Effects of high heat load conditions on body weight, feed intake, temperature, and respiration of Dorper, Katahdin, and St. Croix sheep

Abstract

Forty-six Dorper, 46 Katahdin, and 43 St. Croix female sheep from four regions of the USA were used to evaluate responses to high heat load index (HLI) conditions. There were sequential 2-wk periods with target HLI during day/nighttime of 70/70 (thermoneutral zone conditions), 85/70, 90/77, and 95/81. Rectal temperature (RT) and respiration rate (RR) were measured at 07:00 (before daytime), 13:00, and 17:00 h (preceding nighttime). Region had few and minor effects. Intake of DM (g/day) was not influenced by period. Rectal temperature was considerably less for St. Croix than for Dorper and Katahdin at each time, with differences increasing as period advanced. Similarly, RR in periods 2, 3, and 4 was least for St. Croix, particularly at 07:00 h in period 4. Moreover, RT was slightly less for Katahdin vs. Dorper in period 4 at 13:00 and 17:00 however, RR was less for Katahdin than for Dorper in periods 3 and 4. Variance in RT in periods 3 and 4 ranked St. Croix < Dorper < Katahdin. In conclusion, based on RT and RR, resilience to high HLI conditions ranked St. Croix > Katahdin > Dorper, with lowest variability among individuals for St. Croix and greatest for Katahdin.