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.

We investigated the effects of birth weight and postnatal nutrition on growth characteristics of neonatal lambs. Low- and high-birth-weight male lambs were individually reared on a high-quality liquid diet to grow rapidly (ad libitum access to feed) or slowly (ADG 150 g) to various weights up to 20 kg live weight (LW). Average daily gain tended to be greater in the high- (mean+/-SE 345+/-14 g) than in the low- (329+/-15 g) birth-weight lambs given ad libitum access to feed owing to slower growth by the small newborns during the immediate postpartum period. At birth, on a weight-specific basis, small newborns contained 6.4% less nitrogen and tended to have more ash (8.9%) than the high-birth-weight newborns. Daily rates of fat, ash, and GE accretion were greater, and nitrogen accretion tended to be greater in the rapidly grown large newborns than in their small counterparts. At any given empty body weight (EBW) during rearing, low-birth-weight lambs contained more fat and less ash, resulting in slowly and rapidly grown small newborns containing 39.3 and 42.7 Mcal GE, respectively, at completion of the study (17.5 kg EBW), compared with 34.8 and 40.5 Mcal in their large counterparts. The differences in fatness and energy content between the birth weight categories are attributed to energy requirements for maintenance that were approximately 30% lower, coupled with higher relative intakes in the low-birthweight lambs, during the early postnatal period. At this time, the ability to consume nutrients in excess of lean tissue growth requirements was apparently more pronounced in small than in large newborns, which resulted in lower efficiency of energy utilization for tissue deposition. Furthermore, body composition differences between the slowly and rapidly reared lambs support the notion of a priority of lean tissue over fat when nutrient supply is limited.

This study investigated effects of birth weight and postnatal nutrition on regulation of energy metabolism in the neonatal lamb. Low (mean +/- SD 2.289 +/- 0.341 kg, n = 28) and high (4.840 +/- 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 +/- SEM 8.31 +/- 0.25 vs 6.39 +/- 0.32 mM, P = 0.002) and somatotropin (ST, 49.1 +/- 17.0 vs 10.8 +/- 4.3 ng/mL, P = .045) and lower IGF-I (36.1 +/- 6.8 vs 157.7 +/- 21.8 ng/mL, P < 0.001) than large newborns. Plasma glucose (1.42 +/- 0.23 vs 2.63 +/- 0.95 mM, P = 0.147) and insulin (0.09 +/- 0.02 vs 0.13 +/- 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.

This study investigated effects of birth weight and postnatal nutrition on organ growth in neonatal lambs. Suffolk x (Finnsheep x Dorset) low- (mean +/- SD 2.29 +/- 0.34 kg, n = 28) and high- (4.84 +/- 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.

Striped bass Morone saxatilis under normal pond‐reared conditions usually requires 14–18 mo to grow out to market weight. This includes a winter of comparatively slower growth which could possibly be overcome through hormonally induced acceleration of growth. Thus, the objective of this experiment was to test the hypothesis that bovine growth hormone and bovine placental lactogen increase growth in striped bass in a dose dependent manner. A secondary objective was to determine the effect of these hormones on body composition. Variables tested were weight gain, length gain, condition factor, feed conversion, and body composition. Fish injected biweekly with 10 μg/g body weight, bovine placental lactogen (P < 0.09) or bovine growth hormone (P < 0.11) increased body weight. Fish injected with 1 or 10 μg/g body weight bovine placental lactogen (P < 0.10) or bovine growth hormone (P < 0.10) increased body length during the 12‐wk study period. Proximate analysis indicated that bovine growth hormone increased protein content (10 μg/g; P < 0.10) and decreased fat content (1 and 10 μg/g; P < 0.10). No significant differences occurred in feed conversions. We conclude that bovine growth hormone and bovine placental lactogen are effective in increasing body growth in striped bass.