Growth and carcass characteristics and serum growth hormone, prolactin and insulin profiles in Debouillet lambs treated with ovine growth hormone and(or) zeranol

Sixteen Debouillet wether lambs (approximately 3 mo old) were placed indoors in 1.5- x 3-m pens (14 h light:10 h dark) 28 d after weaning. Lambs received no implant or a 12-mg zeranol implant on d-2 (eight lambs/group). Two days later (d 0), animals received either 0 or 2.5 mg ovine growth hormone (oGH, eight lambs/group) s.c. on alternate days for 42 d. Animals had ad libitum access to water, salt, mineral and a pelleted alfalfa diet (16% CP). After 42 d, lambs were slaughtered to evaluate carcass traits, organ weights and femur characteristics. Zeranol by oGH interactions were not detected (P greater than .20). Zeranol increased (P less than .05) BW, improved (P less than .05) feed:gain during the first 20 d and increased (P less than .10) feed intake during the last 22 d of the 42-d trial compared with controls. Carcass characteristics were not altered (P greater than .10) by 12 mg zeranol. Serum insulin and prolactin were elevated (P less than .05), but serum GH was not influenced by zeranol compared with controls. Exogenous oGH decreased feed intake (P less than .10) and improved feed:gain (P less than .05) during the initial 20 d compared with controls, but did not influence (P greater than .20) these variables during the last 22 d of the study. Carcass traits were not influenced (P greater than .10) by oGH. Exogenous ovine GH dramatically elevated (P less than .05) serum GH, but did not affect serum insulin or prolactin (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of thyrotropin-releasing hormone and a thyrotropin releasing hormone analog on growth and selected plasma hormones in lambs

An 8-wk growth trial was conducted to assess the effects of continuous infusion of thyrotropin-releasing hormone (TRH) and an active TRH analog less than Aad-His-Pro-NH2 (the less than Aad is L-pyro-alpha-aminoadipic acid) on growth trial performance, carcass composition and hormone profiles of growing lambs. Both drugs were infused at 600 micrograms X lamb -1 X d -1 with 16 lambs/treatment. Both TRH and less than Aad-His-Pro-NH2 decreased average daily gain (ADG; P less than .01) and increased feed conversion (FC; P less than .01) compared with saline infused controls. Average daily feed intake was not altered. Carcasses of lambs given TRH or less than Aad-His-Pro-NH2 contained fewer kilograms of moisture (P less than .05) and appeared to contain fewer kilograms of protein. Thyrotropin-releasing hormone and less than Aad-His-Pro-NH2 increased thyroid gland weights (P less than .05), but pituitary gland weights were not different. Plasma thyrotropin (TSH) concentrations were increased by both drugs compared with control lambs, peaking at 4 to 7 d after initiating infusion. However, by 14 d, TSH concentrations returned to control levels. Triiodothyronine (T3) and thyroxine (T4) were elevated by both drugs over the entire 8-wk trial, with peak levels reached at 10 d and maintained for the duration of the study. Both TRH and less than Aad-His-Pro-NH2 increased prolactin over the entire period. Growth hormone levels were not altered by either drug. The effects of less than Aad-His-Pro-NH2 infusion on growth trial performance, carcass composition and hormone profiles of growing lambs were very similar to TRH. The negative effects of TRH and less than Aad-His-Pro-NH2 infusion on ADG, FC and carcass protein appear to be the result of elevated T3 and T4 levels.     

Influence of zeranol and breed on growth, composition of gain, and plasma hormone concentrations

