Performance and carcass merit of growing beef steers with chlortetracycline-modified sensitivity to pituitary releasing hormones and fed two dietary protein levels.

This paper reports the effects of reduced sensitivity to growth hormone-releasing hormone and thyrotropin-releasing hormone through feeding a subtherapeutic level of chlortetracycline (CTC; 350 mg CTC/d) and two levels of dietary CP (10% and 13% of diet DM) on growth performance and carcass merit characteristics. Thirty-two steers (initial average BW, 286 kg) were adapted to a common 13% CP diet consisting primarily of grass hay, corn, and soybean meal fed to gain 1.25 kg/d. The steers were assigned to four treatments (with or without CTC and 10% or 13% dietary CP in a factorial arrangement) and fed ad libitum amounts of diet for 91 d. Feed intake was determined daily and steers were weighed weekly. Steers were killed at the end of the feeding period for carcass merit determinations. Efficiency of BW gain was greater (P < .05) for steers fed the 13% CP diet than for the 10% CP diet and tended to be less for CTC-steers when the 10% CP diet was fed and greater for the CTC-steers when the 13% CP diet was fed (CTC x dietary CP interaction, P < .10). Feeding CTC increased (P < .01) fat over the longissimus muscle and marbling. This study is interpreted to indicate that the sustained effect of subtherapeutic feeding of CTC to cattle appears to increase fat deposition consistent with a reduced growth hormone and thyroid status reported earlier for these same steers. This would tend to increase energy utilization but may not necessarily produce a measurable increase in BW gain.

Modulation of growth performance in disease: reactive nitrogen compounds and their impact on cell proteins.

During life, all animals encounter situations that challenge their capability for optimal growth. In reacting to immune challenges in the form of disease, homeostatic mechanisms attempt to overcome disharmony of the body's internal environment, or simply put, stress. The overall impact of stress revolves around a dynamic relationship between the level of challenge imparted on physiological systems and the degree of host response that is mounted in the process of detecting and reacting to the stress. In growing animals, the majority of milder stress encounters are manifest in terms of energetic inefficiencies and periods of reduced anabolism. In contrast, severe stress is often characterized by frank catabolism and tissue wasting. In some instances a level of stress (that might be termed a "stress breakpoint") is reached at which time the host response itself contributes to the cascade of negative effectors that further cause illness. These "breakpoint" responses are characterized by more intense acute responses to stress or a much more protracted duration of the response than would be expected given the nature of the stress. Key to understanding how growth in the young animal responds to infectious stresses is the recognition that (a) when immune responses that normally maintain health go awry, the reporters and effectors of the immune system (cytokines and the nitric oxide cascade) can contribute to stress disease processes and (b) reactive nitrogen compounds derived from the nitric oxide, as well as super oxide anion can modify intracellular proteins and block otherwise normal biochemical processes that regulate cell function. A key example of this is the loss of regulation of IGF-I by GH. As animals react more severely to disease stress, IGF-I concentrations in plasma decline progressively. Recent data derived from (LPS) challenges performed on young calves suggest that the prolonged decline in IGF-I is associated with the development of hepatic cytotoxicity localized to regions of protein nitration as identified by immunohistochemistry. Identifying biochemical criteria for disease processes provides needed guidance for the further development of intervention strategies to limit the impact of disease on growth.

Influence of chlortetracycline and dietary protein level on visceral organ mass of growing beef steers.

