Regulation of feed efficiency in dairy cattle.

Abstract

Abstract The efficiency with which dairy cows convert feed to milk impacts farm profitability and environmental stewardship. Thus, feed efficiency is a particularly critical trait to the dairy industry as feed costs increase. Feed efficiency is a complex trait influenced by many components, including milk output, nutrient intake, body weight and body weight change. Recent studies show that feed efficiency is low to moderately heritable, indicating it should respond to genetic selection. Progress is being made towards understanding the genetic regulation of feed efficiency, estimation of genomic breeding values and incorporation of feed efficiency into multi-trait selection programmes. However, underlying biological processes that contribute to variation in feed efficiency are poorly understood, particularly in lactating dairy cattle. Selection experiments in beef cattle, pigs, chickens and mice demonstrate that feed efficiency can be altered by selection. Heat production, activity or feeding behaviour, digestibility, muscle turnover and mitochondrial function are associated with variation in feed efficiency in many of these selection lines, but data from lactating dairy cows are currently lacking. A more detailed understanding of underlying biological processes and their relative importance to variation in feed efficiency is crucial for the development of novel strategies to further improve feed efficiency in dairy cattle. The objective of this review is to summarize our current understanding of the genetic and biological regulation of feed efficiency in lactating dairy cows. Insights from the evaluation of feed efficiency in beef cattle and other species are also considered.