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Corpus Luteum Maintenance in Gilts during Hypothalamic Suppression with AIMAX

U. S. Department of Agriculture, Beltsville, Maryland 20705^,2

Abstract

Two trials were conducted using crossbred gilts randomly assigned to three treatments: AIMAX+sham hysterectomy (AS); AIMAX+hysterectomy (AH) and hysterectomy (H). Gilts were hysterectomized or sham hysterectomized on day 8 to 10. In trial I, AS (15) and AH (20) gilts were fed 125 mg AIMAX per day from day 2 to 31. Group H (15) were fed the control diet without AIMAX. All gilts were necropsied on day 32. In trial II, AH gilts (10) were fed 125 mg AIMAX per day from day 20 to 39 and H gilts (7) were fed the control diet without AIMAX. All gilts were necropsied on day 40. In trial I, corpora lutea (CL) regressed in all AS gilts, but CL were maintained in all H gilts. However, only 9 of 20 AH gilts maintained corpora lutea. The degree of CL maintenance was reflected in the total ovarian weights in each treatment. Average weight of maintained CL of AH gilts was significantly (P<.01) lower than that of H gilts. In trial II, CL were maintained in all gilts. The ovarian weights of the AH gilts were nonsignificantly lower than the H gilts. Average CL weight of the AH gilts was significantly (P<.05) lower than that of H gilts. The cellular morphology of all maintained CL in both trials was similar. It was suggested that changes in the luteal tissue which allow CL maintenance beyond the luteal phase of the estrous cycle occur at day 16 to 20 and that AIMAX treatment from day 2 to 31 probably suppressed these "critical" changes. Therefore small CL were maintained in only 9 of 20 gilts. By starting AIMAX on day 20, these changes in the CL were not inhibited. Therefore CL were maintained in 10 of 10 gilts. Luteinizing hormone secretion was probably suppressed but not completely blocked by AIMAX. Therefore, minimal amount of LH were probably available to act alone or in combination with prolactin to produce the luteal maintenance observed in this study.

¹ The authors thank W. Mauck, T. G. Althen, J. J. O'Malley and Mrs. B. J. Davis for their valuable assistance and Ayerst Laboratories, New York, N. Y., for supplying the AIMAX used in this study.

² A.R.S., Animal Science Research Division.