Thirty-two beef steers (285 +/- 3 kg BW) were used to determine the effects of chlortetracycline and dietary protein level on visceral tissue mass, chemical composition, intestinal morphology, and proliferation rate indices. Steers were allotted randomly by weight to a factorial arrangement of dietary treatments consisting of either 10 or 13% CP diets top-dressed with a corn meal carrier (500 g/d) containing either 0 or 350 mg of chlortetracycline. After 84 d, steers were slaughtered and visceral organs removed and separated. Rinsed wet tissue mass was recorded; total RNA, total DNA, tissue DM, and tissue N content were determined; and tissue sections were prepared for immunohistochemical analysis. Thin tissue sections were evaluated to determine crypt depth and villus height as well as proliferation rate by immunohistochemical detection of the nuclear antigen Ki67. Rumen and abomasum weights and small intestinal length were greater (P < 0.04) in steers fed the 13% CP diet than in those fed the 10% CP diet on both an absolute weight basis and a percentage of empty BW. Chemical composition of the small intestinal and ruminal segments were largely unaffected by increased dietary protein. Increasing the dietary CP also increased the villus height in duodenal (P = 0.02) and the crypt depth of jejunal (P = 0.03) sections. Dietary administration of chlortetracycline decreased (P < 0.01) small intestinal weight both on absolute and empty BW bases. Nitrogen and RNA concentrations of the small intestinal segments were unaffected (P > 0.1) by dietary administration of subtherapeutic levels of chlortetracycline; however, because of increases (P < 0.05), or tendencies for an increase (P < 0.1), in the tissue content of DNA, the ratio of N to DNA was decreased (P < 0.05) or tended to be decreased (P < 0.1) in the small intestinal segments of the chlortetracycline-treated animals. The observed decrease in small intestinal epithelial mass does not appear to be due to alterations in cell proliferation rate but rather cell size. Consistent with this finding, cell proliferation, as determined by Ki67 antigen staining, was not affected by dietary treatment. Chlortetracycline administration decreased small intestinal mass that may be a result of decreased cell size.

Effects of growth-promoting implants on morphology of Longissimus and Semitendinosus muscles in finishing steers.

Growth-promoting implants lead to increased muscle accretion in ruminants. To elucidate the effects at a cellular level, muscle fiber distribution and cross-sectional area (CSA) of longissimus (LM) and semitendinosus (ST) muscles were compared in implanted and control steers. Sixty-four Charolais steers were assigned to one of four treatments (16 steers/treatment): (1) no implant, (2) Synovex-S® (estradiol benzoate+progesterone), (3) Ralgro® (zeranol) or (4) Revalor-S® (trenbolone acetate+estradiol-17ß). The experiment was carried out using four slaughter groups (SGRP). Sixteen steers each were slaughtered after 48, 104, 160 and 175 days (four steers/treatment) on trial. Steers on an implant treatment were first implanted at 15 months of age (day 0) and re-implanted at 56 and 112 days. Muscle fibers in the LM and ST (for both live biopsy and post-mortem samples) were characterized as either slow-twitch oxidative (SO), fast-twitch oxidative-glycolytic (FOG) and fast-twitch glycolytic (FG) fibers. Fiber distribution was minimally affected by SGRP in these physiologically mature steers. Implantation with Synovex did not alter fiber distribution in either muscle compared with control steers. Both Synovex-implanted and control steers showed a decrease of FG and an increase of FOG fibers in the LM from day 0 to SGRP 2 followed by an increase of FG and a decrease of FOG fibers. Ralgro- and Revalor-implanted steers had an almost constant fiber distribution in the LM throughout the experiment resulting in higher precentages of FG fibers in SGRP 2 (P<0.05) than SYN or CON steers. Biopsy samples of the LM muscle which were excised 51 days (SGRP 1-3) or 65 days (SGRP 4) before slaughter proved to be suitable for the determination of fiber distribution in live animals. Fiber area increased in post-mortem samples of both muscles from SGRP 1-3 in all treatment groups followed by a plateau. Implantation with Revalor led to an additional increase in fiber area from SGRP 3 and 4 (P<0.05). Synovex did not affect fiber area compared with control steers whereas Ralgro and Revalor implants led to larger fibers in SGRP 3 and 4, respectively. It can be concluded that some growth-promoting implants result in noticeable differences in muscle hypertrophic responses which coincide with their different effectiveness to enhance lean mass accretion.

