Responses of gonadotropin secretion to short-term dietary supplementation in ovariectomized goats with different body weights

The responses of luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion to acute dietary supplementation were studied in goats with different body weights. Ovariectomized Shiba goats (n = 11) were used and were maintained with a feed of 100% of their energy requirement. They were implanted subcutaneously with an oestradiol capsule and were divided into light (LBW; ≤24 kg, n = 6, mean ± S.D., 21.8 ± 2.7 kg) and heavy body weight (HBW; >24 kg, n = 5, mean ± S.D., 32.0 ± 6.3 kg) groups on the basis of their body weights at 8 days before the start of treatment. At the start of treatment (Day 1), the level of a feed changed to 250% of their energy requirement and this level was maintained for 7 days in both groups. Blood samples were collected daily from Day −7 to Day 7 for the analysis of FSH, glucose, and insulin profiles in plasma. Frequent blood samples were also collected at 10 min intervals for 6 h on Day 0, Day 3, and Day 7 for analysis of LH pulses. LH pulse frequency increased significantly on Day 3 as compared with that on Day 0 in both the HBW (7.4 ± 0.5 pulses/6 h vs. 6.2 ± 0.8 pulses/6 h, p < 0.05) and LBW (6.5 ± 0.8 pulses/6 h vs. 5.5 ± 0.5 pulses/6 h, p < 0.05) groups, whereas it decreased on Day 7 (HBW, 6.4 ± 0.9 pulses/6 h; LBW, 6.3 ± 1.6 pulses/6 h, p > 0.05 vs. Day 0). Plasma glucose and insulin concentrations increased temporarily from Day 2 to Day 4 and then decreased to the level before the start of dietary supplementation in both groups. There was no significant difference in the LH pulse frequency or daily concentrations of FSH, glucose, or insulin between the HBW and LBW groups throughout the experimental period. The present study indicated that acute dietary supplementation stimulates pulsatile LH secretion in parallel with a rise of blood glucose and insulin levels. However, the influence of body weight on these responses between light and heavy animals was not observed.