The effect of concentrate supplements differing in ruminal protein degradability on milk production and blood metabolite concentrations of dairy cows grazing perennial ryegrass pasture

An experiment was carried out to compare the milk production of Friesian cows grazing perennial ryegrass pastures when fed an energy supplement or supplements with high levels of undegradable protein. Eighty-seven cows were blocked on the basis of calving date and milk yield and allocated to one of three treatments. The treatments consisted of 1.25 kg/day of concentrates based predominantly on beet pulp, fishmeal or formaldehyde-treated soyabean meal (Sopralin). The cows were grazed as a single group for the duration of the 16-week experiment. Ruminal degradability was measured in three separate cows and the results showed that the fishmeal and Sopralin concentrates had similar contents of undegradable protein, and both had substantially more than the beet pulp concentrate. Milk yields were 17.3, 18.0 and 18.6 (S.E.D. 5 0.46) kg/day, fat yields were 0.67, 0.67 and 0.70 (S.E.D. 5 0.021) kg/day, and protein yields were 0.58, 0.61 and 0.62 (S.E.D. 5 0.015) kg/day for the beet pulp, fishmeal and Sopralin treatments, respectively. The differences in milk and protein yields between the Sopralin and beet pulp treatments were significant (P , 0.05). Milk protein concentrations were 33.9, 34.3 and 33.7 (S.E.D. 5 0.26) g /kg for the beet pulp, fishmeal and Sopralin treatments, respectively. The difference between the Sopralin and fishmeal treatment was significant (P , 0.05). These results show that supplements of undegradable protein at pasture can result in higher milk production than when an energy supplement is fed.  2000 Elsevier Science B.V. All rights reserved.