Poultry genetics has evolved rapidly in the last 2 decades and continues to advance at a steady pace, but research from Cargill Animal Nutrition suggests that birds’ diets need to be updated alongside genetic progress to maximize performance.
With modern broilers often bred for cut parts such as legs, breasts and tenders, there have been significant transformations in the physiology of the birds toward higher muscle and lower fat. This has come alongside improved feed conversions and birds hitting target weights several days before they were doing even a few years ago, explained Jarred Oxford, PhD, a poultry nutritionist for the company.
Although there are other factors involved, such as improved feeding technologies and environmental controls, selection for higher meat yield at a faster pace has required notable shifts in broiler nutrition, with amino acids a key part of these changes. This has reflected the fact that research has highlighted the importance of formulating diets based on an ideal-protein measure rather than a crude-protein measure, Oxford noted, prioritizing birds’ amino acid requirements.
“What we’ve seen is roughly a 50-kilocalorie reduction in energy from 2007 to 2022. We’ve also seen a reduction in crude protein, but at that same point, we’ve seen an increase in amino acids,” he said.
“We’ve seen a five-point increase in digestible lysine. We’ve also seen increasing the ratios of our total sulfur amino acids (methionine and cysteine) and non-sulfur amino acids (threonine and valine). Overall, we’re feeding a lot more amino acid-dense diet than we were.”
Breed matters in honing diets
Cargill research highlights not only that amino acids have a higher impact on feed intake than previously thought but also that different bird breeding lines respond differently to dietary amino acid levels.
One study showed that for a breed commonly raised in production, feeding the birds excess lysine resulted in a reduction in feed intake, with the opposite being true when lysine was reduced. For the other breeds tested, a reduction in dietary lysine had the opposite effect, causing feed intake to decrease.
“This really indicates to us that the genetic-selection pressure is clearly different between the two lines, meaning that although they’ve both selected for better feed efficiency and more breast-meat yields, the criteria that they’ve been selected for to achieve that were different,” Oxford explained. “We really need to adjust our feeding programs to reflect the bird that we’re feeding.”
Exploring energy-lysine interaction
Other work suggests that the old poultry-industry adage that birds eat and grow to an energy requirement may need to be updated, considering genetic changes in the animals, Oxford continued.
Tests have shown that average daily gain is more influenced by dietary lysine levels than energy levels in birds’ diets, while birds fed sub-optimal levels of dietary lysine will regulate their feed intake, eating more to achieve its lysine requirement.
“The assumption that chickens eat to meet an energy requirement may not be so true anymore, at least for today’s broilers,” he noted.
Based on the experimental results, he believes there is a clear case for lysine-to-energy-level ratios in modern broiler diets. However, at present, while this is commonly seen in swine production, it is rarely done in the poultry industry.
Broiler breeder nutrition may need rethinking
For modern broiler breeders, which also have been bred for greater muscle deposition and reduced fat, energy levels have been kept relatively constant in birds’ diets over the last 15 years, while lysine has increased. Much more of the lysine is allocated to egg production1 by the birds compared to energy, which is mainly allocated to maintenance.2
This nutritional shift has meant the protein-to-body-fat ratio has increased significantly over the years, but birds with low body fat have reproductive risks, Oxford explained. Two Cargill studies explored these nutritional impacts, finding that it might be time for producers to reconsider their feeding approaches.
One test was a dose-response trial with broiler breeder pullets using six digestible lysine and crude-protein levels during the rearing period, with birds’ target weights achieved by adjusting feed allowance.3 The research team monitored birds into lay, at which point they fed the birds identical diets. They then took eggs from the birds in the study and hatched them to assess the performance of their progeny.
They found that the birds fed the lower crude protein and lysine in relation to energy required less feed intake during the lay period to maintain their bodyweight at target level. The highest laying percentage was in the group fed a diet containing 10% less crude protein and lysine-to-energy as pullets than a standard diet. Additionally, progeny from broiler breeders in the same group had improved daily gain.
“Even though these diets were only fed in the pullet phase, there is an effect on the progeny during the laying phase,” Oxford noted.
Shifting diets in late lay
For the second trial, they compared a standard feeding program to one in which digestible lysine and crude-protein levels were gradually decreased toward the end of lay, from week 35.4 They also took eggs from the breeders at 56 weeks of age and hatched them to measure progeny bodyweights on day 1 and day 35 of their lives.
The team observed that birds’ average daily feed intake was significantly higher in the reduced crude-protein and lysine group after 46 weeks. While there was no difference in egg production, egg weights were significantly lower from birds fed reduced crude protein and lysine, again from 46 weeks.
After hatching the progeny, the scientists saw that chick weights were significantly lower in the reduced crude-protein and lysine group, both at day zero and day 35. At the latter time point, this represented around 60 grams difference.
“We know that growth is exponential from hatch weight, so it makes sense why we’re seeing this trend,” Oxford said.
Age matters in tailoring amino acids
Together, the studies illustrate that the age of birds is critical in determining optimum amino acid levels. By slightly reducing amino acid levels in pullet diets, carcass fat can be increased along with persistency of lay and improved growth potential of progeny. However, in later lay, reducing amino acids can have the opposite effects: increased demand for feed and reduced egg weights and progeny growth.
“We really need to look more into our programs. We know that these birds, as they mature, change physiologically, so that bird’s requirements are going to change too,” Oxford stressed. “Currently, we’re holding breeder diets relatively constant throughout the lay phase, so you’re feeding a similar diet for roughly 40 to 45 weeks. We need to tailor that program to better reflect that bird’s requirements as they age and potentially add additional breeder diet phases.”
Improving knowledge and feed delivery
Further understanding of optimum broiler breeder body condition at the onset of lay and as the bird ages is also needed, he noted, particularly around optimal fat levels. Here, there are insights from work with layers, in which near-infrared scanners are used to scan fat pads and ultimately help tailor diets to improve persistency of lay. Epigenetics approaches could also be helpful to further improve broiler growth and development and lead to changes in broiler breeder feed.
“Genetics are changing roughly every 2 to 3 years, so we really need to stay dynamic to achieve the full genetic potential of our birds,” Oxford said.
“It’s important to understand the genetic changes that have been made and how that may influence nutrient requirements or even the birds’ physiology. This can really help us make improvements to our breeder nutrition programs.”
To further aid the efficacy of feeding programs and flock uniformity, more attention is also needed around feed delivery.
“You could have the best diet in the world, but if your feed delivery isn’t right, then it’s not going to perform like the best diet in the world. The birds aren’t going to be able to utilize it the way they should. That’s key, especially in broiler breeders,” he added.
“I think we could spend more time looking at how our feed-delivery system is functioning and adjusting our feed run times to make sure that we’re getting enough feed out, as well as getting a uniform presentation to the birds.”
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1 Fisher C. Lysine: Amino acid requirements of broiler breeders. Poult Sci. 1998;77(1):124–33.
2 Pishnamazi A, Renema RA, Paul DC, Wenger II, Zuidhof MJ. Effects of environmental temperature and dietary energy on energy partitioning coefficients of female broiler breeders. J Anim Sci. 2015;93(10):4734–41.
3 Trial LT1502, Cargill Animal Nutrition.
4 Trial LT1501, Cargill Animal Nutrition
