Phenotypic association among performance, feed efficiency and methane emission traits in Nellore cattle

Enteric methane (CH(4)) emissions are a natural process in ruminants and can result in up to 12% of energy losses. Hence, decreasing enteric CH(4) production constitutes an important step towards improving the feed efficiency of Brazilian cattle herds. The aim of this study was to evaluate the relationship between performance, residual feed intake (RFI), and enteric CH(4) emission in growing Nellore cattle (Bos indicus). Performance, RFI and CH(4) emission data were obtained from 489 animals participating in selection programs (mid-test age and body weight: 414±159 days and 356±135 kg, respectively) that were evaluated in 12 performance tests carried out in individual pens (n = 95) or collective paddocks (n = 394) equipped with electronic feed bunks. The sulfur hexafluoride tracer gas technique was used to measure daily CH(4) emissions. The following variables were estimated: CH(4) emission rate (g/day), residual methane emission and emission expressed per mid-test body weight, metabolic body weight, dry matter intake (CH(4)/DMI), average daily gain, and ingested gross energy (CH(4)/GE). Animals classified as negative RFI (RFI<0), i.e., more efficient animals, consumed less dry matter (P <0.0001) and emitted less g CH(4)/day (P = 0.0022) than positive RFI animals (RFI>0). Nonetheless, more efficient animals emitted more CH(4)/DMI and CH(4)/GE (P < 0.0001), suggesting that the difference in daily intake between animals is a determinant factor for the difference in daily enteric CH(4) emissions. In addition, animals classified as negative RFI emitted less CH(4) per kg mid-test weight and metabolic weight (P = 0.0096 and P = 0.0033, respectively), i.e., most efficient animals could emit less CH(4) per kg of carcass. In conclusion, more efficient animals produced less methane when expressed as g/day and per kg mid-test weight than less efficient animals, suggesting lower emissions per kg of carcass produced. However, it is not possible to state that feed efficiency has a direct effect on enteric CH(4) emissions since emissions per kg of consumed dry matter and the percentage of gross energy lost as CH(4) are higher for more efficient animals.