Search

Five studies were conducted to evaluate the effects of lipid source on performance and health of stressed feeder cattle. A total of 332 heifers (195 [+ or -] 2.37 kg initial BW) in trial 1 and 336 heifers (206 [+ or -] 1.70 kg initial BW) in trial 2 were fed diets containing ground flaxseed (FLAX), rolled full-fat soybeans (SOY), or tallow (TAL) at 13, 20, or 4%, respectively (DM basis). All diets were formulated to be isonitrogenous and isocaloric. The ADG and G:F for the first 7 d and for the entire feeding period were greater (P < 0.05) for TAL and FLAX than for SOY. Percentage of animals treated and retreated for bovine respiratory disease did not differ among dietary treatments. The FLAX treatment increased (P < 0.05) total n-3 PUFA concentrations in the plasma, whereas SOY increased (P < 0.05) plasma concentrations of total n-6 PUFA. In trial 3, 18 steers were individually fed diets containing TAL and 18 steers were fed a diet containing SOY (20% of DM). In trials 4 and 5, 18 steers were individually fed diets containing TAL and 18 steers were fed diets containing FLAX (12.9% of DM). On d 14 and 17 of study 3, 4, and 5, 16 steers from each dietary treatment were injected i.v. with Escherichia coli O55:B5 lipopolysaccharide (LPS), and 2 steers from each diet were injected with saline. Rectal temperatures after LPS challenge were lower (P < 0.05) for SOY and FLAX than for TAL, and plasma TNF was greater (P < 0.05) for SOY than for TAL. Serum haptoglobin and blood fibrinogen increased and white blood cell count decreased in response to LPS, but none of these variables was affected by treatment. Although this research failed to measure an effect of lipid source on feedlot morbidity or mortality, these studies indicate that altering the source and type of dietary fatty acids may modify the immune response in stressed feeder cattle and that performance may be hindered by feeding full-fat soybeans to receiving cattle. Key words: endotoxin challenge, immune modulation, lipid, receiving cattle, plasma lipid

To determine the response to alteration in site and form of carbohydrate delivery to the digestive tract, in vitro rates of lipogenesis and lipolysis in mesenteric (MESA), omental (OMA), and subcutaneous (SQA) adipose depots were compared. Forty crossbred beef steers (243[ + or -]2 kg of BW) were fed 161 (LI) or 214 (HI) kcal of ME/(kg of [BW.sup.0.75.sub..d]) or they were fed LI and infused for 35 d into the rumen (R) or abomasum (A) with starch hydrolysate (SH) or into the abomasum with glucose (G). Jugular blood samples were collected, steers were slaughtered, and adipose depots were sampled and prepared for assessment of lipogenesis and lipolysis in vitro. Blood concentrations of glucagon were increased (P = 0.04) in HI-H20 compared with LI-[H.sup.2]O steers, whereas A-SH tended to increase (P = 0.08) circulating IGF-I relative to R-SH, and A-G tended to have elevated (P = 0.09) [T.sub.3] compared with A-SH. Lipolysis, as assessed by NEFA release, was unaffected by treatment. Glycerol release by the MESA and SQA was increased or tended to be increased (P [less than or equal to]0.08) in HI-[H.sub.2]O compared with LI-[H.sub.2]0 steers. In A-G compared with A-SH steers, glycerol release from OMA increased (P = 0.008) and from SQA tended to be increased (P = 0.08). Acetate incorporation into total neutral lipids (TNL) increased or tended to increase with ME intake and SH infusion (P [less than or equal to] 0.09) across all depots. Rates of acetate incorporation into fatty acids (FA) also increased or tended to be increased (P [less than or equal to] 0.1) by SH infusion across all depots, but only that of SQA was increased with ME intake (HI-[H.sub.2]O vs. LI-[H.sub.2]O; P = 0.02). Rates of acetate incorporation into FA and TNL in MESA were increased (P [less than or equal to] 0.03) by A-SH compared with R-SH, but site of SH infusion did not affect the rates in SQA or OMA. Glucose incorporation into TNL for MESA and SQA increased or tended to be increased (P [less than or equal to] 0.1) by dietary and infused energy, whereas for OMA they tended to be increased (P = 0.1) only by SH infusion. In contrast, glucose incorporation into FA was unaffected by energy supply but tended to be increased (P = 0.07) by SH in MESA and tended to be greater (P = 0.08) for A-G than A-SH in OMA. The general across-depot pattern of acetate incorporation rate into FA and TNL was SQA > OMA > MESA, whereas, for glucose incorporation, rates across depots were equivalent. These data provide evidence that the postruminal supply of energy, specifically carbohydrate, stimulates lipogenesis from acetate and glucose and is more pronounced in abdominal depots relative to the subcutaneous depot. Key words: steer, carbohydrate, adipose, metabolism

