Analysis of Repeated Milk Yields and Composition Traits by Mixed Models for Crossbred Holstein Friesian Dairy Cows

Abstract

This study evaluated the effects of milking month, milking time, and lactation stage on milk yield and composition traits of crossbred dairy cows. Twelve crossbred Holstein Friesian cows with the same parity were purposefully selected and categorized into three groups; each consisting of four. All cows were individually managed for 120 days. Milk yield record was done every day for the morning and evening time whereas milk samples were taken every fifteen-day intervals. Data collected were analysed by PROC MIXED procedure of SAS 9.4. The "morning milkings" in all milking months showed the highest variations for "milk yield" whereas the "evening milkings" showed the highest variations for "milk urea nitrogen" in the 1st and 2nd and for "fat" in the 3rd and 4th months. The main findings in this study were the month-to-month variations in milk composition and milk yield within milking times. Milk fat was the only component that was significantly influenced by milking month, milking time, and lactation stage. Finally, this study concluded that repeated measurements for the respective milking times in milk yield and milk composition at a monthly interval showed variations. Further study should be conducted using repeated measurements at a weekly level for early detection of yield and quality alterations and health disturbances of dairy cows.

Keywords: lactation stage; milk compositions; milking month; milking time; milk yield.