SOLUBLE NUTRIENTS IN PROTEIN SUPPLEMENTS AND IN SITU DISAPPEARANCE
The effect of removal of soluble nutrients from soybean meal (SBM) and meat meal (MM) on in situ disappearance of dry matter (DMD) and nitrogen (ND) was measured. All feeds were rinsed with pH 6 buffer (R) without or with subsequent extraction with buffer at pH 5 (5) or pH 7 (7). Feeds were incubated in the rumen of heifers fed diets containing 20 or 80% concentrate (20%C and 80%C, respectively). Ruminal pH was higher (P < 0.05) in heifers fed the 20%C diet than in animals receiving the 80%C ration, while ruminal ammonia concentration tended to be greater with the 80%C diet. In situ DMD and ND were linearly related to incubation time (P < 0.01) with little indication of a quadratic effect of time. In situ ND of feeds extracted at pH 7 was greater (P < 0.05) than ND of feeds extracted at pH 5, but no interaction of diet and extraction pH or feed and extraction pH was apparent. Hence, altered protein solubility due to varied ruminal pH would not appear to be responsible for differences in ND with the different diets. In situ DMD and ND of both feedstuffs were greater (P < 0.01) with the 20%C than the 80%C diet. Hence, differences in microbial types or activities rather than chemical characteristics of the substrate are probably responsible for greater proetein loss with the lower concentrate diet. Key words: In situ, dry matter disappearance, nitrogen disappearance, soybean meal, meat meal