EVALUATION OF STEAM-TREATED WHEAT STRAW AS A ROUGHAGE SOURCE IN DAIRY COW RATIONS

Abstract

Two experiments were conducted involving a total of 24 Holstein cows to evaluate steam-treated (ST) wheat straw as a roughage source in mixed dairy rations. Diets containing ST straw (exp. 1) at 20 and 30% of the ration dry matter (DM) were consumed in amounts similar to a 30% ground alfalfa hay diet and in greater amounts than a mixed diet with 20% untreated (UT) wheat straw. Cows receiving the diet containing 30% alfalfa hay produced more (P < 0.05) milk per day than the group fed a mixed diet with 20% UT straw, but similar amounts to those cows fed the two ST straw diets. Milk fat (%) was not different (P > 0.05) among the four treatments. Cows fed the diet containing 30% ST straw had a lower (P < 0.05) ruminal fluid acetate: propionate ratio compared with a 20% UT straw mixed diet. In the second experiment, cows receiving a diet containing 30% ST straw plus 30% rolled barley in place of 60% corn silage consumed less (P < 0.05) total DM and produced less 4% fat-corrected milk per day with a depressed (P < 0.05) fat test. Propionic acid level in rumen fluid was elevated (P < 0.05), which lowered the acetate: propionate ratio in ruminal fluid of cows receiving the diet containing 30% ST straw compared to cows receiving the corn silage diet. Data from these studies suggest that up to 20% steam-treated wheat straw (DM basis) could be included in total mixed dairy rations without any appreciable influence on animal performance. However, at higher levels ST wheat straw is a less "effective" fiber or roughage source in dairy rations. Key words: steam-treated, wheat straw, Holstein cows, fat depression, feed consumption, effective fiber