The Effects of Different Starch Sources and Protein on Site and the Extent of Nitrogen Digestion and Utilization in Steers

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  • デンプン源および蛋白質源の違いが去勢牛による窒素の消化管部位別消化と窒素出納に及ぼす影響
  • デンプンゲン オヨビ タンパクシツゲン ノ チガイ ガ キョセイ ウシ ニ ヨ

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Abstract

Four steers fitted with ruminal, duodenal and ileal cannulas were used in a 4×4 Latin square design, in order to investigate the effects of four combinations of starch and protein sources on nitrogen utilization in the digestive tracts and nitrogen balance. Starch sources were corn and barley; protein sources were soybean meal (SBM) and corngluten meal (CGM). Treatments were also arranged as 2×2 fractional. Steers (227kg body weight) were fed isonitrogenous (11% CP) diets of 50% hay and 50% concentrate, and provided with sufficient digestible energy to support a growth rate of 0.7kg/d. Microbial nitrogen flow to the duodenum was greater for barley than corn (P⟨0.05), but was not affected by protein sources. Total-and dietary- nitrogen flows to the duodenum, however, were greater for corn than barley and greater for CGM than SBM (P⟨0.01). Nitrogen disappearance from the small intestine increased linearly with increased nitrogen flow to the duodenum; thereby, small intestinal digestibility of nitrogen was not affected by starch and protein sources or by the different ratios of microbial and dietary nitrogens. A regression analysis between duodenal flow and small intestinal disappearance of nitrogen showed 77% true digestibility in the small intestine. Duodenal flow and intestinal disappearance of total essential amino acids did not differ between starch sources, but increased for CGM over SBM (P⟨0.05). No difference in lysine disappearance in the small intestine may result in a similar nitrogen retention among treatments despite different lysine content in duodenal digesta. A combination of corn and CGM seems to increase the amount of nitrogen recycled through the rumen, the small intestine and the liver.

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