In humans and sheep, endotoxin (LPS) administration results in increased growth hormone (GH) concentrations. To determine the role of cytokines in the effect of LPS on GH, sheep were challenged with IL-1[beta] or TNF-[alpha]. GH data were compared with results with LH, where the major effects of LPS are known to act via the hypothalamus. Intracerebroventricular (icv) administration of IL-1[beta] or TNF-[alpha] did not alter plasma concentrations of GH. Endotoxin was then administered intravenously (iv) in combination with icv injection of IL-1 receptor antagonist (IL-1RA), TNF antagonist (sTNF-R1), or saline. Administration of LPS increased GH (P < 0.0001), although coadministration of IL-1ra or sTNF-R1 icv did not alter GH response to LPS. In contrast, plasma concentrations of LH were profoundly inhibited by icv administration of either cytokine (P < 0.03), but the LH response to LPS was not altered by cytokine antagonists. Intravenous administration GH (P < 0.0001). Administration of IL-1RA and sTNF-R1 iv prevented of either IL-1[beta] or TNF-[alpha] increased plasma concentrations of LPS-induced increases in GH. Although LH was suppressed by high iv doses of IL-1[beta] (P = 0.0063), the antagonists did not alter the LH response to LPS. To determine whether LPS might directly activate GH release, confocal microscopy revealed colocalization of CD14, the LPS receptor, with GH and, to a lesser extent, LH and some prolactin (PRL)-containing cells, but not ACTH or TSH. These data are consistent with the effects of LPS on GH secretion originating through peripheral cytokine presentation to the pituitary, as well as a potential to act directly on selective populations of pituitary cells via CD14. luteinizing hormone; cytokines; sheep; CD14; lipopolysaccharide

Beyond their nutritional effect, short-chain fatty acids, especially butyrate, modulate cell differentiation, proliferation, motility, and in particular, they induce cell cycle arrest and apoptosis. A bovine kidney epithelial cell line (Madin-Darby bovine kidney; MDBK) was used to investigate the cell cycle regulatory and apoptotic effects of butyrate. Butyrate not only induced apoptosis but also induced cell cycle arrest at the G1/S boundary and M/G2 in MDBK cells (P < 0.01). The cell responses were concentration-dependent ([r.sup.2] = 0.9482, P Key Words: Apoptosis, Bovine Kidney Epithelial Cell, Butyrate, Caspase-3, Cell Cycle, Proteasome

Four studies were designed to determine whether 1) tumor necrosis factor-[alpha] (TNF) and the Lipopolysaccharide (LPS) binding ligand, CD14, are produced by sheep adipose tissue; 2) nutritional reserves and/or short-term fasting affect circulating concentrations of TNF; 3) there is a relationship between TNF and metabolic factors in sheep; and 4) inflammation alters circulating concentrations of leptin. In Exp. 1 and 2, ewes were assigned, based on ultrasonic assessments of last-rib subcutaneous fat measurements to fat (fat thickness >1 cm; mean = 1.52 [+ or -] 0.03 cm) or thin (fat thickness 0.39). In Exp. 4, wethers were injected with LPS. Blood samples were collected every 15 min for 8 h following injection. Plasma concentration of leptin was not altered by LPS (P > 0.20). These results provide evidence: 1) of TNF-like immunoreactivity within fat tissue; 2) that elements within fatty tissues have CD14 that may allow adipocyte function to be directly affected by LPS; 3) that plasma concentrations of leptin are not altered by LPS treatment; and 4) that circulating concentrations of TNF are elevated with obesity in sheep. Key Words: Fat, Leptin, Lipopolysaccharides, Receptors, Sheep, Tumor necrosis factor.

