The influence of the Maillard reaction upon the nutritive value of fibrous feeds

Abstract

Heating forages and feeds will generate Maillard products of low digestibility which are signalled by a rise in the nitrogen (N) content of acid-detergent fibre (ADIN). Two sets of data from digestion trials with sheep were mathematically examined by the methods of Lucas. The first set, taken from studies of distillers grains, exhibited some digestibility of ADIN, but showed a high positive correlation between fecal N and ADIN and a negative one with nitrogen digestibility and ADIN. Earlier conclusions as to the ineffectiveness of ADIN as a method of evaluation are refuted. The second set of data referred to ammoniated forages with their untreated controls. The treated forages are shown to contain soluble indigestible organic matter and nitrogen in the ratio of 8.83:1 ± 0.11, agreeing with the expected composition of Maillard polymers. With these forages the fecal N loss considerably exceeds the ADIN estimate, in contrast to the distillers grains. The excess is due in part to the presence of indigestible soluble non-ammonia nitrogen (SNAN) that is associated with a soluble indigestible organic fraction. The existence of indigestible soluble N and organic matter constitutes the basis for severe criticism of gravimetric laboratory procedures, including nylon bags, used in evaluating treated forages and feeds, as these procedures will fail to recover the soluble indigestible components and thus over-value treated forages. The use of ADIN as a marker for heat damage and the Maillard reaction is validated, but in treated forages an additional examination for absorbances at 280 and 320 nm, and SNAN is recommended.