Study on Several Factors Affecting the Estimate of Voluntary Intake in Grazing Animal by Chromogen-Cr_2O_3 Method

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  • クロモーゲン-Cr_2O_3法の各種問題点について
  • クロモーゲン Cr2O3ホウ ノ カクシュ モンダイテン ニ ツイテ

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In three seasons from spring to autumn (1970), this experiment was conducted to investigate the several factors affecting on the reliability of chromogen-chromic oxide ratio technique estimating the voluntary intake of grass and its digestibility of grazing steers. The pasture mainly consisted of the perennial ryegrass, and the growing stage of the grass differed in three seasons. The four experimental steers grazed on the pasture were given 15g of chromic oxide at 8:00 a.m. daily per head, during the experimental period. The analyses of chromogen and chromic oxide were performed with the feces sampled at 8:00 a.m. and 4:00 p.m. for three or five days after 7-day preliminary period. The chromogen concentration of grass sampled by the hand-clipping method was determined twice in each experimental period. The dry matter digestibility obtained by the method based on the fecal chromogen concentration was 74.4, 57.6 and 62.3% in three experimental period of spring, summer and autumn, respectively. The dry matter intaker calculated by the method based on the concentrations of two indicators (chromogen and chromic oxide) was 3.2, 1.9 and 2.0% of body weight of animal in three seasons in which the experiment was undertaken, respectively. It was considered that the low digestibilities in summer and autumn experiment were caused by low recovery rate of ingested grass chromogen, because the growing stages of summer and autumn grass were younger than spring grass which was late heading stage. The chromic oxide concentrations in feces sampled at 8:00 a.m. were apparently higher than in feces sampled at 4:00 p.m., in every sampling day. However, both concentrations of chromogen and chromic oxide excreted in feces varied considerably from day to day. From these results, it is suggested that greater accuracy of the estimates may be made by elongation of fecal sampling period and by corrective calculation for the imperfect recovery of ingested chromogen.

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