Enteric methane (CH4) emissions are a natural process in ruminants and can result in up to 12% of energy losses. Hence, decreasing enteric CH4 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 CH4 emission in growing Nellore cattle (Bos indicus). Performance, RFI and CH4 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 CH4 emissions. The following variables were estimated: CH4 emission rate (g/day), residual methane emission and emission expressed per mid-test body weight, metabolic body weight, dry matter intake (CH4/DMI), average daily gain, and ingested gross energy (CH4/GE). Animals classified as negative RFI (RFI<0), i.e., more efficient animals, consumed less dry matter (P <0.0001) and emitted less g CH4/day (P = 0.0022) than positive RFI animals (RFI>0). Nonetheless, more efficient animals emitted more CH4/DMI and CH4/GE (P < 0.0001), suggesting that the difference in daily intake between animals is a determinant factor for the difference in daily enteric CH4 emissions. In addition, animals classified as negative RFI emitted less CH4 per kg mid-test weight and metabolic weight (P = 0.0096 and P = 0.0033, respectively), i.e., most efficient animals could emit less CH4 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 CH4 emissions since emissions per kg of consumed dry matter and the percentage of gross energy lost as CH4 are higher for more efficient animals.

Residual feed intake (RFI) detects animals that consume less dry matter (DM) adjusted for production and maintenance, and differences in the digestibility may explain differences in RFI among contemporaneous cattle. The aim of the study was to evaluate the relationship between digestibility, RFI, and enteric methane emission in growing Nellore cattle (Bos indicus) divergently classified based on RFI phenotypes and also on RFI breeding value. One hundred twenty-two Nellore cattle submitted to performance testing in two test groups (249±4.33 days of age, and 332±4.22 days of age at the beginning of the test) were classified based on residual feed intake (RFI). A sample of 80 animals classified as low RFI (-0.748±0.076 kg DM/day) or high RFI (0.775±0.075 kg DM/day) was evaluated regarding feed compounds digestibility, fecal excretion, and enteric methane (CH4, g/day) emission. There was no significant difference in feed compounds digestibility between the most and least efficient animals. However, DM intake (6.92 vs. 8.66 kg DM/day) and feed conversion (7.93 vs. 9.42 kg/kg) were lower in low RFI animals. On average, low RFI animals emitted 14.3 g less CH4 per day (174 vs. 188 g CH4/day; P=0.02); however, CH4 emission expressed as g/kg DM intake (23.1 vs. 20.1; P<0.01) and the percentage of gross energy intake lost as CH4 (8.13 vs. 7.08%; P<0.01) were higher in these animals. There are clear benefits (economic and environmental) of using more feed efficient animals in the beef production chain, i.e., animals that exhibit lower feed intake, lower fecal excretion and lower enteric methane emission without differences in weight gain or body weight. Variations in feed efficiency among them cannot be explained by differences in DM or feed compounds digestibility. More efficient animals emit less enteric methane (CH4, g/day) than less efficient animals, probably as a result of lower DMI.