Responses to an estrogenic growth promoter in beef steers fed varying nutritional regimens.

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% corn-based 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.75 and .13, .15, .22, and .29 g/kg BW.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.

One editor's views on conflict of interest.

The purpose of this article is to discuss the importance of recognizing conflict of interest or bias situations in the peer review and publication process of research papers and to identify some important guidelines or policies that help to minimize these situations. Communication of thoughts, ideas, and information is the basis of how we function as a society. Communicating research results requires us to clearly and accurately communicate all aspects of the research process, including the appropriate interpretation of results. A working definition for conflict of interest or bias with regard to publishing research results is that conflict of interest is a situation in which personal benefit (either direct or indirect) takes priority over the clarity and(or) accuracy of reporting research. These situations are ethical issues and can represent either real or assumed situations. It is true that the review and publication process is not perfect; thus, some bias probably is always present and can be brought to the review and publication process by either the author or those responsible for the process. However, conflict of interest or bias that detracts from the objective evaluation of research or the integrity of a scientific journal is inappropriate. Conflict of interest or bias situations can occur at all levels of the review and publication process and should be dealt with on a factual basis. This article describes several situations as examples and several important guidelines that help minimize the occurrence of conflict of interest or bias.

Performance and digestibilities of beef cattle fed diets supplemented with either soybean meal or roasted soybeans and implanted with Synovex.

Two 160-d feedlot experiments, each consisting of 20 Angus-Hereford steers (216 +/- 5 kg BW, Exp. 1; 258 +/- 5 kg BW, Exp. 2) and 20 Angus-Hereford heifers (208 +/- 5 kg BW, Exp. 1; 236 +/- 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.

The effect of roasted soybeans in the diet of feedlot steers and Synovex-S ear implants on carcass characteristics and estimated composition.

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 implanted 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.

Effects of oral chlortetracycline and dietary protein level on plasma concentrations of growth hormone and thyroid hormones in beef steers before and after challenge with a combination of thyrotropin-releasing hormone and growth hormone-releasing hormone.

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 2x2 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 microg/kg BW TRH + .1 microg/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 (T4), and triiodothyronine (T3). After 84 d on trial, the steers were slaughtered and the pituitary and samples of liver were collected and analyzed for 5'-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 T4 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.

Field method for monitoring blood glucose in beef cattle.

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.ACE.50; R2 = .99; Sy.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. Predicted YSI; R2 = .87; Sy.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.

Effects of Synovex-S and recombinant bovine growth hormone (Somavubove) on growth responses of steers: III. Muscle growth and protein responses.

We conducted this study to determine whether the growth responses of specific skeletal muscles in crossbred beef steers were differentially affected by treatment with recombinant bovine growth hormone (Somavubove, SbV, .1 mg/kg BW, i.m., daily), Synovex-S (200 mg progesterone + 20 mg 17-beta estradiol benzoate, SYN, ear implant), or a combination of the two. Starting body weights of steers averaged 182+/-1.8 kg. Five steers were used at this average BW to obtain data on weight and composition of individual muscles at d 0, and 20 other steers were assigned in equal numbers to control (C, no implant and placebo daily injection), SYN, SbV, and SYN + SbV treatment groups. After 56 d of treatment with placebo or growth promoters, complete rectus femoris (RF), triceps brachii (TB), supraspinatus (SS), psoas major (PM), and semitendinosus (ST) muscles were dissected, weighed, and then ground for determination of moisture, total protein, and fat. To calculate the average daily muscle wet weight, protein, and fat gains, the initial weight, protein content, and fat content of a muscle were subtracted from those obtained at slaughter and the difference divided by 56. Muscle weight was increased over C in TB and SS by SYN (P < .1); in TB by SbV (P < .09); and in RF (P < .05), TB (P < .03), and SS (P < .03) by SYN + SbV. Overall average daily wet tissue gain was increased over C by SbV + SYN (P < .05) in RF, TB, and SS. Average daily protein gain in RF and TB was increased by SYN (P < .1), SbV (P < .06), and SYN + SbV (P < .01) over that calculated for C. For RF, TB, and SS, average daily protein gain was greater (P < . 1) in SbV + SYN than that obtained with SbV or SYN alone. These data suggest that administration of growth promoters, such as somatotropin and Synovex, to cattle differentially affects growth characteristics in certain muscles and can have additive effects on protein gain when used together.

