J. Anim Sci.
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J. Anim Sci. 1986. 62:1273-1278.
© 1986 American Society of Animal Science
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Response of Body Weight and Clearance and Secretion Rates of Growth Hormone to Photoperiod in Holstein Heifers1,2,

S. A. Zinn, L. T. Chapin and H. Allen Tucker

Michigan State University3, East Lansing 48824

Abstract

Effects of photoperiod on growth, eating patterns and clearance rate, secretion rate and half-life of growth hormone in serum were assessed in Holstein heifers. Sixty-four prepubertal heifers (avg body wt 102 kg) were blocked by weight into four groups of 16. Within block, each animal was randomly assigned to one of four photoperiod treatments: 16 h of cool-white fluorescent light:8 h dark (CW-16L:8D), CW-8L:16D, CW-6L:8D:2L:8D or 16 h of VitaLite® fluorescent light:8D (V-16L:8D). Animals were fed ad libitum a complete mixed diet formulated for heifers to gain approximately .9 kg/d. Average daily body weight gains were .93, .96, .98 and 1.0 kg/d during 112 d of exposure to CW-8L:16D, CW-6L:8D:2L:8D, CW-16L:8D and V-16L:8D, respectively. Heifers exposed to V16L:8D and CW-16L:8D gained more weight (112 and 110 kg; P<.05 and P<.08, respectively) than heifers exposed to CW-8L:16D (104 kg). Body weight gain was not different (P>.10) between heifers exposed to CW-6L:8D:2L:8D (108 kg) or CW-8L:16D, or between heifers exposed to CW-16L:8D or V-16L:8D. Total number of eating events in 30 h and percentage of total events in the lighted period were 549 and 96% and 523 and 50% in heifers exposed to CW-16L:8D and CW-8L:16D, respectively. Clearance rates (620 vs 636 ml/min), secretion rates (3.0 vs 3.8 µg/min) and half lives (17.2 vs 17.9 min) of growth hormone in serum were similar in heifers exposed to CW-16L:8D and CW-8L:16D. Results suggest that exposure to photoperiods of 16L:8D stimulate body weight gain in cattle, but these increases were not associated with several measures of growth hormone secretion.

Footnotes

1 Michigan Agr. Exp. Sta. Journal Article No. 11729. This research was supported in part by USDA grants 901-15-2 and 70-59-2261-1-2-072-1 and USPHS Grant HD 17738.

2 The authors gratefully acknowledge Mr. Woody Bickford and the Duro-Test Corporation for donation of lamps. NIAMDD kindly provided bovine GH.

3 Dept. of Anim. Sci.






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Copyright © 1986 by the American Society of Animal Science.