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This study investigated effects of birth weight and postnatal nutrition on organ growth in neonatal lambs. Suffolk x (Finnsheep x Dorset) low- (mean [+ or -] SD 2.29 [+ or -] 0.34 kg, n = 28) and high- (4.84 [+ or -] 0.45 kg, n = 20) birth-weight male lambs were studied. Lambs within each birth weight category were allocated to be individually grown rapidly (ad libitum fed, ADG 337 g, n = 20) or slowly (ADG 150 g, n = 20) on a liquid diet to live weights up to approximately 20 kg. All organs weighed less at birth in small than in large newborns (P < 0.001), except the adrenals (P = 0.10). At birth, as a percentage of empty body weight (EBW), small newborns had larger testes (0.14 vs. 0.10%, P = 0.023) and smaller thymus (0.17 vs. 0.37%, P = 0.009), and tended to have a larger heart (0.85 vs. 0.75%, P = 0.060) and a smaller spleen (0.10 vs. 0.14%, P = 0.054) than large newborns. During the first 2 to 3 wk postpartum, small newborns had greater fractional growth rates of organs than large newborns, most notably spleen, thymus, and liver. Postnatal growth of organs was more closely associated with EBW than age, except for lungs, testes, and stomach. At completion of rearing to 20 kg of live weight, small newborns had a spleen approximately 30% heavier than large newborns (P < 0.001). Testes weights were 37% and 24% greater in small newborns reared slowly and rapidly, respectively, compared with their high-birth-weight counterparts (P = 0.034). It was also evident that postnatal nutrition altered the mass of individual organs at the conclusion of the rearing period without affecting the combined weight of dissected organs. Slowly reared lambs had a larger pancreas (+27%, P = 0.002), stomach complex (+83%, P < 0.001), large intestine (+39%, P < 0.001), entire gastrointestinal tract (+18%, P = 0.002), and testes (+54%, P = 0.016) and tended to have a larger heart (+6%, P = 0.068) than their rapidly reared counterparts at 20 kg of live weight. Rapidly reared lambs had a larger thymus (+61%, P = 0.003), liver (+34%, P < 0.001), kidneys (+33%, P < 0.001), and small intestine (+17%, P < 0.001) and tended to have a larger thyroid (+13%, P = 0.054) at 20 kg of live weight than slowly reared lambs. The functional significance of the smaller thymus at birth and increase in spleen and testes weights at 20 kg of live weight in low- compared with high-birth-weight lambs warrants further investigation. It also remains to be established whether these differences at 20 kg of live weight persist. Key Words: Birth Weight, Growth, Lambs, Nutrition, Organs

This study investigated effects of birth weight and postnatal nutrition on regulation of energy metabolism in the neonatal lamb. Low (mean [+ or -] SD 2.289 [+ or -] 0.341 kg, n = 28) and high (4.840 [+ or -] 0.446 kg, n = 20) birth weight male Suffolk x (Finnsheep x Dorset) lambs were individually reared on a liquid diet to grow rapidly (ad libitum fed, ADG = 337 g, n = 20) or slowly (ADG = 150 g, n = 20) from birth to live weights (LW) up to approximately 20 kg. At birth, small newborns had higher plasma concentrations of urea nitrogen (mean [+ or -] SEM 8.3 [= or -] 10.25 vs 6.39 [+ or -] 0.32 mM, P = 0.002) and somatotropin (ST, 49.1 [+ or -] 17.0 vs 10.8 [+ or -] 4.3 ng/mL, P = .045) and lower IGF-I (36.1 [+ or -] 6.8 vs 157.7 [+ or -] 21.8 ng/mL, P < 0.001) than large newborns. Plasma glucose (1.42 [+ or -] 0.23 vs 2.63 [+ or -] 0.95 mM, P = 0.147) and insulin (0.09 [+ or -] 0.02 vs 0.13 [+ or -] 0.06 ng/mL, P = 0.264) concentrations did not differ. Urea nitrogen concentration in plasma peaked and then declined rapidly in all lambs during the first week postpartum, and plasma ST declined on a body-weight-related basis from birth. During rearing to 20 kg LW, plasma insulin was higher in low- vs high-birth-weight lambs. Lambs fed ad libitum had greater plasma concentrations of glucose, urea nitrogen, insulin, and IGF-I compared to those fed a restricted diet (ADG = 150 g). The results suggest that during the early postpartum period, newborn lambs exhibit the fetal characteristic of high rates of amino acid oxidation. The results also support the notion that, at birth, low-birth-weight lambs are less mature than high-birth-weight lambs in aspects of metabolic and endocrine development, which may enhance their capacity to utilize amino acids for energy production and to support gluconeogenesis during the immediate postpartum period. Being small at birth also resulted in elevated plasma insulin concentrations when adequate nutriment to support moderate or rapid growth was provided postpartum, although it remains to be elucidated whether this more chronic effect persists in the longer term. Key Words: Growth, Hormones, Lambs, Metabolism, Nutrition