Nutritional modulation of somatotropic axis-cytokine relationships in cattle: a brief review.

The objective of this review is to summarize data on the interrelationships that exist between nutrition, the endocrine system and their modulation of plasma tumor necrosis factor-alpha responses to endotoxin in cattle. During stress, intake of nutrients often is compromised and a percentage of available nutrients are diverted away from growth processes to stabilize other physiological processes of a higher survival priority. Management practices that minimize the magnitude and duration of disease stress will aid in speeding the return to homeostatic equilibrium. However, the shift away from growth during stress is almost inevitable as a mechanism to survive. Some degree of control and management of the metabolic cost of disease stress involves understanding the integration of nutritional, endocrine and immune signals by cells and working with the natural homeostatic processes. Endocrine hormones and immune system cytokine signals participate in redirecting nutrient use during disease stress. In an intricate interplay, hormones and cytokines regulate, modify and modulate each other's production and tissue interactions to alter metabolic priorities. Levels of dietary protein and energy intake affect patterns of hormones and cytokines in the blood after endotoxin challenge and further modulate the biological actions of many of these regulatory effectors. In vivo, administration of growth hormone to young calves has significant effects to decrease the many specific physiological responses to endotoxemia. Many aspects of nutrition can attenuate or facilitate this effect.

Roasted soybeans and an estrogenic growth promoter affect the thyroid status of beef steers.

We investigated the interactive effects of a roasted soybean (RSB)-supplemented diet and an estrogen ear implant [Synovex-S (SYN), 20 mg estradiol benzoate + 200 mg progesterone] in young beef steers on measures of thyroid status before and after challenge injections of thyrotropin-releasing hormone (TRH) + growth hormone-releasing hormone (GHRH). Twenty steers (body weight 255 +/- 5 kg) were assigned to the following treatments: 1) no SYN and a soybean meal-supplemented diet, 2) no SYN and a RSB-supplemented diet, 3) plus SYN and soybean meal, and 4) plus SYN and RSB. Steers were individually fed 1.13 MJ metabolizable energy/kg metabolic body wt daily of an 18% protein diet. After a 5-wk growth period, all steers were challenged (intravenous injection) over a 3-wk period with three dose levels of a combination of TRH + GHRH (0.1 + 0.01, 1.0 + 0.1 and 2.5 + 0.25 microg/kg body wt). There were no dose by SYN or RSB interactions. Across dose levels, values for baseline plasma thyroid-stimulating hormone (TSH) were 0.37, 0.35, 0.61 and 0.33 microg/L for treatments 1, 2, 3 and 4, respectively (SYN, P < 0.07; RSB, P < 0.01; SYN x RSB, P < 0.03; SEM 0.06). Net areas under the response curve for TSH were 66.4, 51.3, 91.4 and 64.4 (microg/L) x min, respectively (RSB, P < 0.08; SEM 12.0). Similar treatment effects and/or numerical differences after challenge were noted for thyroxine (T4) but not triiodothyronine (T3). Baseline (2.22 vs. 2.00 microg/L, P < 0.02) and peak (3.07 vs. 2.03 microg/L, P < 0.03) T3 concentrations were less for steers fed RSB than for steers fed soybean meal. This study indicates that in young growing beef steers, SYN increases TSH release from the adenohypophysis and that the primary effect of RSB is reduced plasma T3, possibly through an effect on peripheral T4 deiodination.

