Ureumammonisering van koring-, hawer- en garsstrooi en hawerhooi. 2. Benutting deur skape

Author: A.A. Brand, S.W.P. Cloete, F. Franck en J. Coetzee
Year: 1989
Issue: 1
Volume: 19
Page: 11 - 18

Urea ammoniation of wheat, oat and barley straw and oat hay. 2. Utilization by sheep.

  Wheat, oat and barley straw, as well as oat hay were ammoniated, using 55 g urea and 400 g moisture kg·1 roughage for a treatment period of 8 weeks. Nutritional values of the treated roughages were subsequently determined in metabolic studies on sheep, involving a voluntary intake and digestibility trial, nitrogen balance, blood and rumen parameters, a rate of passage and an in situ crude protein (CP) degradability study. The voluntary intake of treated oat hay was higher (P 0,05) than that of treated oat straw, and tended to be higher than that of treated wheat straw (P = 0,06) and barley straw (P = 0,08). Little variation regarding DM and OM digestibility existed between the diets. Cell wall and hemicellulose digestibility of treated oat hay was lower than that of the other roughages, possibly due to the substitution effect and/or the depression of cellulolytic activity in the rumen at the observed lower pH levels. The rate of passage of treated wheat, oat and barley straw was slower (P 0,05) than that of treated oat hay by 46%, 26% and 25% respectively. The rate of passage of treated wheat straw was slower (P 0,05) than that of barley and oat straw. The higher (P 0,01) CP content and apparent digestibility of treated oat hay was also reflected in higher (P 0,05) rumen ammonia and plasma urea levels compared to the other roughages. CP digestibility of treated wheat straw was substantially lower (P 0,01) than that of oat or barley roughages, partially cancelling out the advantage of a higher apparent CP digestibility. This observation suggests that a lack of energy probably inhibited efficient protein synthesis, resulting in excess N being excreted in the urine. The N-balance obtained when feeding treated oat hay (1,4 g N day-1) was nevertheless higher (P 0,01) than that of the negative N-balance values observed when treated wheat straw (-1,3 g N day-l) and oat straw (-1,1 g N day-1) were fed. CP-degradation studies suggested that the degradable CP content of treated wheat, oat and barley straw consisted almost entirely of water-soluble NPN compounds, highly susceptible to rumen degradation. The remaining CP was virtually undegradable in the rumen, and likely to be of very limited nutritional value.


Keywords: in vivo digestibility, nitrogen balance, rate of passage protein degradation, Urea-ammoniation, voluntarily intake
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