Observations on some environmental factors connected with fertility in heat stressed cows

A field study was performed using 15 Kibutz dairy herds, in which 4195 cows situated in northern Israel were milked to determine the influence of climatological factors and nutritional regimes on the conception rate during the summer period (July-September). The Overall Conception Rate (OCR) during summer was 28.2% (17.3-41.9%) compared to 40% in the spring (May-June). The conception rate from first inseminations (CRl) was 31.3% during summer and 45.3% during spring. The OCR of the nullipara heifers in the same herds was 59.2% in summer and 60.4% in spring. The OCR in summer was negatively correlated with the minimum temperature (r=-0.53), the relative humidity at 0800 hrs. (r=-0.47), and the relative humidity at 1400 hrs (r=-0.49), whereas the CRl during summer was negatively correlated only with the minimum temperature (r=-0.51). In 12 (13) feeding groups of cows examined in 6 herds, no correlation was found between rectal temperatures and the actual milk productions of the cows. In 14 (15) herds, the milk production in summer was lower than in spring; the decrease varied from 0.9%-18.2% (average 7.8%). A highly significant negative correlation was found between the OCR and the various parameters of protein intake: grams of crude protein/cow/day, grams of crude protein/kg FCM/day, and percentage of protein from total dry matter. Particularly high correlations were found between the OCR and the average amounts of protein/kg FCM/day in milk of all cows (r=-0.84).