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The Relationships between Energy Balance, Milk Production and Ovulation in Postpartum Holstein Cows¹

Cornell University, Ithaca, NY 14853

Abstract

Energy balance and serum progesterone concentrations were monitored during early lactation in a group of high producing Holstein cows. The postpartum interval to normal ovulation averaged 36 ± 6 days (range 6 to 83 days). Average energy balance during the first 20 days of lactation (cumulative daily calculated energy balance divided by days in milk) was inversely related to days to normal ovulation (r = –.60) and to milk production (r = –.80). Milk yield during this period was not closely related to days .to ovulation (r= .30). Milk yield was also not significantly related to serum prolactin concentrations over the first 12 weeks of lactation (r = .27). During early lactation, energy balance was maximally negative until peak milk yield and then began returning toward zero, with the magnitude and duration of negative energy balance being quite variable. On the average, ovulation and the initiation of the first normal luteal phase occurred approximately 10 days after energy balance began returning toward zero. During this 10-day interval, a transient elevation in serum progesterone concentrations occurred in eight of 13 cows. These results suggest that energy balance during the first 20 days of lactation is important in determining the onset of ovarian activity following parturition.

¹ The authors express appreciation to G. Lake and F. Michel, for technical assistance, and to Mrs. Lorraine Taylor, for the preparation of this manuscript. We also thank James R. Harner and the staff of the Cornell Animal Science Teaching and Research Center for caring for the experimental animals. Purified ovine prolactin was kindly supplied by Dr. L. E. Reichert, Jr., and NIH-P-B4 was provided by NIAMDD.

² Dept. of Anim. Sci.

³ Dept. of Anim. Sci., Texas A&M Univ., College Station 77843.