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Tall fescue (Festuca arundinacea Schreb.) infected with the endophyte Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon, and Hanlin) causes fescue toxicosis in cattle grazing the forage, but effects of the endophyte were considered to be abated soon after removal of the animals from pastures. Tasco-Forage, a proprietary extract from the brown seaweed Ascophyllum nodosum, is a known source of cytokinins and has increased antioxidant activity in both plants and the animals that graze the forage. Tasco was applied at 0 and 3.4 kg/ha to infected and uninfected tall fescue pastures in Virginia and Mississippi. Forty-eight steers grazed the pastures at each location during each of 2 yr (n = 192) before being transported to Texas for feedlot finishing. On arrival at the feedlot, steers from Tasco-treated pastures had higher (P < 0.01) monocyte phagocytic activity and tended (P < 0.07) to have higher major histocompatibility complex class II expression than steers that grazed the untreated pastures. A depression (P < 0.05) in monocyte immune cell function due to grazing infected fescue was detected throughout the feedlot finishing period but was reversed by Tasco. Rectal temperatures were elevated (P < 0.07) in steers that had grazed the infected tall fescue when they arrived in Texas, but by d 14 no difference was detected. However, by d 28 the temperature effects of infected tall fescue were reversed. Steers that had grazed infected fescue had lower (P < 0.01) rectal temperatures on d 112 of the feedlot period, demonstrating a much longer-lasting effect of the endophyte on thermoregulatory mechanisms than previously thought. Steers that had grazed Tasco-treated pastures had higher (P < 0.01) rectal temperatures on d 56 than steers that had grazed untreated fescue. Steers that had grazed the Tasco-treated pastures had higher marbling scores (P < 0.05) regardless of the endophyte, but no effect of Tasco or endophyte on gain was measured. Our data suggest that Tasco application to tall fescue pastures alleviated some of the negative effects of tall fescue toxicity.

Tasco-Forage is an Ascophyllum nodosum seaweed-based product that has increased antioxidant activity in both plants and animals. Endophyte (Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon, and Hanlin)-infected and uninfected tall fescue (Festuca arundinacea Schreb.) pastures in Virginia and Mississippi during 1997 were treated or not with 3.4 kg Tasco/ha in April and July. There were two replications of each treatment at each location. Forty-eight steers (6/replication) grazed pastures at each location (n = 96) from April to October prior to transportation to Texas Tech, Lubbock, for finishing during a 160-d period in the feedlot. Blood (antemortem) and liver (postmortem) samples were collected. After slaughter and chilling, the left strip loins (IMPS #180) were collected from three randomly selected steers from within each pasture replication (n = 48). Strip loins were vacuum-packaged and stored at 2 degrees C. At postmortem d 7, 14, 21, and 28, strip loins were removed from packaging and fabricated into 2.54-cm steaks. Following each fabrication day postmortem, the strip loins were repackaged and stored at 2 degrees C until the following postmortem time. After the prescribed fabrication, steaks were overwrapped with polyvinyl chloride film, subjected to simulated retail display at 2 degrees C for up to 3 d, and subjective and objective color were evaluated daily by a trained panel. Steaks from Mississippi steers that had grazed Tasco-treated fescue retained higher (P < 0.05) CIE a* color scores throughout retail display. Steaks were more uniform and had less discoloration and less browning (P < 0.05) if they were from steers that had grazed Tasco-treated fescue, and the effect was greatest for steers from Mississippi (location x Tasco interaction; P < 0.05). The endophyte in tall fescue may decrease uniformity and increase lean discoloration and two-toning of beef steaks when removed from vacuum packaging on or beyond d 21 postmortem (endophyte x Tasco x postmortem day interaction: P < 0.05). Vitamin E in liver was increased (P < 0.06) and serum vitamin E was decreased (P < 0.09) in steers that had grazed the treated pastures. These experiments indicated that Tasco applied to tall fescue during the grazing season can improve color stability and extend beef shelf-life, particularly in cattle grazing infected tall fescue. The mode of action of Tasco is not clear, but antioxidants and specific vitamins may be involved.

