The influence of thermal conditions on rectal temperature, respiration rate and pulse rate of lactating Holstein-Friesian cows in the humid tropics.

The effect of minimum, maximum and mean ambient air temperatures and the temperature-humidity index (THI) of the same and the previous day on morning (a.m.) and afternoon (p.m.) rectal temperatures (RT), respiration rates (RR) and pulse rates (PR) were studied in 17 Holstein-Friesian cows over the first 125 days in the 3rd and 4th lactations. Physiological responses showed a diurnal pattern, being lower in the mornings than the afternoons: 38.6 vs 39.0 degrees C for RT, 52.2 vs 60.7 breaths/min for RR and 58.1 vs 64.1 beats/min for PR. Correlations between RT and RR (r = -0.043 to -0.046) and RT and PR (r = -0.178 to -0.261) were low (P greater than 0.05). Correlations between RR and PR (r = 0.353 to 0.365) were moderate (P less than 0.05). Weather variables, especially ambient temperature of the previous day, were more important and influenced physiological responses to a greater extent than other thermal factors the same day. Generally, physiological responses were influenced to a greater extent by ambient temperature than THI. Weather variables explained variations in RT (5.1-59.6%), in RR (13.0-17.8%) and in PR (22.1-25.4%). Relationships between weather variables the previous day and physiological responses were contradictory, with minimum and maximum values showing a negative relationship in contrast with a positive relationship for mean values.