# The Optimal Digestible Leucine-to-Lysine Ratio in Wheat-Based Diets for Finishing Broilers

## TL;DR

This study finds that a specific leucine-to-lysine ratio in wheat-based diets improves growth and feed efficiency in broiler chickens.

## Contribution

The study identifies the optimal leucine-to-lysine ratio for maximizing performance in finishing broilers fed wheat-based diets.

## Key findings

- Leucine-to-lysine ratios between 0.96 and 1.025 improved body weight gain and feed consumption in broilers.
- A leucine-deficient diet supplemented with L-leucine enhanced growth performance in finishing broilers.
- The European production efficacy factor improved with higher leucine-to-lysine ratios.

## Abstract

In wheat-based diets, the leucine content can be low, especially in a low-crude-protein diet. A low leucine content may limit the maximum performance and thus the efficiency of broiler chickens. The addition of crystalline L-leucine is a possible solution to a low-protein wheat-based diet. However, little is known about the ideal leucine-to-lysine ratio in finishing broilers. Thus, the aim of this study was to determine the optimal ratio to maximize growth performance and slaughter parameters. In a trial facility, 672 male Ross 308 broilers were reared with a commercial starter and grower feed followed by allocation to one of eight dietary treatments with consecutive increasing amounts of L-leucine. The supplementation of L-leucine with a leucine-deficient basal diet led to an increase in the growth and feed intake of finishing broilers. A data analysis of body weight gain, daily feed consumption, and the European production efficacy factor indicated that leucine-to-lysine ratios between 0.96 and 1.025 are required to achieve 95% and 98% of the maximum performance, respectively.

Male Ross 308 finisher (19 to 33 days) broiler chickens (n = 672) were used to determine the standardized ileal digestible (SID) leucine (Leu)-to-lysine (Lys) ratio for the maximum growth performance and slaughter parameters. A basal diet (incl. wheat, triticale, soybean meal, sunflower meal, and synthetic amino acids) deficient in Leu was formulated, and supplementary L-Leu was used to achieve 0.9 and 1.25 SID Leu-to-Lys ratios in increments of 0.05. A slight deficiency in lysine was implemented to truly relate broiler performance to changes in the SID Leu-to-Lys ratio. Diets were fed to broilers in seven pens (12 broilers each). Eight birds per pen were used for carcass evaluation on day 33. Data analysis indicated that SID Leu-to-Lys ratios between 0.96 and 1.025 were required to achieve 95% and 98% of the maximum body weight gain, daily feed consumption, and the European production efficacy factor, respectively. The estimation of recommended SID Leu-to-Lys ratios for the feed conversion ratio and carcass parameters was not possible.