Effect of preservation method on intake and chewing behavior was examined using a first, late vegetative harvest (mid-June) of Kanlow switchgrass (Panicum virgatum L.). For silage (S), forage was harvested with a commercial field chopper (1.5 to 4 cm average chop length) and ensiled directly in silos 1.2 m in diameter and 3.6 m in height. For hay (H), forage was harvested with a flail-chopper (7 to 15 cm average chop length) and cured as hay in a drier at 77 degrees C. Diets of H and S were fed to six Hereford steers (338+/-5 kg) in a single crossover experiment. Chewing behavior was monitored for 4 d with a computerized system. At feeding, H was higher in DM and contained greater concentrations (DM basis) of NDF, CP, and hemicellulose, but lower concentrations of ADF and cellulose, and had lower in vitro DM disappearance values. Steers fed S had higher intakes of DM (P < .02) and NDF (P < .04) and consumed less water from the water supply (P < .01) than animals fed H. However, total amount of water (from water supply and feed) consumed per kilogram of DMI did not differ between diets. Crude protein intake was similar between diets. Preservation method had no effect on eating time, number of boli ruminated, bolus duration, and number of rumination chews per bolus. Steers fed S made fewer eating chews (P < .10) and ruminated for a longer time (P < .05) while making a greater number of rumination chews (P < .04) than steers fed H. Rumination intercycle time was slightly shorter in steers fed H (P < .05) than in steers fed S. When expressed per kilogram of NDF intake, steers fed S spent less time eating (P < .03) and made fewer eating chews (P < .02) than steers fed H; however, rumination time, number of rumination chews, and number of boli ruminated were not affected by preservation method. Steers fed S ingested feed at a greater rate (P < .03), excreted smaller fecal particles (P < .03), had meals of shorter duration (P < .06), spent less time eating during main meals (meals following feed distribution: P < .05), had more rumination periods (P < .01), and a shorter morning (P < .06) latency time (interval between end of main meal and onset of rumination) than steers fed H. These results indicate that preservation method with its concomitant differences in chop length affected forage chemical composition and voluntary intake, and that differences in chewing behavior occurred mostly during eating.

Matua bromegrass (Bromus willdenowii Kunth. cv. Grasslands Matua) was introduced in 1973, but little information exists concerning its potential as a hay for horses. Thus, voluntary intake and apparent digestibility of OM, CP, and fiber components of Matua by 18 Quarter Horse yearlings (mean initial BW 354 kg; SE 5.8) were compared with alfalfa (Medicago sativa L.) and coastal bermudagrass (Cynodon dactylon L.) as hays in a randomized block design. A 15-d adjustment period was followed by a 5-d collection period during which the hays were consumed ad libitum. Voluntary intake of DM was greater (P<.01) for alfalfa (10.9 kg/d) than for the mean of the grasses, and intake of Matua (10.0 kg/d) was greater (P<.001) than that of bermudagrass (7.4 kg/d). Apparent digestibility of OM was greater (P<.001) for alfalfa (74%) than for the mean of the grasses but did not differ between Matua (64%) and bermudagrass (60%). At the end of the digestion trial, each yearling was offered each of the three forage hays during an 11-d period to determine subsequent preference and effect of previous hay experience. Yearlings preferred alfalfa over the grass hays and generally selected more Matua than bermudagrass. All yearlings consumed less of the forage species to which they had been previously exposed compared with unadapted yearlings. The Matua hay fed in this trial was palatable and met most of the nutritional needs for yearling horses.

Five maturities of switchgrass hay harvested at 14-d intervals (vegetative through 20% heading) were fed to Hereford steers (297 kg) in a 5 x 5 Latin square. Relationships with switchgrass maturity were negative and quadratic (P < .05) for DMI and cubic (P < .05) for digestible DMI. Declines in apparent digestibilities of DM, ADF, and cellulose were cubic (P < .05), whereas these were quadratic (P < .05) for NDF, hemicellulose, and CP. Whole masticates from the least, mid, and most mature hays showed linear (P < .05) declines in DM concentration and IVDMD with increasing maturity, whereas NDF concentrations increased linearly (P < .05). Mean retention time of gastrointestinal DM increased linearly (P < .01) from 64 to 94 h from the least to the most mature hay, and the associated rate of passage declined linearly (P < .01) from 3.3 to 2.1%/h. Sieving of masticate DM showed a reduced proportion of large particles (> or = 2.8 mm) and an increased proportion of small particles (< or = .5 mm) with advancing forage maturity. More than 94% of the sieved fecal DM passed a 1.0-mm sieve, but particle sizes showed the same relationship with forage maturity as noted for masticate DM. This occurred despite the comminution from the rumination and digestive processes.

