Is apparent digestibility associated with residual feed intake and enteric methane emission in Nellore cattle?

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.