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Experiments were initiated to measure animal performance, digestibility and metabolism characteristics associated with feeding corn crop residues supplemented with branched-chain fatty acids, urea, molasses, corn steep liquor, soybean meal and corn gluten meal.
Two in vitro and in situ digestibility studies demonstrated a dramatic decrease in the extent of ruminal cellulose (cotton thread) digestibility when sheep were switched from an alfalfa hay diet to a corn cob-based diet. In vitro response to this change was of smaller magnitude than in situ response. Lower in situ digestibilities occurred when sheep were fed the urea treatment, while cotton thread digestibility by BCFA-supplemented sheep was equal or superior to that of sheep receiving the urea plus molasses supplement. An increase in situ digestibility over the six-week experimental period was noted. In vitro fiber digestibility remained constant or tended to decrease with time, with the urea plus molasses-fed sheep having the highest neutral detergent fiber digestibility. In trial 2, casein-supplemented sheep had higher (P < .05) in vitro and in situ digestibilities and lower (P < .05) ruminal ammonia levels than did sheep fed the other non-protein nitrogen supplements, indicating that some factor is lacking in the urea-supplemented diets.
Following the in vitro and in situ digestibility studies, metabolism trials were initiated to determine the effect of supplementing corn cob-urea based diets directly with BCFA or indirectly through the use of natural protein sources. Dry matter and fiber digestibilities tended to be higher when lambs were fed natural protein supplements (soybean meal, corn steep liquor or corn gluten meal), while urea and branched-chain fatty acid supplements tended to result in lower extents of digestion.
Data from steer performance trials utilizing corn stalklage showed that liquid molasses supplements containing urea or urea plus corn steep liquor were inferior to natural protein supplements in terms of their effect on average daily gain and feed efficiency. It appears to be advantageous to feed corn gluten meal with low quality roughages, as higher levels of animal performance were noted.
Following these studies, we concluded that a ruminal BCFA deficiency is not the first-limiting factor affecting the performance of ruminants fed urea-supplemented low quality roughages. (Abstract shortened with permission of author.)
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