Factors Influencing the Conception Rate in Two Dairies with Low or High Altitudes in Southwestern Japan

Abstract

The effect of the season, thermo-humid index (THI) and days in milk (DIM) on the reproductive performance were investigated over eight years (n ＝3,581) in two dairies with different altitudes (38 m vs. 795 m). There was no difference in heat detection rate between the dairies (39.1% vs. 40.9%), whereas the conception rates (CR) fell below 20% when THI exceeded 72 in the dairy at lower altitude. The CR declined to less than 14.2% in cows with DIM on 51-110 during summer in the dairy at lower altitude, whereas no seasonal change was identified in the dairy at higher altitude. These results implied a risk of deteriorating performance on reproduction in dairies at lower altitudes resulting from heat stress.