Estradiol plus progesterone (EP) implants have been shown to favorably alter the time course or decrease the severity of many of the clinical manifestations associated with coccidiosis and endotoxemia in calves. This study evaluated the effect of EP treatment on plasma tumor necrosis factor-[alpha] (TNF), thromboxane (TXB), prostacyclin (PRC), nitrite and nitrate (N[O.sub.[x]]), and cortisol. Holstein steer calves were divided into four groups: control, EP, endotoxin (LPS), and EP+LPS (n = five/group). Estradiol/progesterone pellets (Synovex-S) were implanted subcutaneously when calves reached 20 wk of age. One week after implantation, calves were injected IV with endotoxin (i.e., lipopolysaccharide; LPS, 0.6 [micro]g/kg of BW) or nonpyrogenic saline placebo. Body temperature was measured and blood was collected before injection and at 1, 2, 3, 4, 6, and 8 h thereafter. Plasma concentrations of TNF, cortisol, TXB, PRC, N[O.sub.[x]], were measured. Body temperature increased in both LPS and LPS-EP calves, but had returned to normal by 6 h in the LPS-EP group (P < 0.05). Plasma TNF and cortisol increased after LPS (P < 0.01), but were not differentially affected by EP treatment. Likewise, EP did not affect the magnitude of increase in LPS-induced PRC, but EP decreased the magnitude of increase in TXB (P < 0.05). Plasma N[O.sub.[x]]] levels were increased (P < 0.01) in calves after LPS; treatment with EP attenuated the LPS-associated increase in plasma N[O.sub.[x]] levels. These results suggest that EP exerts specific effects on different components of the proinflammatory cytokine cascade. Although the initiation of responses mediated by TNF, cortisol, and PRC do not seem to be differentially affected by EP, components of the nitric oxide- and TXB-axis responses to LPS are decreased in calves pretreated with EP. Key Words: Cattle, Cortisol, Endotoxins, Growth Promoters, Prostacyclin, Tumor Necrosis Factor

We investigated the influence of DM and(or) energy intake and dietary CP levels on the performance and nitrogen (N) retention of beef steers with and without growth promoter implants. In Exp. 1, four implanted (Synovex-S, 200 mg of progesterone plus 20 mg of estradiol benzoate) Angus steers and four Angus steers that were not implanted were assigned to concurrent 4 x 4 Latin squares. Initial BW averaged 296 kg. Each square consisted of moderate and moderately high DM intake treatments (4 and 6 kg/d) and low and adequate CP intake treatments (450 and 600 g/d) in a 2 x 2 factorial arrangement. Periods were 2 wk of adaptation, 5 wk of growth, and 1 wk of balance collection. Experiment 2 consisted of two replicates of 32 Hereford steers each (initial BW 324 kg). Each replicate was a 4 x 2 factorial in which steers were individually fed for 63 d. All steers had ad libitum access to a 60% cornbased concentrate diet containing either 7.9, 10.0, 12.1, or 14.6% CP (DM basis), and steers were either implanted or not implanted with Synovex-S. Experiment 3 was similar to Exp. 2 except that all steers (initial BW 315 kg) received a low-protein diet (7.6% CP) with calculated energy densities of either 1.86, 2.04, 2.22, or 2.42 Mcal ME/kg DM, and steers were limited to an equalized DM intake of 9.5 kg daily. In Exp. 1, gains for the low CP, moderate and moderately high DM intakes and the adequate CP, moderate and moderately high DM intakes were 240, 555, 208, and 730 g/d, respectively, for steers not implanted and 333, 643, 488, and 988 g/d, respectively, for implanted steers (SEM 102 g/d). Respective values for retained N were .13, .18, .16, and .26 g/kg BW(super .75) and .13, .15, .22, and .29 g/kg BW(super .75) (SEM = .04 g/kg BW'75). Implant response was greater (CP x implant, P < .01) for both gain and retained N when adequate CP compared to low CP diets were fed. For Exp. 2, the lowest CP diet reduced ADG (.97 vs 1.27 kg/d) and efficiency of gain (100 vs 120 g gain/kg DM). Synovex-S was less effective in improving efficiency for the lowest protein diet than for the other diets (11.7 vs 20.2%). During Exp. 3, neither Synovex-S nor dietary energy influenced gain and efficiency. We concluded that adequate dietary protein is necessary to optimize the response to estrogenic growth promoters and that the low response under inadequate protein and energy intake is not improved by increasing the energy density of the diet. Key Words: Energy Intake, Growth, Growth Promoters, Nitrogen Balance, Protein Intake, Steers

