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Current dogma suggests increased dietary roughage may improve calf health at the expense of performance during receiving. In experiment 1, the effects of increasing dietary roughage on performance and clinical health of high-risk heifers was evaluated over a 56-d receiving period. Heifers (n  = 589; initial body weight; BW  = 230 ± 33 kg) were sourced from Oklahoma livestock auctions from April through October of 2019. Heifers were randomly assigned to pens, which were randomly assigned to 1 of 3 experimental dietary treatments in a randomized complete block design. Diets contained either: 1) 15% roughage (R15), 2) 30% roughage (R30), or 3) 45% roughage (R45) in the form of prairie hay. Orthogonal contrasts were used to test for linear and quadratic responses among experimental treatments. There was a linear decrease in overall average daily gain (ADG ; P  ≤ 0.0001) with increasing roughage inclusion which resulted in a linear decrease (P  ≤ 0.0001) in heifer final BW. A linear increase (P  ≤ 0.01) was observed for overall dry matter intake (DMI), and overall gain:feed (G:F) decreased linearly (P  ≤ 0.0001) as dietary roughage concentration increased. A quadratic response to decreasing roughage was observed (P  = 0.02) for the percent of calves treated three times for bovine respiratory disease (BRD). No other responses (P  ≥ 0.11) were detected in animal health variables. In experiment 2, Angus steers (n  = 12) and heifers (n  = 6; BW = 272 ± 28 kg) were acquired from a single ranch in Oklahoma to evaluate the same experimental dietary treatments on serum metabolite concentrations. Animals were randomly assigned to experimental treatments, with animal serving as the experimental unit in experiment 2. Statistical models for serum metabolites in experiment 2 were analyzed using repeated measures with the effects of treatment, time, and treatment × time. In experiment 2, there were tendencies for treatment × time interactions for blood urea nitrogen (BUN ; P  = 0.07) and nonesterified fatty acid (NEFA ; P  = 0.06) concentrations. No metabolites were affected by treatment (P  ≥ 0.11), while all metabolites were impacted by time (P  ≤ 0.02). In summary, growth performance was improved in calves as dietary roughage concentration decreased with minimal impacts on health and serum metabolites. These results suggest that diets containing as little as 15% roughage can be used during receiving to improve calf performance without compromising calf health when fibrous byproducts are included in the diet. [ABSTRACT FROM AUTHOR]

In recent years, substantial progress has been made in understanding the sources of biological variation and genetic components of feed efficiency in growing animals consuming energy-dense mixed diets during the post-weaning phase. Much less is known about within-animal variation of feed efficiency for beef cows consuming moderate to low-quality forage diets common to most cow/calf production systems. Considerable evidence indicates the existence of a genetic by environment interaction for feed efficiency. Phenotype for feed intake and feed efficiency are most practically and cost effectively determined during the post-weaning growing stage. However, due to the additional nutrient sinks associated with gestation and lactation, and the cost, labor and technology required to measure economically relevant traits in mature cows, little is known about forage utilization efficiency in beef cows. The beef cow/calf segment of the industry represents, by far, the greatest opportunity to reduce beef production input costs and reduce the industry's carbon footprint. We reason that selection tools for feed intake and feed efficiency developed over the last 20 years are effective for the post-weaning growing and finishing phases, although only marginally effective for beef cows consuming unprocessed, moderate to low-quality forage. In this session, we will discuss challenges, opportunities, and experiences associated with measuring forage intake and recovered energy in beef cows. [ABSTRACT FROM AUTHOR]

