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Using residual feed intake as a tool to improve dairy feed efficiency
The efficiency of converting feed to milk has has more than doubled over the past century largely as the indirect result of increased milk per cow. In the future, we must begin to focus directly on increased milk per unit feed. Feed inputs are not routinely measured in individuals, so the feed efficiency phenotype for most cows is not known. Genomic selection should help overcome this problem as a reference population of animals with both phenotypic and genotypic data can be used to develop models of predicting genetic merit from genotype. Residual feed intake (RFI) is a tool to quantify feed efficiency independent of production level, body weight (BW), or BW change. A cow with negative RFI is more efficient than her cohorts because she has lower maintenance requirements, digests feed more efficiently, or uses digested feed more efficiently for maintenance, gain, or milk. Recent work in our USDA NIFA project suggests the heritability of RFI in lactating cows is ~15%. Moreover, we have found some genetic loci that seem related to the efficiency trait and may help explain differences in efficiency. We also found that RFI of cows when fed high starch vs high soyhull diets is highly correlated, indicating that efficiency for a cow is repeatable across diets. Others have reported that RFI is a repeatable trait across stage of lactation. Moreover, differences in digestbility might account for as much as 30% of the change in RFI amongst cows. Body temperature also seems correlated to RFI. Future efforts to find efficient cows and examine genomic relationships should help us achieve continued improvements of feed efficiency. We appreciate support from the Agriculture and food Research Initiative Competitive Grant no. 2011-68004-30340.
Keywords: dairy cattle, feed efficiency, genomics