Coastal bermudagrass (Cynodon dactylon [L.] Pers) hay was fed to four ruminally cannulated steers (380 +/- 14 kg BW) of evaluate the effects of intake level on digesta flow kinetics in a 4 x 4 Latin square design. Forage intakes represented 50, 70, 88, and 99% of feed voluntarily consumed per animal during a pre-experimental period. Masticated boli and wet-sieved masticated leaves (ML) and stems (MS) retained by a 4.0-mm sieve and feces retained by a .063-mm sieve were mordanted with chromium or marked with erbium, ytterbium, or dysprosium, respectively. Particle markers and a solution of Co-EDTA were pulse-dosed via the ruminal cannula. A continuous infusion of Co-EDTA was later delivered with peristaltic pumps. Intake level had no effect (P > .10) on fluid and particle passage rate (PR; percentage/hour) of any fractions marked. For all particle fractions, increasing intake level caused linear decreases in mean retention time (MRT; P < .03 to P < .07) and linear increases in gastrointestinal tract fill (FILL; P < .003 to P < .02) and fecal output (FO; P < .001). Estimates of FO and DM digestibility from the pulse dose of Cr mordant and continuous infusion of Co-EDTA did not differ. Kinetic estimates differed in magnitude according to the characteristics of the particle fractions marked. Marked feces gave the shortest estimate of MRT and the smallest estimate of FILL and FO. Kinetics of ML and MS also differed (P < .001), the former having faster PR, shorter MRT, and smaller FILL and FO. Use of representative samples of ingested feed should give more realistic estimates of digesta kinetics than estimates derived from ingesta fractions because kinetics of separated leaf and stem fractions differed.

Eastern gamagrass (Tripsacum dactyloides [L.] L.) has attracted attention as a forage crop, but information on its use is lacking. This 2-yr study compared diet quality, ingestive mastication, and ADG by steers grazing eastern gamagrass (GG), flaccidgrass (Pennisetum flaccidum Griseb.), and Tifton 44 bermudagrass (Cynodon dactylon [L.] Pers.). The design was a randomized complete block with two agronomic replicates. The diet selected by steers from GG in May did not differ from the diet selected by steers from flaccidgrass (FG) for IVDMD (77.3%), NDF (44.0%), CP (19.5%), and mean and median particle sizes of the ingesta (1.8 and 1.4 mm). In July, GG diets had three percentage units less IVDMD (P less than .05), 8.4 percentage units more NDF (P less than .05), and 4.5 percentage units less CP (P = .07) than the mean of FG and bermudagrass (BG). The canopy (July) of GG had the greatest proportion of its DM as leaf (59 vs 26% for FG and 22% for BG) and the least proportion as stem (25 vs 40% for FG and 59% for BG). Mean particle size (millimeters) of masticates differed (P = .05) among forages with GG greatest (2.2), followed by FG (1.6), and BG particles were smallest (1.2). Proportion of large (greater than or equal to 2.8 mm), medium (less than 2.8 greater than or equal to .5 mm), and small (less than .5 mm) particles of the masticate DM, and their IVDMD and NDF concentration, interacted with species (P less than .05). Gamagrass masticate had the greatest proportion (28%) of large particles and BG the greatest proportion (23%) of small particles. The least IVDMD occurred for large particles of BG (62.5%) and small particles of GG (63.8%). Digesta kinetics did not differ among species. Characteristics of GG yielded steer ADG of .82 vs .67 kg for FG and .30 kg for BG (P = .05).