The purpose of this study was to determine the applicability of the Accu-Chek Easy (ACE) human self-monitoring system for monitoring glycemic status in cattle. The ACE method was compared with the Yellow Springs Instrument (YSI) analytical laboratory method in two studies. A preliminary study (62 samples) and a primary study (434 samples) involved a nine-fold range and a 10-fold range, respectively, of glucose concentrations obtained during the acute phase response of growing beef cattle to injections of varying dosages of endotoxin. The ACE monitoring method compared with the YSI analytical method resulted in similar patterns of glucose concentration change, similar ranking of glucose means across endotoxin dosages during hyper- and hypoglycemia, and a close relationship between paired YSI and ACE concentrations from common samples. The ACE method identified all nine animals that displayed hypoglycemic distress during the acute phase response to endotoxin injection. The relationship between the YSI analytical method and the ACE monitoring method was found to be nonlinear (YSI = -38.2 + 13.6[multiplied by][ACE.sup..50]; [R.sup.2] = .99; [S.sub.y[multiplied by]x] = 7.3 mg/dL), and the use of this equation to predict YSI values from ACE values in an independent data set resulted in linearity when YSI was regressed on the predicted YSI values (YSI = -.78 + 1.00[multiplied by]Predicted YSI; [R.sup.2] = .87; [S.sub.y[multiplied by]x] = 6.9 mg/dL). Even though variation seemed greater for ACE than for YSI, we concluded that a system developed for human self-monitoring of blood glucose, such as the ACE, can be used to monitor the glycemic status of cattle. Key Words: Cattle, Glucose, Blood Sugar, Monitoring, Methodology

The objective of this study was to determine the effect of a subtherapeutic level of chlortetracycline (CTC) fed to growing beef steers under conditions of limited and adequate dietary protein on plasma concentrations of GH, thyroid-stimulating hormone (TSH), and thyroid hormones before and after an injection of thyrotropin-releasing hormone (TRH) + GHRH. Young beef steers (n = 32; average BW = 285 kg) were assigned to a 2 x 2 factorial arrangement of treatments of either a 10 or 13% crude protein diet (70% concentrate, 15% wheat straw, and 15% cottonseed hulls) and either a corn meal carrier or carrier + 350 mg of CTC daily top dressed on the diet. Steers were fed ad libitum amounts of diet for 56 d, and a jugular catheter was then placed in each steer in four groups (two steers from each treatment combination per group) during four consecutive days (one group per day). Each steer was injected via the jugular catheter with 1.0 [[micro]gram]/kg BW TRH + .1 [[micro]gram]/kg BW GHRH in 10 mL of saline at 0800. Blood samples were collected at -30, -15, 0, 5, 10, 15, 20, 30, 45, 60, 120, 240, and 360 min after releasing hormone injection. Plasma samples were analyzed for GH, TSH, thyroxine ([T.sub.4]), and triiodothyronine ([T.sub.3]). After 84 d on trial, the steers were slaughtered and the pituitary and samples of liver were collected and analyzed for 5[prime]-deiodinase activity. Feeding CTC attenuated the GH response to releasing hormone challenge by 26% for both area under the response curve (P < .03) and peak response (P < .10). Likewise, CTC attenuated the TSH response to releasing hormone challenge for area under the response curve by 16% (P < .10) and peak response by 33% (P < .02), and attenuated the [T.sub.4] response for area under the curve by 12% (P < .08) and peak response by 14% (P < .04). Type II deiodinase activity in the pituitary was 36% less (P < .02) in CTC-fed steers than in steers not fed CTC. The results of this study are interpreted to suggest that feeding subtherapeutic levels of CTC to young growing beef cattle attenuates the release of GH and TSH in response to pituitary releasing hormones, suggesting a mechanism by which CTC may influence tissue deposition in cattle. Key Words: Antibiotics, Chlortetracycline, Cattle, Somatotropin, Thyroxine, Triiodothyronine

