A Study of the Oestrous Cycle, Artificial Insemination and Embryo Retrieval in Mares

Dickie, Alison M (1995) A Study of the Oestrous Cycle, Artificial Insemination and Embryo Retrieval in Mares. Master of Veterinary Medicine thesis, University of Glasgow.

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The reproductive behaviour of eleven mares was studied from October until June using various techniques including daily teasing, rectal palpation, ultrasound scanning, plasma progesterone and LH assays. It was necessary to combine information from all these sources to determine the exact reproductive state of each of the mares. The average length of oestrus in this study was 6.0 +/- 2.4 days and dioestrus 18.9 +/- 7.2 days. A wide range of cyclic behaviour and anomalies were seen throughout the study. Double ovulations occurred during 9.6% of oestruses and dioestrous ovulations occurred with an incidence of 7.2%. LH peaks were recorded in conjunction with ovulations during silent oestruses but not dioestrous ovulations. The LH assay was also found to crossreact with eCG in pregnant mares beyond day 35. One mare was particularly prone to silent oestruses as well as displaying erratic oestrous behaviour and shortened dioestrous intervals. 55% of the mares continued to ovulate throughout the year without entering anoestrus. Another mare continued to cycle normally and conceive in the presence of a previously physiologically active granulosa cell tumour. A comparison was made between a radioimmunoassay and an ELISA kit for the measurement of plasma progesterone concentrations. The accuracy of the ELISA was found to be 61% with a tendency to give higher results than those obtained using the radioimmimoassay. The most reliable way to use it was in a qualitative manner rather than the semi-quantitative way the manufacturers intended, improving the accuracy to 85.5%. One mare consistently gave lower than expected results suggesting some factor in her plasma prevented reaction with the kit. Mares were inseminated throughout the study using chilled, extended semen of varying age and quality at different intervals before ovulation. An overall pregnancy rate of 61% was achieved, despite the lack of therapeutic interference and operator experience. No difference was found between pregnancy rates obtained using semen less than or greater than 48 hours old, or between insemination less than or more than 3 days before ovulation. The percentage of progressively motile sperm in a sample was found to be a subjective assessment while percentage live spermatozoa was more objective but although both parameters decreased as the semen aged, there was no correlation found between these results and pregnancy rates. The use of prostaglandin injections to bring mares into oestrus was found to have no effect on their fertility. 14 pregnancies were achieved as part of a study on the early development of the equine eye. Three cases of early embryonic death occurred, all between day 13 and 26 of gestation giving an incidence of 21.5%, which is high when compared to previously reported figures. Two cases, involving the same mare, were associated with vesicles which were considered to be undersized for their gestational age and the other appeared normal until it was no longer detected on ultrasound. All were associated with a prolonged luteal phase. Attempts were made to terminate three pregnancies using prostaglandin. One resulted in a return to oestrus and reconception, one resulted in pseudopregnancy and the other maintained her pregnancy. Two sets of twins occurred but in both cases, one was resorbed before day 23. Of six pregnant mares, embryos were successfully collected via the transcervical route from four mares at days 14-15, 17, 22 and 25, giving a success rate using this method of 66%. Two further mares were flushed, one on day 12 and the other on day 21 of gestation with no attempt made to retrieve the conceptus. In both cases, the embryo was lost and they returned to oestrus within 3 days.

Item Type: Thesis (Master of Veterinary Medicine)
Qualification Level: Masters
Additional Information: Adviser: M J A Harvey
Keywords: Veterinary science, Animal sciences
Date of Award: 1995
Depositing User: Enlighten Team
Unique ID: glathesis:1995-75561
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 19:27
Last Modified: 19 Nov 2019 19:27
URI: https://theses.gla.ac.uk/id/eprint/75561

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