In Situ Dry Matter, Nitrogen and Phosphorous Disappearance of Different Feeds for Ruminants

Four feeds, three concentrates (rice bran, soybean meal and flaked corn) and one forage (corn silage) were incubated in four ruminally fistulated Holstein steers over three one week periods in a 3${\times}$4 incomplete latin square design where steers served as blocks and feeds as treatment. The objectives of the study were to investigate in situ DM, N and P degradability characteristics of feeds in order to assess availability of these nutrients by ruminants. In each period, all feeds were incubated in quadruplets (corn silage in triplicates) in the rumen of each steer in a reverse order for 3, 6, 9, 12, 18, 24 and 48 h. The DM 'a' fraction was higher and lower (p<0.001) in corn silage and rice bran respectively. Although corn silage contained the lowest (p<0.01) DM 'b' fraction, flaked corn contained the highest. Rate of DM degradation of flaked corn and corn silage were half (p<0.05) of the rate of DM degradation of either rice bran or soybean meal. Potential or effective DM degradability (p<0.05 to 0.001) at various passage rates were the lowest for rice bran and the highest for soybean meal. Corn silage N 'a' and 'b' was the highest and lowest, respectively (p<0.01). N 'c' of corn silage and rice bran was higher (p<0.001) than other feeds. Potential N degradability was the lowest in flaked corn (p<0.05). P 'a' was high (p<0.01) for corn silage and rice bran. P 'b' fraction was very high (p<0.001) in soybean meal but was absent in corn silage. Availability of DM (p<0.01 or 0.001), N (p<0.001) and P (p<0.05) differed between feeds at various passage rates except P availability at k=0.02 per h (p>0.05). The results demonstrate that the availability of DM, N and P by ruminants depends on feed as well as categories of animal.