Epidemiological studies regarding the "Summer Infertility Syndrome" of sows in confinement housing. / Epidemiologische Studien zum "Summer Infertility Syndrome" bei Sauen in Stallhaltung

In confined pig herds, located in Northwest-Germany and affiliated to a hybrid breeding organisation, 3 retrospective observational studies were performed looking at data collected before and after 1988 to study the effects of seasons on sow fertility. A subsequent field trial with 8 pig herds in 1989-1991 was performed to study the effects of photoperiod and of temperature on sow fertility separately. Associations of economically important fertility disorders and season with 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 inconsistent seasonal findings in the observational studies and a lack of temperature or photoperiod effects in the field trial it is concluded that season and its main contributing climatic factors had no substantial effects on sow fertility in the well-managed herds of this climate zone. Nonclimatic risk factors for the so-called Summer Infertility Syndrome are discussed.