Seven Angus and six Brangus steers averaging 225 and 245 kg, respectively, were assigned randomly to zeranol (36 mg) implant (I) and no implant (NI) treatments. Steers had ad libitum access to a corn silage diet plus .68 kg of a soybean meal-based supplement fed daily. Steers were bled via jugular catheters on d 0, 28, 56, and 84 at 15-min intervals for 4 h before and 4 h after feeding. Concentrations of growth hormone (GH), insulin (INS), triiodothyronine (T3), thyroxine (T4), and glucose were determined. Whole-body protein and fat contents were monitored. A breed x I interaction (for d 56 to 84 and d 0 to 84) was observed for ADG (P less than .05 and P less than .07, respectively), feed conversion (P less than .05 and P less than .07, respectively), and protein deposition (for d 0 to 29 and d 0 to 84; P less than .07 and P less than .05, respectively). These interactions were attributed to a greater response to I by Angus than by Brangus steers. A feeding x period interaction (P less than .10) was observed for mean GH concentration, and INS, T4, and T3 concentrations were higher (P less than .05) during the 4-h postfeeding period than during the 4-h prefeeding period. The implant increased (P less than .08) mean GH concentration but did not alter the frequency, duration, or amplitude of plasma GH peaks. Steers that were implanted had lower (P less than .05) plasma T3. Brangus steers had lower (P less than .05) plasma glucose, T3, and T4 concentrations than Angus steers. Results indicate that growth factors beyond those measured are responsible for the anabolic response to zeranol.     

Carcass composition and adipose tissue metabolism in growing sheep

Experiments were conducted to investigate biological variables that influence fat accretion in growing ram lambs. Carcass composition and adipose tissue development were measured in Columbia-sired ram lambs from 32.0 to 73.9 kg body weight. Five or six ram lambs were slaughtered every 2 mo, from 4 to 10 mo of age. The percentage of carcass fat-free dry matter decreased with age from 30.9 to 27.5% (P less than .05), while the percentage of carcass fat increased from 17.7 to 33.4%. Similarly, offal fat-free dry matter decreased with age (from 24.5 to 21.5), and there was nearly a threefold increase in the percentage of offal fat (P less than .05 for both measures). Subcutaneous adipocyte diameter and lipogenesis in vitro increased from 4 to 6 mo of age, and did not increase further with age. A bimodal distribution of adipocytes was apparent in the 4-mo-old lambs, but was not observed in any other age group. The presence of glucose in incubation media stimulated acetate incorporation into fatty acids in vitro in adipose tissue from 8- and 10-mo-old lambs. However, glucose did not affect the rate of lipogenesis from lactate. The data indicate early, rapid increases in carcass fat accretion, which corresponded to similar increases in lipogenesis and lipogenic enzyme activities.     

The relationship between composition of gain and circulating hormones in growing beef bulls fed three dietary crude protein levels

Twenty-one Simmental crossbred bulls (311 +/- 11 kg, 9 mo of age) were used to determine the effect of feeding 10, 12 or 14% CP on concentration of hormones in blood and the relationship of these hormones to composition of gain. Six bulls were slaughtered on d 0 to provide an estimate of initial carcass composition (9-11 rib section). Remaining bulls were assigned to dietary treatments. Blood samples were collected every 30 min from 0800 to 2000 on d 0, 66, 136 and 202 of treatment; bulls were slaughtered on d 203. Across all treatments, growth hormone (GH) declined (P less than .05) from d 0 to d 202. Free insulin-like growth factor I (IGF-I) was lowest (P less than .05) on d 0. In four randomly selected bulls, IGF-I fluctuated during the 12-h sampling periods. Within each treatment group, insulin was greatest on d 202 (P less than .05). Testosterone (T) increased from d 0 to d 66, then declined. Cortisol (C) was lowest on d 66. Thyroid hormones increased (P less than .05) after d 0. Growth hormone and IGF-I were correlated negatively with carcass fat percentage, fat accretion rate and fat thickness. IGF-I concentrations were correlated positively with percentage of carcass protein. Testosterone:cortisol ratio was not related to composition, but high T coupled with low C may be related to carcass leanness (mean carcass fat = 24.4%). These data suggest that GH and IGF-I are the hormones most related to composition of gain in growing beef bulls.     

