Ammoniation is one method whereby the nutritional value of cereal straws may be increased, It is important if the use of ammonia is to be optimised under a wide range of conditions that the underlying mechanisms of its effect on straw digestion are understood.

Near infra-red reflectance spectroscopy (NIR) is now widely used to predict many nutritional characteristics of forages. However, this predictive approach requires the availability of large calibration sample sets with the parameter to be predicted already determined by traditional means. The technique of mathematically subtracting spectra one from another (difference spectra) to assess changes in straws during digestion and after ammoniation has been reported by Barton et al (1986) and Barnes (1988) respectively. This approach whilst requiring no pre-calibration has so far lacked good definition and has only been used qualitatively.

The purpose of the present work was to assess the ability of new mathematical treatments of the NIR spectra before subtraction to increase definition and yield quantitative data on any observed changes.