45 Effects of Genomic Residual Feed Intake on Performance, Feed Efficiency and Greenhouse Gas Emissions in Holstein Heifers

Abstract The objective of this study was to examine the differences in performance, feed efficiency, and greenhouse gas emissions Holstein heifers with divergent genomic residual intake (RFIg). (n = 55; initial BW 351 ± 64 kg) were classified as either low RFIg 29) or high 26) based on values determined from their breeding (Ecofeed index, STgenetics). Heifers blocked by RFIg, stratified assigned 1 2 pens, each equipped 4 electronic feedbunks (GrowSafe Systems), pen a GreenFeed real-time gaseous-exchange measurement system (GEM; C-Lock). fed corn-silage total mixed ration twice daily. Individual dry matter (DMI) collected for 84 d measured weekly. Phenotypic (RFIp) calculated regression DMI average daily gain (ADG) mid-test BW0.75. As only pens had GEM system, during 84-day rotated between two at 14 day intervals resulting group having three 14-day gaseous exchange periods. A time series analysis measurements, repeated measure period, fixed effect class random conducted. model used other response variables. There no final ADG RFIg; however, consumed 7.3% less (P < 0.05) per than counterparts. Consequently, exhibited more favorable RFIp, RFIp -0.188 0.211 kg/d heifers, respectively. period interactions > 0.10) measured. Low 7.7% methane (g/d) 6.1% carbon dioxide production However, yield (g methane/kg DMI) similar heifers. These results indicate that selection has potential identify cattle efficiency phenotypes. Additionally, provides opportunity produce fewer emissions. Further research is warranted into through indexes improve mitigate environmental impact production.