Part Lactations. I. Age-Correction Factors for Monthly Milk Fat Yields

Abstract

Age-correction factors are developed for monthly milk fat yields of dairy cows in New Zealand. The first test month of the lactation is taken into account, because in any calendar month cows are at different stages of lactation as well as at different ages. The factors obtained decrease as lactation progresses, indicating that in the later part of lactation the production of young cows is very similar to that of mature ones. This is probably due to the poor environment at this time of year masking the age differences. The factors for 2-yr.-olds differ greatly according to the first test month~ but this effect is not apparent in the 3-and 4-yr.-olds, which vary little and are close to the factors for lactation production.