Eating Time as a Genetic Indicator of Methane Emissions and Feed Efficiency in Australian Maternal Composite Sheep

Abstract

Previous studies have shown reduced enteric methane emissions (ME) and residual feed intake (RFI) through the application of genomic selection in ruminants. The objective of this study was to evaluate feeding behaviour traits as genetic indicators for ME and RFI in Australian Maternal Composite ewes using data from an automated feed intake facility. The feeding behaviour traits evaluated were the amount of time spent eating per day (eating time; ETD; min/day) and per visit (eating time per event; ETE; min/event), daily number of events (DNE), event feed intake (EFI; g/event) and eating rate (ER; g/min). Genotypes and phenotypes of 445 ewes at three different ages (post-weaning, hogget, and adult) were used to estimate the heritability of ME, RFI, and the feeding behaviour traits using univariate genomic best linear unbiased prediction models. Multivariate models were used to estimate the correlations between these traits and within each trait at different ages. The response to selection was evaluated for ME and RFI with direct selection models and indirect models with ETE as an indicator trait, as this behaviour trait was a promising indicator based on heritability and genetic correlations. Heritabilities were between 0.12 and 0.18 for ME and RFI, and between 0.29 and 0.47 for the eating behaviour traits. In our data, selecting for more efficient animals (low RFI) would lead to higher methane emissions per day and per kg of dry matter intake. Selecting for more ETE also improves feed efficiency but results in more methane per day and per kg dry matter intake. Based on our results, ETE could be evaluated as an indicator trait for ME and RFI under an index approach that allows simultaneous selection for improvement in emissions and feed efficiency. Selecting for ETE may have a tremendous impact on the industry, as it may be easier and cheaper to obtain than feed intake and ME data. As the data were collected using individual feeding units, the findings on this research should be validated under grazing conditions.

Keywords: eating time; feed efficiency; methane production; methane yield; residual methane.

FIGURE 1

Estimation of residual traits in post-weaning, hogget, and adult Australian Maternal Composite sheep. Residual methane production [RMP; (A)] is the residual of observed methane production (MeP) regressed on predicted MeP. Residual feed intake RFI; (B) is the residual of observed daily dry matter intake (DMI) regressed on predicted DMI. Regressors: DMI, average daily gain (ADG), metabolic mid-weight (MMWT), experiment (EXP), pen nested into EXP (PEN: EXP), and age at the start of the test (AGE).

FIGURE 2

Principal component decompositions of genomic relationship matrix constructed from 38,378 SNP genotypes from post-weaning, hogget, and adult Australian Maternal Composite sheep with two principal components shown (PC1, PC2) and points labelled by sire breed.

FIGURE 3

Annual response to selection on methane production [MeP; (A)], residual methane production [RMP; (A)], methane yield [MeY = MeP/DMI; (B)], and residual feed intake [RFI; (C)] using direct selection, or indirect selection with eating time per eating event (ETE) as indicator trait in post-weaning, hogget, and adult Australian Maternal Composite ewes. Solid lines indicated the estimated responses to selection, and the highlighted areas are the standard errors.