The effects of Regulin melatonin implants and type G progesterone impregnated controlled internal drug releasers (CIDR) on the early breeding of F+ and ++ Booroola x Perendale and Waihora Romney ewes were compared in a 2 x 2 factorial trial, melatonin v no melatonin x progesterone. The melatonin plus progesterone and melatonin only groups were implanted with melatonin on 12 December and 23 December respectively. While CIDRs were inserted on 7 January and removed on 19 January, when fertile rams were joined with all treatments. Progesterone alone induced oestrus and ovulations 2 to 9 d after ram introduction in 39%, 50% and 11% of F+, ++ and Romney ewes, whereas progesterone plus melatonin induced oestrus and ovulations in 68%, 76% and 44% of the ewes respectively. There was no response to treatment in terms of percentage ewes lambing. The response to treatment in terms of the percentage of lambing ewes with multiples was different in the 3 genotypes. There was no response to either melatonin or progesterone by the F+ ewes, whereas the ++ ewes responded to both additively, leading to a difference of 50% between melatonin plus progesterone and the control groups. The Romney ewes responded only to melatonin leading to an overall melatonin response of 21%.
Proceedings of the New Zealand Society of Animal Production, Volume 48, , 81-86, 1988
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