Factors affecting the nutritive value of fat for calves. I.—the mode of incorporation into milk diets

The merits of different methods of incorporation of fat into milk diets for calves were studied by determining the apparent digestibility of the fat and its ability to promote a high efficiency of nitrogen retention. All the diets were reconstituted with water and fed in liquid form. Butterfat included in a diet by melting and then blending with spray‐dried separated‐milk powder had an average digestibility of 71.8 ± 5.9% compared with 95.2 ± 1.5% for the butterfat in a spray‐dried whole‐milk powder. The poorer digestibility was associated with markedly lower nitrogen retention. The inclusion of 3.3% of lecithin in the blended butterfat increased the average digestibility of the fat to 88.3 ± 4.2% and also brought about a substantial improvement in nitrogen retention. Palm‐kernel oil in an homogenised spray‐dried milk powder had a mean digestibility of 94.1 ± 1.4%. An addition of 3.3% of lecithin to the oil was associated with a slightly higher digestibility (96.3 ± 1.0%). Tallow containing 3% of added lecithin had a mean digestibility of 70.7 ± 4.44; when melted and then blended with spray‐dried separated‐milk powder compared with 86.8 ± 2.2% when in an homogenised spray‐dried milk powder. It was concluded that, for optimum digestibility of fat in filled (lipid supplemented) milk diets, the fat must be adequately homogenised. Since the inclusion of lecithin is associated with slightly higher digestibility of homogenised fat, its addition is considered desirable to ensure maximum digestibility of the fat. The mean digestibility of tallow added to reconstituted spray‐dried separated milk as a concentrated fat homogenate containing emulsified tallow 30%, separated‐milk solids 3% and water 67% was 85.7 ± 2.5%, compared with 86.5 ± 3.4% for tallow in a reconstituted homogenised spray‐dried powder.