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Development of near infrared analysis of faeces to estimate non-grass proportions in diets selected by cattle grazing tropical pastures

Coates, D.B. and Dixon, R.M. (2008) Development of near infrared analysis of faeces to estimate non-grass proportions in diets selected by cattle grazing tropical pastures. Journal of near Infrared Spectroscopy, 16 (5). pp. 471-480.

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Article Link(s): http://dx.doi.org/10.1255/jnirs.815

Publisher URL: http://www.impublications.com/nir/page/nir

Abstract

Grass (monocots) and non-grass (dicots) proportions in ruminant diets are important nutritionally because the non-grasses are usually higher in nutritive value, particularly protein, than the grasses, especially in tropical pastures. For ruminants grazing tropical pastures where the grasses are C-4 species and most non-grasses are C-3 species, the ratio of C-13/C-12 in diet and faeces, measured as delta C-13 parts per thousand, is proportional to dietary non-grass%. This paper describes the development of a faecal near infrared (NIR) spectroscopy calibration equation for predicting faecal delta C-13 from which dietary grass and non-grass proportions can be calculated. Calibration development used cattle faeces derived from diets containing only C-3 non-grass and C-4 grass components, and a series of expansion and validation steps was employed to develop robustness and predictive reliability. The final calibration equation contained 1637 samples and faecal delta C-13 range (parts per thousand) of [12.27]-[27.65]. Calibration statistics were: standard error of calibration (SEC) of 0.78, standard error of cross-validation (SECV) of 0.80, standard deviation (SD) of reference values of 3.11 and R-2 of 0.94. Validation statistics for the final calibration equation applied to 60 samples were: standard error of prediction (SEP) of 0.87, bias of -0.15, R-2 of 0.92 and RPD of 3.16. The calibration equation was also tested on faeces from diets containing C-4 non-grass species or temperate C-3 grass species. Faecal delta C-13 predictions indicated that the spectral basis of the calibration was not related to C-13/C-12 ratios per se but to consistent differences between grasses and non-grasses in chemical composition and that the differences were modified by photosynthetic pathway. Thus, although the calibration equation could not be used to make valid faecal delta C-13 predictions when the diet contained either C-3 grass or C-4 non-grass, it could be used to make useful estimates of dietary non-grass proportions. It could also be ut :sed to make useful estimates of non-grass in mixed C-3 grass/non-grass diets by applying a modified formula to calculate non-grass from predicted faecal delta C-13. The development of a robust faecal-NIR calibration equation for estimating non-grass proportions in the diets of grazing cattle demonstrated a novel and useful application of NIR spectroscopy in agriculture.

Item Type:Article
Corporate Creators:Animal Science
Additional Information:© NIR Publications.
Keywords:Faecal NIR spectroscopy; diet composition; non-grass; cattle, northern Australia; fecal NIRS equations; in-vivo digestibility; reflectance spectroscopy; goats; c-13.
Subjects:Technology > Technology (General) > Spectroscopy > NIR (Near Infrared)
Animal culture > Rangelands. Range management. Grazing
Animal culture > Cattle
Animal culture > Feeds and feeding. Animal nutrition
Deposited On:14 Apr 2009 06:38
Last Modified:17 Jun 2011 01:06

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