Some factors affecting apparent nitrogen digestibility of roughage diets fed to cattle

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Abstract
Published and unpublished results for apparent nitrogen digestibility from 107 digestibility trials with Zebu (Africander, Brahman and their crosses with British cattle) and British breeds of cattle were analysed by regression analyses to determine its relationship with dry matter intake and dietary nitrogen content.The linear regression of apparent nitrogen digestibility on the reciprocal of dietary nitrogen content was an adequate mathematical description of the relation (r = 0·92) and the addition of the reciprocal of nitrogen intake as an independent variable improved the description (r = 0·95) particularly for diets with a low nitrogen content. Both these equations have a physiological basis.Estimates of the true nitrogen digestibility and metabolic faecal nitrogen from the linear regression of apparent nitrogen digestibility on the reciprocal of dietary nitrogen content were 86·8% and 0·49 g/100 g dry-matter intake. Independent estimates of these parameters from a multiple regression of total faecal nitrogen on dry-matter intake and nitrogen intake were 88·7% and 0·46 g/100 g dry-matter intake. The analyses on the breeds suggested that the Zebu cattle may have a higher true digestibility and a lower metabolic faecal nitrogen than the British cattle, although the differences were small and could not be subjected to statistical tests.

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