Our objectives were to 1) determine diet selection of goats and cattle grazing woody plant-encroached tallgrass prairie, and, 2) determine the effect of the presence of goats on cattle diet selection. In 2019, pastures (n = 6) were allocated to 1 of 2 experimental grazing treatments. Pastures (n = 3) grazed by cattle only (crossbred Angus yearling heifers) were moderately grazed year-round at 4.2 ha per heifer. Pastures (n = 3) grazed by cattle (similar heifers) and goats (Boer x Spanish crossbred mature does) were moderately grazed year-round at 4.7 ha per heifer and 2.3 ha per goat simultaneously. Each pasture was burned in 6 patches (2 patches per year) to facilitate range management objectives. Every 35 d from May 2022 until June 2023, fecal samples were collected from all animals and stored frozen and later composited into 2 composites per animal species per pasture. Composites were then analyzed by a commercial lab with DNA barcoding and high-throughput sequencing. For statistical analysis, the top 50 Exact Sequence Variants (ESVs), representing species of forage, across all treatments were used for analysis. Each ESV was georeferenced to eliminate plants that did not grow in the study area, and assigned to a representative functional group: graminoid, forb, legume, and woody plant. Analysis of variance and Tukey's post-hoc separation of estimated marginal means were performed to assess the effects of season, grazer species, and the interaction. The interaction of season and grazer species was significant (P < 0.01) for the percentage of diet selected from each functional group of plants. As expected, goats selected a greater percentage of their diet as woody plants in summer (57%) and winter (74%) compared with cattle (27%). Cattle selected more grass in winter (34%) than goats (11%). Goats selected more forbs in spring (33%) than cattle (10%). However, goats selected a lesser percentage of their diet as legumes in summer (16%) than cattle (58%), which was unexpected. Overall, these results indicate that both species of grazers select a diverse diet from these diverse pastures, and selection is dynamic over time. Goat presence in a pasture does not seem to drastically alter cattle selection, actually complementing cattle in these pastures where goats can be used to target species cattle do not prefer. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the impacts of cow breed type and age on maintenance requirements, feed energy utilization, and voluntary forage intake. The main effect of breed type included Angus (ANG; n = 32) and Hereford × Angus (HA; n = 27) lactating cows. The main effect of age included 2- and 3-yr-old (YOUNG; n = 29) and 4- to 8-yr-old (MATURE; n = 30) cows. Within breed type and age class, cows were randomly assigned to 1 of 2 pens for a total of 8 pens, each housing 7 to 9 cow/calf pairs. To determine maintenance energy requirements, cows and calves were limit-fed for 105 d to body weight (BW) and body condition score (BCS) stasis. There were no differences between breeds in cow hip height, BW, average milk yield (P > 0.31), diet digestibility, or cow maintenance energy requirement (P = 0.54). Crossbred cows had greater BCS (P < 0.05) throughout the experiment. Efficiency of calf growth was not different between breeds when expressed as feed intake of the cow/calf pair nor as energy intake of the pair per unit of calf BW gain (P ≥ 0.31). Young cows produced less milk per day and per unit of BW0.75 (P < 0.01); however, there was no effect of cow age on maintenance energy requirement, diet digestibility, or efficiency of calf growth (P > 0.10). Subsequently, a 45-d experiment was conducted to determine voluntary low-quality forage intake. Cows were housed in dry-lot pens equipped with shade, windbreaks, and feed bunks with free-choice access to clean water and a chopped hay ration was provided ad libitum to determine forage intake. Daily forage intake was lower (P = 0.05) for HA compared with ANG (123 vs. 132 g/kg BW0.75, respectively) although there was no difference in BW. However, HA cows sustained greater BCS (P < 0.01). There was no difference (P = 0.60) in forage intake per unit of BW0.75 due to cow age. Results indicate similar calf growth efficiency among breed types although crossbred cows maintained greater body energy stores and consumed less low-quality forage during the voluntary intake experiment. These differences could not be attributed to lower maintenance energy requirements. Neither maintenance energy requirement nor calf growth efficiency was different between young and mature cows. [ABSTRACT FROM AUTHOR]

The California Net Energy System (CNES) has been successfully used for many years to generate estimates of grazing animal energy requirements, supplemental needs, and energy value of grazed forage diets. Compared to pen feeding situations, validation of feed nutritive value estimates or animal performance projections are extremely difficult in grazing animals because many of the system inputs are constantly changing. A major difficulty in applying this or any energy accounting system in the field is acquiring accurate estimates of forage intake. We discuss the various equations available to estimate forage intake for grazing animals with emphasis on beef cows. Progress has been made in recent years although there remains substantial discrepancy among various equations, particularly in the upper range of forage digestibility. Validation work and further development is needed in this area. For lactating cows, our conclusion is that the adjustment of intake for milk production (0.2 kg increase in forage intake per kg of milk produced) needs to be increased to a minimum of 0.35. A particular challenge with the CNES for grazing beef cows is the dramatic interaction that can occur between genetic potential for production traits and nutrient availability. Examples from literature are provided and a case study is presented demonstrating that energy requirements are dynamic and depend on nutrients available in grazing systems. The CNES is a useful tool in grazing beef cattle management although there remains substantial opportunity and need to improve inputs and validate the system in grazing situations. [ABSTRACT FROM AUTHOR]

