Within Breed Variations in Milk Composition and Estimating the Average Composition of Milk for the Lactation from Partial Records

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Abstract
Milk composition was determined at monthly intervals for 4 years on 2,842 milk samples from 178 cows to compare variation of the components. The within breed standard errors of estimate were 0.26, 0.20, 0.14 and 0.12% for milk fat, solids-not-fat (SNF), protein and lactose, respectively, when average composition of a 305-day lactation was used to estimate the next (62 pairs); similarly compared, repeatabilities were 0.76, 0.72, 0.67 and 0.65. Also, composition for partial lactations was compared with completed lactations. The individual breed linear regressions for per cent milk fat and SNF were significantly different for single test periods 1-8 and for accumulative test periods 2-8; the breed regressions were similar for consecutive accumulative tests 6-8 and 2-8, respectively, for average per cent protein and lactose. Average per cent NSF, protein and lactose for lactation periods could be estimated from partial records if accumulative averages for three or more consecutive tests were used.