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Endocrine Activity of Corpora Lutea from First-service and Repeat-breeder Dairy Heifers¹

Department of Genetics, University of Wisconsin, Madison

ABSTRACT

Comparisons of weight, per cent of functional luteal cells, progesterone concentration, and total progesterone content of corpora lutea were made between seven first-service and seven repeat-breeder dairy heifers and between corpora lutea from two consecutive estrual cycles within these groups. Each heifer was allowed to have at least one normal estrual cycle and on the 14th day after heat the corpus luteum was removed through a supravaginal incision, leaving both ovaries intact. Most of the heifers returned to heat and ovulated within three or four days after the operation, and from them a second corpus luteum was removed on the 14th day, either by operation or slaughter.

Differences between first-service and repeat-breeder heifers were statistically nonsignificant for all four variables. The first corpus luteum was significantly heavier than the second for first-service and repeat-breeder heifers combined (P < 0.05). None of the other three variables differed significantly between first and second corpora lutea.

Repeatability from first to second corpora lutea, as estimated by intraclass correlations, was as follows: corpora lutea weights, 0.34, per cent functional cells, 0.16, progesterone concentration, 0.53, and total progesterone content, 0.53.

There was a tendency for both first-service and repeat-breeder heifers to develop cystic follicles or to produce twin ovulations following the removal of one or two corpora lutea.

¹ Published with the approval of the director of the Wisconsin Agricultural Experiment Station. Paper No. 743 from the Department of Genetics, University of Wisconsin. This work was done under a cooperative agreement between the Wisconsin Agricultural Experiment Station and the Dairy Husbandry Research Branch, USDA, and is supported in part by this federal agency. The repeat-breeding heifers were secured through the help of Badger Breeders' Cooperative and Tri-State Breeders' Cooperative.

² Agent of the Dairy Husbandry Research Branch, USDA.