Bias when predicting crude protein dry matter digestibility and voluntary intake of tropical grasses by near ir reflectance

Minson, D.J.; Butler, K.L.; Grummitt, N.; Law, D.P.

Animal Feed Science and Technology 9(3): 221-237


ISSN/ISBN: 0377-8401
Accession: 004822795

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A study was made of the bias (non-random error) of regressions for predicting crude protein (CP) content, dry matter digestibility (DMD) in vivo and voluntary intake (VI) of forage from its near-IR reflectance (NIRR) properties measured at 19 wavelengths. The regression was derived from 97 samples including 6 tropical grasses [Chloris gayana, Digitaria decumbens, Panicum maximum var. trichoglume, Paspalum dilatatum, Pennisetum clandestinum and Setaria sphacelata], leaf and stem fractions, pelleted and chopped forms and regrowths varying from 28-150 days. When nutritive-value is predicted by NIRR, the estimates may often be biased according to the grass species, plant part or physical form of the sample tested and the pattern of bias may be complicated. To obtain accurate predictions from NIRR full account must be taken of this bias. This might be achieved by correcting the nutritive value estimates made from an NIRR regression, based on a large number of feed types, by addition of the bias associated with the feed type being estimated.