Studies on the application of an undegradable protein system to high yielding dairy cattle in Taiwan

To compare the crude protein and new protein systems of the National Research Council (NRC), diets were formulated with two protein levels and two different undegradable protein (UDP) levels. The protein level and the protein undegradability of the rations were respectively: Diet 1, 16.5% and 33.5%; Diet 2, 16.5% and 37.0%; Diet 3, 15.0% and 37.0%. The experimental diets were fed as total mixed rations (TMR) with concentrates and roughage in a ratio of 50:50 (dry matter (DM) basis). akes were 18.2 kg, 17.8 kg and 16.7 kg day−1 for Diets 1, 2 and 3, respectively. Milk yields amounted to 26.4 kg, 28.6 kg and 27.5 kg, with milk fat percentages of 3.26, 3.05 and 2.99. Average percentage of milk protein was 3.03, 2.96 and 2.92. Average total solids comprised 11.42%, 10.96% and 10.96%, respectively. Cows fed the high-level UDP gained the most body weight compared with the other groups. It appears that application of the undegradable protein system is better than the crude protein system with respect to yield and efficiency of milk production. The UDP with 1.5% less crude protein can give the same performance as the crude protein standard.