ENVIRONMENTAL-INFLUENCES AND INTERACTIONS BETWEEN FERTILITY AND MILK-PRODUCTION IN HIGH-YIELDING COWS IN THE USA

The relationship between milk yield and fertility was investigated in a dairy herd with an annual average milk production of 10, 000 litres in the north east of the USA. Examination of post partum ovarian function indicated that early heifer utilisation and a high milk yield are not directly responsible for reproductive disorders. The high production potential results in competing physiological stresses only near the time of insemination. This negative effect was observed more often in loose housed animals than in tethered housing. The annual production accounted for 6-11% of the variation in the calving interval. The poor adaptation of these animals to their environment was evident from the high frequency of treatment, a high culling rate and the short average reproductive life span of 2.2 lactations.