Processed animal proteins could reduce the environmental impact of broiler production while maintaining bird performance, according to an analysis of alternative ingredients for poultry feed.
Researchers found that diets containing meat and bone meal performed better overall than those using several other soy substitutes. Microalgae, despite its potential as a feed ingredient, increased greenhouse gas emissions and water use in their model.
The study, by researchers at Queen’s University Belfast and LGC and published in Poultry Science, combined a review of 102 broiler feeding studies with environmental modelling of selected ingredients in a UK production system.
What makes a useful soy alternative?
Soybean meal is widely used to supply protein in broiler diets, but for producers in countries that import it, alternative ingredients could be more sustainable and cost-effective.
An ingredient’s origin is only part of the picture, however: If chickens need more feed to reach the same weight, that can offset any environmental advantage from producing the alternative ingredient.
The researchers reviewed studies published over 20 years, comparing how birds performed on diets containing processed animal proteins, grain processing by-products, rapeseed, seed and leaf meals, and proteins from microbes and aquatic sources. They examined growth, feed intake and feed conversion, which measures the amount of feed needed for weight gain.
They then modelled the environmental effects of three ingredients in diets for a UK Ross 308 broiler flock: swine meat and bone meal, wheat dried distillers’ grains with solubles (DDGS), and microalgae. DDGS is a protein-containing by-product of grain processing, including bioethanol production. Each ingredient was assessed at two inclusion rates against soybean-based diets.
How did the alternatives compare?
Processed animal protein delivered the strongest overall results, the researchers said. At inclusion rates of 10% and 15%, it reduced modelled greenhouse gas emissions, land use and water consumption per 1,000 kg of chicken carcass produced. Its main drawback was an increase of around 7% to 8% in terrestrial acidification, an environmental impact associated with emissions including ammonia.
Wheat DDGS also reduced the environmental impacts calculated for chicken production overall. However, several impacts associated specifically with the birds’ manure increased, showing why the result depends on what is measured.
Microalgae showed a more difficult trade-off. Compared with the soybean diets, its inclusion at 10% and 15% increased modelled greenhouse gas emissions by 16% and 27% respectively, while water use rose by 49% and 77%. The researchers linked this partly to the resources needed to grow, harvest and process it. They cautioned that the microalgae figures relied on estimates from other published studies because suitable production data were unavailable.
Bird age changes the picture
The review found that birds’ responses to alternative proteins varied according to the ingredient, its inclusion rate, the broiler strain and the stage of growth. Starter birds were more sensitive to changes in their diets than finishers. In studies that measured digestibility, increasing the inclusion of alternative proteins reduced the proportion of feed nutrients the birds appeared to absorb.
That could make the grower and finisher stages more promising points for replacing some soy, particularly as birds eat most of their feed later in production. The researchers did not directly test a programme that introduced alternative ingredients only at those stages.
The environmental figures come from a model of UK production rather than a comparison of commercial farms. Ingredient sourcing, feed formulation and energy use could change the results elsewhere, they said, while the study did not establish whether any of the alternatives would reduce feed costs.
Key takeaways
- Processed animal protein showed the strongest overall potential to replace soybean meal while reducing the modelled environmental impact of broiler production.
- Wheat DDGS also reduced impacts per kilogram of chicken produced, although several impacts associated with manure increased.
- Microalgae increased modelled greenhouse gas emissions and water use at both inclusion rates tested.
- Starter birds were more sensitive to alternative proteins than finishers, suggesting the stage at which soy is replaced matters.
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