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Effects of Variation in Light, Month of Year and Nutrient Intake on Reproductive Phenomena in Ewes during the Breeding Season

U. S. Department of Agriculture, Dubois, Idaho and Utah State University, Logan^,3

Abstract

The effects of various light treatments (control, continuous light, dark and intermittent light) and three levels of nutrition (75%, 100% and 150% of NRC recommendations for maintenance) and time of the estrous cycle when applied (day 0 to 8 and 8 to 16) on bodyweight gains and reproductive phenomena were studied during the middle of the breeding season in 1964 and 1965.In general, light treatment had little or no effect on bodyweight changes. Gains for the ewes on 75%, 100% and 150% NRC maintenance rations were 5, 59 and 118 gm. per head per day, respectively. Only two of the variables had significant effects on the reproductive phenomena studied. These include light treatment effect on ovulation rate in 1964 and on the number of embryos per CL subsequent to first breeding in 1965. The intermittent light treatment appeared to cause the greatest decline in ovulation rate between the first and third observation. The dark treatment caused a decline in ovulation rate intermediate between the control and intermittent treatment groups. The dark treatment also gave the poorest performance in number of embryos per CL. Month of year had a significant effect on ovulation rate each year.

Changes in bodyweight were not significantly correlated with ovulation rate but were significantly correlated with number of normal embryos (r=–.22, P<.01).Initial ovulation rate was significantly correlated with both initial and final weight (r=.2l and .21, P<.01). Also, ovulation rate following flushing was significantly correlated with both initial and final bodyweight (r=.14 and .18, P<.05). The number of live embryos was not significantly correlated with either initial or final bodyweight (r=.O7 and .09).

¹ U. S. Sheep Experiment Station, Dubois, Idaho.

² Utah State University, Logan.

³ From the U. S. Sheep Experiment Station, Sheep and Furb Animal Research Branch,Animal Husbandry Research Division, A.R.S., Dubois, Idaho in cooperation with the University of Idaho, Moscow and from Utah State University.Published with the approval of the Director of Utah Agricultural Experiment Station, Logan, as Research Paper No. 687.