Study finds broiler chickens unresponsive to dietary leucine enrichment

AUSTRALIA- A study published in the journal Animal Feed Science and Technology found that elevated branched chain amino acids inclusions in wheat-based diets did not increase performance in broiler chickens.

The study notes that branched chain amino acids (BCAA), isoleucine, leucine and valine are of particular interest in broiler nutrition.

The researchers have cited in their work previous studies indicating how broiler chickens may benefit from elevated dietary leucine concentrations.

Hypothesizing that, doing so might require higher isoleucine and valine inclusions as well to counter antagonistic BCAA interactions in poultry.

Therefore, their study aimed to investigate whether elevated leucine inclusions in reduced crude protein (CP) diets would advantage broiler growth performance, provided concomitant elevations in isoleucine and valine were employed.

The researchers allocated 378 male broilers to 9 dietary treatments, each with 7 replicate cages and 6 birds in each. All diets were wheat-based with 190 g/kg CP.

The assessed parameters included nutrient utilization, growth performance, relative abdominal fat-pad weights, apparent jejunal and ileal digestibility coefficients and disappearance rates of starch, protein (N), amino acids and free amino acid concentrations in systemic plasma.

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They found that elevated BCAA inclusions did not enhance growth performance. That in fact, elevating isoleucine plus valine from 17.21 to 20.32 g/kg in the 15.02 g/kg leucine diet significantly compromised weight gain by 6.82%.

However, they discovered that elevating isoleucine plus valine inclusions from 17.21 to 20.32 g/kg decreased relative fat-pad weights by 8.49%.

While dietary enrichment with leucine had diverse impacts on amino acid digestibility coefficients coupled with free amino acid plasma concentrations, elevating leucine levels significantly depressed energy utilization.

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Increasing dietary leucine concentrations improved ileal digestibility of leucine by 4.74% but also significantly increased ileal digestibility coefficients of another 10 amino acids by an average of 3.37% ranging from 1.60% (methionine) to 4.96% (threonine), they reported.

Overall, the results showed that elevations of BCAA in wheat-based, reduced-CP diets did not advantage broiler growth performance.

“That broiler chickens failed to respond to elevated BCAA inclusions appeared to be due to both BCAA antagonisms coupled with diverse responses in amino acid digestibility coefficients,” concluded the researchers.

Ultimately, they found no real benefit to exceeding the ratios, leucine 109, isoleucine 67, valine 77 concurrent with lysine proposed in earlier studies.

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