Repeatability of Heat Tolerance Observations

Abstract

Respiration counts of 20 Holstein cows taken in the pasture at 2:45 p.m. daily for 14 days during the summer of 1946 were compared to those taken < 1 hr. later on the same cows in the milking barn. The rates averaged 78.5 times per min. in the barn. 13 of the 20 had higher average rates in the barn but ? the relative rankings were about the same. Computation of the repeatability of a single respiration record of the same cow resulted in 0.366 for pasture observations and 0.446 for barn observations. Repeatability for body temp, observations made in the barn was 0.288. The mean body temps, for the 20 Holstein cows during the 14-day period was 103.4[degree]F. Computations are presented which show how the use of several observations increases the variance due to permanent differences between cows, much of which is genetic. With 6 respiration records this portion of the variance increased from an average of 0.4 to 0.8, and with seven body temp, observations the increase was from the average of 0.25 to 0.7. It is concluded that respiration observations taken in the barn are as reliable as and perhaps slightly more reliable than those taken in the pasture. The use of averages for observations plus those for body temp, made on approx. 6 or 7 relatively warm days should result in measurements that are relatively accurate for use in selecting cattle for a high degree of tolerance to heat.