Early weaning is used to minimize cow nutrient requirements in situations where feed inputs are scarce or expensive. For many years, maintenance energy requirements have been assumed to be 20% greater in lactating compared with non-lactating beef cows. While not well established, maintenance energy requirements are thought to be greatest in primiparous cows and to decline with age. Consequently, early weaning primiparous cow–calf pairs should improve overall efficiency, particularly in situations where mid-to-late lactation forage or feed nutritive value is low. The objective of this study was to determine the biological efficiency of early weaning and maintenance energy requirements of lactating versus non-lactating primiparous cows. Experiments were conducted in two consecutive years using 90 primiparous cows and their calves (48 in yr 1, 42 in yr 2). Pairs were randomly assigned to one of the six pens (8 pairs/pen yr 1, 7 pairs/pen yr 2) and pens were randomly assigned to 1 of 2 treatments; (1) early weaning (130 d ± 15.4; EW, n = 6) and (2) traditional weaning (226 d ± 13.1; TW, n = 6). Late lactation cow and calf performance and feed consumption were measured for 92 d (yr 1) and 100 d (yr 2). Cows were limit-fed to meet maintenance requirements, while calves were offered ad libitum access to the same diet in a creep-feeding area. Calves were not allowed access to the cows' feed. Cow feed intake, body condition score, body weight (BW), milk yield and composition, and calf body weight gain and creep feed intake were recorded. After accounting for lactation and retained energy, there was a trend for greater maintenance energy requirements of lactating primiparous cows (P = 0.07). From the early weaning date to traditional weaning date, calf average daily gain (ADG) was greater (P < 0.01) for TW calves. Feed and energy efficiency of the pair was improved for the TW system (P < 0.01). Greater ADG were reported for EW calves during the stocker period (P = 0.03), but there were no differences during the finishing period (P > 0.40). At harvest, BW was greater (P = 0.02) and gain to feed ratio tended (P = 0.06) to be improved for TW calves. The increased TW calf performance offset the additional maintenance costs of their lactating dams, resulting in the TW system converting total feed energy to kilograms of calf BW gain more efficiently. [ABSTRACT FROM AUTHOR]

The objective was to compare whole cottonseed (WCS) with a more traditional supplement (20% breeder cube; BC) to determine the impacts on animal performance, metabolites, and methane emissions in beef cows. Cows (n = 24) were assigned to 1 of 2 experimental treatments (BC vs. WCS) based on age and body weight (BW). Supplements were fed individually at 0.9, 1.8, or 2.7 kg per day, resulting in 12 animals per supplement treatment and 4 animals per supplementation level within treatment. Two additional cows served as negative controls. Cows were fed 4 days per week, with supplementation levels being prorated at 1.6, 3.2, and 4.8 kg per feeding. Data collection occurred in 28-day intervals through d 84, with a final collection on d 99 after all cows finished calving. An amount fed per d × d interaction for BW change (P = 0.001) was detected. Cattle that were not supplemented (control) or received 0.9 kg per day lost more BW than cows that received 1.8 or 2.7 kg of supplement per day. There was a body condition score (BCS) change interaction for amount fed per d × d (P = 0.009). There was an amount fed per d × d interaction for back fat thickness (BFT; P = 0.02), and a tendency for an effect of amount fed per day on BFT (P = 0.07). There was a tendency for an amount fed per d × d interaction for fecal score (FS; P = 0.09) indicating that cattle receiving different amounts of supplement had varying trends in FS over time. A day effect was also observed for fecal score (P = 0.00003). There were no interactions (P = 0.55), effect of treatment (P = 0.85), or effect of amount fed per d (P = 0.45) for fecal pH. A treatment × amount fed per d × d interaction for plasma glucose concentrations (P = 0.04) was detected. An amount fed per d × d interaction was detected for plasma lactate concentrations (P = 0.01) indicating that cattle receiving different amounts of supplement had different trends in lactate concentrations over time. An effect of amount fed per d on plasma lactate concentrations (P = 0.05) was also observed. A tendency for an amount fed per d × d interaction for plasma urea nitrogen (PUN; P = 0.06) was observed indicating that cattle receiving different amounts of supplement had varying trends in PUN over time. No treatment effect on methane emissions was observed between cows consuming BC and WCS (P = 0.68). This experiment suggests that the supplementation of BC or WCS had minimal impacts on performance, metabolites, or methane emissions, but some interactions existed between supplementation source or level and day. [ABSTRACT FROM AUTHOR]

