Department of Physiology and Environmental Studies, University of Nottingham School of Agriculture, Sutton Bonington, Loughborough, Leicestershire
(Received 20th November 1974)
It has been shown that administration of a single intravenous injection of 150 or 300 μg synthetic LH-releasing hormone (LH-RH) to seasonally anoestrous Clun Forest ewes induced LH release in all animals and ovulation in the majority (Foster & Crighton, 1973, 1974). The induced LH peak was, however, much smaller than that observed at oestrus (Foster & Crighton, 1974). Luteal function, as assessed by peripheral plasma progesterone levels, was absent in the majority of treated animals (Crighton, Foster, Haresign, Haynes & Lamming, 1973; Haresign, Foster, Crighton, Haynes & Lamming, 1975), possibly because of an inadequate release of LH before ovulation. As an alternative means of administration to simulate more accurately the natural preovulatory LH peak, a single dose of 150 μg LH-RH was administered subcutaneously or intramuscularly instead of intravenously,
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