Date of Award

3-10-2025

Document Type

Doctoral Thesis

Department

Department of Biological Sciences

First Advisor

Dr. Deirdre Purfield

Second Advisor

Dr. Ross Evans

Abstract

Enteric methane is the largest source of agricultural greenhouse gas emissions in Ireland, accounting for 63% of the sector’s total. Achieving the legally binding target of a 25% reduction in agricultural emissions by 2030 requires low-cost, scalable mitigation strategies. Genetic selection offers a cumulative and permanent solution, with potential to reduce emissions without compromising productivity. This thesis aimed to quantify the genetic variability of methane and carbon dioxide emissions in growing beef cattle, investigate their relationships with economically important traits, and evaluate the feasibility of incorporating a methane trait into the Irish national beef breeding objective. Emissions data were collected on 1,835 growing cattle during the finishing period using GreenFeed Emission Monitoring systems between 2018 and 2024, alongside records for dry matter intake, liveweight, ultrasound muscle depth, carcass traits, and pedigree. Methane was low to moderately heritable increasing from 0.09 (±0.03) to 0.43 (±0.11) as the averaging period increased, while carbon dioxide heritability ranged from 0.17 to 0.50. Ample genetic variation existed suggesting genetic improvement in reducing methane emissions is possible. Validation of several methane trait estimated breeding values showed spot measure methane to be favourable across three metrics. Methane emissions were moderately positively correlated with carcass weight (0.44 to 0.50), indicating that heavier animals produce more methane, while a moderate negative correlation with age at finish (–0.27 to –0.18) suggests that earlier-finishing animals emit more daily methane. When a direct methane trait is incorporated in the Irish Terminal beef index, annual reductions of approximately 30,459 tonnes of carbon dioxide equivalents are achievable under a high carbon price scenario (€160/tonne). Continued methane phenotyping and the strategic integration of a direct enteric methane trait into national breeding goals will enable cumulative and scalable reductions in beef sector emissions, contributing meaningfully to national climate targets while maintaining genetic progress in economically important traits.

Access Level

info:eu-repo/semantics/openAccess

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