Effect of dose and frequency of administration of a potent analog of human growth hormone-releasing factor on hormone secretion and growth in pigs

Ninety-six pigs (49.5 +/- .5 kg BW) were allotted to six treatments and were injected once (SID) or three times daily (TID) s.c. with a [desamino-Tyr1, D-Ala2, Ala15] human growth hormone-releasing factor (1-29) NH2 analog (GRF-AN). Treatments were T1, noninjected control; T2, saline-injected control (TID); T3, GRF-AN (1.66 micrograms/kg BW, TID); T4, GRF-AN (3.33 micrograms/kg BW, TID); T5, GRF-AN (6.66 micrograms/kg BW, TID) and T6, GRF-AN (10 micrograms/kg BW, SID). Feed protein levels were 14% for T1 and 18.8% for T2 through T6. The GRF-AN increased serum growth hormone (GH) concentration for the entire growing period (about 56 d) in a dose-related manner and did not induce desensitization of the somatotroph cells; in fact, an increase (P less than .05) in the GH response to GRF-AN was observed in T4 and T5 after 1 mo of treatment. This GRF-AN produced (P less than .05) a dose-dependent effect on several variables in animals grown to 110 kg BW: in comparison to T2, T5 increased meat in carcass (6%), carcass length (3%), loin eye area (13%), liver weight (19%), kidney weight (30%), improved feed efficiency (20%) and decreased total feed intake by 50 kg (26%). Compared to T2, average daily gain was increased (P less than .05) by 13% by the 3.33 micrograms/kg TID dose. Blood parameters were measured on d 1, 29 and 57. Increased serum glucose and insulin levels were observed. Triiodothyronine and thyroxine concentrations were increased and decreased, respectively after 28 d of treatment but were unchanged on d 57. This potent GRF analog maintained high GH concentration for at least 56 d and affected several growth parameters and carcass characteristics in a dose-related manner similar in magnitude to that reported in studies using porcine GH.     

Failure of photoperiod to alter body growth and carcass composition in beef steers

In each of two experiments, 70 crossbred steers were blocked by BW and assigned to initial slaughter groups or to treatments in a 2 x 2 design. In Exp. 1, treatments were 168 d of photoperiod (8 h of light [L]:16 h of dark [D] or 16L:8D) and plane of nutrition (high energy [HPN] or low energy [LPN]). On d -22, 67 and 155, blood was sampled every 20 min for 8 h. Relative to LPN, HPN increased (P less than .01) ADG by 28%, carcass weight by 26% and accretion of carcass fat by 109% and carcass protein by 20%. On d 155, compared with LPN, HPN increased (P less than .01) serum insulin (INS; 1.09 vs .64 ng/ml) and lowered (P less than .05) growth hormone (GH; 2.14 vs 3.70 ng/ml), but prolactin was not affected. Photoperiod did not affect BW gains, carcass composition or serum hormones. In Exp. 2, treatments were 113 d of photoperiod (8L:16D or 16L:8D) and Synovex-S implant (presence [IMP] or absence [NONIMP]). On d 93, blood was sampled every 30 min for 10 h. Relative to NONIMP, IMP increased (P less than .01) ADG by 12% and accretion of carcass protein by 16%. Implants did not affect carcass weight or accretion of fat. Compared with NONIMP, IMP increased (P less than .05) GH (3.16 vs 2.39 ng/ml) and INS (.68 vs .46 ng/ml) but did not affect PRL. Photoperiod did not affect BW gain, carcass composition or serum hormones. We conclude that photoperiod fails to influence growth and carcass composition of steers.     

Growth performance and carcass composition of lambs infused for 28 days with a growth hormone-releasing factor analogue.

A human growth hormone-releasing factor analogue, [DesNH2Tyr1,D-Ala2,Ala15]hGRF(1-29)NH2 (GRF-A), was infused s.c. into lambs for 28 d to determine its effects on growth performance and carcass composition. Twenty crossbred wethers weighing 47.0 +/- .5 kg were implanted with 7-d osmotic minipumps at weekly intervals. Minipumps contained either vehicle (dimethyl sulfoxide:H2O, 1:1) or GRF-A, released at a rate of 208 pmol (or .7 micrograms).h-1.kg-1. During the infusion period, plasma GH levels were increased (P less than .01) in GRF-A-treated wethers compared with control wethers (15.0 vs 9.3 ng/ml) and were higher on days that closely followed minipump implantation. Plasma IGF-I and hepatic IGF-I RNA concentrations were similar in lambs of both groups. Analogue treatment improved feed conversion (4.9 vs 5.8 kg dry matter/kg gain, P less than .05), increased average daily gain (.35 vs .30 kg, P = .05) and had no effect on feed intake, wool growth and body, carcass, selected organ and pituitary weights. Carcasses from GRF-A-infused lambs had less adjusted fat depth, a lower percentage of fat and a higher percentage of protein (P less than .05) than carcasses from control lambs. Magnitude of most effects of GRF-A on carcass measurements were correlated with the mean GH level that a lamb had during the infusion period. In conclusion, s.c. infusion of GRF-A improved feed utilization and altered carcass composition of feeder lambs in a relatively short period of time (28 d).     

