Abstract

Summer heat load in dairy cows is recognised as a potential stressor to animal comfort, however, the effects of heat load on production remains to be fully elucidated. The economic case for farmers to invest in improved heat mitigation could be strengthened if the cost of head load on milk yield is better understood. We explored the interactive effects of weather variables on milk production in two commercial dairy farms that were equipped with a weather station and milking machinery able to measure daily yields at cow level. The study was conducted in the Waikato, over the 2024-25 summer period and included data from 1,304 Holstein-Friesian and Holstein-Friesian-Jersey crossbred cows. Generalised Linear Mixed Models were used to determine the effect of weather on milk yield. Results indicated declines in milk yield were associated with higher temperatures, and this effect was greater under high humidity or high solar radiation conditions.

Reed, C., Chambers G., Edwards J.P., Jago J., and Verhoek K.J.

Hamilton, Volume 85, Hamilton, 45-48, 2025