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P. S. GRANT and ANNE McLAREN

Summary.

Mice were treated with one of the potent progestagens, medroxyprogesterone acetate (MAP) or melengestrol acetate (MGA), at different stages of the oestrous cycle. They were tested for deciduoma induction, or for egg implantation, by oestradiol treatment combined with either injection of air into the uterine lumen or transfer of blastocysts to the uterus. The two important variables for both deciduoma induction and egg implantation were the MAP-oestradiol interval and the stage of the oestrous cycle during which the progestagens were injected. Maximal uterine sensitivity was obtained after the injection of MAP during oestrus with a 4-day MAP-oestradiol interval. Under these conditions, 34% of the transferred blastocysts developed to full-term viable fetuses. The injection of MAP or MGA did not usually induce pseudopregnancy as judged by the activation of cyclic CL; hence, the pregnancies were maintained by the activity of the injected progestagens.

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E. C. Hellgren, R. L. Lochmiller, M. S. Amoss Jr, S. W. J. Seager, S. J. Magyar, K. P. Coscarelli and W. E. Grant

Summary. Blood samples and testicular measurements were obtained from 4–8 captive adult collared peccaries monthly for 18 months and from wild adult males during summer (N = 16) and winter (N = 22) seasons. Serum concentrations of testosterone were determined by radioimmunoassay. Semen samples were collected monthly by electroejaculation from captive males for 1 year. Serum testosterone concentrations and testicular measurements varied in a low-amplitude circannual pattern, with maximum mean testosterone concentrations in fall and winter (1150–1400 pg/ml) and minimum values in summer (500–700 pg/ml). Circannual rhythms appeared to be related to dominance. Serum testosterone levels in wild males generally were lower than in captive males, although this difference was not significant (P > 0·05). Semen characteristics did not exhibit a circannual rhythm. These results suggest that the male peccary remains reproductively fertile throughout the year, yet may undergo a facultative summer quiescence influenced by ambient temperature and social factors.

Keywords: collared peccary; dominance; reproduction; seasonality; semen; testosterone