Effects of Relative Humidity, Maximum and Minimum Temperature, Pregnancy, and Stage of Lactation on Milk Composition and Yield

Abstract

Composite monthly single-day milk samples from the Florida Agricultural Experiment station [USA] dairy herd 1959-1974 were analyzed for composition. Data were 22,972 observations on 5 dairy breeds, but major satistical analyses were limited to Jerseys and Holsteins. Minimum relative humidity and maximum and minimum temperatures on day of evening sample were associated with 1.6-5.6% of variability within lactation (range for 2 breeds) of milk and milk constituent yields and 1.1-16.5% of constituent percentages. Yields of milk and constituents of the Holsteins seemed more sensitive to climatic variation than did Jersey, but Jersey constituent percentages were more sensitive. Yields were affected only slightly by increasing maximum daily tempertures from 8-29.degree. C but declined rapidly at > 29.degree. C; fat and protein percentages declined from 8-37.degree. C; Cl- content increased > 21.degree. C. Stage of lactation and pregnancy effects accounted for .apprx. 50% of the variability of yields and 3-23% of percentages. Effects were detected also for Cl- and acidity percentages, specific gravity and ratios of solids-not-fat to fat and protein to fat.