Effect of long-term administration of porcine growth hormone-releasing factor and(or) thyrotropin-releasing factor on growth hormone, prolactin and thyroxine concentrations in growing pigs

Long-term administration of porcine growth hormone-releasing factor (pGRF(1-29)NH2) and(or) thyrotropin-releasing factor (TRF) was evaluated on serum concentrations of growth hormone (GH) thyroxine (T4) and prolactin (PRL). Twenty-four 12-wk-old female Yorkshire-Landrace pigs were injected at 1000 and 1600 for 12 wk with either saline, pGRF (15 micrograms/kg), TRF (6 micrograms/kg) or pGRF + TRF using a 2 x 2 factorial design. Blood samples were collected on d 1, 29, 57 and 85 of treatment from 0400 to 2200. Areas under the GH, T4 and PRL curves (AUC) for the 6 h (0400 to 1000) prior to injection were subtracted from the postinjection periods (1000 to 1600, 1600 to 2200) to calculate the net hormonal response. The AUC of GH for the first 6 h decreased similarly (P less than .05) with age for all treatments. The GH response to GRF remained unchanged (P greater than .10) across age. TRF alone did not stimulate (P less than .05) GH release but acted in synergy with GRF to increase (P less than .05) GH release. TRF stimulated (P less than .001) the net response of T4 on all sampling days. Animals treated with the combination of GRF + TRF showed a decreased T4 AUC during the first 6 h on the last three sampling days. Basal PRL decreased (P less than .05) with age. Over the four sampling days, animals injected with TRF alone showed (P less than .01) a reduction (linear effect; P less than .01) followed by an increase (quadratic effect; P less than .05) in total PRL concentration after injection; however, when GRF was combined with TRF, such effects were not observed (P greater than .10). Results showed that 1) chronic injections of GRF for 12 wk sustained GH concentration, 2) TRF and GRF acted synergistically to elevate GH AUC, 3) TRF increased T4 concentrations throughout the 12-wk treatment period, 4) chronic TRF treatment decreased the basal PRL concentration and 5) chronic GRF + TRF treatment decreased the basal concentration of T4.     

Effect of prenatal trenbolone acetate treatment on lamb performance and carcass characteristics

Forty-three pregnant Dorset and Dorset crossbred ewes were assigned randomly to a control group or implanted with either 300 mg trenbolone acetate (Low TBA) or 1,200 mg trenbolone acetate (High TBA) between d 40 and 60 of gestation. Adjusted weaning weights for ewe lambs were 23.3% less (P less than .10) with vs without TBA treatments. Postweaning ADG of ewe lambs was lower (P less than .05) but ADG of ram lambs was greater (P less than .05) for high TBA vs low TBA. Ewe lambs receiving high TBA had 19% less (P less than .05) gain per unit of feed than those receiving low TBA. Days on test for ewe lambs was greater (P less than .05) due to TBA treatment and for high TBA vs low TBA. Days on test for ram lambs was decreased (P less than .05) due to high TBA compared to low TBA. Subcutaneous fat over the ribeye and lower rib were greater (P less than .05) for high-TBA ewe lambs vs low-TBA ewe lambs. Percentage kidney and pelvic fat of ewe lambs was lower (P less than .05) due to TBA treatments. Ribeye area per unit of carcass weight was lower (P less than .05) in high-TBA ewe lambs vs low-TBA ewe lambs. Yield grade of ewe lambs was lower (P less than .05) for low TBA vs high TBA. Prenatal trenbolone acetate treatment of ewe lambs did not improve their subsequent postnatal growth performance and carcass traits. In addition, TBA implantation of the pregnant ewe produced dystocia and less milk production, as evidenced by the need for more lambs to be grafted.     

Influence of frame size and zeranol on growth, compositional growth and plasma hormone characteristics

A 2 X 2 factorially arranged trial was conducted to compare effects of implant (zeranol) and frame size on weight and compositional gain, and plasma hormone concentrations. Angus, Charolais X Hereford and Hereford X Angus yearling steers (34 steers averaging 270 kg body weight) were randomly assigned to treatments of small (SF) vs large frame (LF) and implant (I) vs no implant (NI). Steers were implanted at 0 and 97 d and individually fed an 81% whole shelled corn and 11.5% corn silage-based diet (dry basis) for a 175-d period. Shrunk weights and body measurements for frame size determination were taken initially and at approximately 28-d intervals; blood was collected via venipuncture at 14-d intervals for analyses of insulin (IN), triiodothyronine (T3), thyroxine (T4) and glucose concentrations. Steers were also counted in a whole body counter for measurement of 40K content and prediction of whole body protein and fat. The I steers showed an improvement (P less than .05) in daily gain regardless of frame size for the total trial. The I LF steers required 18% more dry matter to attain higher daily gain for 97 to 175 d; I steers were more efficient (P less than .05) at converting dry matter to gain during 0 to 97 d and 0 to 175 d. Daily fat deposition was increased (P less than .05) in I steers, while protein deposition was not affected by I. Plasma IN concentrations were numerically elevated (P less than .10) in I steers regardless of frame size, during the initial 97 d. Implant did not influence (P greater than .10) plasma T3, T4 and glucose concentrations regardless of frame size. Steers responded differently to zeranol implant over time regarding plasma T4 concentrations (P less than .003). Steers differing in frame size responded similarly in rate of gain, in feed conversion and in patterns of plasma insulin concentrations to zeranol implants.     

Plasma somatotropin response to exogenous growth hormone releasing factor in lambs

Two experiments were performed to examine the ability of human pancreatic growth hormone releasing factor (hGRF) administration to stimulate endogenous growth hormone (GH) secretion in lambs. Each study utilized eight Dorset wether lambs in replicated 4 X 4 Latin square experiments. Growth hormone response (integrated area under the curve for 150 min post-injection) for 0, 1, 5 and 10 micrograms hGRF/kg body weight averaged 13, 23, 92 and 134 units, respectively. While the 1-microgram hGRF dose was not different (P greater than .05) than the response to saline injection, there was an increased (P less than .01) GH response to 5 or 10 micrograms hGRF. Overall the GH response increased in a log dose-response fashion. There was distinct variation between lambs in their response to hGRF. Study II examined the optimal method to administer 40 micrograms hGRF/kg body weight to maximize GH concentration over 24 h. Continuous infusion (CI) was compared with eight (8X), four (4X), or two (2X) injections/d. Hourly blood samples were obtained from all lambs. Growth hormone response (area under the curve for 24 h) was 162, 305, 306 and 220 units for CI, 8X, 4X and 2X, respectively. Growth hormone response to CI was inferior to discrete injections, and the GH response to 4X or 8X was superior to 2X/d. Results demonstrate that, in spite of lamb-to-lamb variation, one can utilize exogenous hGRF to enhance GH secretion in lambs. Thus, the ability of exogenous hGRF to enhance growth performance merits further study.     

Growth performance, serum hormones, and metabolite responses before and after weaning in lambs weaned at 42 days of age: effect of preweaning milk and postweaning alfalfa or grass hay diets.

