EFFECT OF INCREASING DIGESTIBLE UNDEGRADED PROTEIN SUPPLY TO DAIRY-COWS IN LATE-GESTATION ON THE YIELD AND COMPOSITION OF MILK DURING THE SUBSEQUENT LACTATION

Effects of feeding a protein supplement to dairy cows during the dry p eriod on performance during the following lactation were investigated in two experiments. Holstein-Friesian cows were paired towards the end of lactation, and, after drying off one of each pair received a typic al dry cow management regime of ad libitum grass silage (experiment I) , or a mix of grass silage and distillers' grains or pressed beet pulp (experiment 2). The other cows were offered restricted access to the same basal diet, together with ad libitum access to barley straw and 0 .5 kg/day high protein maize gluten meal. During the following lactati on, animals from both groups were treated without reference to dry per iod treatment, and were offered equal access to the same lactation die t. Data were analysed by analysis of variance of experiment means and by parallel curve analysis using sample means. In experiment 1, milk y ields were similar (27.2 v. 27.9 (s.e.d. 2.12) kg/day for control and supplemented animals respectively) but milk protein yields, and hence concentrations, were significantly higher (P < 0.001) from supplemente d animals (28.9 v. 31.8 (s.e.d. 0.58) g/kg). In experiment 2, milk yie lds were significantly higher (P < 0.001) from supplemented animals (m ean 33.3 v. 35.4 (s.e.d. 1.66) kg/day; however, milk protein yields we re also significantly increased (P < 0.011) and the change in milk pro tein concentration was small. No difference in dry-matter intake teas recorded in a subset of animals during early lactation in experiment 2 . It is hypothesized that the maternal labile body protein pool was ma intained or replenished during the dry period by the provision of the protein supplement, and that this had a significant effect on subseque nt lactation performance.