Low crude-protein diets are a well-proven practice to reduce diet cost and minimize excess nitrogen and excreta, thereby benefiting profitability, health and welfare in broilers and swine. However, the laying-hen industry is far behind in understanding the interaction and requirement of lower amino acids (AAs), which include valine (Val) and isoleucine (Ile) (fourth, fifth or sixth limiting AA in the diet).
“These AAs become increasingly important in diets containing distillers’ dried grains with solubles (DDGS) and corn, as leucine (Leu) is disproportionately higher than Val and Ile in corn and corn byproducts,” said Pratima Adhikari, PhD, principal investigator at Mississippi State University.
Amino acid requirements
The published requirement of digestible-Leu:digestible lysine(Lys) for poultry is 110. However, the US industry diets containing corn, soy, DDGS and meat bone meal usually have a digestible-Leu:digestible-Lys ratio above 180. Additionally, the National Research Council requirement for a total Leu:total Lys ratio is 93. Such a high level of Leu above these requirements has been shown to negatively affect performance and profitability and has caused marginal deficiencies of Val and Ile in broilers, swine and turkeys.
Unfortunately, Adhikari explained, no research has been conducted to evaluate the interaction of all three branched-chain AAs at different levels in laying hens and to understand the effect of high Leu on production, egg weight, egg mass, feather quality and bone formation.
Research in layers has demonstrated that including Val or Ile singly in the diet has improved egg mass and egg weight. However, it remains to be known whether this is due to additional Val and Ile balancing the excessive Leu in the diet or meeting the fifth and sixth limiting AA demand.
Study design
Researchers hypothesized that practical corn-soybean meal-DDGS diets with a high Leu:Lys ratio can create an imbalance, negatively impacting the performance, egg weight, feather quality, economics and sustainability of laying hens. Different strategies are required to maintain egg production before or after the peak cycle.
This study evaluated the requirements of Ile, Leu and Val on Hy-Line W-36 layers during the young and laying phases. The objective was to determine the effect of different Leu, Val and Ile levels and their interaction on pullet performance and bone quality during the grower phase (6 to 12 weeks of age) and developer phase (12 to 18 weeks of age), as well as layer performance and egg quality during the lay phase (20 weeks long).
Performance, bone-quality results
The researchers observed varying performance- and bone-related results in each phase.
Pullet grower phase
During the pullet grower phase, at week 6 of the study, feed intake was optimized at the lowest Val:Lys ratio (65). Bone breaking strength was optimized at the highest Val:Lys ratio (95), moderate Ile:Lys ratio (77) and the lowest Leu:Lys ratio (120).
A trend toward significance was also observed for the feed-conversion ratio, which was optimized at the lowest Ile:Lys ratio (58) and the highest ratios of Val:Lys and Leu:Lys (220). Bone ash was optimized at the lowest Val:Lys ratio and Leu:Lys ratio (120) and the highest Ile:Lys ratio (88).
Developer phase
In the developer phase, total feed intake was optimized at the lowest Val:Lys ratio and highest Ile:Lys and Leu:Lys ratios. Bone ash was optimized at the lowest Val:Lys and Leu:Lys ratios and the highest Ile:Lys ratio.
Laying phase
During the laying phase, feed intake was significantly increased at moderate ratios of Val:Lys (87) and Ile:Lys (75) and the lowest Leu:Lys ratio. However, feed intake decreased when the Val:Lys ratio was lowered and the Ile:Lys and Leu:Lys ratios were kept constant.
Hen-day egg production (HDEP) was significantly increased at a high Val:Lys ratio (91) and moderate ratios of Ile:Lys (75) and Leu:Lys (184). Notably, HDEP decreased as Val:Lys and Ile:Lys ratios decreased. Egg weight was significantly increased at a high Val:Lys ratio (93) and the highest Ile:Lys ratio (91) and lowest Leu:Lys ratio(120).
“Future research should include a similar study in the later phase of laying hens to summarize overall phases and the requirement of branched-chain AAs,” Adhikari concluded.
The research was funded by USPOULTRY and the USPOULTRY Foundation. Click here to view the industry summary.
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