Fourteen fall-born lambs were used to determine the effects of diet before and after weaning on intake, growth, serum hormones, and metabolite profiles. Before weaning, lambs were intensively sampled for 6 h at 35 and 42 d of age. Before sample collection, lambs were allowed to suckle, and milk intake was recorded. At 42 d of age, lambs were weaned and randomly allotted to ad libitum access to either alfalfa or grass hay. Blood samples were collected at 49 and 56 d of age for 6 h. Milk intake did not differ (P greater than .10) between groups. After weaning, lambs fed alfalfa hay consumed more (P less than .05) hay and had greater (P less than .05) ADG than lambs fed grass hay. Postweaning diet had no effect (P greater than .10) on serum insulin, growth hormone (GH), insulin:GH ratio, prolactin, cortisol, glucose, or nonesterified fatty acids (NE-FA) concentrations. Lambs consuming alfalfa had higher (P less than .05) serum urea nitrogen (SUN) at 49 and 56 d of age than lambs consuming grass. At 35 and 42 d of age, (P less than .05) serum insulin and insulin:GH ratio were higher (P less than .05) after milk intake than at 49 and 56 d of age after hay intake. Serum GH was higher (P less than .05) in lambs at 35 and 42 d of age for 2 h postfeeding, but by h 3 through 5, lambs consuming milk had lower (P less than .05) values than lambs consuming hay.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine and metabolic changes during altered growth rates in beef cattle

Eight steers from a group of 14 were fed ad libitum from 240 to 510 kg live weight, gaining at 1.4 +/- .2 kg/d. The six other steers were diet-restricted and grew at .37 +/- .09 kg/d from 240 to 307 kg, prior to ad libitum realimentation on the same diet to a final weight of 510 kg. Blood samples taken during the growth phases from both treatments were analyzed for insulin-like growth factor-I (IGF-I), triiodothyronine (T3), thyroxine (T4), glucose (GLU), nonesterified fatty acids (NEFA), and blood urea nitrogen (BUN) and (or) growth hormone (GH). During restricted growth, mean serum concentrations of GH were elevated (45.6 vs 23.4 ng/ml; P less than .05), serum concentrations of IGF-I decreased (108 vs 167 ng/ml; P less than .05) compared with control steers with ad libitum access to feed. Levels of T4 and GLU also were lower (P less than .05) during restricted than during normal growth. During early realimentation, levels of GLU (P less than .05), IGF-I (P less than .01), T4 and BUN (P less than .01) increased. Levels of T3 remained unchanged, whereas concentration of NEFA declined (P less than .001). Blood urea nitrogen decreased during early realimentation despite a large increase in diet protein intake and in protein storage, suggesting an increased efficiency of nitrogen use for protein synthesis. During realimentation, IGF-I levels rose above those of control steers and remained higher at the final weight of 510 kg (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of long-term administration of pituitary-derived bovine growth hormone and estradiol on growth in steers

Sixty-three Friesian steers (9 mo old, 257 kg; n = 15 or 16/treatment) were employed in a 2 x 2 factorial to test bovine growth hormone (bGH) and estradiol (Compudose implant). Steers received daily subcutaneous injections of vehicle or bGH (40 micrograms/kg body weight) for 22 wk. Steers were slaughtered 8 wk after the end of bGH treatment (wk 30). Steers had ad libitum access to silage plus a fixed amount (4 to 5.5 kg/d) of concentrate. Average daily gain (ADG) and feed conversion efficiency (FCE) improved (P less than .05) in response both to bGH and to estradiol during wk 0 to 22. Although bGH did not affect ADG or FCE during wk 23 to 30, estradiol improved (P less than .05) them; bGH and estradiol appeared additive (nonsignificant interactions) during wk 0 to 22. At slaughter, estradiol increased (P less than .05) carcass weight and carcass and leg length while decreasing (P less than .05) conformation score and percentage of kidney, knob and channel fat (KHP); bGH decreased (P less than .05) KHP. Although both bGH and estradiol increased (P less than .01) plasma GH, their effects were not additive. Both bGH and estradiol increased (P less than .01) plasma somatomedin-C and decreased (P less than .01) plasma urea nitrogen concentrations; effects were additive. Estradiol, but not bGH, increased (P less than .05) plasma glucose, whereas neither bGH nor estradiol altered plasma creatinine and nonesterified fatty acids. In summary, both bGH and estradiol improved growth and FCE, and their effects appeared to be additive. It is likely that some of their effects were mediated by somatomedin-C.     

