Investigation on adaptations of broiler chickens to high dietary free amino acid levels in nitrogen utilisation and plasma amino acid concentrations

ABSTRACT

1. A reduction in crude protein (CP) in feed for broiler chickens necessitates elevated free amino acid (AA) levels to meet the requirement of each AA. This study investigated adaptations following a change to diets with increasing free AA concentrations and possible reasons for the limitation caused by the inclusion of more free AA.

2. Male Ross 308 broiler hatchlings received a starter diet (164 g CP/kg containing 80 g/kg soy protein isolate (SPI)) until d 7. From d 7–22, birds received a diet almost identical to the starter diet or two other diets, where 50% or 100% of digestible AA in SPI were substituted with a free AA mixture. Birds were allocated to metabolism units located in the same barn to determine performance (n = 7 units) and blood traits (n = 14 birds). Total excreta collection was performed on d 7–8, 8–9, 9–10, 11–12, 14–15 and 21–22. Blood samples were collected on d 7, 8, 9, 11, 14 and 21.

3. Average daily weight gain (ADG) and average daily feed intake (ADFI) was unaffected at 50% AA substitution but decreased at 100% AA substitution on d 7–22 (p ≤ 0.001). The 100% substitution led to a decline in ADG and ADFI consistently on all days (p ≤ 0.037) except on d 11–12. A 50% AA substitution resulted in lower ADFI on d 7–8 and 14–15 (p ≤ 0.032). Nitrogen utilisation efficiency (NUE) was on a level of ~ 0.74 and was only affected by treatment up to d 11–12 (p ≤ 0.008). Concentrations of 10, 9, 8, 10 and 4 plasma free AA were affected on d 8, 9, 11, 14 and 21, respectively (p ≤ 0.037).

4. Following a change to diets containing high levels of free AA, NUE and free AA concentrations in the circulation became more balanced within 3 to 7 d. The results suggested that peptide-bound and free AA did not cause different NUE, particularly 3 and 7 d after the diet change.

KEYWORDS:

• Broilers
• peptide-bound
• free amino acids
• metabolism
• insulin

Acknowledgments

The authors appreciate the support of K. Huber and her group for insulin analyses and chemical analyses performed by the staff of the Department of Animal Nutrition. Evonik Nutrition and Care GmbH, Hanau, Germany, and CJ Europe GmbH, Frankfurt am Main, Germany, provided free AA.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authors’ contributions

A. I., M. R. and W. S. designed the research and performed the trial; A. I. and W. S. were responsible for data collection, statistical analyses and carrying out chemical analyses. A. I., M. R., and W. S. contributed to the drafting of the manuscript. All authors have read and approved the final version of the manuscript.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00071668.2024.2315079.

Additional information

Funding

This work was funded by the German Research Foundation [DFG project SI 2258/3-1].