This study investigated effects of birth weight and postnatal nutrition on growth and development of skeletal muscles in neonatal lambs. Low (L; mean +/- SD 2.289 +/- .341 kg, n = 28) and high (H; 4.840 +/- .446 kg, n = 20) birth weight male Suffolk x (Finnsheep x Dorset) lambs were individually reared on a liquid diet to grow rapidly (ad libitum fed, ADG 337 g, n = 20) or slowly (ADG 150 g, n = 20) from birth to live weights (LW) up to approximately 20 kg. At birth, weight of semitendinosus (ST) muscle in L lambs was 43% that in H lambs; aggregate weights of ST and seven other dissected muscles were similarly reduced. In ST muscle of L lambs, mass of DNA, RNA, and protein were also significantly reduced to levels 67, 60, and 34%, respectively, of those in H lambs. However, myofiber numbers of ST, tibialis caudalis, or soleus muscles did not differ between the L and H birth weight lambs and did not change during postnatal growth. During postnatal rearing, daily accretion rate of dissected muscle was lower in L than in H lambs. Accretion of muscle per kilogram of gain in empty body weight (EBW) was reduced in the slowly grown L lambs compared with their H counterparts, although the difference was less pronounced between the rapidly grown L and H lambs. Throughout the postnatal growth period, ST muscle of L lambs contained less DNA with a higher protein:DNA ratio at any given muscle weight than that of H lambs. Slowly grown lambs had heavier muscles at any given EBW than rapidly grown lambs. Content of DNA and protein:DNA ratio in ST muscle were unaffected by postnatal nutrition, but RNA content and RNA:DNA were greater and protein:RNA was lower at any given muscle weight in rapidly grown lambs. Results suggest that myofiber number in fetal sheep muscles is established before the presumed, negative effects of inadequate fetal nutrient supply on skeletal muscle growth and development become apparent. However, proliferation of myonuclei may be influenced by fetal nutrition in late pregnancy. Reduced myonuclei number in severely growth-retarded newborn lambs may limit the capacity for postnatal growth of skeletal muscles. Key Words: Lambs, Nutrition, Birth Weight, Skeletal Muscle, Myofibrills, Nucleic Acids

The objective of this study was to quantify effects of maternal protein nutrition on N accretion or loss in conceptus and maternal tissues of ewes during late pregnancy. Ewes, pregnant with twins, were fed low (LP, 79 g CP/kg DM), medium (MP, 116 g CP/kg DM), or high (HP, 157 g CP/kg DM) protein diets, each with an estimated ME concentration of 2.7 Mcal/kg DM, between d 111 and 140 of pregnancy; all ewes had been fed the same diet (2.7 Mcal ME, 120 g CP/kg DM) for the previous 30 d (d 80 to 110). Dry matter intakes were varied (LP = 1.0, MP = 1.2, and HP = 1.4 kg/d) according to predicted energy costs of protein deposition for each diet. Nitrogen accretion was estimated by comparative slaughter (d 140 minus d 110) and by collection of excreta between d 120 and 130. Fresh weights of maternal and gravid uterine tissues were measured at slaughter, before proximate analysis of these components. Whole-body N retention was directly and linearly related to N intake, but efficiency of deposition of apparently absorbed N decreased linearly with increasing N intake (LP, .79; MP, .70; HP, .62). Nitrogen accretion in the gravid uterus, maternal viscera, and mammary gland was significantly less in LP than in MP or HP ewes. Nitrogen balance in maternal carcass tissues was linearly related to N intake, ranging from a negative value in LP ewes to a positive value in HP ewes (LP, -63 g; MP -39 g; HP, 55 g). These data provide the basis for estimating N requirements for protein accretion in the conceptus and in maternal tissues during late pregnancy. They also highlight the capacity of maternal carcass tissues to mobilize or deposit amino acids in response to variations in dietary protein supply. Key Words: Sheep, Pregnancy, Protein Intake, Chemical Composition, Nitrogen Metabolism

