SEASONAL EFFECTS OF TROPICAL CLIMATE ON SHADED AND NON-SHADED COWS AS MEASURED BY RECTAL TEMPERATURE, ADRENAL-CORTEX HORMONES, THYROID-HORMONE, AND MILK-PRODUCTION

  • 1 January 1979
    • journal article
    • research article
    • Vol. 40  (12) , 1792-1797
Abstract
Rectal temperatures and hormone concentrations were monitored at intervals of 2-3 wk and milk, milk fat and California mastitis test scores, at intervals of 1 wk in 5 shaded and in 4 nonshaded early lactation cows. Measurements were taken from Sept.-Dec. in the mildly heat stressing climate of Oahu, Hawaii. The daily ambient temperature flux ranged from 22-29.degree. C in Sept. to 20-25.degree. C in Dec. Average daily temperature-humidity index (THI) values were 75 to 70 for Sept. and Dec., respectively. Average daily THI values were correlated with rectal temperatures in nonshaded cows and were negatively correlated with plasma adrenal cortex hormones (corticoids) in shaded cows, plasma thyroid hormone in shaded and nonshaded cows and with milk production in nonshaded cows. Estimated milk production decline per unit increase in THI was 0.32 kg. Nonshaded cows had higher rectal temperatures, a trend for lower plasma corticoids, produced less milk and milk fat and had higher California mastitis test scores. Shaded cows maintained a higher fat percentage at THI > 74. Average plasma thyroid hormone values were not different between treatment groups. Both groups failed to attain normal rectal temperatures at night. Afternoon rectal temperatures were more highly correlated with the rectal temperature with which the cow started the day than they were with the THI of the day itself.

This publication has 1 reference indexed in Scilit: