Modelling the production, profit, and greenhouse gas emissions of Irish sheep flocks divergent in genetic merit

Highlights

• Field data from animals divergent in genetic merit was input to bio-economic and life-cycle analysis models.

• The flock of high genetic merit had net profit €18/ewe higher than the flock of low genetic merit.

• Higher ranking on the replacement index had larger increases in profit than from the terminal index.

• GHG emissions intensity was 6.9% lower for the flock of high genetic merit.

• Farmers can improve profitability while reducing GHG emissions intensities through selection using the national indices.

Abstract

CONTEXT

Sheep production industries face the challenge of increasing farm production and profit while reducing environmental impacts.

OBJECTIVES

Genetic selection using multi-trait breeding indices can be used to improve flock productivity, profitability, and greenhouse gas (GHG) emissions intensities (kg CO₂-eq /kg of product), however validation of the improved performance of animals ranked higher on breeding indices at a flock level is required.

METHODS

Phenotypic data from 387,580 production records of animals born between 2018 and 2020 of known genetic merit in commercial flocks were inputted to an established bio-economic model. Two contrasting flocks were compared, a flock of ewes ranked High (top 20%) on the Irish replacement Index bred with rams ranked High on the replacement and terminal indices, and a flock of ewes ranked Low (bottom 20%) on the Irish replacement Index bred with rams ranked Low on the replacement and terminal indices. The two flocks were then simulated using life cycle assessment to estimate the GHG emissions profile for both systems.

RESULTS AND CONCLUSION

Flock weaning rates were 1.70 and 1.53 lambs weaned per ewe presented for breeding for the High and Low genetic merit flocks, respectively. The flock of High genetic merit ewes sold 0.17 more lambs per ewe, equating to 3.29 kg more lamb carcass per ewe, than the flock of Low genetic merit ewes; lambs from the High genetic merit flock were also sold at an earlier age. The greater production of the High genetic merit flocks resulted in an additional €18/ewe net profit than the Low genetic merit flock. Although total flock GHG emissions were higher for the High genetic merit flock, GHG emissions intensities were lower at 21.7 and 23.3 kg CO₂-eq /kg lamb carcass sold for the High and Low genetic merit flocks, respectively. The lower emissions intensity of the High genetic merit flock was due to the dilution effect of higher lamb production and lambs being drafted for slaughter ealier.

SIGNIFICANCE

The results suggest Irish sheep producers can make substantial profit gains through selection according to the national breeding indices while also reducing their environmental impact, and farmers should consider genetic merit when purchasing their rams, particularly sires of replacement ewe lambs.