Background: Certain weather parameters (temperature, light) influence livestock fertility. Objectives: To determine the influence of weather parameters (temperature, humidity, radiation and sunshine; individually and in combination) prevailing in Western/Central Europe during different phases in cycle and in early pregnancy on the pregnancy result in mares.Study design: A retrospective study linking reproductive data of an opportunistic sample of research mares with weather parameters obtained from the local weather station. Methods: Over a period of 4 years, 19 mares (Equus caballus) were induced to oestrus hormonally and then subsequently inseminated with sperm of different stallions (n = 26). Oestrus was repeatedly induced after termination of prior pregnancy (n = 246 year-round distributed inseminations in total). Generalized linear mixed models were used to analyse the influence of various weather parameters and their combinations on pregnancy result (pregnant/not pregnant).Results: The temperature-humidity index had a significant effect on fertility in ovulation (p=0.036) when considering only inseminations with fresh semen. Considering all inseminations, a moderate diffuse solar radiation (500 J/cm2 - 1000 J/cm2) during ovulation showed a significant effect (p=0.0160) on fertility. Higher rates of pregnancy could be achieved with weaker (<2000 J/cm2) rather than higher (>3000 J/cm²) longwave downward radiation during follicular maturation (p=0.0146). Without, but not with the use of a light program, increasing hours of sunshine during follicular maturation had a positive effect on fertility (P=0.0409) cycle. Conclusion: Albeit low, there is an influence of the examined weather parameters on pregnancy rates of mares in Germany s temperate climate, such that heat stress and too strong radiation during ovulation negatively affect fertility.
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