This experiment was carried out at the Dairying Research Corporation, Hamilton, New Zealand, to evaluate the heat challenge imposed on dairy cows during spring and summer. The diurnal temperature profiles of 18 Friesian cows were recorded over five days in November and five days in January. Temperature-humidity index and black globe temperature were used to assess the potential of the environment to induce heat stress. Cows in January had higher maximum (39.5 versus 38.9 ± 0.09 °C), minimum (37.9 versus 37.6 ± 0.09 °C) and mean (38.6 versus 38.4 ± 0.05 °C) daily body temperatures than in November, corresponding with higher ambient temperatures and solar radiation in January. Temperature-humidity indices were highest in January between 09:30 h in the morning and 19:30 h at night and within the range reported to cause mild heat stress in dairy cows (72 to 78). Respiration rate (47 versus 37 ± 1.4 breaths/minute) and water intake (51 versus 18 ± 2.3 l/cow/day) were both higher in January than in November.
Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 226-229, 2000
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