[Epidemiological studies regarding the "summer infertility syndrome" of sows in confinement housing]

In confined pig herds, located in Northwest-Germany and affiliated to a hybrid breeding organisation, 3 retrospective observational studies were performed to study the effects of "meteorological seasons" on sow fertility. A subsequent field trial was performed to study the effects of photoperiod and of temperature on sow fertility separately. Associations of economically important fertility disorders and season resp. climate categories were determined by adjusted Relative Risks in stratified analysis (observational studies), or by Odds Ratios in the Multiple Logistic Regression Analysis (field trial). Due to nonconsistent seasonal findings in the observational studies and a lack of temperature or photoperiod effects in the field trial we conclude that season and its main contributing climatic factors had no substantial effects on sow fertility in the well-managed herds of our climate zone. Nonclimatic risk factors for the so-called "Summer Infertility Syndrome" are discussed.