Abstract
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.
Highlights
Enteric methane (CH4) emission is a natural process in ruminants that can result in losses of 2 to 12% of the total energy consumed by the animal [1]
RFI: Residual feed intake; SEM: Standard error of the mean; CH4: Enteric methane emission; CH4/DMI: CH4 emission expressed per dry matter intake; CH4/ADG: CH4 emission expressed per average daily gain, CH4/MBW: CH4 emission expressed per mid-test body weight; CH4/BW0.75 = CH4 emission expressed per metabolic body weight; CH4Res: Residual CH4 emission; CH4/GE: % consumed gross energy lost as CH4
Performance, feed efficiency and methane emission traits in cattle consumed on average 13% less DM than animals classified as positive RFI; feed conversion (FC) and residual ADG higher for more efficient animals
Summary
Enteric methane (CH4) emission is a natural process in ruminants that can result in losses of 2 to 12% of the total energy consumed by the animal [1]. The higher the dry matter intake (DMI), the higher the daily enteric emissions of CH4 since a larger amount of substrate will be available for fermentation in the rumen and more hydrogen will be available for methanogenesis [8,9]. The use of more efficient animals may reduce enteric CH4 emissions proportionally to the lower feed intake [10]. It is unclear whether the differences in enteric CH4 emissions are due to the variation in digestive efficiency between negative and positive RFI animals or the result of from the lower DMI associated with negative RFI animals [11,12]
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