Abstract
Feed intake and average daily gain (ADG) in Nellore cattle were determined to calculate residual feed intake in two performance tests: first during the growth phase (RFIgrowth) and then during a measurement of the methane emission phase (RFImet). During the RFIgrowth test, 62 males and 56 females were classified as low-, medium-, and high-RFI. Enteric methane emission was measured in 46 animals; 23 males used for RFImet measurement plus 23 females (22 low-RFIgrowth and 24 high-RFIgrowth). Diet consisted of Brachiaria brizantha cv. Marandu hay (445 g/kg DM) and concentrate (555 g/kg DM). During the RFIgrowth and RFImet phases, DMI was lower in the animals with low RFI, with no difference in ADG. Residual feed intake was -0.359 and 0.367 kg DM/d for low- and high-RFI animals. Enteric methane emission (g/d, g/kg BW0.75 and g/kg ADG) did not differ between RFIgrowth classes. Enteric methane emission (g/d) was higher in high RFImet and lower in low RFImet males. Spearman correlations among traits obtained during both tests, which were high between metabolic BW (r = 0.959) and between DMI (r = 0.718), and zero between ADG (r = -0.062), resulted in moderate correlation between RFIgrowth and RFImet (r = 0.412). However, it is not possible to confirm that high-efficiency animals release less enteric methane, since different results were obtained when enteric methane was compared between the RFIgrowth and RFImet classes.
Highlights
Residual feed intake (RFI) is an attractive measure of feed efficiency, as it does not depend on body size, growth rate, or body composition measures (Durunna et al, 2012)
Enteric methane emission was measured in 46 animals; 23 males used for RFImet measurement plus females (22 low-RFIgrowth and high-RFIgrowth)
Fitzsimons et al (2013) offered grass silage to heifers and observed that both DMI and methane emission (g/d) were lower for low-RFI compared with high-RFI animals, and Jones et al (2011) reported that DMI was similar between divergent RFI groups and that methane emission was similar when animals grazed low-quality pastures but were lower for lowRFI compared with high-RFI animals when grazing highquality pastures
Summary
Residual feed intake (RFI) is an attractive measure of feed efficiency, as it does not depend on body size, growth rate, or body composition measures (Durunna et al, 2012). Studies have shown that selection of animals for low RFI (high feed efficiency) reduces methane emissions in cattle (Nkrumah et al, 2006; Hegarty et al, 2007; Fitzsimons et al, 2013). There are inconsistencies in relation to differences in feed intake and corresponding methane emissions between low- and high-RFI animals. The conflicting observations regarding the variation in methane emission of high- and low-efficiency animals between studies suggest that selection of cattle for increasing feed efficiency does not necessarily result in a reduction in methane emission (Freetly and BrownBrandl, 2013). To date, published studies relating RFI and methane emission are limited to Bos taurus cattle, and little information is available on Bos indicus cattle
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