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Nutritional Significance of Soluble Nitrogen in Dietary Proteins for Ruminants¹

Iowa Agricultural and Home Economics Experiment Station, Ames

Abstract

The nutritional significance of soluble nitrogen in protein feeds for ruminants was investigated in studies of its relationship to in vitro rumen ammonia production, in vitro cellulose degradation, in vivo digestibility and nitrogen balance and lamb performance. No definite relation between nitrogen solubility and rate of ammonia production was evident; however, nitrogen solubility in rumen fluid was generally more indicative of ammonia formed than solubility in dilute soduim hydroxide or distilled water. The influence of a number of feed proteins on cellulose digestion in the artificial rumen was comparable to the extent of microbial attack of the proteins as measured by ammonia formation. Corn gluten meal and heat treated soybean oil meal (110° C. for 24 hours) were particularly low in soluble nitrogen, only slowly converted to ammonia by rumen microbial degradation and poor sources of nitrogen for in vitro cellulose digestion by washed suspensions of rumen microorganisms. Solvent processed soybean oil meal, linseed oil meal, casein and purified soy protein were rapidly converted to ammonia and were good sources of nitrogen for in vitro cellulose digestion.

Lambs fed low quality roughage rations, containing either regular or heated soybean oil meals at 7, 10 and 13% protein levels, performed equally well. Both regular and heated soybean oil meals and linseed oil meal were similar in promoting feed consumption and growth when fed to lambs consuming semi-purified rations and were superior to corn gluten meal. No apparent differences in protein digestibility and nitrogen retention were detected when lambs were fed corn gluten meal or regular soybean oil meal as protein sources in the semi-purified ration. Cellulose digested by lambs fed regular soybean oil meal was significantly higher than cellulose digested by lambs fed corn gluten meal.

Additions of lysine and methionine to corn gluten meal appeared to be of little value; however, the addition of urea to corn gluten meal markedly improved its value in stimulating in vitro rumen cellulose digestion and in increasing feed consumption and gains in lambs.

¹ Journal Paper No. J-4431 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1208.

² Present Address: Department of Animal Science, University of Kentucky, Lexington, Ky.