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Hormonal and Lactational Responses to Growth Hormone-Releasing Hormone Treatment in Lactating Japanese Black Cows

H. Shingu¹, K. Hodate², S. Kushibiki^1,*, Y. Ueda¹, E. Touno¹, M. Shinoda^1, and S. Ohashi³

¹ Department of Animal Production and Grasslands Farming, National Agricultural Research Center for Tohoku Region, Morioka, Iwate, 020-0198, Japan
² School of Veterinary Medicine and Animal Sciences, Kitasato University, Towada, Aomori, 034-8628, Japan
³ National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, 305-8561, Japan

Corresponding author: H. Shingu; e-mail: shinguu{at}affrc.go.jp.

Ten multiparous lactating Japanese Black cows (beef breed) were used to evaluate the effects of bovine growth hormone-releasing hormone (GHRH) analog on milk yield and profiles of plasma hormones and metabolites. The cows received 2 consecutive 21-d treatments (a daily s.c. injection of 3-mg GHRH analog or saline) in a 2 (group) x 2 (period) Latin square crossover design. The 5 cows in group A received GHRH analog during period 1 (from d 22 to 42 postpartum) and saline during period 2 (from d 57 to 77 postpartum), and those in group B received saline and GHRH analog during periods 1 and 2, respectively. Mean milk yield decreased in saline treated compared with that during the 1-wk period before treatment 7.4 and 19.1% during periods 1 (group B) and 2 (group A), respectively. Treatment with GHRH analog increased milk yield 17.4% (period 1, group A) and 6.3% (period 2, group B). Treatment with GHRH analog induced higher basal plasma concentrations of growth hormone (GH), insulin-like growth factor-1 (IGF-1), insulin, and glucose compared with saline-treated cows. In glucose challenge, the GHRH analog-treated beef cows had greater insulin secretion than the saline-treated beef cows. In insulin challenge, however, there were no significant differences in the areas surrounded by hypothetical lines of basal glucose concentrations and glucose response curves between GHRH analog- and saline-treated cows. These results demonstrate that GHRH analog treatment facilitates endogenous GH secretion in lactating Japanese Black cows, leading to increases in milk yield and plasma concentrations of IGF-1, insulin, and glucose.

Key Words: bovine growth hormone-releasing hormone • hormone • milk yield • Japanese Black cow

Abbreviation key: A15-DAbGHRH = analog with D-Ala and Ala substitutions in position-2 Ala and -15 Gly of bovine GHRH (1-29)-NH₂, respectively, AUC = area under the response curve, dAUC = decreased AUC, GH = growth hormone, GHRH = growth hormone-releasing hormone, IGF-1 = insulin-like growth factor-1