Cellulase vs rumen fluid for in vitro digestibility of mixed diets

Abstract

Nutritional studies frequently require an estimate of animal diet digestibility, but current in vitro techniques require costly fistulated animals, and variation in rumen fluid activity often results in poor precision. Hoping to find a more precise, yet cheaper, alternative, we examined estimates of organic matter digestibility of cattle diets based on a cellulase technique and compared them to those based on in vitro digestions. Diets were determined using microhistological analysis of native range forages, weeping lovegrass, and wheat pasture from May 1985 through May 1986. The 2 techniques offered estimates that were highly correlated (r = 0.91 to 0.94) when diets consisted of cool-season grasses and forbs. Digestibility estimates of diets by the 2 techniques for predominantly warm-season species on native range were less well correlated (r = 0.81 to 0.86). Agreement between the 2 techniques was relatively poor for mixed species diets from weeping lovegrass pastures (r = 0.48). We conclude that in vitro digestion using cellulase offers a promising approach for assessing diet quality, particularly with diets dominated by graminoids.