Photoperiod induction of fertile oestrus and changes in LH and progesterone concentrations in yearling dairy goats (Capra hircus)

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Abstract
Summary. Oestrus and ovulation were induced in a group of 19 yearling dairy goats which had been maintained for 70 days on a 19 h/day photoperiod regimen. Six yearling females, raised under natural photoperiod, served as controls. An intact, light-treated male was introduced to each group 42 days after termination of the artificial lighting. Behavioural, endocrine and kidding observations indicated that 15 of the experimental females (79%) ovulated within 21–30 days after introduction of the male, that 12 (63%) conceived at the induced ovulation, and that 10 (53%) gave birth to live kids, while none of the controls ovulated during this time. The breeding season was advanced between 60 and 80 days. In experimental and control nannies there was a brief, small surge (320 ± 42 pg/ml) of plasma progesterone which occurred 19·5 days after introduction of the male and which closely preceded oestrus in the nannies that ovulated and at 25 days in control females. Ovulatory surges of LH (to 70 ng/ml plasma) were closely associated with oestrus, and remained above basal levels for 9·0 ± 0·75 h, in 7 experimental females. Two of 6 control nannies also showed LH surges but they did not ovulate.