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Endocrinology of the Postpartum Period in the Pelibuey Ewe^1,2,

Asociación Mexicana de Producción Animal, Tampico, Tamaulipas, Mexico and University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0

Abstract

The postpartum (PP) period in the Pelibuey ewe was studied. Laparotomies were performed on 14 ewes in the first year at d 10, 20 and 30 PP, and at d 10 and 20 PP in the second year on 17 ewes. Progesterone concentrations were determined in serum taken daily, from 4 to 7 d after parturition until estrus. Temporal fluctuation of luteinizing hormone (LH) was determined in samples taken at 30-min intervals for 4 h weekly. The mean interval from lambing to first ovulation was longer (P<.001) in 1980 (59 ± 4.9 d) than 1979 (26 ± 3.1 d), the mean interval from lambing to first estrus was also longer (P<.001) in 1980 (91 *#x00B1; 5.6 d) than 1979 (51 ± 5.5 d). Follicles were present on the ovaries of the majority of the ewes at d 10. The mean diameter of the largest follicles on each ovary was reduced (P<.025) in ewes in 1980 (6 mm) compared with 1979 (7.7 mm). Corpora lutea (CL) occurred in 67 and 75% of the ewes by d 20 and 30, respectively in 1979; no CL were found by d 20 in 1980. Progesterone profiles suggested that the PP period was composed of a period of anestrus, and a period of cyclic ovarian activity with one, two or three ovulations without behavioral estrus. In some ewes, the first cycle was of shorter duration, and its CL secreted less progesterone (P<.05) relative to CL of silent and regular estrous cycles. Luteinizing hormone peaks were recorded as early as 6 d PP. When progesterone concentrations were elevated to luteal phase levels, the frequency, but not magnitude, of LH peaks per 4-h bleeding period was reduced (P<.05) relative to anestrus. It is concluded that there are periods of anestrus and of silent cycles, which precede the first postpartum estrus in Pelibuey ewes.

¹ Supported by grants from IDRC and NSERC (Canada) and CONACYT (Mexico).

² Appreciation is expressed to Drs. G. D. Niswender and N. C. Rawlings for antisera and to L. E. Reichert for LH for iodination. Thanks also are expressed to D. Dyck for preparation of figures and to J. Ryan for typing.

³ Dept. of Biol., Univ. of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0.

⁴ Asociacion Mexicana de Produccion Animal, Tampico, Tam., Mexico.

⁵ Please address correspondence to this author.

⁶ Dept. of Vet. Physiol Sci. WCVM, Univ. of Saskatchewan, Saskatoon, Saskatchewan, Canada.