Research has revealed that metabolisable energy levels in the diets of young meat chickens can be lowered without affecting bird performance. The finding offers important flexibility for industry nutritionists amid an environment of fluctuating ingredient costs.
Metabolisable energy levels in the diets of young meat chickens can be lowered without impacting bird performance, according to comprehensive new research published by a University of Sydney team.
The finding, contained in the results of a multi-year study led by Dr Mehdi Toghyani, could save the Australian chicken meat industry millions of dollars on feed ingredients annually amid an environment of fluctuating input costs and global market dynamics.
As part of the project Optimising energy and amino acid levels in meat chickens' diet, Dr Toghyani and colleagues undertook four feeding studies investigating the impact of dietary nutrient density on performance. Their aim was to understand whether the energy and amino acid contents in diets could be adjusted for maximum production efficiency and economic return.
Performance metrics measured included body weight gain (BWG), feed intake (FI) and feed conversion ratio (FCR), but also breast meat yield and quality, nutrient excretion to the environment, white striping and woody breast conditions.
"Energy is probably the most expensive component of the feed. When AgriFutures was running the Open Call in 2021, prices for canola oil and animal tallow were at historic highs. Both fat sources are commonly used to supplement the feed and balance the energy," Dr Toghyani said.
The start of this latest research coincided with Australia's two major meat chicken breeding companies, Aviagen and Cobb-Vantress, publishing new nutrition specifications for their breeds. These specifications lowered the energy component of diets by close to100 kcal/kg particularly for older birds.
"So we had to move our baseline 50 to 100 kcal lower, but even with the updated reduced energy requirements published in 2022, we saw that we can go further down in terms of energy density, especially for younger birds, without impacting performance," Dr Toghyani said.
The results differed across growth stages - starter, grower, finisher and withdrawal - but were most pronounced for birds aged less than 24 days. Given the potential savings on feed costs, especially with fluctuating oil prices, such reductions could provide the industry annual savings.
With regards to amino acid density, the research found levels 3% higher increased BWG by 90 g per bird, while an additional 3% resulted in a further 50 g gain per bird.
At the time of the study, however, the economics to realise the performance benefits - measured by feed cost per kilogram of bodyweight - did not stack up, although Dr Toghyani noted soybean meal and amino acid prices have since fallen.
"At least what we have been able to quantify is, if you increase amino acid density by this much, you see an improvement in terms of bodyweight gain and feed conversion ratio. So when the prices change and you've got a source of protein, it's very easy doing a bit of simple maths to see if the extra investment pays off.
"What we've done is establish a baseline, so when you are investing, you know how much you're going to harvest. Therefore, when it's economically viable to have higher-amino-acid-density diets, you can choose to increase the cost by $10 or $15 per tonne and have more certainty that because of the better feed conversion ratio and higher gross margin, you are increasing your profit by this much'."
In a similar vein, increasing the digestible lysine-to-metabolisable energy (dLys:ME) ratio in feed beyond the breeder's recommendation for each growth phase was found to improve performance. The dLys:ME ratio is used by nutritionists to ensure changes to amino acid and energy densities are proportional.
Based on the results of the feeding studies, the optimal densities for each growth phase are:
- Starter: 2875 kcal - digestible Lys 1.32% (dLys:ME ratio of 460)
- Grower: 2975 kcal - digestible Lys 1.18% (dLys:ME ratio of 397)
- Finisher: 3100 kcal - digestible Lys 1.08% (dLys:ME ratio of 348)
- Withdrawal: 3150 kcal - digestible Lys 1.027% (dLys:ME ratio of 326)
Dr Toghyani said nutritionists could use the dataset generated to make informed decisions when balancing nutrition requirements with feed costs.
"If a nutritionist wants to cut back on the energy, depending on the age of the birds, they know what it's going to do. Older birds, 50 kcal less will reduce feed efficiency by two points, but how much is it saving?
"The dataset allows them to have some level of prediction of what's going to happen to the performance if they make whatever adjustment, either upwards or downwards, in response to the ingredient prices."
Dr Toghyani's passion for poultry nutrition was sparked during his teenage years in Isfahan, in central Iran. His older brother was completing his master's thesis, and Dr Toghyani was helping place day-old chicks. "I thought it was very interesting how quickly they grow."
He completed his PhD at the University of New England, graduating in 2016, and worked there for a further three years. In 2019, he shifted to The University of Sydney, where he is a lecturer in poultry production. He is also a nutrition consultant and formulates diets for the Sustainable precision feeding in broiler chickens in Australia consortium project.
Dr Toghyani said his energy and amino acid research was a first in the Australian context.
"Existing research was done quite a few years ago with the old recommendations of the breeders, and the energy levels were already high," he said.
"Many people are doing this kind of research overseas, but this is the first project that has utilised Australian-like diets, which are quite unique in their own way. We have wheat-based diets, with canola seed and sometimes canola meal. Our supplemental fat is either canola oil or animal tallow particularly poultry tallow.
"If you go to South America or North America, or parts of Europe, the diets are all corn-based, with soybean oil. The dynamics of the formulations are completely different, meaning that sometimes, similar research from overseas cannot be translated for the Australian context."