Beef steer carcasses from three 2 x 2 factorial feeding experiments (Exp. 1, 20 carcasses; Exp. 2 and 3, 19 carcasses each) were evaluated to study the influence of supplementing with roasted soybeans (RSB; 127 [degrees] C for 10 min) vs soybean meal (SBM) and implanting with the estrogenic growth promoter Synovex-S (SYN, 20 mg estradiol benzoate and 200 mg progesterone) on carcass merit, composition of dissected 9-10-11th rib section, estimated edible carcass composition, and cooking characteristics of strip loin steaks. In all experiments, steers were fed diets consisting of 15% corn silage, 15% orchardgrass silage, and 70% corn-based concentrate. There were no treatment interactions found in this study. Final BW averaged 480.4, 498.5, and 500.7 kg for Exp. 1, 2, and 3, respectively, and hot carcass weights averaged 288.4, 296.4, and 309.1 kg. Across experiments, hot carcass weight was 8.3 kg less (P < .03) for RSB steers than for SBM steers. Fat weight (P < .01) and percentage of fat (P < .01) were less and percentage of bone (P < .04) was greater in the 9-10-11th rib section of RSB steers than of SBM steers. Estimated percentage of fat (P < .02) was less and percentage of bone (P < .04) was greater in edible carcass of RSB steers than in that of SBM steers. Total 9-10-11th rib section weight tended to be less for RSB steers (P < .08) than for SBM steers. Carcass merit measurements were not affected (P > .10) by supplement, but numerically the percentage of kidney, pelvic, and heart fat was 11% greater for RSB steers than for SBM steers in Exp. 2 and 3. Final BW and carcass weight were 38.7 and 22.6 kg greater (P < .01), respectively, for SYN-implanted steers than for steers not implanted. Longissimus muscle area was greater (P < .01), percentage of kidney, pelvic, and heart fat (P < .02) was less, USDA quality grade tended to be less (P < .09), and shear force of strip loin was greater (P < .01) for SYN-implanted steers than for steers not implanted. The 9-10-11th rib section and estimated carcass compositions were not different (P > .10) between SYN-implanted steers and steers not imp]anted but reflected a somewhat leaner carcass. The authors conclude from this study that in feedlot steers, either implanted or not implanted, there is no benefit from supplementing with RSB in place of SBM, and that the use of RSB in place of SBM in feedlot diets may reduce the amount of edible carcass. Key Words: Steers, Feedlots, Soybeans, Estrogens, Progesterone, Carcass Composition

Two 160-d feedlot experiments, each consisting of 20 Angus-Hereford steers (216 [+ or -] 5 kg BW, Exp. 1; 258 [+ or -] 5 kg BW, Exp. 2) and 20 Angus-Hereford heifers (208 [+ or -] 5 kg BW, Exp. 1; 236 [+ or -] 5 kg BW, Exp. 2), were used to investigate the effects of supplementing diets with either roasted soybeans (RSB, roasted at 127 [degrees] C for 10 min) or soybean meal (SBM) and implanting or not implanting with an estrogenic growth promoter (SYN; Synovex-S, 20 mg of estradiol benzoate plus 200 mg of progesterone or Synovex-H, 20 mg of estradiol benzoate plus 200 mg of testosterone) on performance. The cattle were fed a basal diet of 15% orchardgrass silage, 15% corn silage, and 70% corn-based concentrate. Treatments were 1) no SYN and fed a SBM-supplemented diet, 2) no SYN and fed a RSB-supplemented diet, 3) SYN and SBM, and 4) SYN and RSB. Cattle in the SYN groups were reimplanted at 80 d. Four additional Angus-Hereford steers were used in a digestion and nitrogen balance experiment conducted during the first half of Exp. 1. For the total 160-d feedlot experiments, DMI for RSB compared with SBM was lower (P < .01; 8.5 vs 9.2 kg/d, SEM = .07) and ADG/DMI tended to be higher (P < .10; 165 vs 157 g/kg, SEM = 1.3). Final BW of steers fed RSB was similar (P > .10) to that of steers fed SBM (473 vs 478 kg, SEM = 5.6), as was ADG (1.39 vs 1.43 kg/d, SEM = .02). Dry matter intake for SYN-implanted steers was higher (P < .01) than for steers not implanted (9.2 vs 8.5 kg/d). Likewise, final BW (491 vs 460 kg) and ADG (1.49 vs 1.33 kg/d) were higher (P < .01), and ADG/DMI (166 vs 157 g/kg) tended to be higher (P < .10), for SYN-implanted steers than for steers not implanted. During the more rapid muscle growth period (0 to 80 d), DMI for RSB compared with SBM was lower (P < .01; 7.8 vs 8.6 kg/d, SEM = .07) and ADG/DMI was similar (P > .10; 181 vs 172 g/kg, SEM = 1.8). Dry matter intake for SYN-implanted steers was higher (P < .05) than for steers not implanted (8.4 vs 8.0 kg/d), as was ADG/DMI (P < .01, 182 vs 171 g/kg). During this more rapid growth period, the supplement x implant interaction for ADG was significant (P < .05; 1.35, 1.36, 1.59, and 1.44 kg/d for Treatments 1, 2, 3, and 4, respectively, SEM = .04). There were no differences in digestibilities or N balance. The results suggest that there is no improvement in performance under feedlot conditions when RSB replaces SBM in the diet of beef cattle, and, in young cattle, RSB may reduce the response expected by an estrogenic growth promoter. Key Words: Feedlots, Beef Cattle, Soybean Oil Meal, Soybeans, Estrogens, Progesterone

