Evans N M, Hacker R R, Hoover J
Department of Animal and Poultry Science, University of Guelph, ON, Canada.
J Dairy Sci. 1991 Jun;74(6):1821-9. doi: 10.3168/jds.S0022-0302(91)78347-1.
The objective of this study was to determine if a skeletal photoperiod administered at the appropriate time of a 24-h day could stimulate prolactin and somatotropin release in dairy cattle. Cows in mo 8 of gestation were exposed to either 12 to 13 h of continuous light or to three skeletal photoperiods consisting of a total of 8 h of light. Cows in the skeletal photoperiod light regimens received 6 h of light from 0500 to 1100 h and a 2-h light pulse at either 1500 to 1700 h, 1800 to 2000 h, or 2100 to 2300 h. Cows exposed to the light regimen pulse at 1800 to 2000 h exhibited a circadian rhythm of prolactin and somatotropin release. The mean prolactin and somatotropin concentrations were also higher in this treatment. It is concluded that a circadian rhythm with a photosensitive phase is present for prolactin and somatotropin release in the lactating dairy cow. The photosensitive phase for both hormones occurs between 13 and 15 h after subjective dawn. The expression of the circadian rhythm of these hormones depends on the photoperiod to which cows are exposed.
本研究的目的是确定在24小时一天中的适当时间给予骨骼光周期是否能刺激奶牛的催乳素和生长激素释放。妊娠8个月的奶牛要么暴露于12至13小时的持续光照下，要么暴露于总共8小时光照的三个骨骼光周期下。处于骨骼光周期光照方案下的奶牛在0500至1100小时接受6小时光照，并在1500至1700小时、1800至2000小时或2100至2300小时接受2小时的光脉冲。在1800至2000小时接受光照方案脉冲的奶牛表现出催乳素和生长激素释放的昼夜节律。该处理中催乳素和生长激素的平均浓度也更高。得出的结论是，泌乳奶牛催乳素和生长激素释放存在具有光敏阶段的昼夜节律。两种激素的光敏阶段出现在主观黎明后13至15小时之间。这些激素昼夜节律的表达取决于奶牛所暴露的光周期。