A procedure to estimate dimensions of digesta particles was developed and evaluated. After wet sieving, particles of masticated switchgrass and bermudagrass hays retained on sieves with apertures of 1.0 mm2 or larger were placed on moist white filter paper, separated manually, and photographed. Photographs were scanned with a flat-bed scanner, scaled to size, and digitized. Projected area, perimeter, length, and width of particles were determined by a microcomputer system. Variables derived for each particle included the form factor, which was defined as (4 x pi x area)/perimeter2, and each particle's length: width ratio. Ninety-three percent of data from two trials with steers had significant lack of fit (P less than .05 to P less than .0001) to normal, lognormal, Weibull, or gamma distributions. As an alternative, individual particle measurements were summed on a cumulative percentage basis for each variable and were fit to an inverted Gompertz function to estimate median, mode, and mean dimensions of scanned particles. Estimates from the equation fit the distribution well; asymptotic SE averaged 3.5 and 1.4% of parameter means for dimensions of masticated switchgrass and bermudagrass hay particles, respectively. No analytic solution exists for the mean, which must be estimated numerically, but analytic solutions are available for the median and mode. Use of this equation will prevent bias caused by lack of fit to a particular distribution and yield more accurate estimates of mean particle dimensions than arithmetic means.

In traditional grazing trials, per animal and per hectare productivity are determined, but pasture and animal measurements are generally inadequate to address reasons for different treatment responses. This 2-yr study examined the diet and diet characteristics of steers grazing tall fescue (Festuca arundinacea Schreb.), switchgrass (Panicum virgatum L.), flaccidgrass (Pennisetum flaccidum Griseb.), and bermudagrass (Cynodon dactylon [L.] Pers.) pastures. A randomized complete block design was used with two agronomic replicates. In vitro DM disappearance (IVDMD) of masticates from tall fescue (TF), switchgrass (SG), and flaccidgrass (FG) generally were similar; all exceeded 70% (70.3 to 79.9%), except for bermudagrass (BG), which was lowest (63.5 to 65.0%). Sieving the masticate DM showed BG to contain the highest proportion (20 to 29%) of particles passing a .5-mm sieve and the lowest proportion (6 to 8%) of particles retained on a 2.8-mm sieve. This resulted in BG having the smallest mean (1.29 mm) and median (1.08 mm) particle sizes in yr 1 and a mean (1.10 mm) and median (.91 mm) particle size smaller than SG in yr 2. Except for BG, the IVDMD of the masticate DM was lowest for small particles. Canopies showed BG and SG to have the highest proportion of stem (47 and 52%, respectively); the BG canopy was composed of fractions that were consistently lowest in IVDMD. In general, BG offered the grazing animal a canopy inferior in IVDMD concentration and had canopy characteristics that limited the animals' selection of a diet with quality as high as that of TF, SG, or FG.

Animal responses to treatments in grazing experiments frequently remain unexplained because of inadequate pasture and(or) animal measurements. This 2-yr study examined DMI, gastrointestinal tract fill of undigested DM (FILL), rate of digesta passage (ROP), and digesta mean retention time (MRT) for steers grazing tall fescue (Festuca arundinacea Schreb.), switchgrass (Panicum virgatum L.), flaccidgrass (Pennisetum flaccidum Griseb.), and bermudagrass (Cynodon dactylon [L.] Pers.). A randomized complete block design was used with two agronomic replicates. Comparisons in June (yr 1) among continuously grazed switchgrass (SG), flaccidgrass (FG), and bermudagrass (BG) or in May (yr 2) among tall fescue (TF), SG, and FG showed similar digesta kinetics, but different DMI (kg.d-1.100 kg BW-1), among these forages within each sampling. In the June evaluation, the DMI of SG and FG were similar (means = 3.09), DMI of bermudagrass (BG) was lowest (2.23), and fecal DM output (FO) was similar among forages. In the May evaluation, DMI by steers grazing SG (3.90) was higher than that by steers grazing FG (2.97); DMI of tall fescue (TF) was intermediate (3.41) but similar to DMI of FG. Differences in DMI were due to differences in diet in vitro DM disappearance (IVDMD) rather than to differences in digesta kinetics. In July (yr 2), the MRT was highest for BG (84 h) and similar for SG and FG (57 h). Steers grazing different forages exhibited similar ROP and FILL, but FO (kg.d-1.100 kg BW-1) among steers varied (.37 for steers fed BG; .74 for steers fed SG and FG).(ABSTRACT TRUNCATED AT 250 WORDS)

