PREDICTION OF GROSS ENERGY CONTENT OF EWE MILK

The interpretation of the results of feeding trials with lactating ewes and their sucking lambs can be improved considerably when milk energy production is known. The determination of gross energy (GE) however is time consuming and expensive. Therefore an equation to predict GE from milk constituents would be helpful. Using multiple regression analysis a GE-prediction equation was derived with milk samples mainly from crossbred ewes. The concentrations of milk constituents were determined by infrared spectrometry (calibrated with cow milk). Fat concentration ranged between 43.8 and 125.0 g/kg, protein concentration between 32.4 and 53.1 g/kg and lactose concentration between 38-9 and 52.9 g/kg. GE (adiabatic bomb calorimetry) of the samples under consideration ranged between 3500 to 6800 kJ/kg. The following equation, including fat (f), protein (p) and lactose (1), is recommended and predicts GE as kJ/kg fresh milk using constituents in g/kg fresh milk: GE = 41.94 X f + 15.85 X p + 21.41 X l (residual s.d. = 92, adj.R2 = 0.98). This equation has, in the GE range 4500 kJ to 6000 kJ, an almost constant confidence interval with an average of +/- 25 kJ and an almost constant prediction interval, with an average of +/- 187 kJ. In the period until weaning it would appear justified to use the derived equation regardless of stage of lactation. The equation is valid for milk samples from sheep breeds with relatively high fat and low protein contents and where milk constituents have been determined by cow milk calibrated infrared spectrometry.