Effects of heat stress on reproductive activity in dairy cows bred in the Potenza district

The effect of heat stress on the reproductive performance in dairy cows reared in Apennines areas of Southern Italy was evaluated. Reproductive parameters obtained from three farms during the period 2007-2012 were related to either season variations or the temperature-humidity index (THI), i.e., a complex climate parameter obtained by the maximum temperature and minimum relative humidity. The THI was able to assess the HS effects on parameters as conception rate on an annual basis (CRY) (R=-0.437; P <0.01) but was less efficient for parameters as the conception rate (CR). Whereas (i) CRY is influenced by both heat detection rate (HDR) and CR; (ii) an indirect analysis detected a significant (P< 0.001) reduction in the HDR along with THI increase; and (iii) CR was only partially affected by either THI or season, it follows that the main cause of reduced fertility in the farms surveyed was the HDR. The number of days open was significantly larger in the animals calved from January to July than in those calved between August and December (163±33 vs 123±36; P< 0.001); this increase may be because of the rescue of reproduction activity in the cows calved during the former period coincides with heat stress occurrence.