Factors associated with the reproductive performance of ewes inseminated laparoscopically in England and Wales: A longitudinal study.

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.