G. C. Duff

Metabolic adaptations to heat stress in growing cattle.

To differentiate between the effects of heat stress (HS) and decreased dry matter intake (DMI) on physiological and metabolic variables in growing beef cattle, we conducted an experiment in which a thermoneutral (TN) control group (n=6) was pair fed (PF) to match nutrient intake with heat-stressed Holstein bull calves (n=6). Bulls (4 to 5 mo old, 135 kg body weight [BW]) housed in climate-controlled chambers were subjected to 2 experimental periods (P): (1) TN (18 degrees C to 20 degrees C) and ad libitum intake for 9 d, and (2) HS (cyclical daily temperatures ranging from 29.4 degrees C to 40.0 degrees C) and ad libitum intake or PF (in TN conditions) for 9 d. During each period, blood was collected daily and all calves were subjected to an intravenous insulin tolerance test (ITT) on day 7 and a glucose tolerance test (GTT) on day 8. Heat stress reduced (12%) DMI and by design, PF calves had similar nutrient intake reductions. During P1, BW gain was similar between environments and averaged 1.25 kg/d, and both HS and PF reduced (P<0.01) average daily gain (-0.09 kg/d) during P2. Compared to PF, HS decreased (P<0.05) basal circulating glucose concentrations (7%) and tended (P<0.07) to increase (30%) plasma insulin concentrations, but neither HS nor PF altered plasma nonesterified fatty acid concentrations. Although there were no treatment differences in P2, both HS and PF increased (P<0.05) plasma urea nitrogen concentrations (75%) compared with P1. In contrast to P1, both HS and PF had increased (16%) glucose disposal, but compared with PF, HS calves had a greater (67%; P<0.05) insulin response to the GTT. Neither period nor environment acutely affected insulin action, but during P2, calves in both environments tended (P=0.11) to have a blunted overall glucose response to the ITT. Independent of reduced nutrient intake, HS alters post-absorptive carbohydrate (basal and stimulated) metabolism, characterized primarily by increased basal insulin concentrations and insulin response to a GTT. However, HS-induced reduction in feed intake appears to fully explain decreased average daily gain in Holstein bull calves.

Serum luteinizing hormone, testosterone, and thyroxine and growth responses of ram lambs fed locoweed (Oxvtropis sericea) and treated with vitamin e/selenium

Sixteen ram lambs (5 m.o. old, 45 +/- 1.5 kg) received a control diet (50% concentrate, no locoweed, n = 4), locoweed (20% locoweed for 21 d, n = 4), MUSE (2 mL i.m. of MUSE containing 5 mg selenium and 50 mg vitamin E/mL, n = 4) on Days 21 and 35([Day 0 = first day of trial]), or locoweed + MUSE (n = 4). The rams were maintained in individual pens (3 x 9 m) with free access to feed, water, salt and shade. On Day 7 after initiating locoweed, serum alkaline phosphatase (AP) increased (P < 0.01), and serum thyroxine (T4) decreased (P < 0.01) in locoweed-fed rams. Effects on serum AP and T4 remained constant in rams during the 21 d of locoweed feeding. Treatment with MUSE did not influence (P > 0.10) AP or T4. Locoweed-fed rams had reduced (P < 0.05) intake and body weight for the 2-wk period after locoweed feeding ended. The MUSE regimen or diet had no effect on intake or body weight (P > 0.50). Neither locoweed nor MUSE affected serum LH before or after GnRH administration on Day 22 (P > 0.10). On Day 50, however, area under the LH curve (AUC) was 966 units in locoweed-fed rams and 1,373 units (+/- 154) in controls (P = 0.09). Serum testosterone (T) was reduced in locoweed-fed rams before and after (P < 0.05) GnRH on Day 22. On Day 50, the T AUC was numerically lower (P = 0.14) in locoweed-fed rams (1,252 units) than in controls (1,539 +/- 130 units). Conversely, MUSE treatment resulted in increased (P = 0.02) T AUC on Day 50 (1,148 and 1,643 +/- 130 units in control and MUSE-treated ram lambs, respectively). During the 6-wk period after locoweed feeding, serum immunoglobulin G averaged 14.0 and 18.6 (+/- 1.1) mg/mL in control and locoweed-fed rams (P < 0.01), respectively. Twenty percent dietary locoweed for 21 d exerts adverse effects on feed intake, growth, and reproduction in young ram lambs and MUSE was not effective in reversing these effects.

