Genetic parameters of plasma and ruminal volatile fatty acids in sheep fed alfalfa pellets and genetic correlations with enteric methane emissions1

Abstract

Animal-to-animal variation in methane (CH4) emissions determined in respiration chambers has a genetic basis, but rapid phenotyping methods that can be applied on-farm are required to enable increased genetic progress by the farming industry. Fermentation of carbohydrates in the rumen results in the formation of VFA with hydrogen (H2) as a byproduct that is used for CH4 formation. Generally, fermentation pathways leading to acetate are associated with the most H2 production, less H2 formation is associated with butyrate production, and propionate and valerate production are associated with reduced H2 production. Therefore, VFA may constitute a potential correlated proxy for CH4 emissions to enable high-throughput animal screening. The objective of the present study was to determine the genetic parameters for ruminal and plasma VFA concentrations in sheep fed alfalfa (Medicago sativa L.) pellets and their genetic (rg) and phenotypic (rp) correlations with CH4 emissions. Measurements of CH4 emissions in respiration chambers and ruminal (stomach tubing 18 h from last meal) and blood plasma (3 h post-feeding) VFA concentrations were made on 1,538 lambs from 5 birth years (2007 and 2009 to 2012) aged between 5 and 10 mo, while the animals were fed alfalfa pellets at 2.0 times maintenance requirements in 2 equal size meals (0900 and 1500 h). These measurements were repeated twice (rounds) 14 d apart. Mean (± SD) CH4 production was 24.4 ± 3.08 g/d, and the mean CH4 yield was 15.8 ± 1.51 g/kg DMI. Mean concentration of total ruminal VFA was 52.2 mM, with concentrations of acetate, propionate and butyrate of 35.97, 8.83, and 4.02 mM, respectively. Ruminal total VFA concentration had heritability (h2) and repeatability estimates (± SE) of 0.24 ± 0.05 and 0.35 ± 0.03, respectively, and similar estimates were found for acetate, propionate, and butyrate. Blood plasma concentrations of VFA had much lower estimates of h2 and repeatability than ruminal VFA. Genetic correlations with CH4 yield were greatest for total concentrations of ruminal VFA and acetate, with 0.54 ± 0.12 and 0.56 ± 0.12, respectively, which were much greater than their corresponding rp. The rp and rg of ruminal VFA proportions and blood VFAs with CH4 emissions were in general lower than for ruminal VFA concentrations. However, minor ruminal VFA proportions had also moderate rg with CH4 yield. Pre-feeding concentrations of total VFA and acetate were the strongest correlated proxies to select sheep that are genetically low CH4 emitters.

Impact of breeding for reduced methane emissions in New Zealand sheep on maternal and health traits

“…Low to moderate relationships were observed between methane yield, fleece weight, body weight and body condition score at mating. It has been shown previously that low-emitting animals tend to have a greater amount of lean tissue (Elmes et al, 2014), possibly due to greater ratios of propionate and valerate to acetate and butyrate coming from the rumen (Jonker et al, 2019). Also, Bilton et al (2021) showed that low methane ewes similarly had different volatile fatty acid profiles in their rumen fluid and less short-chain fatty acids in their milk.…”

A meta‐analysis of the genetic contribution to greenhouse gas emission in sheep

“…Therefore, genetic selection for lower gas emissions may be a feasible mitigation possibility, provided that the GHG emission traits have no high undesirable genetic correlations with animal performance traits (Elmes et al, 2014; Pinares‐Patiño et al, 2011). To this end, an efficient and valid method of ranking animals for their GHG emissions is mandatory (Jonker et al, 2019). Also, breeding plans for sheep should consider the interrelationships between productivity and the environment (Jonker et al, 2019).…”

“…To this end, an efficient and valid method of ranking animals for their GHG emissions is mandatory (Jonker et al, 2019). Also, breeding plans for sheep should consider the interrelationships between productivity and the environment (Jonker et al, 2019). The low standard errors and 95% CI of the mean heritability estimates for most gas emission traits could indicate the appropriate accuracy for these estimates.…”

Substituting ryegrass-based pasture with graded levels of forage rape in the diet of lambs decreases methane emissions and increases propionate, succinate, and primary alcohols in the rumen

“…The location of the fluid sampling might not be consistent with the stomach tubing method, and samples can contain variable quantities of saliva contamination. These factors may affect the absolute pH and concentrations of fermentation metabolites in the rumen fluid, but not of fermentation product percentages and ratios ( Larsen et al, 2020 ), and the relative values of pH and SCFA concentrations were previously found to be useful for ranking CH 4 /DMI in sheep ( Jonker et al 2019 ).…”