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Effect of Lactation and Energy Intake on Postpartum Ovarian Activity in the Cow

Iowa State University of Science and Technology, Ames^{1, 2,} 50010

Abstract

Twenty-seven primiparous Holstein females were studied in a 3 x 3 factorial experiment comparing the effect of suckling two calves, milked twice daily or non-lactation and low (66% N.R.C.), normal (100% N.R.C.) or high (133% N.R.C.) energy intake on postpartum reproductive function. Lactation significantly delayed postpartum follicular growth and ovulation. Low energy intake also had a delaying effect, especially when only the lactating animals were considered. Both energy intake and lactation treatment had a significant effect on plasma glucose levels during the first 8 weeks postpartum. There was a significant negative correlation between plasma glucose level and postpartum interval to occurrence of a 10 mm follicle and ovulation. Neither lactation nor energy intake appeared to exert a significant effect on normal involution of the uterus. However, animals that failed to experience a postpartum ovulation had significantly smaller uteri 56 days postpartum. This was due, at least in part, to smaller cell size in the myometrial layers.

¹ Veterinary Medical Research Institute.

² The authors gratefully acknowledge the technical assistance of I. Adams and P. A. Harris.