Genotype differences and their impact on digestive tract function of ruminants: a review

Abstract

Physiological factors that cause between-animal variation in digestive function were evaluated as possible selection traits to achieve improved growth and feed-use efficiency by ruminants. Comparative studies of the digestive function of Bos taurus and Bos indicus cattle, as well as selection lines of dairy cows and sheep were reviewed to determine the scope and significance of diversity in rumen function. All investigations indicated differences in digesta retention time between genotypes. Therefore, the digesta retention time, either the total mean retention time (MRT) or the ruminal retention time (RRT), may be suitable selection traits for improving animal productivity.Differences in MRT and RRT may affect animal productivity by changing the number and diversity of rumen microorganisms, the volatile fatty acid (VFA) pattern, the composition and maintenance energy requirement of the microbes, and thus the energetic efficiency of microbial growth. Further effects associated with changed RRT include a possible reduction in methane production and increased long-chain fatty acid (LCFA) synthesis in the rumen, which may consequently affect the energetic efficiency of the ruminant. It is concluded that despite strong evidence of genetic diversity in gut function, the central role of MRT and RRT in digestive metabolism has not been fully appreciated, nor have their contribution to productivity differences among livestock of similar or divergent genotypes been adequately investigated.