Effects of plane of nutrition, growth hormone and unsaturated fat on growth hormone, insulin and prolactin receptors in prepubertal lambs

The influence of plane of nutrition, growth hormone (GH) treatment and dietary polyunsaturated fat on serum concentrations of GH and insulin (INS) and binding capacities of GH, INS and prolactin (PRL) in liver, mammary parenchyma and adipose tissue was assessed in prepubertal ewe lambs. Ten lambs were assigned to each of four treatment groups. Treatments included: (A) lambs with ad libitum access to a high-energy ration; (G) lambs fed as group A and treated with bovine GH (.08 mg/kg/d); (R) lambs with feed intake restricted to limit ADG to about 120 g; and (S) lambs with ad libitum access to a ration including formaldehyde-protected sunflower seed. Diets, all approximately isonitrogenous and isocaloric, were fed from about 7 to 22 wk of age. Weekly blood samples were collected during wk 6 to 14 of the trial. Averaged across sampling dates, mean serum concentrations of GH were elevated in G lambs (P less than .05) and INS concentrations differed in the order G greater than A greater than R = S (P less than .05). Crude membranes for binding assays were prepared from liver, mammary parenchyma and adipose tissue. Mean concentrations of GH receptors in liver and PRL receptors in mammary parenchyma were elevated in group S lambs (P less than .01). Dietary polyunsaturated fat increased the number of GH receptors in liver and PRL receptors in mammary parenchyma. Increased availability of receptors may mediate the stimulation of mammary growth observed in lambs fed polyunsaturated fat.     

Feedlot performance of beef heifers implanted with Synovex-H: effect of melengestrol acetate, ovariectomy or active immunization against GnRH

The effects on anabolic steroid implantation on feedlot performance and carcass composition and quality were examined in control (CNTRL), ovariectomized (OVX) or melengestrol acetate-fed (MGA) beef heifers or heifers actively immunized against GnRH (Anti-GnRH). Heifers (n = 112) were assigned randomly to a 2 x 4 factorial experiment. The two classes were made up of heifers not implanted and those implanted with Synovex-H. The four treatments were 1) CNTRL, 2) MGA, 3) OVX and 4) Anti-GnRH. Heifers were housed in individual pens and fed a high-energy diet for the 4-mo study. Synovex-H increased final live weight (P less than .005), carcass weight (P less than .005), ADG (P less than .0001) and feed efficiency (P less than .005) but did not alter carcass quality and yield grade (P greater than .05). Synovex-H increased deposition of protein (P less than .0001) and reduced deposition of fat (P less than .0001). Oral administration of MGA had no significant effect on feedlot performance or carcass quality. For heifers not implanted, active immunization against GnRH, but not ovariectomy, depressed ADG (P less than .05) and increased fat deposition (P less than .05) while reducing protein deposition (P less than .05). These effects of active immunization were reversed by concurrent administration of Synovex-H. Feedlot performance and carcass composition of heifers were improved by administration of anabolic steroids. When heifers were housed singly, neither ovariectomy, active immunization against GnRH nor oral administration of MGA improved feedlot performance of heifers implanted with Synovex-H.     

Effect of immunization against somatostatin in the pregnant ewe on growth and endocrine status of the neonatal lamb

Absorption of somatostatin (SRIF) specific antibodies from colostrum of ewes actively immunized against SRIF may improve growth rate of the neonatal lamb by neutralizing the inhibitory effects of SRIF on pituitary and thyroid function. Growth and endocrine parameters in the offspring of SRIF immunized (SI) and control (C) crossbred ewes were examined. Lamb weight was recorded at birth and twice each week to 24 days of age. Blood samples were collected prior to first suckle and twice each week. At 21 to 24 days of age, in separate experiments, lambs were infused with glucose (0.29 g/kg), arginine (0.25 g/kg) or thyrotropin-releasing hormone (TRH; 0.33 microgram/kg). A strong correlation (R = 0.88; P less than .01) was observed between anti-SRIF titre in the ewe at parturition and in the lamb at 3 days of age. No effect on lamb birth weight (SI 4.28 +/- 0.27 kg; C 4.35 +/- 0.23 kg) was observed. At 24 days of age cumulative gain in SI lambs (5.4 +/- 0.32 kg) was greater (P less than .05) than in C lambs (4.5 +/- 0.32 kg). The growth hormone secretory responses to glucose or arginine were not affected by treatment. Plasma IGF-I, plasma thyroxine (T4) and the plasma thyrotropin and T4 responses to TRH were not different between treatments. Plasma triiodothyronine (T3) was higher (P less than .05) in SI (2.46 +/- .10 ng/ml) than in C (2.01 +/- .05 ng/ml) lambs, however, the plasma T3 response to TRH was lower in SI lambs. Plasma glucose (mg/dl) was higher (P less than .05) in SI (118.4 +/- 1.7) than in C (106.0 +/- 4.0) lambs. Plasma insulin was not affected by treatment. Increased plasma T3 and glucose concentrations during SRIF immunoneutralization in the neonate lamb may be important factors contributing to the growth response observed.     