Four years of feedlot performance and carcass characteristics were pooled on spring-(SPRING) and fall-(FALL) born steers (n=460) into a mixed model to evaluate the effects of calving season, sire breed (Angus [AN], Charolais [CHAR] or Hereford [HER]) and their interaction on feedlot performance and carcass traits. Initial and final BW, DOF, ADG, DMI, and G:F were evaluated as performance measures and HCW, YG, FT, REA, and MS were collected at harvest. There was no season by breed interaction for entry or final BW (P >0.05). SPRING steers (400.2 kg, 686.4 kg) weighed more than FALL (350.9 kg, 668.3 kg) upon entering and leaving the feedyard (P< 0.001). CHAR weighed 14.3 kg less than AN upon feedlot entry (P=0.01) although final BW did not differ by breed (P >0.05). SPRING steers (21.8 kg/d) consumed more feed than FALL steers (18.8 kg/d; P=0.002), but there was no difference in gain:feed due to calving season nor sire breed (P=0.575). A calving season by sire breed interaction was present for ADG and DOF (P=0.014). FALL AN (1.70 kg/d) and FALL HER (1.80 kg/d) gained more than FALL CHAR (1.55 kg/d;P< 0.001) and FALL AN were fed over a shorter period than FALL CHAR and FALL HER (P=0.006). However, average daily gain of SPRING calves did not differ by breed (P >0.05). There was a tendency for FALL (400.9 kg) steers to have lighter carcasses than SPRING steers (407.9 kg; P=0.068). HER carcasses were 18.0 kg heavier than AN carcasses (P< 0.001), but did not differ from CHAR (P=0.13). CHAR had larger REA (93.5 cm2) than both AN (87.7 cm2) and HER steers (88.5 cm2;P=0.001). Fall-born steers had less YG than spring-born steers (P< 0.042). Feedlot performance was generally less for fall-born steers finished during the winter months. Under these conditions, numerous performance and carcass traits were influenced by the interaction of breed and season. [ABSTRACT FROM AUTHOR]

Two experiments (EXP1 and EXP2) evaluated the effects of NutraGen (NG) on calf health following exposure to bovine viral diarrhea virus (BVDV) on d -3 and Mannheimia haemolytica (Mh) infection on d 0. For each EXP, steers (BW = 251 ± 38.2 kg) were randomly allocated to 1 of 3 treatments (TRT). Treatments included a placebo (CON; EXP1 n = 5; EXP2 n = 5), a placebo fed from d -18 to d -3 followed by NG fed from d -3 to d 28 (CHLG; EXP1 n = 5; EXP2 n = 6), and NG fed from d -18 to d 28 (PREC; EXP1 n = 6; EXP2 n = 5). There was no treatment by time interaction (TRT×TME) or TRT effect for rectal temperatures (RT) or clinical scores (CS) in EXP1 or CS in EXP2 (P = 0.26). There was a TRT×TME for respiration rates (RR) during the first 24 h following Mh infection (P = 0.04), and a tendency for a TRT effect from d -3 to d 14, and overall in EXP1 (P ≥ 0.10). There was a tendency for a TRT×TME for RT from d -3 to d 14 in EXP2 (P = 0.04). There was a TRT effect for RR from d -3 to d 14 and overall in EXP2 (P ≥ 0.05). There was a TRT×TME for leukocytes during the first 24 h following Mh infection in EXP1 (P = 0.03) and overall in both EXP (P ≥ 0.001). There was no TRT×TME or TRT effect for neutrophils (NEU), lymphocytes (LYM), or NEU:LYM in EXP1 (P = 0.19); however, there were multiple TRT×TME and TRT effects for NEU, LYM, and NEU:LYM in EXP2 (P ≥ 0.05). These experiments suggest that NG has the potential to alter clinical and cellular responses during a bovine respiratory disease challenge. [ABSTRACT FROM AUTHOR]

