Navigating nitrogen through poultry diets for sustainability gains

As broilers grow increasingly efficiently, nitrogen emissions go down considerably. Photo: Evonik

The world population has undergone rapid growth in the second half of the 20^th century and is expected to reach 9.7 billion in 2050 and nearly 10.4 billion in the mid-2080s, according to the United Nations. Animal protein demand and consumption is on the rise and – as of 2023 – the most popular animal products in the world are poultry meat and eggs.

The global chicken market was valued at US$312.11 bn in 2022 and is predicted to grow to US$429.11 bn by 2028. While this is good news for producers, it also amplifies the need to address industry challenges – including the nitrogen (N) emissions produced by animals and the impact of production on natural resources. There is good data to support that emissions can be reduced without compromising welfare, health, performance or profit by reducing feed protein while simultaneously balancing the amino acid (AA) profile in poultry diets.

Protein content in broiler feeds

The German Association for Animal Nutrition published a report on the protein content in broiler feed from 2000 to 2021 and a forecast until 2030. Feed protein content fell continuously from an average of 20.8% in 2000 to 19.7% in 2020, while final broiler weight increased and feed conversion ratio decreased. Consequently, protein and N excretions reduced by 35% in relation to live weight during that time. The report’s authors forecast further reductions in feed protein and, consequently, excretions by 2030, so that N excretions per kg live weight would be reduced by 47% compared to 2000. As a result, broilers are already among the most efficient protein utilisers among agricultural livestock.

A 2021 review by the Poultry Research Foundation at the University of Sydney, Australia, looked at ways to lower crude protein (CP) content in broiler diets with an objective of mitigating N and ammonia emissions and N pollution. The findings underscored that dietary CP reductions led to fluctuations in AA digestibility coefficients and indicated that birds were better at digesting the remaining protein after a reduction because it contained AA that were easier to absorb. Overall, the evaluation of scientific trials on protein reduction in broiler feed is promising and suggests there is still untapped potential. Australian scientists, for example, were able to show that the CP content in feed for growing broilers could be reduced to 16.1% without performance loss. This considered all essential AA, some of which are not yet approved in the EU. Research in this area is crucial because N pollution is considered by the UN Environment Programme to be one of the most pressing pollution issues facing humanity, due to its environmental and economic impact.

Commercial feed trials

In cooperation with Osnabrück University of Applied Sciences and a commercial feed manufacturer, three trials on feed protein reduction were carried out in succession on a broiler fattening farm in Lower Saxony, Germany. Each trial involved ten houses each containing 41,000 broilers; five houses were fed standard commercial feeds and the other five fed trial variants with reduced protein levels. Protein content was reduced progressively (Table 1), down to 1.1% in trial 3. The standard feeds were in line with German average standards. All diets were based on wheat, maize, soybean meal and rapeseed meal. Field peas were also available during trial 1, allowing for a reduction in soybean meal content (Table 1).

Lowering protein content allowed for soybean meal to be reduced by up to 17%, indicating a successful strategy for reducing imported protein sources. The feeding concept included adding whole wheat in proportions of 5, 10 and 12% in the grower 1, grower 2 and finisher diets, respectively. AA balancing was achieved using DL-methionine, L-lysine, L-threonine, L-valine, L-arginine and L-isoleucine. The AA concept followed recommendations from AMINOChick 3.0 (Evonik), with adjustments made based on the latest low protein research. Starter diets were not reduced in protein content to ensure an adequate AA supply for the chickens’ development.

The results showed that the protein reduction had no negative effect on weight development or the corresponding feed conversion in any of the trials (Table 2). Conversely, the utilisation of the feed protein – and the N it contains – can be significantly increased with an adequate AA supply. In trials 1 to 3, N excretion was around 16% lower than average for the area. This was influenced by good biological performance on the farm. The reduction in feed protein content by 1.1% in trial 3 resulted in a further reduction of nitrogen excretion by 11-27% below the local average.

Moreover, an improvement in manure quality and footpad health was also observed. While there was no cause for concern for the standard feed variants, reducing CP by 0.3% in trial 1 resulted in 98% of the flock scoring 0 (no injuries), an increase from 87%. Corresponding increases were achieved in the other trials. Litter analyses revealed a higher dry matter content and a lower N content, suggesting that the feet of the broilers were exposed to less aggressive fluid in the manure and reduced overall fresh manure. The greenhouse gas potential (GHG) in the standard variant of trial 1 was around 5% lower compared to the standard variants of the following trials (Table 3). The main explanation for this was the use of peas which significantly reduced the proportion of soy extraction meal (Table 2). The latter carries a large CO₂load due to the land use effect, attributed to deforestation, although the EU strives to use only deforestation-free soy, carrying a much lower CO₂ load.

About 60% of factors associated with acidification and eutrophication are due to animal husbandry and manure management. Ammonia emissions from livestock housing, manure storage and spreading account for roughly 50% of the total acidification potential. Since ammonia is closely linked to N excretion, reducing feed protein by 1.1% in trial 3 led to a decrease in acidification potential. Similarly, more than 50% of the eutrophication potential comes from ammonia emissions in housing and manure. Therefore, reducing protein in feed had a positive impact on both acidification and eutrophication potential, achieving nearly a 10% reduction. However, the GHG potential was largely influenced by the origin of the soybean meal.

Low protein strategy

Reductions in the protein content of animal feed – even small – together with a balanced AA profile, has positive effects on both the environment and poultry health. A reduction of just 1.1% on average can be achieved using currently available registered feed AA, without harming animal performance. Additionally, this approach reduces reliance on imported soy. The results from these commercial trials show that N utilisation can be increased to a level today that is not forecast until 2030. The prerequisite for this is the implementation of a low-protein strategy or an AA concept, as developed by Evonik Animal Nutrition.