EFFECTS ON MILK-YIELD AND COMPOSITION OF INTRAABOMASAL INFUSIONS OF SODIUM CASEINATE, AN ENZYMATIC HYDROLYSATE OF CASEIN OR SOYA-PROTEIN ISOLATE IN DAIRY-COWS

Six lactating dairy cows receiving a diet of grass silage and barley were given the following treatments as infusions into the abomasum, in a replicated 3 x 3 Latin square with 10 d periods: sodium caseinate (C), an enzymic hydrolysate of casein (CH) and soya-protein isolate (SPI). The C and CH treatments supplied approximately 185 g/d and the SPI treatment approximately 160 g/d of amino acids. Milk yield was similar for all treatments. Yields of milk protein were 605. 604 and 582 (P > 0.05) g/d for C. CH and SPI respectively. For C, CH and SPI respectively, concentrations (g/kg) of fat were 39.6, 45-7 and 41.9 and yields (g/d) of fat were 790, 931 and 827; values for CH were significantly (P < 0.01) higher than for either of the other treatments. It is concluded that the form in which amino acid residues of casein are supplied to the abomasum (protein v. peptide-amino acid mixtures) can influence the partition of use of nutrients between body tissues and the mammary gland.