Biological functions and mechanisms of boron in poultry

SUMMARYBoron has attracted increasing attention in poultry nutrition because of its potential biological and metabolic effects, although it is not currently recognised as an essential trace element. This review critically evaluates evidence on the effects of boron supplementation on growth performance, skeletal integrity, eggshell quality, reproductive traits, metabolism, antioxidant status, and health in poultry. Available studies indicate that boron may improve feed efficiency, bone mineralisation, and mineral utilisation, particularly when calcium (Ca), phosphorus (P), or vitamin D3 supply is marginal. Studies on laying hens and pullets reported changes in eggshell characteristics, bone strength, selected serum biochemical indices, and egg yolk lipid composition following boron supplementation. Evidence from breeder flocks and other poultry species, including geese and quail, suggested potential effects on follicular development, fertility, hatchability, and reproductive physiology. Mechanistically, boron may influence mineral metabolism, endocrine signalling, redox balance, and metabolic regulation through interactions with the Ca–P–vitamin D3 axis and related pathways, although direct molecular validation in poultry remains limited. Responses are dose-dependent: supplementation levels in the lower nutritional range commonly examined in poultry studies (approximately 5–75 mg kg−1, depending on species and dietary context) are associated with beneficial effects or no significant change in measured outcomes, whereas studies using much higher experimental exposures (≥200–400 mg kg−1) reported impaired growth performance, reduced feed intake, decreased egg production, or metabolic disturbances. Poultry boron studies generally use conventional experimental designs comparable to those used for other trace elements; the main challenge for synthesis is the broad range of boron inclusion levels and nutritional contexts evaluated. Accordingly, boron should be regarded as a potentially functional, context-dependent dietary component for which an essential requirement has not been established in poultry. The broad range of boron doses evaluated limited molecular characterisation of underlying mechanisms and scarce data on long-term safety.