The objective was to determine if restricting drinking water affects animal performance and hematological responses in cattle grazing high-moisture-content, fresh wheat pasture. Angus-cross steers (n = 10, 411 kg ± 24.5 kg) were randomly assigned to either 100% or 50% of baseline (d -7 to 0) water intake. The design of this experiment was a completely randomized design with 5 replications, with steer as experimental unit. Steers were individually hand-watered 1X per d for the entire experiment (d -7 to 28). Body weight, packed-cell volume (PCV), plasma total solids (PTS), fecal DM (F_DM), eyeball recession score (ERS) and skin turgor score (STS) were recorded from each steer weekly. Forage mass and forage DM were calculated weekly by hand-clipping ten, randomly-located samples using a 0.96-m forage hoop. Data were analyzed using ANOVA methods in SAS v9.4, and pairwise comparisons of means were completed using Fisher's LSD methods at the nominal 0.05 level of significance. Restricted steers gained less than unrestricted steers (P < 0.01, 1.04 vs. 1.35 kg / d, respectively). Fecal DM percentage did not differ (P = 0.26). There was no difference in PCV (P = 0.15) or PTS (P = 0.27); however PCV and PTS linearly decreased (P < 0.001) from d -7 to 28 for both treatment groups. Eyeball recession score and STS did not differ between treatment groups (P = 0.34). The mean forage mass and forage DM (d -7 to 28) were 2,229 kg per hectare and 24%, respectively. In conclusion, restricting water intake to cattle grazing wheat pasture resulted in lower ADG; however differences in hematological measures of dehydration were not observed in this study. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the impact of previous human interaction on the behavior of beef cows while they are being handled. To achieve this, 84 F-1 Angus x Brahman cows were randomly assigned to one of two human interaction treatments. The positive human-animal interaction group (P) was subjected to daily contact with a herdsman (on foot) for 15 minutes and was fed supplement by the herdsman. The control group (N) was checked daily and fed from a vehicle, with no direct human interaction. Each acclimation procedure was replicated in 2 pastures/herds (n = 16 to 26 cows in each herd). During routine processing times for these herds (d 0, 256, and 317), herds were gathered from their pastures and temperament was assessed. Chute and alley scores were assigned to individual animals by the same trained observer and ranged from 1 (calm) to 5 (aggressive). Chute exit velocity was also measured. Temperament variables were evaluated with ANOVA as a split plot with acclimation procedure in the whole plots and pasture as the whole-plot experimental unit, and processing time in the split plot. Neither human interaction (P = 0.99) nor time (P = 0.13) affected chute exit velocity. Chute score increased through time (P = 0.01) but was not affected by human interaction (P = 0.70). Alley score was not affected by human interaction (P = 0.32) or time (P = 0.81). Neither time nor the specific type of human acclimation we implemented affected cattle temperament, indicating other traits may be more important. Alternatively, different acclimation procedures may be more effective to improve cattle temperament. [ABSTRACT FROM AUTHOR]

