Hot topic: Selecting cattle for low residual feed intake did not affect daily methane production but increased methane yield

摘要

Reducing enteric methane (CH4) production andimproving feed conversion efficiency of dairy cows isof high importance. Residual feed intake (RFI) is onemeasure of feed efficiency, with low RFI animals beingmore efficient in feed conversion. Enteric CH4 is animportant source of digestible energy loss in ruminantsand, because research in beef cattle has reported a positiverelationship between RFI and daily CH4 production,we hypothesized that low RFI dairy heifers, whichare more feed efficient, would produce less CH4/d. Wemeasured the daily methane production (g of CH4/d),methane yield [g of CH4/kg of dry matter intake (DMI)],and CH4 per kilogram of body weight (BW) gain for 56heifers (20–22 mo old) in a 2 × 2 factorial arrangement:factors included 2 breeds (Holstein-Friesian andJersey; n = 28/breed), with equal numbers of animalspreviously determined as being either high [+2.0 kg ofdry matter (DM)/d] or low RFI (−2.1 kg of DM/d; n= 28/RFI category). All heifers were commingled andoffered unrestricted access to the same diet of driedalfalfa cubes. Between RFI categories, heifers did notdiffer in BW or BW gain but low RFI heifers had 9.3and 10.6% lower DMI and DMI/kg of BW, respectively,than high RFI heifers. Similarly, RFI category did notaffect CH4/d or CH4/kg of BWg, but CH4/kg of DMIwas higher in low RFI heifers because of their lowerDMI. These results might reflect more complete digestionof ingested feed in the more efficient, low RFIheifers, consistent with previous reports of greater apparentdigestibility of organic matter. Holstein-Friesianheifers were heavier and consumed more total DM thanJersey heifers, but breed did not affect DMI/kg of BWor BWg. Jersey heifers produced less CH4/d, but notCH4/kg of DMI or CH4/kg of BWg. We detected no interactionbetween breed and RFI category in any of thevariables measured. In conclusion, differences in RFI indairy heifers did not affect daily CH4 production (g/d);however, low RFI heifers had a greater CH4 yield (g/kgof DMI) on a high forage diet.