Seasonality of Boer goats in northern Europe and induction of estrus out of season
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Seasonality in Boer goats in Northern Europe and attempts to overcome it is addressed in three studies. In Experiment 1, monitoring of estrus and serum progesterone,concentration in sexually mature nulliparous Boer goat crosses indicated that ovarian activity ceased in February/March and was resumed from August onward. In 63.7% of 22 does the first estrus of the season was preceded by one or two ovulations, indicated by an increase in progesterone; in 22.7% first estrus and first ovulation coincided and in the remaining 13.6% the first estrus was not succeeded by formation of a functional corpus luteum. In Experiment 2, 31 Boer goats, weaned between July and September, were treated with progestogen-containing intravaginal sponges and 250 IU eCG either one (n = 11), seven (n = 10) or fourteen (n = 10) days after weaning. All but two does showed estrous symptoms and were naturally mated. Transrectal ultrasonography 45 days after mating revealed a pregnancy rate of 42%. All of these carried to term (36% treated immediately after weaning, 40% treated one week later and 50% treated two weeks later) and gave birth to, on average, 2.1 kids. In Experiment 3, of 18 nulliparous does, 9-12 months of age, subjected to progestogen-eCG treatment out-of-season, 15 (83%) responded by showing estrous symptoms; 14 were naturally mated and six were diagnosed as pregnant five weeks later. One of the pregnant does aborted two weeks before parturition was due; in the others pregnancy had ceased at an earlier stage without visible symptoms. In conclusion, in northern Europe, Boer goats undergo a period of reduced ovarian activity, although to a lesser degree than dairy breeds. In most cases acyclicity was overcome by hormonal stimulation and, if mated, part of the weaned does carried to term, whereas in young nulliparous does pregnancy was not maintained.
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