In an experiment to determine the effects of mastication and microbial contamination on in situ forage disappearance, samples of masticated (M) or nonmasticated alfalfa hay (AH), orchardgrass hay (OGH) and bermudagrass hay (BGH) were incubated in the rumen of two steers for 6, 12, 24, 48 and 96 h. Using diaminopimelic acid as a marker, microbial DM and CP contamination ranged from 10.3 to 22.3% and 46.3 to 95.3% of residual DM and CP, respectively. Percentage contamination was influenced by both time of incubation and forage treatment (P less than .001). Corrected DM and CP disappearances (DMD and CPD) were higher than apparent disappearances (P less than .001). Maximal NDF and ADF disappearances (NDFD and ADFD) obtained at 96 h were 58.2, 52.4; 62.7, 62.3 and 56.7, 52.6% for AH, OGH and BGH, respectively. Lag times (h) for corrected DMD and CPD were shorter (at least P less than .05) than for apparent disappearances, except for corrected CPD of AH. There were no differences (P greater than .10) in lag time of NDFD or ADFD among forages. Rates of disappearance (%/h) of corrected DMD and CPD were faster (at least P less than .01) than for apparent disappearances. The total quantity of microbial CP (mg CP/g DM) associated with residues varied with time depending on forage type (P less than .001). There was a significant relationship between the quantity of microbial CP contamination and the extent of disappearance. Masticated forages followed trends similar to those of nonmasticated forages, but the effect of mastication was not consistent. Results support the need for microbial correction of in situ forage residues.

Samples of digesta from the ruminal upper strata (RUS) and feces (F) were taken from four ruminally cannulated steers fed Coastal bermudagrass hay (78% NDF) in the long form to evaluate the effects of feeding level and time postfeeding on particle breakdown. The experimental design was a 4 x 4 Latin square with 18-d periods. Treatments based on previous intakes were set at 50, 70, 90 and 110% (3.1, 4.4, 5.5 and 6.7 kg/d, respectively) of feed consumed per animal and fed at 12-h intervals. Samples were taken at 2, 6 and 12h postfeeding and wet-sieved. Dry matter weight distribution of total recovered particles was used to partition RUS and F digesta among percentages of large (greater than 4.0 mm), medium (greater than 4.0 and less than or equal to 1.0 mm), small (less than 1.0 and greater than or eual to .125 mm) and fine (less than .125 and greater than or equal to .0027 mm) particles. With increasing feeding level, the percentage of medium RUS particles increased linearly (P less than .02), whereas the percentage of fine RUS particles decreased linearly (P less than .01). Increased time postfeeding resulted in a linear decrease in the percentage of large RUS particles (P less than .01), a linear increase in the percentage of small RUS particles (P less than .01) and in a quadratic increase in the percentage of fine RUS particles (P less than .01). Percentage of medium RUS particles remained unchanged. Increasing feeding level resulted in linear increases in mean RUS (P less than .01) and F (P less than .02) particle sizes. Percentages of RUS and F material passing through a 1.0-mm sieve averaged 52.8 and 88.8%, respectively. Animal-to-animal variation in proportions of RUS and mixed reticuloruminal particles was not entirely removed by rumination and was still reflected in the percentages of F particles. Factors such as particle entrapment in the fiber mat, reticular sedimentation, changes in specific gravity, swelling and hydration capacity, reticuloruminal motility and amount of digesta exiting per contraction appear to be more important than particle size reduction in the regulation of the passage of digesta from the reticulorumen.

