Effect of shade on various parameters of Friesian cows in a Mediterranean climate in South Africa. 2. Physiological responses

Author: C.J.C. Muller, J.A. Botha, W.A. Coetzer and W.A. Smith
Year: 1994
Issue: 2
Volume: 24
Page: 56 - 60

The effect of a shade structure on some physiological parameters of lactating Dutch-type Friesian cows was determined over three consecutive summer periods. Plasma cortisol concentration of no-shade cows was significantly (P < 0.05) higher than that of shade cows during the 1985/86 experimental period as well as the combined analysis over the two experimental periods. Cortisol levels were increased (P < 0.05) owing to higher temperatures during the 1984/85 period only. Plasma thyroxine concentration of the no-shade cows tended to be lower than that of shade cows. Thyroxine levels were reduced (P < 0.01) by increasing maximum ambient temperatures during the 1984/85 experimental period only, while a negative trend was observed during 1985/86. The average respiration rate and the average rectal temperature of no-shade cows were higher (P < 0.01) than those of shade cows at 11:00, 13:00 and 15:00 on hot days (maximum day-time temperature, 25.1 °C) but there was no difference at any time of the day on cool days (maximum ambient temperature -< 25.0 °C). Both respiration rate and rectal temperature of shade and no-shade cows increased (P < 0.01) with increasing ambient temperatures.

Keywords: cortisol, dairy cows, heat stress, rectal temperature, respiration rate, shade, thyroxine
Read article