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The effects of prostaglandin F2a on the fertility of artificially inseminated merino ewes

Fairnie, Ian James (1985) The effects of prostaglandin F2a on the fertility of artificially inseminated merino ewes. PhD thesis, Murdoch University.

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Artificial insemination (AI) of sheep is a technique being adopted by an increasing number of sheep breeders in Australia and a system to synchronise ovulation should make the technique more efficient. The discovery of the luteolytic activity of prostaglandin F2a (PGF2a) and its analogues in the early 1970's lead to experiments which evaluated the potential of PGF2a to regulate the oestrous cycle of sheep.

This thesis presents the results of a number of field and laboratory studies which examined various aspects of the fertility of parous Merino ewes after treatments with one of the analogues of PGF Cloprostenol. The studies involved treating ewes with two injections of Cloprostenol, spaced either eight, 11 or 14 days apart, with the first treatment always given 4 to 14 days following detection of behavioural 2a’ oestrus.

While nearly all ewes ovulated following treatments, a variable number were detected in behavioural oestrus in the period up to 64 hours following the second treatment. There was also some variability in the time of onset of oestrus between treatments with the results indicating earlier onset of oestrus in ewes treated twice 8 days apart than those treated twice at longer intervals.

Some ewes were artificially inseminated (under the same conditions as practiced commercially in Australia) and their fertility, as measured by fertilisation, embryo survival or lambing rates, was usually poorest in ewes treated twice with Cloprostenol 8 days apart.

It was postulated that the shortened luteal phase of the oestrous cycle due to its interruption with Cloprostenol was the cause of these effects and that exogenous progesterone might overcome the infertility demonstrated. Although increasing the length of time between the second treatment of Cloprostenol and the onset of oestrus, no other change could be demonstrated in ewes treated with progesterone prior to the second Cloprostenol treatment.

A review of the literature suggested that poor sperm transport within the ewe may result from PGF2a treatments, but this could not be demonstrated in experiments conducted under the field conditions of normal AI programmes.

It was concluded that Cloprostenol, an analogue of PGF2a, while effective in synchronising ovulation in Merino ewes when given during the luteal phase of their cycles, is not sufficiently reliable and predictable to be recommended for use in artificial insemination programmes as currently conducted in Australia.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Wales, Ray
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