Evaluation of Energy Balance of Friesian X Bunaji Dairy Cows Using Milk Composition Based Indicator Traits
The potentials of using milk composition as indicators of energy balance (EB) in dairy cows were evaluated. Milk composition traits (milk protein, fat and lactose percentages) from thirteen (13) primiparous and 47 multiparous (F1) Friesian x Bunaji cows were studied. The milk composition was analyzed weekly from 4 to 300 days postpartum. The analyzed percentage milk fat, protein and lactose were used to calculate the other milk composition parameters. The mean estimates of EB based on milk measures for all the 3 stages of lactation were positive. However, the magnitude of the average estimates of the EB increased with stages of lactation; 21.99, 46.514 and 59.097MJ/d for stages 1, 2 and 3 respectively. The magnitude and direction of the correlations between EB and milk composition traits varied across stages of lactation; the correlation coefficient was relatively stronger in the 3rd stage than the 1st and 2nd stages of lactation. The potential indicators of EB identified from this study were the protein contained variables, such as milk protein content (MPC), fat-protein ratio (FPR), change in milk protein content (dmPc), change in fat-protein ratio (dFPR) and change in protein-lactose ratio (dPLR). These variables had strong relationship with EB both within and across lactation stages. However, dmPc seems to be the variable most common to all of these potential milk production variables. It had very strong and positive relationship with EB both within and across lactation stages. This suggested that high milk protein is associated with positive EB, while the decrease in milk protein content is associated with negative energy balance (NEB). Therefore, the dynamics of changes in milk composition measures during lactation could be used to monitor the EB status of dairy cows.