Few data are available to evaluate the Metabolisable Protein (MP) System (AFRC, 1992) as an aid to ration formulation for dairy cows. Responses of lactating dairy cows to MP were evaluated in two experiments.
In Experiment One, groups of 10 Holstein cows were offered grass silage ad libitum and 7kg DM/d of one of six (treatments 1-6) compound foods from 39d after calving, for eight weeks. All rations were isoenergetic, assuming silage intake of 11kg DM/d (typical for the herd). Ratios between MP supply (calculated from in situ protein degradability measurements) and requirement (calculated for a standard cow: 565kg live weight, 281 milk/d, 40g/kg butterfat, 33g/kg milk protein, liveweight change =0kg/d) were 1.00, 1.02, 1.06, 1.06, 1.1 and 1.17 for treatments 1-6, respectively.