Genetic parameters for greenhouse gas emissions in Texel sheep measured using portable accumulation chambers

This study aimed to produce the first preliminary genetic parameters for methane (CH4) and carbon dioxide (CO2) emissions in UK Texel sheep. Globally, there is an awareness for the need to investigate mitigation strategies to reduce greenhouse gas (GHG) emissions from ruminants, with one option being through genetics. The Texel breed has significant influence on the UK sheep industry, being the most commonly used ram breed, and playing an increasingly important maternal role (1). Internationally, the UK population has valuable genetic links with several other countries. However, before recommendations can be made to include traits relating to GHG emissions in future breeding programmes, their genetic control must be understood.

Data were collected using portable accumulation chambers (PACs) from 581 Texel lambs (334 females, 247 entire males), born across 2 years and 3 flocks. The number of lambs recorded at each flock ranged from 115 to 240. Of the 581 lambs, 531 had duplicate measurements (~14 days apart). The average age and live weight of the lambs at PAC measurement was 158 days (range 109 – 204) and 48kg (range 29 – 75), respectively. A total of 1,112 CH4 and 1,079 CO2 emission measurements were available for analysis, calculated as g/d, rescaled to lot and population means (2). Fixed effects were tested using Generalized Linear Models and stepwise regression (Genstat 24th Edition). Univariate analyses in ASReml (Version 4.2) fitted animal models including fixed effects of live weight, lamb sex, litter size during rearing and visit contemporary group (combining flock, round of measurement and year). A permanent environmental effect, to account for duplicate PAC measurements, was also fitted. The pedigree file used contained sire and dam information for 2,211 animals.

Large amounts of phenotypic variation were observed within and across flocks for the PAC-measured traits (Table 1). Phenotypic analyses found significant sex differences (p< 0.001) for both CH4 and CO2 (females > males), and significant sire differences. Univariate heritabilities estimated were low and positive (0.17 and 0.18 for CH4 and CO2 respectively), as were permanent environmental effects, resulting in moderate repeatability estimates (Table 1).

These preliminary results indicate that there is substantial variation in CH4 and CO2 emissions in UK Texel lambs, which is under partial genetic control. This suggests scope for the inclusion of these traits in future breeding programmes, which could help to reduce GHG emissions. However, further work is required to assess relationships between CH4, CO2 and other traits in the UK Texel breeding programme.

References

1Pollot G and S. Boon (2021) The breeding structure of the British sheep industry 2021 - Results of the 2020 survey of sheep breeds in Great Britain, https://ahdb.org.uk/knowledge-library/sheep-breed-survey-2021

2Jonker A. et al. (2020) Ministry for Primary Industries, NZ, pp.55-62. https://www.mpi.govt.nz/resources-and-forms/publications/