Effect of Exposure to Various Durations of Light on Serum Insulin-Like Growth Factor-I in Prepubertal Holstein Heifers
L.J. Spicer, B.A. Buchanan, L.T. Chapin and H.A. Tucker
DOI : 10.3844/ajavsp.2007.42.45
American Journal of Animal and Veterinary Sciences
Volume 2, Issue 2
Our objective was to determine if prolonged exposure to various durations of light (i.e., photoperiod) would affect serum IGF-I concentrations in heifers. Thus, 16 Holstein heifers, 2 to 4 mo of age, were exposed during a 5-wk pretreatment period to 12 h of cool-white fluorescent light (L) at an intensity of 1200 lux and 12 h of dark (D). At 5 wk, photoperiods were adjusted to 24 L: 0 D (24 L), 20 L: 4 d (20 L), 16 L: 8 D (16 L) or 8 L: 16 D (8 L) per 24 h (n=4 heifers per photoperiod treatment). Blood was sampled at 5 wk and monthly for 4 mo. During each sampling period, blood was collected at 16-h intervals for 48 h and serum IGF-I was determined by RIA. Photoperiod treatment, month of experiment and their interactions affected serum IGF-I concentrations. Averaged over months, concentrations of serum IGF-I was greatest in heifers on 16 L; heifers on 20 L had IGF-I concentrations similar to 8 L, 16 L and 24 L and heifers on 24 L had concentrations similar to that of heifers on 8 L. Heifers in all treatment groups exhibited an increase in serum IGF-I concentration during the 4 mo of treatment. Heifers on 16 L and 20 L exhibited the greatest difference in serum IGF-I concentrations compared with 8L heifers after 3 mo of treatment. In conclusion, 16 L increases concentrations of serum IGF-I above that seen for heifers treated with 8 L or 24 L.
© 2007 L.J. Spicer, B.A. Buchanan, L.T. Chapin and H.A. Tucker. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.