Effects of gonadotrophin releasing hormone (buserelin) on sheep fertility

W.H. McMillan, T.W. Knight and K.L. MacMillan

Whatawhata Hill Country Research Centre, Ministry of Agriculture and Fisheries, Hamilton and Ruakura Animal Research Station, Ministry of Agriculture and Fisheries, Hamilton

Proceedings of the New Zealand Society of Animal Production. 1986, 46: 161-164

An agonist of gonadotrophin releasing hormone (GnRH) improves dairy cow pregnancy rates when injected at an appropriate stage after insemination. These studies were extended to ewes and hoggets in a series of trials to determine the effects of a single injection of GnRH made at varied intervals after mating. All sheep were mated at a synchronised oestrus (day of oestrus = day 0) with treated ewes being injected on a set date with 2 or 4 痢 of the GnRH analogue buserelin. Among ewes injected on days 10, 11, 12, 13 or 14 post-mating, the increases in % ewes lambing were (number of ewes in brackets): 18(65), 1(204), 12(150), 4(131) and 8(20) respectively. Similarly, the increases for hoggets treated on days 12 and 13 were 23(98) and 5(86) respectively. Among ewes that did not conceive at the synchronised oestrus, GnRH did not affect return to service pregnancy rates, although return to service intervals were increased (17.5 v 16.9 days P<0.01). These studies showed that a single injection of a small dose of a potent GnRH agonist had an effect on fertility and cycle length. The mechanism by which GnRH increased pregnancy rates probably involved corpus luteum function.

Keywords: NZSAPAB; Gonadotrophin releasing hormone; GnRH; buserelin; sheep fertility; hoggets; oestrous cycles

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Last Updated 18-03-1997