Interpretive Summary: Association between residual feed intake and enteric methane emissions in Hereford steers
By: Jackie Walling
An article published in the January 2019 Issue of Translation Animal Science measured enteric methane emissions related to contrasting levels of residual feed intake (RFI) in a confined environment of Hereford steers. RFI is a heritable trait associated with methane production and measures how efficient animals convert feed to products. A low RFI indicates animals maintain their body condition consuming less food and therefore produce less emissions. This suggests selection for low RFI could help reduce methane emissions to the atmosphere.
There were 112 steers, from a three-year project to form a training population for genomic selection for RFI, underwent 70 days of RFI testing. Intake of a fully mixed ration fed twice daily was recorded with GrowSafe, an automated feeding system. Concluding the test, 18 steers (divided equally) with extreme RFI values (high = HRFI, low = LRFI) were chosen to continue diet for 20 days and undergo methane collection. Sulfur hexafluoride (SF6, a marker for gas emissions) tracer technique quantified methane emissions. SF6 was given to eight steers in each group leaving two controls. Collection containers for SF6 and enteric methane were placed in rooms for two consecutive 5-day periods. Exhaled gases were collected with two containers placed on each side of the animals’ heads. Then steers were grazed on pasture for 6-10 months, slaughtered at 500 kg, and DNA was extracted from a ruminal content sample to quantify methyl coenzyme-M reductase gene (mcrA), a marker measuring methanogens.
Results showed LRFI steers were more efficient than HRFI steers. LFRI had a higher feed rate meaning they consumed less, spent less time with their heads down, and had a 26.8% lower methane emission (RFI = -.78kg DMI/d) compared to HRFI (RFI = .83kg DMI/d) steers. No differences between the two groups existed for average meal size, number of meals, or average daily gain. Total methanogens were also similar with the average number of copies for mcrA gene not differing.
Highly efficient animals (low RFI) spent less energy on feeding activities leading to higher ingestion rates that did not appear to affect digestibility. Previous studies with varying dietary and management conditions reported varying associations between RFI and methane emissions questioning RFI use as a mitigation strategy. This study, however, showed a significant difference in methane emissions between LRFI and HRFI steers suggesting breeding selection for low RFI values could help reduce emissions. This could potentially be a long-term solution to help decrease livestock’s contribution to anthropogenic gas emissions. To further understand potential benefits of focusing on RFI, its association with the quantification of methanogen activity should addressed.
To read the full article, visit Translational Animal Science.