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This Article Full Text (PDF) All Versions of this Article: jas.2008-1220v1 87/4/1247    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Shingu, H. Articles by Ohashi, S. Search for Related Content PubMed PubMed Citation Articles by Shingu, H. Articles by Ohashi, S.

Effects of GHRH treatment on milk production and plasma hormones and metabolites in lactating Japanese Black cows under negative energy balance

H. Shingu^*, K. Hodate, S. Kushibiki , E. Touno^*, A. Oshibe^*, Y. Ueda^* , M. Shinoda^* and S. Ohashi

^* Department of Animal Production and Grasslands Farming, National Agricultural Research Center for Tohoku Region, Morioka, Iwate, 020-0198, Japan , School of Veterinary Medicine, Kitasato University, Towada, Aomori, 034-8628, Japan , Department of Animal Physiology and Nutrition, National Institute of Livestock and Grassland Science, Tsukuba, Ibaraki, 305-0901, Japan Kanazawa Institute of Technology, Hakusan, Ishikawa, 924-0838, Japan

shinguu{at}affrc.go.jp

Abstract

The current study was performed to clarify the effects of GHRH treatment on milk production and plasma hormones and metabolites in lactating Japanese Black cows (a beef breed) under negative energy balance (EB). Ten multiparous lactating beef cows were offered normal energy diet daily (110% of ME requirements for maintenance and lactation) until 5 d in milk (DIM) to standardize the cows before dietary treatment. From 6 DIM to the experimental final days (63 DIM), the cows were allotted to experimental dietary treatment: 5 cows offered a diet formulated for 130% [high energy diet (HED)] and remaining 5 cows offered a diet formulated for 80% [low energy diet (LED)] of ME requirements for maintenance and lactation. In addition, all cows received daily s.c. injections of 3 mg of bovine GHRH from 36 to 56 DIM (GHRH treatment period). Differences in BW of HED and LED cows at 63 DIM were +28.4 and –7.2 kg compared with BW at 6 DIM, and HED and LED cows were under positive EB (+23.7 MJ/d) and negative EB (–11.6 MJ/d) throughout the experiment period. Treatment with GHRH increased (P < 0.01) average daily milk yield to 6.2 kg in HED cows compared with milk yield of 5.3 kg for 7 d before GHRH treatment period (pre-treatment period); LED cows had no increase in milk production due to GHRH treatment. Plasma GH, IGF-1, insulin, and glucose concentrations increased (P < 0.05) after GHRH treatment in both HED and LED cows; GHRH treatment also induced an increase (P < 0.05) in the net area under the curve of plasma insulin after glucose challenge in both HED and LED cows. Plasma urea N concentration were decreased (P < 0.05) by GHRH treatment in HED cows, but not in LED cows. Plasma NEFA concentration was unaffected by GHRH treatment in both HED and LED cows. We conclude that GHRH treatment of lactating Japanese Black cows stimulates endogenous GH and subsequent IGF-1 secretion and might induce a rise in insulin resistance, irrespective of EB; however, compared with lactating dairy cows, both galactopoietic and lipolytic effects of GHRH might be insufficiently exerted under negative EB in lactating beef cows.

Key Words: beef breed • energy balance • GH • GHRH • insulin • lactation