Composition analysis of beef rib sections by dual-energy X-ray absorptiometry.

Dual-energy X-ray absorptiometry (DXA) was used as a non-invasive method to measure composition of 9, 10,11 - rib sections obtained from 80 beef carcasses. The weights of the rib sections ranged from 2986 g to 6394 g. Each rib section was scanned twice by DXA, once in a horizontal or standing rib position (DXA-1) and once in a vertical position (DXA-2). After scanning, each rib section was dissected into fat, muscle and bone. The intramuscular fat content of the longissimus muscle was measured chemically. Dissected lean and fat values were adjusted for the amount of intramuscular fat. DXA lean values were adjusted for amount of bone (less bone mineral content). Both DXA measurements consistently overestimated the amount of fat relative to dissection. The DXA-1 scan position measured more lean and less fat than did DXA-2. The correlation (r) between the amount of dissected lean and DXA-1 and DXA-2 lean was 0.91 and 0.85, respectively and between the amount of dissected fat and DXA-1 and DXA-2 fat was 0.94 and 0.92, respectively. The high correlations between DXA and dissection results indicate that DXA could be used as a non-destructive method for evaluating composition of cuts of beef; however, attention must be given to orientation of the cut during the DXA scan.

Effects of Synovex-S and recombinant bovine growth hormone (Somavubove) on growth responses of steers: I. Performance and composition of gain.

The influence of Synovex-S (SYN) ear implant (200 mg progesterone and 20 mg estradiol benzoate) and Somavubove (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 +/- 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.75 daily) 20 g of CP and 252 Kcal of ME and consumed 5.5 +/- .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.

Effects of Synovex-S and recombinant bovine growth hormone (Somavubove) on growth responses of steers: II. Muscle morphology and proximate composition of muscles.

Twenty crossbred beef steers (initial BW 182 +/- 1.8 kg) were used in a 2 x 2 factorial to determine the effects of implantation with Synovex-S (SYN; 20 mg 17-beta estradiol benzoate + 200 mg progesterone, ear implant) and administration of recombinant bovine growth hormone (Somavubove SbV, .1 mg.kgBW-1.d-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 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.

Roasted soybeans and an estrogenic growth promoter affect growth hormone status and performance of beef steers.

This study investigated the effects of a roasted soybean (RSB)-supplemented diet and an estrogen implant (SYN; Synovex-S ear implant, 20 mg estradiol benzoate plus 200 mg progesterone) in young crossbred beef steers on their performance and plasma growth hormone (GH) response to challenge injections of thyrotropin-releasing hormone (TRH) + GH-releasing hormone (GHRH). Twenty individually fed steers (body weight 255 +/- 5 kg) were assigned to the following treatments: 1) no SYN and fed a soybean meal-supplemented diet, 2) no SYN and fed the RSB-supplemented diet, 3) plus SYN and soybean meal, and 4) plus SYN and RSB. Steers were fed 1.13 MJ metabolizable energy/kg metabolic body weight daily of an 18% protein diet. After a 5-wk growth period, all steers were challenged (intravenous injection) over a 3-wk period with three levels of a combination of TRH + GHRH (0.1 + 0.01, 1.0 + 0.1, 2.5 + 0.25 microg/kg body weight, respectively). After an additional 3 wk, steers were reimplanted and a second 5-wk growth period was followed by a single challenge of the 1.0 + 0.1 TRH + GHRH dose level. Plasma nonesterified fatty acid concentration was greater when steers were fed the RSB compared with soybean meal (265 vs. 205 micromol/L; P < 0.01; SEM = 9.5). Body weight gains for treatments 1, 2, 3 and 4 were 1.35, 1.21, 1.47 and 1.38 kg/d, respectively (RSB, P < 0.10; SYN, P < 0.07; SEM = 0.06). Gain/dry matter intake (g/kg) means were 184, 167, 197 and 184 (RSB, P< 0.04; SYN, P < 0.07; SEM = 7.5). Feeding roasted soybeans results in depressed area under the GH response curve [907, 555, 827 and 989 microg/(L*min) (SYN x RSB, P < 0.03; SEM = 117)] and depressed peak response (37.2, 26.6, 33.5 and 41.1 microg/L [SYN x RSB, P < 0.05; SEM = 4.5]), an effect alleviated by estrogen for young growing steers (Period 1) but not for heavier steers (Period 2).