Coastal bermudagrass (Cynodon dactylon [L.] Pers.) hay was fed in the long form to four ruminally cannulated steers to evaluate the effects of intake level on the physical reduction of feed particles during ingestive mastication. The experimental design was a 4 x 4 latin square with 18-d periods. Treatments based on previous intakes were set at 50, 70, 90 and 110% of feed consumed per animal and fed at 12-h intervals. Boli of ingested, masticated hay were collected at the cardia and separated by wet-sieving into fragments retained on sieves of .0027 to 4.0 mm (mesh aperture). In addition, particles retained on the 4.0-mm and 2.0-mm sieves were scanned by image analysis. Ingestive mastication resulted in a linear decrease (P less than .05) in the proportion of boli particles retained on the top (4.0-mm) sieve and linear increases on the 2.0- (P less than .02), 1.0- (P less than .06) and .25-mm (P less than .06) sieves with increasing level of intake. Sixteen to 21% of the ingested hay particles passed through a 1.0-mm sieve. Mean particle size, as determined by sieving data, decreased linearly (P less than .05) as feeding level increased. Image analysis showed no differences in length (L) or width (W) of particles retained on the 4.0- and 2.0-mm sieves as feeding level increased, but L/W decreased linearly (P less than .05) on both sieves. The frequency of jaw movements following feeding was very similar across feeding levels and averaged 71.3 chews/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Samples of forage fragments were obtained from the upper (RUS) and lower (RLS) strata of the reticulorumen and feces (F) of four Brahman X Jersey steers grazing Coastal bermudagrass (CB) of two maturities with dry matter digestibilities (DMD) of 54.8 and 64.3%. Forage fragments were separated by particle size and evaluated histochemically for tissue type and fragmentation pattern. Fragmentation pattern was similar to that previously observed due to ingestive mastication. There was longitudinal separation of vascular bundles (VB) and severing at VB ends. Microscopically, similar size fragments from RUS were indistinguishable from those of RLS. The major difference between RUS and RLS was the distribution of different size particles. Larger particles were associated with the RUS in cattle consuming immature and mature CB. More large particles were associated with mature compared with the immature CB in the RUS and RLS. The distribution of different size particles in the F was similar for both maturities, suggesting that similar particle size reduction was required regardless of maturity. Smaller particles in the rumen and F appeared to contain more lignin (determined histochemically) and were composed of indigestible fragments of cuticle and lignified vascular tissue. Cattle grazing mature CB had higher ruminal fills (2.40 vs 2.02 kg dry matter/100 kg body weight), reduced rates of passage and lower voluntary intake (2.50 vs 3.14 kg DM/100 kg body weight). Lower intake of mature CB may have resulted from a reduced rate of particle size reduction. Similarities in fragmentation patterns due to ingestive and ruminative mastication were interpreted to indicate that mastication was responsible for most of the particle size reduction of CB and that mastication facilitated digestion of potentially digestible tissues.

Coastal bermudagrass hay was labeled with Cr by the Cr-mordant procedure and with 177Lu applied to the same fiber. Neutral detergent fiber prepared from the same Coastal bermudagrass hay was labeled with Yb, 169Yb, Tb and 160Tb by soaking overnight following by thorough washing and drying. Wood chips were similarly labeled with Sm or La, and Solka Floc was labeled with 147Nd and 141Ce. The carriers, labels and times of administration to cattle were: bermudagrass fiber with both Cr and 177Lu, bermudagrass fiber with 169Yb and Solka Floc labeled with 147Nd at 0 h; bermudagrass fiber with Yb, Solka Floc with 141Ce and wood chips with Sm at 24 h; wood chips with La at 48 h; and bermudagrass fiber labeled with 160Tb at the beginning and labeled with Tb at the end of a meal. Fecal collection followed and passage characteristics were determined with a two-compartment, age-dependent model. Markers labeling the different fiber sources had different (P less than .01) passage rates (Solka Floc greater than Coastal bermudagrass greater than wood chips), but there was no difference within fiber source for rare earth passage. There also was no difference between the passage characteristics of Cr-mordant and 177Lu. However, passage rate of particles administered at the beginning of the meal (160Tb) was 42% higher than for particles at the end of the meal (Tb).(ABSTRACT TRUNCATED AT 250 WORDS)