Effects of zilpaterol hydrochloride on growth rates, feed conversion, and carcass traits in calf-fed Holstein steers.

Two experiments were conducted to evaluate the effectiveness of zilpaterol hydrochloride (ZH) to enhance growth performance and carcass characteristics in calf-fed Holstein steers. In Exp. 1, Holstein steers (n = 2,311) were fed in a large-pen trial in 2 phases at a commercial feed yard in the desert Southwest. In Exp. 2, a total of 359 steers were fed in a small-pen university study. In Exp. 1 and 2, cattle were implanted with a combination trenbolone acetate-estradiol implant approximately 120 d before slaughter. Cattle were fed ZH for 0, 20, 30, or 40 d before slaughter at a rate of 8.3 mg/kg (DM basis). A 3-d withdrawal was maintained immediately before slaughter. Cattle within an experiment were fed to a common number of days on feed. During the last 120 d before slaughter, ADG was not enhanced by feeding ZH for 20 d (P = 0.33 in Exp. 1, and P = 0.79 in Exp. 2). Gain-to-feed conversion was increased by feeding ZH for all durations in Exp. 1 (P < 0.05). Feeding ZH increased HCW by 9.3 (Exp. 2) to 11.6 (Exp. 1) kg at 20 d compared with the control groups. Across both experiments, dressing percent was increased for all durations of feeding ZH (P < 0.05). Although skeletal maturity score, liver integrity, lean color, fat thickness, and KPH were not affected by feeding ZH for 20 d in either experiment (P >or= 0.6), LM area was increased for all durations of feeding ZH (P < 0.05). The percentage of carcasses identified as USDA Choice was reduced (P < 0.01) for all durations of feeding ZH in Exp. 1. This effect was not observed in Exp. 2. Holstein steers clearly respond to the beta-agonist ZH, and 20 d of feeding ZH with a 3-d withdrawal significantly increased carcass weights, muscling, and carcass leanness.

Effects of housing and feeding systems on performance of neonatal Holstein bull calves.

As the dairy industry continues to grow, more dairy calves are available for dairy, beef, and veal purposes. Rearing systems must be highly efficient to make this industry cost efficient, making the evaluation of rearing methods important to establish the most practical method. A study was designed and conducted to evaluate effects of housing and feeding systems on performance of neonatal Holstein bull calves. Treatments (2 × 2 factorial arrangement) consisted of: 1) individually housed, bottle-fed (n = 5 bull calves); 2) individually housed, bucket-fed (n = 5 bull calves); 3) group-housed, bottle-fed (n = 5 pens; 4 bull calves/pen); and 4) group-housed, bucket- (trough) fed (n = 5 pens; 3 or 4 bull calves/pen). Feeding treatments began on d 7 when calves had been acclimated to their new environment. Body weight measurements were collected every 7 d and blood samples were collected on d 0, 28, 55, and 66 for β-hydroxybutyrate (BHBA) concentration as a gross indicator of ruminal development. No housing × feeding interactions or feeding treatment effects were observed (P > 0.10). Average DMI (dry feed plus milk replacer) was increased (P < 0.05) for group-housed vs. individual animals after d 41, and final BW was greater (P < 0.05) for group-housed calves compared with individually housed calves. Feed efficiency and ADG, however, remained similar (P > 0.10) for all treatments. Fecal scores (P > 0.26), CV for BW (P > 0.26), and BHBA concentrations (P > 0.14) showed no differences among treatments. Housing system had greater effect on calf performance compared with milk feeding regimen.

Effect of Ractopamine Hydrochloride on Growth Performance and Carcass Traits in Calf-Fed and Yearling Holstein Steers Fed to Slaughter

Five studies using 2,105 calf-fed and yearling Holstein steers were conducted to evaluate the effects of ractopamine hydrochloride (RAC) on performance and carcass characteristics when fed for the final 28 to 38 d of the finishing period. In 4 calf-fed Holstein studies, RAC was incorporated to achieve intakes of approximately 0 (control), 200, and 300 mg/steer daily. In the yearling Holstein study, RAC was fed at 0 or 200 mg/steer daily. Each study consisted of 4 to 14 pens/treatment with 4 to 72 steers/pen, depending on study site. In the 4 calf-fed Holstein studies, ADG was increased (P 0.05) were noted in any carcass trait measurements. These data demonstrate that RAC improves growth performance, hot carcass weight, and LM area in both calf-fed and yearling Holstein steers while having a minimal impact on quality grade.

