Journal of Animal Science, Vol 74, Issue 1 57-69, Copyright © 1996 by American Society of Animal Science

JOURNAL ARTICLE

Hormonal status, metabolic changes, and resting metabolic rate in beef heifers undergoing compensatory growth

E. S. Yambayamba, M. A. Price and G. R. Foxcroft
Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Canada.

Twelve recently weaned Hereford crossbred heifers weighing 227 kg (12 kg SD) and aged 230 d (8 d SD) on d 0 were used to investigate physiological responses associated with compensatory growth. Six heifers were allotted to ad libitum intake (ADLIB) and six were restricted to a maintenance diet for 95 d followed by realimentation (REST). Plasma collected from all heifers during feed restriction (d 0, 20, 48) and realimentation (d 104, 125, 153, 195) was analyzed for growth hormone (GH), insulin-like growth factor I (IGF-I), thyroid hormones (thyroxine [T4] and triiodothyronine [T3]), insulin, glucose, nonesterified fatty acids (NEFA), blood urea nitrogen (BUN), and 3-methyl histidine (3-MH). Resting metabolic rate (RMR) was measured 5 d before and 15 and 36 d after the beginning of realimentation. Feed restriction was associated with higher (P < .05) plasma concentrations of GH and NEFA and lower (P < .05) concentrations of IGF-I, T4, T3, insulin, and glucose. The BUN concentration was lower (P = .05) in REST than in ADLIB heifers on d 48, whereas 3-MH was not affected during the first 48 d of feed restriction. The RMR was lower (P < .05) in REST than in ADLIB heifers during feed restriction. During realimentation, the ADG of REST heifers was higher (P = .001) than that of ADLIB heifers. Concentrations of IGF-I, insulin, glucose, and NEFA in REST heifers increased and no differences (P > .05) between treatments were observed on d 104 (d 10 of realimentation) and thereafter. Conversely, GH concentration in REST heifers remained elevated through d 104 but dropped to ADLIB levels by d 125 (d 31 of realimentation). The T4 and T3 concentrations remained lower (P < .05) in REST than in ADLIB heifers after 10 d of realimentation but rose to control levels by d 31 of realimentation. The RMR was lower (P < .05) in REST than in ADLIB heifers 15 d into realimentation; however, no difference was found between treatments by d 36 of realimentation. These results indicate that enhanced growth rates in the early phase of compensatory growth are associated with the physiological response of the GH-IGF-I-insulin axis coupled with reduced maintenance requirement due to slower metabolic rate in restricted-refed heifers.

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