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

Background: Laparoscopic insemination (Lap-AI) of ram semen is used in sheep genetic improvement programmes. Lambing rate (LR) (proportion of ewes inseminated that lamb) following Lap-AI is variable. Previously, one small UK study investigated factors associated with LR without adjustment for dependencies or confounding in the data.Methods: Data on 11,493 inseminations carried out commercially in Southwest England and Wales were collected annually from 1995-2005, and analysed using multilevel multivariable analyses.Results: Mean unadjusted average LR was 71%. However, ewes inseminated with fresh semen on days when the maximum ambient temperature (MAT°C) was <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 time increased between sponge removal and insemination (OR 0.08, 95%CI: 0.01-0.87), and varied between months and years. Limitations: Individual ewe- and ram-level factors could not be investigated. Some breeds were less-well represented.Conclusion: Keeping ewes and rams cool on the day of insemination when ambient temperature is ≥25°C and inseminating ewes earlier after sponge removal may improve LR.