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 the temperature-humidity index (THI). A significant lower number of conceptions evaluated per month on an annual basis (NCY), i.e., a parameter obtained by subtracting gestation length to the calving date, was found during the summer months; furthermore, this parameter decreased along with THI increase. The number of heats detected varied equally to NCY and represented the main cause of the 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 time 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 losses in dairy farms located in southern Apennines that are mainly due to a lower number of heats detected as well as a larger number of days open and semen doses used.