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Factors associated with the reproductive performance of ewes inseminated laparoscopically in England and Wales: A
Mike J Glover1,2, Laura E Green3, Rachel Clifton4
1Horsepond Veterinary Centre, South Molton, UK.
Background:
Laparoscopic intrauterine artificial insemination (Lap-AI) is used in sheep genetic improvement programmes. However, the lambing rate (LR) (i.e., the proportion of inseminated ewes that lamb) following Lap-AI is variable. Previously, one small UK study investigated factors associated with LR, but it did not adjust for dependencies or confounding in the data.
Methods:
Data were collected from 11,493 Lap-AIs carried out commercially in Southwest England and Wales between 1995 and 2005. Multilevel multivariable analyses were then used to identify factors associated with LR.
Results:
The mean unadjusted average LR was 71%. However, ewes inseminated with fresh semen on days when the maximum ambient temperature (MAT°C) was lower than 25°C had a higher LR (adjusted LR ∼78%; OR 1.51, 95% CI 1.30-1.77) than ewes inseminated with frozen semen (adjusted LR ~70%). LRs were lower on days when MAT°C was ≥25°C (adjusted LRs: fresh ~64%; frozen ~65%). LR decreased as the time between sponge removal and insemination increased (OR: 0.08, 95% CI: 0.01‒0.87) and varied between months and years.
Limitations:
Due to the design of the study, individual ewe- and ram-level factors could not be investigated. Furthermore, some breeds were less well represented, which hindered breed-level analysis.
Conclusion:
Keeping ewes and rams cool on the day of insemination and inseminating ewes earlier after sponge removal may improve LR.
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