Roughage Source and Level in Beef Cattle Finishing Diets1

Three experiments were conducted to evaluate the effects of roughage level and source in beef cattle finishing diets. In Exp. 1,228 crossbred beef heifers (initial BW = 346 kg) were fed diets containing 7.5 or 15% roughage (DM basis), with alfalfa hay, sudangrass hay, or cottonseed hulls as roughage sources. Daily gain was not affected (P > 0.10) by roughage level, but DMI was increased (P 0.10)among roughage sources, but heifers fed alfalfa were least efficient. In Exp. 2, 224 crossbred beef steers (initial BW = 308 kg) were fed 90% concentrate diets with either whole-shelled or steam-flaked com as grain sources and either alfalfa hay or sudangrass hay as roughage sources. Daily gain was not affected by grain source, but DMI and feed:gain were greater (P 0.10) between sudangrass and alfalfa, but steers fed sudangrass had greater (P 0.10) daily gain. Daily DMI was increased (P < 0.03) for diets with sudangrass vs alfalfa, and responded quadratically (P < 0.11) to sudangrass level, with maximum DMI at 7.5% sudangrass. Feed:gain did not differ between the roughage sources but increased linearly (P < 0.11) with increasing level of sudangrass. These results indicate that roughage level and source alter DMI and performance by finishing beef cattle. Sudangrass hay consistently increased DMI relative to alfalfa hay in high-concentrate beef cattle finishing diets, but responses in daily gain and feed efficiency were not consistent between these two roughages. Further research is needed to characterize the relationship between chemical and physical characteristics of roughages and finishing beef cattle performance.

Effect of two dietary concentrate levels on tenderness, calpain and calpastatin activities, and carcass merit in Waguli and Brahman steers

The objective of this study was to compare carcass characteristics of a newly introduced breed, the Waguli (Wagyu x Tuli), with the carcass characteristics of the Brahman breed. Brahman cattle are used extensively in the Southwest of the United States because of their tolerance to adverse environmental conditions. However, Brahman carcasses are discounted according to the height of their humps because of meat tenderness issues. The Waguli was developed in an attempt to obtain a breed that retained the heat tolerance of the Brahman but had meat quality attributes similar to the Wagyu. Twenty-four animals were used. Six steers from each breed were fed a 94% concentrate diet and 6 steers from each breed were fed an 86% concentrate diet. Eight steers, 2 from each group, were harvested after 128 d, after 142 d, and after 156 d on feed. Waguli steers had larger LM, greater backfat thickness, greater marbling scores, and greater quality grades than the Brahman steers (P < 0.05). The Japanese Wagyu breed is well known for its highly marbled and tender meat, and these traits are also present in the Waguli. The Waguli had significantly lower Warner-Bratzler shear force values than the Brahman steers after 7 and 10 d of postmortem aging (P < 0.05); this difference decreased after 14 d postmortem (P = 0.2), when tenderness of the slower aging Brahman had increased to acceptable levels. Toughness of the Brahman has been associated with high levels of calpastatin in Brahman muscle, and the Waguli LM had significantly less calpastatin activity (P = 0.02) at 0 h postmortem than the Brahman LM. At 0-h postmortem, the total LM calpain activity did not differ between the Brahman and Waguli (P = 0.57). Neither diet nor days on feed had any significant effect on the 0-h postmortem calpain or at 0-h postmortem calpastatin activity, nor an effect on Warner-Bratzler shear-force values. In conclusion, LM muscle from the Waguli steers had a high degree of marbling, lower shear force values, and low calpastatin activity, all of which are related to more tender meat.

Influence of saline water on intake, digesta kinetics, and serum profiles of steers.

