Dr Shemil Macelline, University of Sydney
Reducing the inclusion of soybean meal (SBM) in broiler diets could help lessen the Australian poultry industry’s reliance on imported feed ingredients. It may also contribute to lowering the industry’s carbon footprint, as the long-distance transport of SBM from countries such as Argentina to Australia requires substantial fossil fuel use. One potential strategy is to formulate diets with lower crude protein (CP) levels than current recommendations while maintaining the requirements for the most limiting essential amino acids through supplementation with non-bound amino acids (NBAA).
Lower dietary CP levels in broilers have previously been associated with several environmental and welfare benefits. These include reductions in nitrogen pollution, drier litter conditions, and lower incidences of footpad dermatitis and hock burns in broiler chickens. However, broiler responses to low-CP diets have been inconsistent, particularly when diets are formulated using wheat rather than maize.
As Australian broiler diets are primarily wheat-based, it is important to explore strategies that may mitigate the negative effects sometimes associated with wheat-based, low-CP diets. In a PHA-funded project, Dr Shemil Macelline from the University of Sydney investigated whether supplementing low-CP wheat-based diets with natural betaine and/or a double dose of xylanase could maintain growth performance in broiler chickens.
Betaine was included in the study because of its role as an osmolyte that may help maintain gut integrity, which can be compromised in diets containing higher levels of wheat due to increased non-starch polysaccharides. The study also evaluated the effect of double dosing xylanase, an enzyme used to degrade arabinoxylans—an anti-nutritional factor in wheat that can limit nutrient digestibility and bird performance.
The study found that reducing dietary CP by 2.5 percentage points below breeder recommendations compromised broiler growth performance, particularly during the grower to withdrawal phases. Supplementation with a double dose of xylanase did not further improve growth performance, suggesting that the standard inclusion rate of 2000 U/kg is sufficient for wheat-based reduced-CP diets.
Interestingly, betaine supplementation reduced feed intake during the finisher and overall phases while improving feed efficiency, indicating that betaine may enhance nutrient utilisation in reduced-CP diets. This finding contrasts with previous studies that reported increased intake and growth when betaine was used in conventional-CP diets.
Overall, the findings highlight the complexity of formulating wheat-based reduced-CP diets and the need for further research into strategies that can mitigate the adverse effects of lowering dietary protein. The results suggest that reducing CP in finisher diets with betaine supplementation does not compromise feed conversion ratio (FCR), while the combined use of betaine and double-dose xylanase can support FCR improvements in low-CP diets with reduced total sulphur amino acids.
In addition to performance outcomes, dietary CP reductions also had positive welfare impacts. Birds fed reduced-CP diets showed lower litter moisture levels and reduced incidences of footpad dermatitis and hock burns, indicating potential benefits for both bird welfare and environmental management.
