K K Schillo

N-methyl-d, l-aspartate stimulates growth hormone but not luteinizing hormone secretion in the sheep.

The objective of this experiment was to determine the effects of N-methyl-d, l-aspartate (NMA) on luteinizing hormone (LH) and growth hormone (GH) secretion in castrated male sheep. Blood was sampled from Hampshire wethers every 15 min for 8 hr on day 1. At 4 and 6 hr after the initiation of the experiment, wethers were treated i.v. with NMA at a dose of 12 mg/kg body weight (n = 5) or .9% saline (n = 5). The dosage of NMA was within the range of doses that was previously demonstrated to stimulate LH secretion in monkeys. Blood samples were also collected every 15 min for 1 hr on day 2, beginning 24 hr after the first injection of NMA or saline. Treatment with NMA had no effect on mean LH concentrations, LH pulse frequency or LH pulse amplitude during the 4 hr period following the first injection on day 1. On day 2, however, mean LH concentrations were lower (p less than .01) in NMA versus saline-treated wethers. Conversely, administration of NMA evoked a dramatic increase (p less than .02) in mean GH concentrations on day 1. The mechanisms responsible for the effects of NMA described herein and whether or not these effects are relevant to the physiological control of LH and GH release in the sheep warrants further scrutiny.

Effects of Age on Fasting-Induced Changes in Insulin, Glucose, Urea Nitrogen, and Free Fatty Acids in Sera of Sheep

Abstract The hypothesis that prepubertal ewe lambs are metabolically different from postpuberal ewes was tested. Ovariectomized ewes (4 years of age; n = 4) and lambs (6 months of age; n = 4) were fasted for 72 hr. Serum concentrations of insulin, glucose, urea nitrogen, and free fatty acids (FFA) were measured in blood samples taken at 6-hr intervals between 30 hr before and 72 hr after feed removal. Serum concentrations of urea nitrogen and glucose were not different (P > 0.20) between age groups before fasting. Serum concentrations of insulin in ewes increased toward the end of the prefast period whereas those in lambs did not (age × time, P < 0.01). Serum concentrations of FFA in ewes tended to be lower (P < 0.07) than those in lambs prior to fasting. During fasting, concentrations of insulin decreased (P < 0.02) over time in ewes and lambs and did so in a similar manner (age × time, P > 0.70). Urea nitrogen increased (P < 0.0001) in both fasted ewes and fasted lambs in a comparable manner (age × time, P > 0.20). Concentrations of glucose during fasting were not significantly affected (P > 0.90) by age. There was a tendency (P = 0.08) for concentrations of glucose to change over time but the pattern did not appear to be related to fasting. During fasting, concentrations of FFA tended to be higher (P < 0.07) in lambs than in ewes and increased (P < 0.0001) in both groups in a similar fashion (age × time, P > 0.10). The findings herein suggest that turnover of FFA in lambs may be slightly greater than that in ewes during the fed and fasted states.

Growth and endocrine responses of lambs fed rumen-protected ornithine and arginine

Twenty Hampshire × Western wether lambs (initial body weight (BW) 29.9 ± 1.5 kg) were used in a 42-day study to evaluate growth and endocrine responses to rumen-protected ornithine or arginine. Treatments consisted of no supplemental amino acid (CON), or supplements that provided 0.42 g day−1 ornithine HCl per kg BW (ORN), 0.5 g day−1 arginine HCl per kg BW (L-ARG) or 0.75 g day−1 arginine HCl per kg BW (H-ARG). Amino acids were incorporated into a protective matrix containing ground corn, coconut oil and zein. Serum ornithine and urea N concentrations were increased (P 0.05) by treatment. Serum insulin-like growth factor-I (IGF-I) concentrations were higher (P 0.05) by the consumption of rumen-protected ornithine or arginine compared with CON lambs despite increased STH and IGF-I concentrations. Average daily gain of L-ARG lambs was increased (P < 0.05) compared with H-ARG lambs, resulting in heavier (P < 0.05) BW on Day 42 and improved (P < 0.05) feed efficiency. These data provide further evidence that increasing post-ruminal supplies of arginine and ornithine may increase circulating STH and IGF-I concentrations in growing lambs. However, performance may not be improved by these amino acid-induced responses.