Nine yearling Holstein steers (avg weight 234 kg) were used to evaluate the influence of water salinity on feed and water intake, as well as several ruminal and serum characteristics. The ruminally cannulated steers were individually fed low-quality mixed hay simulating a range diet. Steers were assigned randomly to receive either control (C) water containing 350 ppm total dissolved solids (TDS) or a treated water (HS) containing 2,300 ppm TDS. The experiment included a 14-day adjustment period and a 15-day measurement period. High-saline water did not affect (P = 0.18) feed or water intake, although there was a tendency for greater consumption of both feed and water in HS steers. The HS steers had slower (P = 0.10) particulate passage rates and longer (P = 0.06) rumen retention times on day 1 of the measurement period, indicating possible differences in particle density and (or) particle size. On day 1, undigested dry matter (DM) fill was greater (P = 0.05) in HS steers compared with C (80.7 vs 61.5 g/kg BW); similar trends occurred on day 8. The HS steers also had greater (P = 0.02) rumen fluid volumes, but similar (P = 0.45) fluid dilution rates compared with C steers. No in situ DM disappearance differences were detected (P greater than or equal to 0.38) at incubation times ranging from 12 to 72 hours. No clinical or sub-clinical toxicological symptoms were observed in HS compared with C steers. This study suggests that cattle can ingest saline water containing 2,300 ppm TDS on a short-term basis with no adverse effects.

Effects of Degree of Processing and Nitrogen Source and Level on Starch Availability and in Vitro Fermentation of Corn and Sorghum Grain

Ruminal fluid from two heifers (384 ± 2 kg) fed an 85% concentrate diet was used to determine effects of degree of processing and N source and level on in vitro DM disappearance (DMD), starch availability, pH changes, and NH3 concentrations of corn and sorghum. In Exp. 1, treatments (2 × 4 factorial) were unprocessed corn and sorghum (UP) and each grain steam-flaked to bulk densities (BD) of 0.38, 0.33, and 0.28 kg/L (C38, B33, A28, respectively). Treatments in Exp. 2 (2 × 2 × 3 factorial within grain type) were UP and A28 with 0, 10, or 20 mg of N/g provided by either urea (U) or casein hydrolysate (CH). Starch availability of both grains increased linearly (P 0.10) DMD of corn or sorghum beyond 4 h, but DMD increased linearly (P<0.04) as N level increased at 8, 12, 18, and 24 h for corn and at all incubation times for sorghum. At 8 through 24 h, CH and U increased NH3 of UP and A28 corn linearly (P<0.001), but the magnitude was greater (P<0.001) for U than for CH; the same trends were evident (P<0.001) at 12, 18, and 24 h for NH3 of sorghum treatments. Increasing N level increased pH of corn linearly (P<0.05) at 4, 8, 18, and 24 h, with a greater increase for U than for CH. Increasing N level increased pH of sorghum linearly (P<0.03) at 1 through 24 h, but to a greater extent for U than CH at 1, 2, 12, and 18 h. Degree of processing and level of supplemental N were positively related to in vitro DMD, whereas no benefit was evident from supplementing amino acid N compared to U.

Potential Foraging Decisions by a Desert Ungulate to Balance Water and Nutrient Intake in a Water-Stressed Environment

Arid climates have unpredictable precipitation patterns, and wildlife managers often provide supplemental water to help desert ungulates endure the hottest, driest periods. When surface water is unavailable, the only source of water for ungulates comes from the forage they consume, and they must make resourceful foraging decisions to meet their requirements. We compared two desert bighorn sheep (Ovis canadensis nelsoni) populations in Arizona, USA: a treatment population with supplemental water removed during treatment, and a control population. We examined whether sheep altered their seasonal diets without supplemental water. We calculated water and nutrient intake and metabolic water production from dry matter intake and forage moisture and nitrogen content, to determine whether sheep could meet their seasonal daily water and nutrient requirements solely from forage. Diets of sheep were higher in protein (all seasons) and moisture (autumn and winter) during treatment compared to pretreatment. During treatment, sheep diet composition was similar between the treatment and control populations, which suggests, under the climatic conditions of this study, water removal did not influence sheep diets. We estimated that under drought conditions, without any surface water available (although small ephemeral potholes would contain water after rains), female and male sheep would be unable to meet their daily water requirements in all seasons, except winter, when reproductive females had a nitrogen deficit. We determined that sheep could achieve water and nutrient balances in all seasons by shifting their total diet proportions by 8–55% from lower to higher moisture and nitrogen forage species. We elucidate how seasonal forage quality and foraging decisions by desert ungulates allow them to cope with their xeric and uncertain environment, and suggest that, with the forage conditions observed in our study area during this study period, providing supplemental water during water-stressed periods may not be necessary for desert bighorn sheep.