and 2 and for 70 d in trials 3 and 4 by using a GrowSafe feeding system. Meal duration (min/d) and meal frequency (events/d) were calculated for each bull from feeding behavior recorded by the GrowSafe sys- tem. Ultrasound measures of carcass 12th-rib fat thick- ness (BF) and LM area (LMA) were obtained at the start and end of each trial. Residual feed intake (RFIp) was computed from the linear regression of DMI on ADG and midtest BW 0.75 (metabolic BW, MBW), with trial, trial by ADG, and trial by midtest BW 0.75 as random effects (base model). Overall ADG, DMI, and RFIp were 1.44 (SD = 0.29), 9.46 (SD = 1.31), and 0.00 (SD = 0.78) kg/d, respectively. Stepwise re- gression analysis revealed that inclusion of BW gain in BF and LMA in the base model increased R 2 (0.76 vs. 0.78) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted residual feed intake (RFIc) were moderately correlated with DMI (0.60 and 0.55, respectively) and feed conversion ratio (FCR; 0.49 and 0.45, respectively), and strongly correlated with partial efficiency of growth (PEG; −0.84 and −0.78, respec- tively), but not with ADG or MBW. Gain in BF was weakly correlated with RFIp (0.30), FCR (−0.15), and PEG (−0.11), but not with RFIc. Gain in LMA was weakly correlated with RFIp (0.17) and FCR (−0.19), but not with PEG or RFIc. The Spearman rank cor- relation between RFIp and RFIc was high (0.91). Meal duration (0.41), head-down duration (0.38), and meal frequency (0.26) were correlated with RFIp and ac- counted for 35% of the variation in DMI not explained by MBW, ADG, and ultrasound traits (RFIc). These results suggest that adjusting residual feed intake for carcass composition will facilitate selection to reduce feed intake in cattle without affecting rate or composi- tion of gain.

Angus bulls and heifers from lines divergently selected for serum IGF-I concentration were used to evaluate the effects of IGF-I selection line on growth performance and feed efficiency in 2 studies. In study 1, bulls (low line, n = 9; high line, n = 8; initial BW = 367.1 +/- 22.9 kg) and heifers (low line, n = 9; high line, n = 13; initial BW = 286.4 +/- 28.6 kg) were adapted to a roughage-based diet (ME = 1.95 Mcal/kg of DM) for 24 d and fed individually for 77 d by using Calan gate feeders. In study 2, bulls (low line, n = 15; high line, n = 12; initial BW = 297.5 +/- 34.4 kg) and heifers (low line, n = 9; high line, n = 20; initial BW = 256.0 +/- 25.1 kg) were adapted to a grain-based diet (ME = 2.85 Mcal/kg of DM) for 32 d and fed individually for 70 d by using Calan gate feeders. Blood samples were collected at weaning and at the start and end of each study, and serum IGF-I concentration was determined. Residual feed intake (RFI) was calculated, within study, as the residual from the linear regression of DMI on midtest BW(0.75), ADG, sex, sex by midtest BW(0.75) and sex by ADG. In study 1, calves from the low IGF-I selection line had similar initial and final BW and ADG, compared with calves from the high IGF-I selection line. In addition, DMI and feed conversion ratio were similar between IGF-I selection lines; however, calves from the low IGF-I selection line tended (P < 0.10) to have lesser RFI than calves from the high IGF-I selection line (-0.26 vs. 0.24 +/- 0.31 kg/d). In study 2, IGF-I selection line had no influence on performance or feed efficiency traits. However, there was a tendency (P = 0.15) for an IGF-I selection line x sex interaction for RFI. Bulls from the low IGF-I selection line had numerically lesser RFI than those from the high IGF-I selection line, whereas in heifers, the IGF-I selection line had no effect on RFI. In studies 1 and 2, weaning and initial IGF-I concentrations were not correlated with either feed conversion ratio or RFI. However, regression analysis revealed a sex x IGF-I concentration interaction for initial IGF-I concentration in study 1 and weaning IGF-I concentration in study 2 such that the regression coefficient was positive for bulls and negative for heifers. These data suggest that genetic selection for postweaning serum IGF-I concentration had a minimal effect on RFI in beef cattle.

Campylobacter are important human foodborne pathogens known to colonize the gastrointestinal tract of cattle. The incidence of Campylobacter in cattle may be seasonal and may vary among age groups and type (beef versus dairy). Less is known about other factors that could influence the prevalence, colonization site, and shedding of Campylobacter in cattle. The objectives of this study were to evaluate the prevalence and enumerate Campylobacter at two sites along the digestive tract of beef and dairy type cattle consuming either grass or feedlot diets. In an initial study, Campylobacter was not recovered from rumen samples of any of 10 ruminally cannulated (six dairy and four beef type) pasture-reared cattle and there was no difference (p0.05) between cattle types on fecal Campylobacter recovery, with 50% of each type yielding culture-positive feces (overall mean +/- SE, 0.75 +/- 0.001 SEM log(10) colony-forming units [CFU]/g feces). When calculated from Campylobacter culture-positive animals only, mean fecal concentrations were 1.50 +/- 0.001 SEM log(10) CFU/g. In a follow-up study with feedlot and pasture-reared cattle (n = 18 head each), 78% of rumen and 94% of fecal samples from pastured cattle were positive for Campylobacter while 50% of the rumen and 72% of the fecal samples were positive in concentrate-fed animals. Overall mean concentration of Campylobacter was greater in feces than ruminal fluid (p0.05). When only Campylobacter-positive animals were analyzed, concentrations recovered from feces were higher (p0.05) in concentrate-fed than in pasture-fed cattle (4.29 vs. 3.34 log(10) CFU/g, respectively; SEM = 0.29). Our results suggest that the rumen environment and its microbial population are less favorable for the growth of Campylobacter and that concentrate diets may provide a more hospitable lower gastrointestinal tract for Campylobacter.