Twelve Holstein bull calves (6 to 8 wk of age) were used to determine the influence of supplemental dietary Cr on ACTH, cortisol, and immune responses of calves experimentally inoculated with bovine herpesvirus-1 (BHV-1). Calves supplemented with Cr received 3 mg Cr/d (Chromium, n = 6) of a high-Cr-yeast product. Following 53 d of treatment, all calves were fitted with jugular catheters, and blood samples were collected every 4 h into tubes containing EDTA. Twenty-four hours later, all calves were inoculated intranasally with BHV-1 (1 x [10.sup.7] plaque-forming units in each naris). Serial blood collection continued at 4-h intervals for 6 d. Plasma was harvested, immediately frozen in liquid nitrogen, and stored at -20 [degrees] C. Individual rectal temperatures and urine samples were collected at the same time each day. Rectal temperatures were elevated (P < .05) on d 2, 3, 4, and 5 but were not affected by Cr treatment. Treatment with Cr did not affect secretion of ACTH, cortisol, or plasma tumor necrosis factor-[Alpha], although clear circadian variation in ACTH and cortisol occurred. No differences were detected in the concentrations of trace minerals excreted daily in the urine, lymphocyte proliferative response to mitogen stimulation, and neutrophil bactericidal function. The acute phase proteins, ceruloplasmin and fibrinogen, also were not affected by treatment or viral challenge. These data suggest that Cr supplementation using high-Cr yeast (3 mg/d) did not alter stress responses of calves experimentally inoculated with BHV-1. Key Words: Chromium, Calves, Stress, Trace Elements

