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 ([Formula: see text]) emissions in ewes separated in [Formula: see text] respiration and eructation traits. The generated longitudinal [Formula: see text] data structure was used to estimate phenotypic and genetic relationships between ewe [Formula: see text] records and energy efficiency indicator traits from same ewes as well as from their lambs (intergenerational perspective). In this regard, we recorded [Formula: see text] 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 Rhön 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 ([Formula: see text] L L [Formula: see text]) determinations in the exhaled air, we considered short time measurements (3 min). Afterwards, [Formula: see text] emissions were portioned into a respiration and eructation fraction, based on a double normal distribution. Data preparation enabled the following [Formula: see text] trait definitions: mean [Formula: see text] concentration during respiration and eructation ([Formula: see text]), mean [Formula: see text] concentration during respiration ([Formula: see text]), mean [Formula: see text] concentration during eructation ([Formula: see text]), sum of [Formula: see text] concentrations per minute during respiration ([Formula: see text]), sum of [Formula: see text] concentrations per minute during eructation ([Formula: see text]), maximal [Formula: see text] concentration during respiration ([Formula: see text]), maximal [Formula: see text] concentration during eructation ([Formula: see text]), and eructation events per minute ([Formula: see text]). Large levels of ewe [Formula: see text] emissions representing energy losses were significantly associated with lower LBW ([Formula: see text]), lower EBW ([Formula: see text]) and lower BFT ([Formula: see text]). For genetic parameter estimations, we applied single- and multiple-trait animal models. Heritabilities and additive genetic variances for [Formula: see text] traits were small, i.e., heritabilities in the range from <0.01 ([Formula: see text] , [Formula: see text] , [Formula: see text] , [Formula: see text]) to 0.03 ([Formula: see text]). We estimated negative genetic correlations between [Formula: see text] traits and EBW in the range from [Formula: see text] 0.44 ([Formula: see text]) to [Formula: see text] 0.05 ([Formula: see text]). Most of the [Formula: see text] traits were genetically negatively correlated with BCS ([Formula: see text] 0.81 for [Formula: see text]) and with BFT ([Formula: see text] 0.72 for [Formula: see text]), indicating same genetic mechanisms for [Formula: see text] output and energy efficiency indicators. Addressing the intergenerational aspect, genetic correlations between [Formula: see text] emissions from ewes and LBW ranged between [Formula: see text] 0.35 ([Formula: see text]) and 0.01 ([Formula: see text] , [Formula: see text]), indicating that breeding on reduced [Formula: see text] emissions (especially eructation traits) contribute to genetic improvements in lamb weaning performance.