Samples of alfalfa hay, barly grain, soybean meal and fish meal were incubated in the rum~n of four holstein steers (300z 15 kg, body weight). animals fed diets containing different concentrate:alfalfa hay ratios as 60:40, 70:30, 80:20 and 90:lOin a latin square design. ground (2 mrn) samples (5 g dm) were placed in artificial silk bags (lOx20 em, 50 ~m pore size) and incubated in the rumen for 0.0, 2, 4, 8, 16, 24, 48, 72 and 96 h (n=8). data of protein degradation were adjusted to a logarithmicmodel of [1=«In(do)-In(dj))/-kd]; where 1= lag time, do= potentially degradable residues, dj= potentially degradable fraction uf protein and kd~fractional rate constant of degraration (/h). minimum daily ruminal ph decreased from 6.40 to 5.34 when level of concentrate was increased. there was a significant difference when ruminal degradation lag time of protein of various feeds was considered. ruminal degradation lag time of protein of alfalfa and soybean meal was markly increasedwhen rumen ph declined. therefore, it was concluded that the ruminal degradation lag time of protein of the feed samples evaluated in the present study was influenced by the rumenph.

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