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Abstract

Adequate knowledge of the ruminal degradation characteristics of feedstuffs fed to ruminants is paramount to successful ration formulation using the recently proposed protein rationing systems. In the first of two trials, in situ rumen degradation characteristics of cereal grains with or without steam rolling, roughages and agro-byproducts were evaluated. In vitro starch release of the cereals by the enzyme amyloglucosidase was also investigated. Steam rolling (SR) significantly reduced the in situ rate of degradation of DM, CP and starch of cereal grains. Compared to unprocessed cereals, in situ rate of degradation of these parameters was significantly lower for corn than for barley or wheat, for both the steam rolled and the unprocessed treatments. However, SR tended to increase the in vitro starch release by amyloglucosidase from cereal grains. In situ degradation characteristics varied significantly (P<0.01) among roughages and agro - byproducts, with alfalfa hay and rye distillers grains having higher rates of degradation. Beet pulp had the highest neutral detergent fiber (NDF) (P<0.01) effective degradability among the agro - byproducts. In the second trial, twelve lactating dairy cows were used to determine the effect of diets matched for rate of carbohydrate and protein degradation on feed intake, digestibility, rumen and blood components, and the yield and composition of milk. Four diets; steam - rolled corn - fish meal (SRC-FM), steam - rolled corn - canola meal (SRC-CM), steam - rolled barley - fish meal (SRB-FM) and steam - rolled barley - canola meal (SRB-CM) were all fed with alfalfa hay to the cows four times per day. Feed intake was not influenced by source of carbohydrate or protein (P>0.10), but the digestibility of most nutrients was significantly influenced (P