Characterization of luteinizing hormone secretion in the primiparous, lactating sow: relationship to blood metabolites and return-to-estrus interval
Tokach, M.D. | Pettigrew, J.E. | Dial, G.D. | Wheaton, J.E. | Crooker, B.A. | Johnston, L.J.
Lactating, primiparous Landrace X Yorkshire sows were used to characterize LH secretion during lactation in sows that experienced an early (< 9 d; n = 14) or late (> 15 d; n = 9) return to estrous postweaning and to evaluate the relationship between LH secretion and blood metabolites. Twenty-three sows were fed one of nine corn-soybean meal diets to achieve a matrix of lysine (15 to 45 g/d) and energy (6.5 to 16.5 Mcal of ME/d) intakes and a range in metabolite concentrations and return-to-estrus intervals. Blood samples for LH analysis were collected every 15 min for 6 h on d 0, 7, 14, 21, and 28 of lactation. Circulating concentrations of glucose, amino acids, insulin, triglycerides, urea N, and nonesterified fatty acids also were measured on d 7 and 21. Mean LH concentrations were .27 and .42 ng/mL at farrowing for sows with an early and late return to estrus, respectively, but decreased (P < .01) to .12 ng/mL by d 7 in both early and late groups. Mean LH and number of LH peaks per 6 h increased linearly (P < .01) from d 7 to 28 for early sows. Early sows had a higher LH mean and more LH peaks per 6 h on d 14, 2 1, and 28 than did late sows (P < .05). Early sows had higher serum insulin on d 7 (P < .05) and d 21 (P < .01) than did late sows. Concentrations of other metabolites did not differ (P > .10) between early and late sows. Insulin concentration on d 7 was correlated (P < .05) with number of LH peaks on d 14 (r = .50), d 21 (r = .70), and d 28 (r = 43). These results demonstrate that alterations in LH profile as early as d 14 of lactation are associated with a delayed return to estrus after weaning, and that insulin levels during early lactation may be associated with subsequent reproductive function.
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