Diets deficient in rumen undegraded protein did not depress milk production

The objective of this study was to evaluate the National Research Council's recommendations for feeding levels of rumen undegraded protein (RUP) for c ows fed a one-group total mixed ration. Sixty Holstein cows were paired by parity (1 to 6) and DIM (23 to 315) and were randomly assigned to one of tw o treatment sequences. Diets contained alfalfa silage (30% diet DM) and cor n silage (26% diet DM), and were isonitrogenous (16% CP) and isocaloric (1. 71 Mcal/kg). Soybean meal, protected soybean meal (Soy Best), and urea were used to make ration protein fractions that were predicted to be 35 or 29% RUP. The 35% RUP diet was formulated to provide 98 and 105% of the average requirement for RUP and rumen degraded protein (RDP), respectively. The rat ion containing 29% RUP provided 79 and 117% of average required RUP and RDP , respectively. All cows were group-fed the high RUP diet during a 2-wk. pr etreatment period, and then were fed one ration for 4 wk followed by the ot her for 4 wk according to their assigned treatment sequence. Data were coll ected in the last wk of each period. Mean milk production, milk fat, and mi lk protein were 32.6 kg/d, 4.35%, and 3.36%, respectively, with no treatmen t differences. Treatment response was not affected by degree of predicted R UP deficiency. National Research Council requirements for RUP may be too hi gh for cows fed diets similar in energy to a one-group total mixed ration. Alternatively, estimates of RUP content of feedstuffs may be low.