A 72-d trial was conducted to estimate the combined effect of forage allowance and a fiber-based energy supplement in stocker cattle grazing wheat. Eight pastures (2.7 to 5.1 ha) each contained seven test steers (initial BW = 210 ± 36 kg). Weekly, additional steers were stocked in each pasture in a put and take method to achieve forage allowance of either 2.5 or 5.5 kg forage DM / kg steer BW (4 pastures each). Two pastures in each forage allowance were fed daily with a supplement containing 50% wheat midds and 50% soybean hulls at the rate of 1.5 kg per steer. Forage mass was measured twice weekly using a calibrated rising plate meter. Cattle were weighed weekly on calibrated scales. Data were analyzed using linear regression with pasture as the experimental unit. Mean ADG was 1.36 kg/d. One pasture in the high forage allowance, non-supplemented treatment was removed because we were unable to maintain the designed forage allowance. The interaction of forage allowance and supplement was not significant (P = 0.37) for ADG, and supplementation did not affect ADG (P = 0.20), however increased forage allowance tended to improve ADG (P = 0.06, 0.21 kg ADG per kg forage allowance). To further investigate forage DMI, a 14-d trial began on day 36. Three of the seven test steers in each pasture were randomly chosen and administered 7 ± 0.1 g of TiO2 daily at 0700 as an external marker to estimate fecal output. Forage DMI (at an assumed 72% DM digestibility) averaged 2.1% of midpoint BW, below our expectation. Additional forage allowance tended to improve estimated forage DMI (P= 0.06), but supplement had minimal effect (P = 0.30). [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the relative effects of stocker-phase implant strategies on growth and carcass characteristics of beef steers. In each of 2 locations (OK and MS), steers were grazed on cool-season annual pastures in fall 2018 through spring 2019. Steers (n = 300 in MS, n = 240 in OK) were randomly assigned to one of three implant treatments, 1) a single Synovex® One Grass implant at d 0, 2) a single Component® TE-G with Tylan implant at d 0, or 3) a reimplant treatment receiving Component® TE-G with Tylan at d 0 and again at d 82 (OK) or 85 (MS). Steers from each treatment were commingled in 2 (OK) or 3 (MS) pastures for 159 (OK) or 161 d (MS). Following grazing, steers were shipped to a commercial feedyard for finishing, sorted into 3 pens based on BW with each treatment equally represented in each pen, and were managed according to that site's BMPs. Steers from all treatments were implanted identically in the feedyard. Steers were slaughtered when the pen was visually estimated to be at 1 cm backfat. Carcass data of individuals were collected by camera grading equipment in the packing plant. Data were analyzed as a completely random design with animal as the experimental unit, treatment as a fixed effect, and pasture within location as a random effect. Marbling score tended to be greater in the single Component® TE-G with Tylan (treatment 2) vs. the other 2 treatments (425 vs 408 and 410, P = 0.07). No other production variables, including stocker-phase ADG, approached a significant difference (P > 0.39). No evidence was found to recommend stocker-phase reimplanting even in relatively long stocker phases with high ADG, and producers should consider selecting the most cost-effective implant at grazing initiation. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to evaluate the effects of virtual fencing on stress in beef cattle. In both experiments, cattle were contained by either physical, 2-strand electric fencing or by use of a proprietary, GPS-based virtual fencing collar, with no physical interior fencing. In both studies, hair from the tail switch was collected at the end of the experiment, and analyzed for cortisol concentration to measure the accumulated stress experienced by the cattle. Additionally, a subset of cattle were fitted with pedometers to measure behavior responses. In the initial pilot experiment, 55 heifers were grazed for 28 d in either 1 physically-fenced pasture or 1 virtually-fenced pasture. In the second experiment, 59 mature cows and heifers were grazed for 56 d in 1 of 2 physically-fenced or 1 of 2 virtually-fenced pastures (4 pastures total). In the second experiment, blood samples were also collected and NEFA and lactate were quantified in plasma. Only descriptive statistics were summarized for the pilot experiment, which indicated that hair cortisol concentrations were within published ranges for both fence types (0.39 ± 0.32 and 0.37 ± 0.15 pg/mg for physically- or virtually-fenced animals, respectively), and step count and motion index appeared elevated in the first few days of adaptation to virtual fence. The second experiment was analyzed with analysis of variance as a completely random design with pasture as the experimental unit. No effect of fence type was found for behavior (number of steps, standing time, lying bouts, or motion index; P > 0.16). Further, no difference was observed in cortisol, lactate nor NEFA (P > 0.14) concentrations due to fence type. None of this data suggests that virtual fencing is different from physical fencing in the effects on cattle stress and behavior, indicating further research and development of virtual fencing technology are warranted. [ABSTRACT FROM AUTHOR]

New technologies have enabled autonomous measurement of intake and feeding behavior of pen-fed animals and this has piqued interest in utilizing similar technologies in grazing experiments. Various feeding systems are currently available, but individual supplementation and feeding experiments have been conducted for years using individual feeding stanchions, which are the lowest level of technology for measuring supplement intake. These experiments are laborious as they require animals to be trained and acclimated, gathered at each feeding, and sorted into individual stalls for supplementation--thereby disrupting the animals grazing activities. In the mid-1980s Calan Gate systems (American Calan; Northwood, NH) became popular in pasture supplementation experiments, but still have many of the same disadvantages. Newer, more automated systems, reduce labor and possibly have less disruption of the animal's grazing behavior, but are reliant on the animal's willingness to use the system and ability to access it when more dominant peers are present. Individuals also do not always follow the "averages"-based rules we often hold true and behave differently in groups. Recent research with automatic feeders show steers consumed average of 60% of the potential supplement with supplement intake CVs of 50 to 100%. These technologies lead many to question the paradigm of experimental units in experimental designs. The experimental unit is defined as the smallest independently assigned unit to which the treatment is applied. This definition of experimental unit is somewhat limiting when taken to the extreme, but still applies well for experiments utilizing individual animal feeding, regardless of the level of technology involved. In many cases where the aforementioned technologies are used, the individual animal can be both the observational and experimental unit. This symposia presentation will discuss attributes of different feeding options and the implications on study design, experimental power, and the designated experimental unit. [ABSTRACT FROM AUTHOR]

