Interrelationships in lactating Holsteins of rectal and skin temperatures, milk yield and composition, dry matter intake, body weight, and feed efficiency in summer in Alabama.

Thirty-two lactating, multiparous Holstein cows were utilized in a 91-d experiment in Auburn, Alabama, during summer to determine whether rectal and skin temperatures and respiration rates are repeatable and interrelated and whether whole cottonseed or calcium salts of long-chain fatty acids (Megalac, Church & Dwight Co., Inc., Princeton, NJ) affected milk production or its constituents. Treatments were (I) control, (II) I plus 10.4% whole cottonseed, (III) I plus 2.6% Megalac, and (IV) I plus 5.2% whole cottonseed plus 1.3% Megalac. Data included 358 to 2644 measurements analyzed as a split-plot design of experiment. Only milk protein percentage and protein-to-fat ratio were significantly affected by dietary treatment. Milk protein percentage was depressed by dietary fat additions, especially by the combination of whole cottonseed and Megalac. Within lactation repeatabilities for milk, fat, protein, and SCM yields ranged from 0.44 to 0.66; two percentages and protein to fat ratio, 0.21 to 0.32; feed efficiency, 0.18; dry matter intake (DMI) and body weight, 0.98 and 0.84; rectal and skin temperatures and respiration rate, 0.001 to 0.055. Partial and simple correlations were similar in sign and magnitude. Noteworthy were partial correlations between milk yield and DMI, 0.367; milk yield and rectal temperature, -0.135; milkyield and respiration rate, 0.102. Skin temperature was unrelated to other variables. Respiration rate was correlated with DMI, 0.270. Results should help researchers designing future experiments involving these responses to predict the number of measures needed to detect differences.