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The use of faecal nitrogen as an index for estimating the consumption of herbage by grazing animals

Published online by Cambridge University Press:  27 March 2009

G. W. Arnold  and
M. L. Dudzinski
G. W. Arnold
Affiliation:
Division of Plant Industry, C.S.I.R.O., Canberra, A.C.T.
M. L. Dudzinski
Affiliation:
Division of Mathematical Statistics, C.S.I.R.O., Canberra, A.C.T.
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Extract

Data from thirty-five digestibility trials with sheep in metabolism cages were used to investigate statistically the relationships between organic matter intake (I), faecal organic matter output (F), and the nitrogen concentration in faecal organic matter (N).

The data fell easily into groups due to botanical or seasonal differences in the feed. These groups of data were homogeneous and provided highly significant linear equations of the forms I = bF + cFN and I = a + cFN. When compared these groups of data sometimes showed differences in slope, position or both. A quadratic expression

I = bF + cFN + dFN2

was found to accommodate a majority of the data but to be less precise than I = a + cFN.

A further expression incorporating N as an independent variable was also examined,

I = a + cFN2 + eN.

This expression, although far from being universally adequate, proved to be generally better than existing formulae. When applied to the data of Greenhalgh et. al. (1960), it substantially reduced heterogeneity between data for spring and data for summer pastures.

Causes of variation in the relationship between organic-matter intake and nitrogen in faeces, and some of the hazards of extrapolation from empirical regression relations, are discussed.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 61 , Issue 1 , August 1963 , pp. 33 - 43
Copyright
Copyright © Cambridge University Press 1963

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