J. Anim Sci.
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Published online first on April 9, 2009
J. Anim Sci. 1910. doi:10.2527/jas.2008-1716
© 2009 American Society of Animal Science
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Initial body condition score affects hormone and metabolite response to nutritional restriction and repletion in yearling post-pubertal beef heifers

J. M. Cassady*, T. D. Maddock{dagger}, A. DiCostanzo* and G. C. Lamb{dagger}

* Department of Animal Science, University of Minnesota, St. Paul 55108 {dagger} North Florida Research and Outreach Center, University of Florida, Marianna 32446

gclamb{at}ufl.edu

Abstract

Twenty Simmental x Angus, half-sibling, post-pubertal heifers (initial BW 443 ± 9 kg) were allotted randomly into 2 treatment groups to evaluate if initial BCS affects response of the hypothalamic-pituitary-ovarian axis to metabolic signals elicited by energy restriction and repletion. During a preliminary feeding period, diets were formulated so that each heifer in the designated treatment would reach either a BCS of 5 (moderate condition; MOD) or a BCS of 7 (heavy condition; FAT). Once each heifer had reached desired BCS, diets were formulated to supply 30% of NEm requirements until each heifer became anestrous (serum concentrations of P4 < 1 ng/mL; restriction period). Blood collections took place on d 1 of each period, on d 43 of energy restriction and d 44 of energy repletion, and when heifers were confirmed to recommence estrous cycles. When heifers were cycling, their estrous cycles were synchronized to ensure hormone sampling occurred during late diestrus or early proestrus. Energy restriction resulted in decreased concentrations of LH (FAT P = 0.02; MOD P < 0.001), IGF-1 (FAT P < 0.001; MOD P = 0.003), and insulin (P < 0.001); in contrast, concentrations of GH (P < 0.001) and PUN (P < 0.001) increased. During repletion, LH concentration increased (P = 0.03) in MOD condition heifers but was still lower (P = 0.002) than d 1 of restriction, whereas LH concentration tended to increase in FAT heifers (P = 0.06) until it was similar (P = 0.40) to d 1 of restriction. Repletion also increased concentrations of IGF-1 (P < 0.001), insulin (P < 0.001), and glucose (P < 0.001), whereas concentrations of GH (P < 0.001), NEFA (P < 0.001), and PUN (P < 0.001) decreased. For both treatments, concentrations of GH following repletion were similar (FAT P = 0.88, MOD P = 0.10) to those on d 1 of restriction. Following repletion, FAT condition heifers had lower concentrations of IGF-1 (P < 0.001), insulin (P < 0.05), and glucose (P < 0.001), but higher concentrations of acetate (P < 0.01) and butyrate (P < 0.05), than MOD heifers. Anestrus or resumption of estrous cycles seems to be activated gradually in response to dietary manipulation, unrelated to certain metabolite changes.

Key Words: Body condition • energy • heifer • insulin • insulin-like growth factor-I • luteinizing hormone






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