Methane profiles assessment in growing Simmental bulls with divergent feed efficiency.

There is a considerable interest in animal genetic selection to reduce the livestock sector's environmental impact, representing a permanent mitigation strategy. The methane (CH4) total production was correlated to animal efficiency in different studies on dairy cows and steers. Several methods for CH4 quantification have been proposed, such as the laser methane detector (LMD), a reliable, cheap and easy alternative to gold standard methods when CH4 is assessed in vivo. The aim of this study was to characterize the CH4 profile of growing Simmental bulls collected using an LMD and to relate the CH4 production, as total or expressed in different ways, with the feed efficiency. For this purpose, 1,164 CH4 profiles collected from 194 Italian Simmental bulls were analyzed to evaluate their main characteristics as peak type, number, and intensity. Subjects were divided into two feed efficiency groups, high (n = 50) and low (n = 49) efficiency, based on their residual feed intake (RFI), and the main traits of CH4 production were compared. The total number of peaks observed did not differ between the two groups, with a similar average concentration (51.9 ppm-m). Likewise, the eructation peaks had shown a similar trend with no differences detected in total number and concentration. The CH4 profile converted to g/day has shown similar values between groups. Instead, the CH4 yield (g/kg DMI) was higher in highly efficient animals when compared to low-efficient animals (30.4 vs. 25.3 g/kg). Similarly, the residual methane emission (RME), calculated as the difference between the measured CH4 and that estimated, was higher in the high efficiency group (74.7 vs. 35.7 g/day). Contrary to the common idea that efficient animals produce less CH4, results indicate that total production may be similar across animals with different RFI. Instead, values could be unfavorable for highly efficient animals when CH4 yield or RME are considered.