Evidence of Heterogeneity of Variance in Milk Yield among Holstein-Friesian Herds in Kenya

Abstract

Three thousand, nine hundred and seventy five lactation records of Holstein- Friesian cows between 1968 and 1984 were used to investigate the existence of heterogeneity of variance in milk yield in Kenya. Coefficient of variation and standard deviations across herds were used to test heterogeneity of variance. Average herd standard deviation and coefficient of variation after correcting for the fixed affects were 672.2kg and 26.7% respectively, while scaled standard deviations between herds were 180.1kg and 3.4%.The scaling of observation s within individual herds by sample standard deviation minimized heterogeneity of variance of milk yield thereby increasing accuracy of selection. It was concluded that significant heterogeneity of variance in milk yield existed among herds and should be accounted for in sire and cow evaluation.