Heat stress affects reproductive performance of high producing dairy cows bred in an area of southern Apennines

A 5-year retrospective (from 2008 to 2012) survey was carried out by analyzing data of high producing dairy cows reared in farms located in an area of southern Apennines. The indicators of fertility obtained were related to either season variations or temperature–humidity index (THI). Conceptions were evaluated per month on an annual basis (NCY), i.e., a parameter obtained by subtracting gestation length to the calving date. A significant reduction of NCY was found during the summer months; furthermore, this parameter decreased along with THI increase. The number of heats detected varied similarly to NCY and represented the main cause of lower fertility consequent to heat stress (HS). The age at first calving was not significantly affected by either the season or the THI. The mean number of AI/pregnancy in relation to the calving date was significantly affected by the season but it was not related to THI. The number of days open was significantly larger in the animals calved from January to July than from August to December (163±33 vs 123±36 days; P<0.001); this causes an annual economic loss of several thousand euro in each farm analyzed. In conclusion, HS causes severe economic loss in dairy farms located in southern Apennines that is mainly due to a lower number of heats detected as well as to a larger number of days open and semen doses used.