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Effects of Suckling and Mastectomy on Bovine Postpartum Reproduction¹

U.S. Department of Agriculture and Montana Agricultural Experiment Station, Miles City 59301 and University of Manitoba

Abstract

The effects of suckling and mastectomy on postpartum reproduction independent of nutrient intake were studied in 34 Angus cows. Twelve cows were suckled intact (S), 13 were nonsuckled intact (NS) and nine were non-suckled mastectomized (M). Udders were removed from the M cows before 150 days of gestation. The calves were removed from the NS and M cows at birth and calves from the S cows were run continuously with their dams. S cows received 13.6 kg of hay per day following calving while the NS and M cows received 6.8 kilograms. These feed levels approximately maintained the immediate post-calving body weights.

Nonsuckling and nonsuckling plus mastectomy progessively shortened the interval from calving to first estrus (S vs. NS+M and NS vs. M, P<.01). These effects were not observed in the interval to conception since the shorter intervals to first estrus required more services per conception (S vs. NS+M and NS vs. M, P<.10). Estruses occurring less than 20 days postpartum were infertile. Weekly rectal palpations failed to detect any cows which ovulated prior to the first postpartum estrus (no quiet ovulations detected). The length of the first estrous cycle following calving was shorter than the second cycle in 14 cows that hadn't settled by second service (13.1 vs. 19.1 days, P<.01) and the correlation between first estrous cycle length and interval to first estrus was 0.05.

Blood samples taken at 7 and 21 days postpartum indicated that plasma progesterone was very low and not affected by stage postpartum or treatment even though 12 cows in the NS and M groups had ovulated by day 21. Plasma LH values were low at both days in the S cows but were elevated at 7 days in the NS and M cows (Day x S vs. NS+M, P<.05). The higher LH values of the NS and M cows at day 7 were not caused by cows being near or at estrus.

¹ This study was a contribution to Western Regional Research Project W-95, Endocrine Mechanisms Controlling Bovine Reproduction. Publication has been approved by the Director of the Montana Agricultural Experiment Station, Journal Series No. 276.

² U. S. Range Livestock Experiment Station, A.S.R.-A.R.S., U.S.D.A., Box 790, Miles City, Montana 59301.

³ Department of Animal and Range Sciences, Montana State University, Bozeman 59715.

⁴ Department of Oral Biology, University of Manitoba, Winnipeg 3, Manitoba, Canada.

⁵ Authors express appreciation to: Dr. R. R. Woodward, American Breeders Service, DeForest, Wisconsin, for supplying semen; Dr. I. I. Geschwind, University of California, for antiovine LH serum- Dr. L. E. Reichert, Jr., Emory University, and the Endocrine Study Section, NIH, for LH preparations; D. C. Anderson, A. Knapp, H. E. Traweek and W. E. Wolf for technical assistance and care of animals during the study.