The influence of Synovex-S[R] (SYN) ear implant (200 mg progesterone and 20 mg estradiol benzoate) and Somavubove[R] (SbV) recombinant bovine growth hormone (.1 mg/kg BW i.m., daily) on live animal performance, tissue growth, and the partitioning of energy gain was determined using a slaughter-balance protocol with 25 young MARC II x (Angus-Hereford crossbred) beef steers (initial BW 182 [+ or -] 1.8 kg). Following 21 d of adjustment to individual pens and to a diet of 80% concentrate and 20% corn-grass (1:1) silages, five groups of five steers per group were assigned to initial slaughter or a 2 x 2 factorial arrangement of treatments of CTL (no implant + daily placebo i.m. injection of bicarbonate-saline), SYN (implant + placebo), SbV, or SYN + SbV and slaughtered at 56 d on treatment. Steers were fed (per kilogram [BW.sup..75] daily) 20 g of CP and 252 Kcal of ME and consumed 5.5 [+ or -] .07 kg/d DM across treatments. Empty body and carcass gains were affected (SYN, P < .01; SbV, P < .01) by treatments (CTL, SYN, SbV, and SYN + SbV: 1.26, 1.43, 1.63, 1.78 kg/d, SEM = .05, and .78, .97, .97, 1.08 kg/d, SEM = .04, respectively). Noncarcass gain was .45, .48, .60, and .60 kg/d (SEM = .03; SbV, P < .01). For empty body, both protein and water gains were greater for SYN-implanted steers (P < .05) than for steers not implanted and for SbV-injected steers (P < .01) than for placebo-injected steers. Treatments did not influence the efficiency of energy gain. The proportional amount of energy deposited as protein was greater (P < .01) for SbV-injected steers than for placebo-injected steers. The proportional amount of protein deposited was not influenced by SYN (P > .10); however, means were numerically greater for SYN-implanted steers than for steers not implanted, the largest mean being for the SYN + SbV treatment group. Somavubove increased (P < .01) the efficiency of energy deposited as protein in both the empty body and carcass compared with steers not receiving SbV. Efficiency of energy deposited as protein in the empty body tended to be greater (P < .10) for SYN-implanted steers than for steers not implanted. The efficiency with which total feed energy was deposited as protein in empty body was 10% greater for the SYN group than for the CTL group, 21% greater for the SbV group than for the CTL group, and 37% greater for the combined SYN + SbV treatment than for the CTL group. The data from this study are interpreted to indicate that SYN and SbV act in an additive manner to improve growth and protein deposition in young growing steers. Key Words: Steers, Beef, Growth Promoters, Estrogens, Somatotropin, Tissue Protein

Twenty crossbred beef steers (initial BW 182 [+ or -] 1.8 kg) were used in a 2 x 2 factorial to determine the effects of implantation with Synovex-S[R] (SYN; 20 mg 17-[Beta] estradiol benzoate + 200 mg progesterone, ear implant) and administration of recombinant bovine growth hormone (Somavubove[R] SbV, .1 mg[multiplied by]kgB[W.sup.-1][multiplied by][d.sup.-1], i.m.) on the morphology of six muscles (longissimus, psoas major, supraspinatus, triceps brachii, semitendinosus, rectus femoris) of growing steers. Implantation with SYN decreased the percentage distribution of FOG fibers and increased FG fibers in the supraspinatus and rectus femoris muscles (P < .05). Steers treated with SYN had a larger area of SO and FG fibers in the psoas major muscle (P < .05). The administration of SbV decreased the percentage distribution of FOG fibers and increased FG fibers in the rectus femoris muscle (P < .05). Steers administered SbV had larger SO, FOG, and FG fibers in the psoas major muscle and SO fibers in the supraspinatus and semitendinosus muscles (P < .05). The combined administration of SYN and SbV had minimal, if any, effect on the percentage distribution of fiber types (P > .05) but increased (P < .05) the fiber areas of all muscles (18.5 to 54.8%) except the rectus femoris (P > .05). Proximate composition of the muscles was generally not affected (P > .05) by any of the treatments. The only observations were decreases in fat content for psoas major and rectus femoris muscles as a result of the combined administration of SYN and SbV. These results indicate that both growth-promoting agents, SYN and SbV, have a potential to increase muscle fiber size, but muscles respond differently to the administrations of SYN and SbV. However, when SYN and SbV are administered in combination, the combined effects result in an additive increase in muscle fiber hypertrophic response. Key Words: Steers, Beef, Growth Promoters, Estrogens, Somatotropin, Muscle Morphology

