Modelling management change on production efficiency and methane output within a sheep flock
Authors: G J Cruickshank, B C Thomson, P D Muir
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Executive summary
An model has been developed in Microsoft Excel which enables us to test the impact of different management strategies such as hogget lambing, improving lambing percentage and increasing ewe longevity on the methane production (relative to farm output) of a hypothetical 1000 ewe sheep flock.
The data used in the model has been obtained from the Poukawa Elite Lamb flock which comprises some of the only data available on “modern” sheep genotypes. The dataset used involves some 6000 ewe records from four genotypes and 8100 lamb records over 8 years. The base flock of 1000 ewes with 160% scanning produced 989 lambs for sale (a further 288 lambs are kept as replacements) and resulted in the production of 15.99 kg CH4/lamb sold. Methane production is linked to feed intake and factors that improved flock efficiency meant that more lamb was produced for the same amount of dry matter intake. This resulted in reductions in methane per lamb sold.
- Lambing hoggets had the biggest impact and reduced methane/lamb sold by 13.6%. This was because the flock was producing more lambs without the maintenance cost of running any more ewes.
- Increasing ewe scanning percentage from 160 to 180% reduced methane output by 7.8%. This is assuming no increase in ewe liveweight and is achievable with Androvax or a breed change.
- Increasing ewe longevity from 5 to 6 years reduced methane output by 6.4%. In this scenario, fewer replacement hoggets need to be maintained to enter the flock.
These reduction are not necessarily cumulative as a ewe flock is a complex dynamic system and altering one factor will alter other components in the system and impact on methane output. Nevertheless, the combined effect of increasing longevity from 5 to 6 years, hogget lambing and increasing the scanning percentage from 160 to 180% resulted in a reduction of 21% in methane output per lamb sold.
Improving farm efficiency will not impact on the amount of methane produced at either the farm or a national level. However, management strategies which improve efficiency will change the amount of methane produced per unit of saleable product. Management practices which increase performance without markedly contributing to ewe maintenance requirement will have the biggest impact.
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