INTERACTIONS BETWEEN BODY CONDITION AT CALVING AND COOLING OF DAIRY-COWS DURING LACTATION IN SUMMER

This study examined the interactions between dietary manipulation for increased body condition during the last trimester of pregnancy (spring) and postpartum cooling (summer lactation). Effects of diet on milk production of Holstein cows were examined to determine whether body stores could compensate for reduced DMI during heat stress. Cows calving between May and July with high (3.8 on a six-point scale) or low (2.7) body condition scores were assigned postpartum to be cooled by sprinkling and ventilation or to serve as uncooled controls. Cooled cows ate 1.6 kg more DM/d and consumed 9 L less of water/d than uncooled cows. Cooled cows maintained body temperatures below 38.9 degrees C during day hours; peak body temperature for uncooled cows was 39.7 degrees C. For 8 wk postpartum, glucose and insulin concentrations in plasma were unaltered by cooling or body condition. The NEFA were lower, and urea was slightly higher, for cows with low body condition. Milk production increased 1.9 kg/d with cooling, fat production increased with both body condition and cooling, and protein production increased with cooling but not with body condition. Performance was lowest for the uncooled subgroup with low body condition. Among cooled cows, no advantage was attributable to high body condition. An additive effect of high body condition and cooling on milk production in summer was not evident.