Abstract
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.
Highlights
Methane (CH4) is a by-product of microbial fermentation processes in ruminants (Henderson et al, 2015) and a potential greenhouse gas
We identified a high agreement between statistically defined eructation events and ewe eructation during trait recording
CH4 recording via laser methane detector (LMD) technique was successfully implemented in sheep under field conditions
Summary
Methane (CH4) is a by-product of microbial fermentation processes in ruminants (Henderson et al, 2015) and a potential greenhouse gas. CH4 emissions reflect an unused proportion of gross energy intake (Johnson and Ward, 1996; Baker, 1999). There is an increasing interest to breed animals with improved productivity and feed efficiency (i.e., feed intake in relation to body weight gain), possibly via selection on low individual CH4 emissions (Paganoni et al, 2017). Pickering et al (2015) and Paganoni et al (2017) indicated genetic variation and small to moderate heritabilities for CH4 traits in dairy cows and sheep, and Rösler et al (2018) described an individual variation in enteric CH4 emissions in female goats. The economic benefits from selection scenarios including CH4 traits (Robinson and Oddy, 2016) suggest consideration of CH4 or of CH4 indicator traits into overall sheep breeding goals
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