Hormonal and nutritional modulation of hepatic arginase activity in growing cattle.

The hormonal and nutritional modulation of hepatic arginase activity (HARG) was characterized in growing cattle in two studies. In the first study, 20 steers (initial weight, 182 +/- 2 kg) were assigned in equal numbers to either Synovex-S (SYN) (ear implant), recombinant bovine somatotropin (Somavubove; SbV; 0.1 mg/kg intramuscularly daily), SYN + SbV, or nothing (control). Steers were individually fed, for 56 d, a concentrate (80% diet dry matter [DM]) and silage (20% diet DM) diet providing 20 g of crude protein (CP) and 252 kcal metabolizable energy (ME) per kg body weight0.75. On Day 57, samples of liver were obtained at slaughter and subsequently assayed for HARG by the incubation of a tissue homogenate for 2 hr with 250 mM arginine, with and without Mn2+ and heat activation, and the measurement of the resulting urea. HARG was uniformly increased by divalent cation (Mn2+) and heating. SYN had no effect on HARG, whereas SbV treatment resulted in an overall 34% decrease in HARG. Plasma urea nitrogen (PUN) was decreased by SbV but not consistently affected by SYN. In the second study, 16 steers (avg. initial weight, 284 +/- 5 kg) were initially fed a concentrate basal diet consisting of 11% CP and 1.96 Mcal ME for 21 d. Steers were then assigned to one of four dietary treatments (6.4 kg DM/hr per day) in a factorial arrangement of high and low CP (8 and 14%) and two levels of energy (1.96 and 2.67 Mcal ME/kg of diet DM) for 210 d and slaughtered. HARG and PUN were higher in steers fed 14% CP but were lower at each level of CP fed at the higher level of ME. The data suggest that hormonal repartitioning compounds and diet composition may modulate nitrogen metabolism by affecting the activity of arginase in the liver as well as by affecting the total content of arginase in association with changes in organ size.

Endotoxin administration decreases plasma insulin-like growth factor (IGF)-I and IGF-binding protein-2 in Angus x Hereford steers independent of changes in nutritional intake.

Endotoxemia and sepsis cause severe shifts in metabolism towards catabolic events. The objective of the research was to determine whether endotoxin administration changes plasma concentrations of IGF-I and IGF-binding protein-2 (IGFBP-2) in Angus x Hereford steers. In Experiment 1, mean feed intake in endotoxin-treated steers (n = 6) decreased 60% within the first 24 h after endotoxin and averaged, for the duration of the 96 h test period, an intake 35.5% lower than the mean ad libitum intake recorded prior to endotoxin. Plasma concentrations of IGF-I averaged 182 ng/ml in steers before endotoxin (E. coli, 055:B5, 0.2 micrograms/kg, i.v. bolus) and decreased an average of 24.2% at 24 to 96 h after endotoxin. In Experiment 2, a paired feeding strategy was used to determine whether the reduced feed intake was a significant factor in changing plasma concentrations of IGF-I and IGFBP-2 after endotoxin challenge. Steers were divided into endotoxin (0.2 micrograms/kg, i.v., n = 6) or control (saline, i.v., n = 3) treatments. Each of three endotoxin-treated steers was paired to a specific control. In this fashion, the adjusted feed intake of each endotoxin-treated steer was fed to it's paired control every 24 h through 96 h after endotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)