Growth hormone, insulin, prolactin and glucose levels in ewe and ram lambs during normal and compensatory growth

Two trials were conducted to determine the effect of compensatory growth on plasma glucose and serum growth hormone (GH), prolactin (PRL) and insulin concentrations in lambs. The trials consisted of a normal growth (NG) period (4 to 7 mo of age), a restricted feed/weight loss period and a compensatory growth (CG) period. The lambs in Trial 1 were 13 mo of age and in Trial 2, 11 mo of age at the start of the respective CG periods. Compensatory growth rate was 61 to 67% greater than NG rate in Trial 1 and 2, respectively. Twenty-four hour blood collections were performed during NG and CG in each trial. Normal growth blood collection for Trial 1 was performed in April (ram, n = 7; ewe, n = 6) and the CG blood collection in November (ram, n = 6; ewe, n = 6) while for Trial 2 blood collection dates were November (ram, n = 6; ewe n = 6) and March (ram, n = 4; ewe, n = 5). Trial 1 ram lambs had lower plasma glucose concentrations during CG than during NG while plasma glucose concentration was not altered in ewe lambs. Type of growth had no effect on plasma glucose in Trial 2. There was a type of growth by sex interaction for insulin in both Trial 1 and Trial 2. Insulin concentration decreased during CG in ram lambs but remained unchanged (Trial 1) or increased in ewe lambs (Trial 2) during CG. The effect of CG on PRL concentration in Trial 1 was confounded by photoperiod and the only effect in Trial 2 was a small decrease in the amplitude of PRL peaks during CG. The overall mean GH concentration (GHmn) was increased (P less than 0.01) two fold during CG in Trial 1. This effect was also seen in Trial 2 but the increase was sex dependent (P less than 0.005) with the effect of CG on GHmn in ram lambs being six times that seen in ewe lambs. The GH profile characteristics responsible for the increase in GHmn during CG differed between sexes and trials.     

Alterations in postmortem degradation of myofibrillar proteins in muscle of lambs fed a beta-adrenergic agonist

Dietary administration of 4 ppm of the beta-agonist L-644,969 (Merck Sharpe and Dohme Research Laboratories) to finishing lambs induced a decrease (10 to 14%, P less than .05) in extractable calpain I activity in the longissimus muscle (LD) at death (d 0). At 4 d postmortem (d 4), extractable calpain I levels in the LD of both control and treated lambs were reduced (P less than .001) from those present at d 0, but the extractable activity in the LD was reduced to a greater extent in control than in treated lambs. Calpain II activity was increased 42% (P less than .005) in LD of treated lambs; however, no significant differences were observed between d 0 and d 4 calpain II activity within treated or control LD samples (P greater than .1). Calpastatin activity was higher in the LD of treated lambs (74% on d 0, P less than .001 and 430% on d 4, P less than .001) than in the LD of control lambs. Measurable cathepsin B activity was decreased (29% on d 0, P less than .05) and measurable cathepsin H activity was increased (10% on d 0, P less than .05 and 10% on d 4, P less than .05) in the LD of treated lambs compared with controls. On d 2, 4 and 6 postmortem, degradation in myofibrils isolated from the LD was lower for treated than for control lambs. Warner-Bratzler shear values for loin chops from treated lambs were higher on both d 3 (111%) and 6 (108%) postmortem than for chops from control lambs (P less than .001). L-644,969-induced decreases in muscle proteolytic capacity may limit postmortem myofibril degradation and contribute to the reduced tenderness observed. This decreased proteolytic capacity may contribute to increased muscularity of L-644,969-treated lambs.