Effects of 5-Aminolevulinic Acid as a Supplement on Animal Performance, Iron Status, and Immune Response in Farm Animals: A Review

Simple Summary 5-aminolevulinic acid is an amino acid that promotes the formation of heme-an essential constituent of hemoglobin. It has been recently used as a novel feed supplement to enhance the productivity of farm animals, but the current understanding of its effects on livestock is not clear. We systematically evaluated the literature for the effects of 5-aminolevulinic acid supplementation on animal performance, iron status, and immune response in farm animals. Extensive search of PubMed and Web of Science resulted into 16 eligible controlled trials. Findings revealed that iron status and immunity were most responsive to 5-aminolevulinic acid. Other parameters displayed hardly any tangible effect. Studies were highly heterogeneous (regarding species, dose, treatment duration, use of other supplements), which may limit the conclusion. Standard procedures and outcome measures are needed to confirm the benefits of 5-aminolevulinic acid. Attention should also be paid to any adverse effects. Efforts directed toward enhancing animals' productivity are focused on evaluating the effects of non-traditional feed additives that are safer than antibiotics, which have been banned because of their health hazards. Many studies used an amino acid that contributes to heme biosynthesis, known as 5-aminolevulinic acid (5-ALA), to promote the productivity of farm animals. However, these studies demonstrate inconsistent results. In order to develop a clear understanding of the effects of 5-ALA in farm animals, we comprehensively searched PubMed and Web of Science for studies evaluating 5-ALA effects on the performance, iron status, and immune response of different farm animals. The search retrieved 1369 publications, out of which 16 trials were relevant. The 5-ALA-relevant data and methodological attributes of these trials were extracted/evaluated by two independent researchers, based on a set of defined criteria. Samples were comprised of pigs, chickens, and dairy cows. The 5-ALA doses ranged from 2 mg to 1 g/kg of feed, and treatment duration ranged from 10 to 142 days. Overall, 5-ALA improved iron status in most studies and increased white blood cells count in 3 out of 10 studies, in addition to improving animals' cell-mediated immune response following immune stimulation with lipopolysaccharide. Inconsistent findings were reported for growth performance and egg production; however, a combination of 10 mg/kg of 5-ALA with 500 mg/kg of vitamin C promoted the highest egg production. In addition, 5-ALA improved milk protein concentration. In conclusion, 5-ALA can enhance farm animals' iron status and immune response; however, the heterogeneity of the reviewed studies limits the generalizability of the findings. Standard procedures and outcome measures are needed to confirm the benefits of 5-ALA. Attention should also be paid to any adverse effects.