Interest in automated, precision feeding equipment is increasing, and users need information about how to effectively use this new approach. Our objective was to determine the effect of competition for a feeding space at an automated supplement feeder on supplement intake behavior. Mixed breed beef steers (n = 128, initial BW = 257 ± 29.2 kg) were randomly assigned to 8 paddocks. One paddock (16 steers) was selected to have continuous access to the feeder for the duration of the 16-wk trial; this paddock was designated the "tester" paddock. The automated feeder consisted of a large bin that dispensed supplement into 4 feeding stations. Supplement dispense was triggered by the presence of an eligible animal's RFID tag; each steer was limited to 0.50 kg supplement/d by the electronics of the feeder. Weekly, additional paddocks were commingled with the tester paddock to increase competition for the feeder, resulting in a stocking density from 4 to 32 steers per feeding station in various weeks. Approximately 30% of the steers did not voluntarily use the feeder; therefore effective competition was less than the study design. Supplement intake and GPS location were recorded for steers in the tester paddock, and averaged for each wk; week was the experimental unit (n = 16). Weekly mean supplement intake and time spent near the feeder were regressed on feeder stocking density. Tester steers consumed an average of 0.36 kg supplement/d. Competition for a feeder space numerically reduced (P = 0.15) supplement intake by 0.002 kg/d per steer of competition. Steers spent 6% of the time within 15 m of the feeder regardless of competition (P = 0.82). This data illustrates that in scenarios similar to these experimental conditions, the feeder can be stocked with at least 80 animals with minimal effects on supplement intake. [ABSTRACT FROM AUTHOR]

Automatic feeding systems are being used more frequently to understand individual cattle behavior and intake variation when cattle are group housed. The objective of this experiment was to evaluate if bunk preference exists, and if so, how bunk preference affects performance, intake, or efficiency of feedlot steers. Angus steers (n = 123; initial BW = 293 ± 33.8 kg) were blocked by BW and sire and assigned to 1 of 4 pens, each containing 6 automated feed bunks (Insentec RIC; Hokofarm Group, Marknesse, Netherlands), in a randomized complete block design. Steers were fed a common diet and free to consume feed from any bunk within the pen without restriction. A steer's preferred bunk was defined as the bunk from which the most feed was consumed. In any week, 80% of steers consumed less than 29% of that week's total feed intake from the preferred bunk, indicating no strong preference for a specific bunk. The maximum weekly feed intake consumed from a preferred bunk was 57%. Further, the percentage of intake from the preferred bunk did not affect overall ADG, feed intake, or G:F (P > 0.64). These results suggest that a few steers may have a relatively strong preference for a specific feed bunk; however, this preference was not associated with performance, intake, or efficiency. Researchers can design experiments (at a stocking density of 5 steers per bunk) that restrict or alter an individual animal's access to any specific bunk, because such access, or lack of access, does not alter the animal's performance or feed intake. [ABSTRACT FROM AUTHOR]

The objective of this research was to determine the effect of competition for a feeding space at an automated supplement feeder on supplement intake behavior. A 2 yr study was conducted; each yr, 128 mixed-breed beef steers (n = 256, initial BW = 245 ± 27.5 kg) were randomly assigned to 8 paddocks. One paddock each yr (n = 16 steers) was selected to have continuous access to the feeder for the duration of the 16 wk trial; this paddock was designated the "tester" paddock. The automated feeder had 4 feeding stations that dispensed supplement after eligible animal's RFID tags were read by the electronics of the feeder. Steers were limited to 0.50 kg supplement/d. Weekly, additional paddocks were commingled with the tester paddock to increase competition for the feeder. This resulted in a stocking density from 4 to 32 steers per feeding station. For yr 2, one feeding station was disabled, resulting in a stocking density of 5.3 to 42.7 steers per feeding station. Approximately 31% of the steers did not voluntarily use the feeder; therefore, effective competition was less than the study design. Mean weekly supplement intake and GPS location were recorded for steers in the tester paddock. Additionally, pedometer data were collected in yr 2. Weekly mean supplement intake and time spent near the feeder were regressed on actual feeder stocking density with yr as a random variable; wk was the experimental unit (n = 16 wk). Tester steers consumed an average of 0.27 kg supplement/d. Competition for a feeding station numerically reduced (P = 0.01) supplement intake by 5 g/d per steer of additional competition. Steers spent 4.4% of the time within 15 m of the feeder regardless of competition (P = 0.54). As competition increased, steers took more steps (P < 0.01). These data illustrate that in environments similar to this experiment, the feeder can be stocked with at least 20 animals per feeding station with minimal effects on supplement intake. [ABSTRACT FROM AUTHOR]

