Feed Efficiency: towards a better understanding of it as a key element of sustainable livestock systems

Abstract

Feed efficiency is an increasingly important driver for livestock systems, as it contributes not only to farm economy but also to sustainability. Feed efficiency can be studied at different levels, in this review we focus on the animal level and on variation between individuals. The review starts by considering the different definitions of efficiency with two broad classes of definition, those based on ratios of products to intake and those based on identifying residuals relative to average performance. Among the latter, the residual feed intake method is the most widely used and is accordingly described. Subsequent sections deal with the underlying biological mechanisms. With respect to digestive efficiency, retention time in the rumen and the microbial population are key. With respect to metabolic efficiency, the mechanisms involved in heat production, mitochondrial respiration, protein turnover, etc., as well as the influence of body reserves, are highlighted. The challenges and opportunities for generating sufficient phenotypic records to allow genetic selection for feed efficiency are discussed in the context of the opportunities provided by the advent of on-farm technologies. Finally, the links between efficiency and resilience are explored, as there are differences when comparing short- and long-term evaluations, with the latter being especially important for sustainability.