Six Holstein steers (245 kg initial BW) were surgically prepared with chronic catheters to allow measurement of blood flow and nutrient flux across the hindlimb. Steers were used in a single-reversal design with 16-d treatment periods of daily i.m. injection of either excipient (control) or recombinantly derived bovine somatotropin (120 [[micro]gram]/kg BW). On d 15 of each period, whole-body and hindlimb glucose metabolism were studied during a primed continuous infusion of [[6.sup.-3]H]glucose, under both basal conditions and during a hyperinsulinemic/euglycemic clamp. Somatotropin increased (P < .01) basal blood glucose and serum insulin by 7 and 150% respectively, with no change in glucose irreversible loss rate (ILR). There was no effect of somatotropin on hindlimb blood flow or oxygen consumption. In contrast, hindlimb lactate uptake (P < .02) and the ratio of glucose to oxygen uptake (P < .08) were reduced by somatotropin. Insulin infusion stimulated (P < .01) glucose ILR and inhibited (P < .02) endogenous glucose production to a lesser extent during somatotropin treatment. Basal plasma nonesterified fatty acid concentrations were increased (P < .01) during somatotropin treatment and decreased (P < .02) during insulin infusion. Insulin infusion increased hindlimb blood flow and glucose uptake to similar extents during both treatment periods. These data demonstrate that somatotropin treatment of growing steers decreases response of tissues to insulin (sensitivity in muscle, sensitivity, and responsiveness in liver and adipose tissue), thereby increasing glucose availability to other tissues. Key Words: Steers, Hindlimb, Somatotropin, Glucose, Insulin, Gluconeogenesis

Parmacokinetic parameters for the beta-2-adrenergic agonist, cimaterol (CIM), were determined in growing Holstein steers. Compartmental analysis was used after measurement of CIM in body fluids by affinity chromatography and HPLC using UV detection. Recoveries from spiked plasma and urine standards were 70 plus or minus 1.2% and 68 plus or minus 1.1%, respectively. The minimum detection level in plasma was 1 ng/mL and the average CV was 5.1% for concentrations that ranged from 1 to 30 ng/mL. Four steers (276 plus or minus 24 kg) received 15 mg of CIM by bolus intravenous injection. Plasma CIM levels declined in a biphasic manner with half-lives of 2.5 min for the distribution phase and 54 min for the elimination phase. A two-compartment open model was used to describe the disappearance of CIM and the following pharmacokinetic parameters were obtained: central compartment volume (V(sub c)) = .76 L/kg, apparent volume of distribution (V(sub d)) = 4.1 L/kg, and transfer rate constants from the central to peripheral compartment (k(sub 12)) = .177/min, from the peripheral to central compartment (k(sub 21)) = .054/min and elimination from the central compartment (k(sub el)) = .074/min. After 8 h, total urinary CIM accounted for only 18.3% of the administered dose. Results suggest that circulating concentrations of CIM in growing steers are influenced by its accumulation in an unidentified peripheral pool and its conversion into unknown metabolite(s) before elimination.

The influence of porcine somatotropin (pST) on the rate of in vivo lipogenesis and glucose kinetics in growing pigs was evaluated by testing for these physiological processes in animals injected with the hormone. Treatment with pST decreases both the inclusion of glucose in fat tissues and the accumulation of fat. This is due to the reduction of lipogenesis, particularly the production of new triglycerides. On the other hand, exogenous insulin heightened the lipogenesis rate by around 50%.

Nonesterified fatty acid (NEFA) and glycerol kinetics in pigs administered with porcine somatotropin (pST) were evaluated to find out the effect of the hormone on fatty acid metabolism. Analysis of the uptake of infused tritium-marked glycerol and oleic acid revealed that a growing pig's lipid catabolism is very low indicating that the pig is in a lipogenic stage. Lipolysis and NEFA kinetics increased with the administration of pST, but not by a considerble amount. Other mechanisms beside lipolysis and NEFA kinetics may be responsible for the reduction of fat accumulation during pST treatment.

The effect of porcine somatotropin (pST) on plasma glucose, insulin, glycerol, nonesterified fatty acids (NEFA) and plasma urea nitrogen (PUN) concentrations was examined. Analysis of blood from pigs receiving intramuscular pST injections revealed that transient hyperglycemia and hyperinsulinemia occurs after injection. Glycerol and NEFA exhibited temporary elevation of concentration, but PUN showed reduced levels. This pattern in the blood metabolite concentrations could be explained by the reduced metabolic activities illicited by pST, which also resulted in the reduction of food intake.