Spring (SPRING) and fall (FALL) born steers (n = 211) were used in a mixed effects model to evaluate calving season and conception method [artificial insemination (AI) or natural service (NS)] on finishing performance and carcass traits. SPRING were weaned in October, grazed dormant range for 90 days and grazed wheat pasture for 90 days before shipping to finish. FALL were weaned in May, and grazed tallgrass prairie for 120 days before shipping to finish. Initial and final BW, days on feed, ADG, DMI, and gain to feed efficiency were evaluated as performance measures. Dry matter intake and gain:feed were analyzed on pen basis. Hot carcass weight, yield grade, fat thickness, ribeye area, and marbling score were collected at harvest. Bodyweight of SPRING and AI steers were heavier (P ≤ 0.05) entering and leaving the feedlot than FALL and NS steers, respectively. Compared to FALL steers, ADG (P < 0.01) and DMI (P = 0.03) were greater for SPRING and required less days on feed (P ≤ 0.05). Calving season and conception method (P ≥ 0.2) did not affect gain:feed. Conception method (P = 0.5) did not affect ADG, DMI, and days on feed. SPRING had higher yield grades (P < 0.01) and increased in fat thickness (P = 0.01) compared to FALL steers. There were no differences (P = 0.2) in hot carcass weight, ribeye area, and marbling score due to season of birth. Steers born from AI mating had greater hot carcass weight (P = 0.01) and marbling score (P = 0.02), but conception method did not affect yield grade, fat thickness, and ribeye area (P > 0.2). These results demonstrate SPRING steers are heavier entering and leaving the feedlot, have higher ADG and DMI, and require less days on feed; however, gain:feed, hot carcass weight, ribeye area, and marbling score did not differ from FALL steers. An economic analysis is needed to validate an AI program based on calving season in north-central Oklahoma. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the effects of supplementation level and type on forage intake of steers grazing a high-quality native range. This study was conducted in late May through the end of June. On d 0, steers (n=16, initial BW = 193.7 kg ± 14.3 kg) were randomly assigned to one of 5 dietary treatments, fed once daily in individual stalls for 28 d. Treatments were control (no supplement, n=4), or supplemented with either cottonseed meal or dry rolled corn, each at either 0.45 kg or 1.81 kg as-fed/d (n=3 for each combination). Beginning on d 7, steers were orally administered titanium dioxide boluses (10 g/steer) once daily for 21 d. Fecal samples were collected from the rectum once daily for 14 d, analyzed for Ti concentration via a handheld X-ray fluorescence analyzer, and total fecal output was estimated. Diet digestibility was estimated after a 288-h in situ incubation of forage and fecal samples to determine indigestible NDF. Some steers had orts, therefore actual mean supplement intake was used in analysis. Results were analyzed with regression, with animal as the experimental unit. Mean estimated forage DMI of unsupplemented animals was 1.6% BW. Contrary to expectation, corn supplemented steers exhibited greater forage DMI as a percentage of BW than cottonseed meal supplemented steers (P = 0.01; 1.5 vs. 1.1, respectively). [ABSTRACT FROM AUTHOR]

Interest in automated, precision feeding equipment is increasing, and users need information about how to effectively use this new approach. Our objective was to determine the effect of competition for a feeding space at an automated supplement feeder on supplement intake behavior. Mixed breed beef steers (n = 128, initial BW = 257 ± 29.2 kg) were randomly assigned to 8 paddocks. One paddock (16 steers) was selected to have continuous access to the feeder for the duration of the 16-wk trial; this paddock was designated the "tester" paddock. The automated feeder consisted of a large bin that dispensed supplement into 4 feeding stations. Supplement dispense was triggered by the presence of an eligible animal's RFID tag; each steer was limited to 0.50 kg supplement/d by the electronics of the feeder. Weekly, additional paddocks were commingled with the tester paddock to increase competition for the feeder, resulting in a stocking density from 4 to 32 steers per feeding station in various weeks. Approximately 30% of the steers did not voluntarily use the feeder; therefore, effective competition was less than the study design. Supplement intake and GPS location were recorded for steers in the tester paddock, and averaged for each wk; week was the experimental unit (n = 16). Weekly mean supplement intake and time spent near the feeder were regressed on feeder stocking density. Tester steers consumed an average of 0.36 kg supplement/d. Competition for a feeder space numerically reduced (P = 0.15) supplement intake by 0.002 kg/d per steer of competition. Steers spent 6% of the time within 15 m of the feeder regardless of competition (P = 0.82). These data illustrate that in scenarios similar to these experimental conditions, the feeder can be stocked with at least 80 animals with minimal effects on supplement intake. [ABSTRACT FROM AUTHOR]