Effects of Milking at Unequal Intervals for a Complete Lactation on Milk Yield and Composition

Abstract

The effects of milking at unequal intervals for a complete lactation were studied with 82 cows of the Holstein, Ayrshire, and Brown Swiss breeds. They were milked at intervals of either 12.5 and 11.5 (Equal Intervals) or 14.5 and 9.5 (Unequal Intervals) during their first lactation, then switched to the alternative intervals during the second lactation.With standardized 266-day lactation periods and the cows milked at equal or unequal intervals, the yields were 4,920, 4,811; 186, 181; 456, 441; and 647, 617kg of milk, milk fat, solids-not-fat (SNF), and total solids (TS), respectively. A least squares analysis indicated that the cows produced 160±90kg (3.5%) more milk (P ≅ .08), 9±4kg (5.0%) more milk fat (P<.05), 16±11 (4.0%) more SNF (P ≅ .15), and 32±4kg (5.5%) more TS (P<.05) per lactation while being milked on equal intervals than on the unequal intervals. A within-breed and sequence regression of the difference in yields resulting from equal and unequal intervals of milking on total yields indicated that 7.0, 5.8, 5.9, and 3.5% of the variation in the difference in yields of milk, milk fat, SNF, and TS, respectively, were accounted for by the first and second powers of level of production. The milk obtained after the long (14.5 hr) interval was lower in per cent milk fat than was that following the short (9.5 hr) interval (3.56 vs. 4.07%). Distribution of SNF percentage between am and pm milkings was not affected by the milking intervals. As lactation progressed, proportionately more of the milk was obtained after the long interval.