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