Modelling of digestive interactions and methane production in ruminants

Abstract

The adequacy of feed allowances to animal requirements, and the accurate prediction of their responses to practical rationing systems require the quantification of the possible digestive interactions (non-additive effect of potential values of feeds within a diet). Two data bases were built separately to model the specific effects of feeding level (FL) and proportion of concentrate (PCO) on dietary organic matter digestibility (OMd), energy loss in faeces, urine and methane emission in order to estimate the impact on energy values. The first data set, BOVIDIG, included 571 papers (1482 treatments) on OMd with cattle, and the second one, RUMENER, 151 papers (1021 treatments) on calorimetric experiments with cattle, sheep and goats.

The results from these sets globally fitted together : an increase in FL decreased OMd, or energy digestibility, which was partly counterbalanced by lower energy losses as urine and methane. An increase in PCO increased OMd. This was more and more important when the associated forage was of low digestibility or the FL was low. CH4 losses were curvilinearly linked with PCO. These results show that the assessement of energy impact of digestive interaction cannot be accurately determined from OMd only.

The proposed equations allowed the estimation, with simple dietary criteria (FL or PCO), of corrections for the calculation of energy values of diets fed to several ruminant species. These corrections were slightly higher than the present ones proposed by the INRA systems for medium diets, but are equal for the intensive diets with high values of FL and PCO.