ABSTRACT
The aim of the present study was to derive individual methane ( CH 4 ) emissions in ewes separated in CH 4 respiration and eructation traits. The generated longitudinal CH 4 data structure was used to estimate phenotypic and genetic relationships between ewe CH 4 records and energy efficiency indicator traits from same ewes as well as from their lambs (intergenerational perspective). In this regard, we recorded CH 4 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 (478â¯ML, 151â¯RH). The interval between repeated measurements (for ewe traits and lamb body weight (LBW)) was 3 weeks during lactation. For methane concentration ( µ Lâ¯L - 1 ) determinations in the exhaled air, we considered short time measurements (3â¯min). Afterwards, CH 4 emissions were portioned into a respiration and eructation fraction, based on a double normal distribution. Data preparation enabled the following CH 4 trait definitions: mean CH 4 concentration during respiration and eructation ( CH 4 r + e ), mean CH 4 concentration during respiration ( CH 4 r ), mean CH 4 concentration during eructation ( CH 4 e ), sum of CH 4 concentrations per minute during respiration ( CH 4 rsum ), sum of CH 4 concentrations per minute during eructation ( CH 4 esum ), maximal CH 4 concentration during respiration ( CH 4 rmax ), maximal CH 4 concentration during eructation ( CH 4 emax ), and eructation events per minute ( CH 4 event ). Large levels of ewe CH 4 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 CH 4 traits were small, i.e., heritabilities in the range from <0.01 ( CH 4 r + e , CH 4 r , CH 4 rmax , CH 4 esum ) to 0.03 ( CH 4 rsum ). We estimated negative genetic correlations between CH 4 traits and EBW in the range from - 0.44 ( CH 4 r + e ) to - 0.05 ( CH 4 rsum ). Most of the CH 4 traits were genetically negatively correlated with BCS ( - 0.81 for CH 4 esum ) and with BFT ( - 0.72 for CH 4 emax ), indicating same genetic mechanisms for CH 4 output and energy efficiency indicators. Addressing the intergenerational aspect, genetic correlations between CH 4 emissions from ewes and LBW ranged between - 0.35 ( CH 4 r + e ) and 0.01 ( CH 4 rsum , CH 4 rmax ), indicating that breeding on reduced CH 4 emissions (especially eructation traits) contribute to genetic improvements in lamb weaning performance.
