Assessment of methane emission traits in ewes using a laser methane detector: genetic parameters and impact on lamb weaning performance.

The aim of the present study was to derive individual methane (CH4) emissions in ewes separated in CH4 respiration and eructation traits. The generated longitudinal CH4 data structure was used to estimate phenotypic and genetic relationships between ewe CH4 records and energy efficiency indicator traits from same ewes as well as from their lambs (intergenerational perspective). In this regard, we recorded CH4 emissions via mobile laser methane detector (LMD) technique, body weight (EBW), backfat thickness (BFT) and body condition score (BCS) from 330 ewes (253 Merinoland (ML), 77 Rhon sheep (RH)) and their 629 lambs (478 ML, 151 RH). The interval between repeated measurements (for ewe traits and lamb body weight (LBW)) was 3 weeks during lactation. For methane concentration (mu L L-1) determinations in the exhaled air, we considered short time measurements (3 min). Afterwards, CH4 emissions were portioned into a respiration and eructation fraction, based on a double normal distribution. Data preparation enabled the following CH4 trait definitions: mean CH4 concentration during respiration and eructation (CH4r+e), mean CH4 concentration during respiration (CH4r), mean CH4 concentration during eructation (CH4e), sum of CH4 concentrations per minute during respiration (CH4rsum), sum of CH4 concentrations per minute during eructation (CH4esum), maximal CH4 concentration during respiration (CH4rmax), maximal CH4 concentration during eructation (CH4emax), and eructation events per minute (CH4event). Large levels of ewe CH4 emissions representing energy losses were significantly associated with lower LBW ( P<0 :05), lower EBW ( P<0 :01) and lower BFT ( P<0 :05). For genetic parameter estimations, we applied single- and multiple-trait animal models. Heritabilities and additive genetic variances for CH4 traits were small, i.e., heritabilities in the range from <0.01 (CH4r+e, CH4r, CH4rmax, CH4esum) to 0.03 (CH4rsum). We estimated negative genetic correlations between CH4 traits and EBW in the range from 0.44 (CH4r+e) to 0.05 (CH4rsum). Most of the CH4 traits were genetically negatively correlated with BCS ( 0.81 for CH4esum) and with BFT ( 0.72 for CH4emax), indicating same genetic mechanisms for CH4 output and energy efficiency indicators. Addressing the intergenerational aspect, genetic correlations between CH4 emissions from ewes and LBW ranged between -0.35 (CH4r+e) and 0.01 (CH4rsum, CH4rmax), indicating that breeding on reduced CH4 emissions (especially eructation traits) contribute to genetic improvements in lamb weaning performance.