This experiment examined the effect of daily administration of 3,5,3'-triiodothyronine (T(sub 3)) on plasma profiles of T(sub 3), thyroxine (T(sub 4)), 3,3',5'-triiodothyronine (reverse T(sub 3); rT(sub 3)) and thyrotropin (TSH) in beef steers in which protein accretion was increased by using implants of Synovex-S(R) (SYN). Twenty-four Angus-Hereford steers (302 plus or minus 16 kg) were individually fed a diet of a corn-based concentrate and silage mixture for 56 d at equal energy intake per steer (ME/unit BW. to the 75). A 2 x 2 factorial arrangement of treatments was used in which treatments were SYN ear implants (200 mg of progesterone and 20 mg of estradiol benzoate) or no implants and s.c. injections of T(sub 3) in polyethylene glycol (2 micron g of T(sub 3)/kg BW every 48 h) or no injections of T(sub 3). Blood samples were collected every 2 wk. Plasma T(sub 3) concentration during the experimental period was increased in T(sub 3)-treated steers (3.0 plus or minus .1 vs 2.2 plus or minus .1 ng/mL, P < .01) and was decreased in SYN-implanted steers (2.4 plus or minus .1 vs 2.7 plus or minus .1 ng/mL, P < .01). Plasma T(sub 4) and rT(sub 3) concentrations were reduced (22 plus or minus 4 vs 75 plus or minus 2 and .04 plus or minus .01 vs .12 plus or minus .01 ng/mL, respectively, P < .01) in T(sub 3)-treated steers. Concurrently, plasma TSH concentration was decreased in T(sub 3)-treated steers (.37 plus or minus .01 vs. 51 plus or minus .02 ng/mL, P < .02). Synovex-S increased BW gain (21.0%, P < .01) and protein gain (35.6%, P < .01) compared with that of nonimplanted steers. Body weight gain and protein gain were not affected by treatment with T(sub 3). These data indicate that long-term administration of T(sub 3) to steers inhibits endogenous thyroid secretion without affecting normal and SYN-stimulated BW gain and protein deposition. The results support the suggestion that the growth-promoting action of SYN in steers is associated with a reduction in peripheral generation of T(sub 3) and(or) increased T(sub 3) metabolism, although decreased plasma concentration of T(sub 3) is not directly involved in the mechanism of SYN action on growth.

Treatment of cows with recombinant bovine somatotropin (bST) decreased hematocrit and influenced leukocyte fractions. Eosinophil and lymphocyte fractions were significantly decreased, although the absolute leukocyte count was not affected. Milk yield was increased by BST treatment, with the largest increase coinciding with the periods when hematocrit was affected greatest. Blood levels of insulin-like growth factor-I were higher in bST-treated cows, and are thought to be partially responsible for the leukocyte effects. These bST effects were found to transient.

The influence of unsaturated fatty acids and phospholipids in high-forage diet on total lipid content, cholesterol content, and fatty acid composition in 43 lamb carcasses was determined by assigning the lambs into 4 groups with varied dietary treatments: control, with canola seed (CS), with soy lecithin(SL), and with both conala seed and soy lecithin(CSSL). Lean tissue analysis by gas-liquid chromatography revealed CS fed lambs had reduced total polyunsturated fatty acids (PUFA) while an increase was noted with the SL fed group. With adipose tissue, CS fed lambs showed lower saturated fatty acids and SL group, increasedPUFA. The effects of CSSL feeding was not significant.

The effect of growth hormone-releasing factor (GRF) on energy metabolism and nitrogen utilization at two feeding regimen was assessed to approximate the energy budget for basal metabolism and growth as well as energy allotted for protein and fat synthesis. Energy allotted for maintenance and growth were not affected by the administration of GRF. However, more energy for growth was channeled to protein synthesis rather than lipogenesis in GRF-treated steers. GRF also had slight effects on metabolizable and heat energy of steers indicating that it may have other effects on metabolism besides increasing growth hormone concentrations.

Metabolism of carbon-based nutrients in the portal-drained viscera and liver was assessed to determine the effect of growth hormone-releasing factor (GRF) on nutrient metabolism of crossbred steers. Increasing the food intake elevated blood flow and mobilization of most nutrients. On the other hand, GRF administration decreased liver clearance of amino acid and ammonia nitrogen and the release of urea nitrogen. Nitrogen retention over the net amino acid assimilation of the gastrointestinal tract increased with the administration of GRF.

The effects of growth hormone-releasing factor (GRF) and feed intake on the serum concentration and visceral metabolism of growth hormone (GH), insulin-like growth factor-I (IGF-I), somatostatin, glucagon and insulin were determined in six crossbred steers. Results showed that GRF elevated serum concentrations of insulin, IGF-I and GH independent of splanchnic metabolism. On the other hand, the elevation of arterial concentrations of insulin and glucagon resulting from the increase in feed intake was mediated by the hormones' release from portal-drained viscera.