Effect of the Duration of Progesterone Treatment on Synchronising Oestrus outside the Natural Breeding Season in Merino Ewes
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Date
2022
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University of Zululand
Abstract
This study aimed to evaluate the effect of the duration of progesterone treatment on
the reproductive performance of South Africa Merino ewes during the spring breeding
season. The study compared the effect of long and short-term progesterone treatment
and its combination with or without equine chorionic gonadotropin on oestrous
response and hormonal profiles. Seventy-six (76) Merino ewes aged between 2–5
years were allocated into two groups, 40 for long-term and 36 for short-term
progesterone treatments. For the long and short-term progesterone treatment groups,
controlled internal drug release devices were inserted for 14 and 11 days, respectively.
At the withdrawal of the controlled internal drug release device, half of each group
were injected intramuscularly with 300 IU of equine chorionic gonadotropin, resulting
in four treatment groups. The oestrous response was monitored using teaser rams.
Blood samples were collected to measure the serum progesterone and oestradiol
concentrations. One-way ANOVA of the SPSS® software (IBM SPSS Statistics,
Version 23.0, 2015, Armonk, NY., USA) was used for statistical analysis. The means
were considered significant at P < 0.05. The overall oestrous response obtained was
96%. A greater proportion of the ewes showed oestrous signs at 48 and 60 hours post
controlled internal drug release withdrawal. There was no significant difference (P >
0.05) in oestrous response and duration between the treatment groups. Overall, the
mean interval to the onset of oestrus in this study was 46.8 ± 1.4 hours. Most ewes
began exhibiting oestrus at 24 and 36 h post controlled internal drug release
withdrawal. There was no significant difference (P = 0.07) in the mean interval to the
onset of oestrus between the treatment groups. Progesterone hormone did not differ
significantly (P > 0.05) between the treatment groups at controlled internal drug
release insertion and removal and 48 hours post removal. However, oestradiol was
significantly higher at controlled internal drug release removal and 48 hours post
removal (P < 0.05) than at insertion in all treated groups. Therefore, it was concluded
that using the progesterone synchronisation protocol, regardless of the duration or
conjunction with eCG treatment, can effectively synchronise oestrus during the spring
breeding season in South Africa Merino ewes. For seasonal breeders who use South
Africa’s spring breeding season, the progesterone oestrous synchronisation protocol
is recommended to improve the reproduction activity in Merino ewes.
Description
A thesis submitted to the Faculty of Science, Agriculture and Engineering in fulfilment of the requirements for the Degree of Master of Science in the Department of Agriculture at the University of Zululand, South Africa, 2022
Keywords
oestrous synchronisation, long-term progesterone, short-term progesterone