| الوصف: |
The manipulation of photoperiod is useful to improve dairy cattle milk production and may be useful to improve beef cattle production efficiency. Studies were conducted to investigate the threshold intensity of supplemental light for inhibition of melatonin secretion and to examine the efficacy of supplemental light and evening feeding for improvement of production efficiency of beef cattle housed outdoors in the winter. The threshold intensity of supplemental light for inhibition of melatonin secretion was investigated in dairy heifers using a 5 x 5 Latin Square design with repeated measures. Light treatments were exposure to 0, 50, 100, 200 and 400 lx for 8 h following an 8 h control period at 400 lx. Two experiments (Exp. 1, 1998; Exp. 2, 1999) were conducted to investigate the effects of supplemental light and evening feeding on heifer growth and efficiency, carcass composition, plasma prolactin concentration, and hair shedding of outdoor housed beef heifers (n = 48) in winter. The experiments were conducted using a 2 x 2 Factorial Design and treatments were morning (09:00-10:00 h) or evening (20:00 h) feeding and natural or supplemental light (SL). (Abstract shortened by UMI.) |