Physiological Function of Inulin and Its Application in Livestock Production

Inulin is a natural, plant-derived soluble dietary fibre that functions as an indigestible carbohydrate and acts as a prebiotic. Inulin is fermented by the gut microbiota into short-chain fatty acids (SCFAs) in the rumen of ruminants and in the hindgut of monogastric animals. These SCFAs exert biological effects through activation of G protein-coupled receptors (GPRs), including GPR41, GPR43, and GPR109A, as well as through inhibition of histone deacetylase activity. Collectively, these mechanisms may contribute to the enhancement of intestinal barrier integrity, attenuation of oxidative stress, suppression of inflammatory responses, and maintenance of immune homoeostasis. These physiological effects are closely associated with measurable animal outcomes, including improved average daily gain and feed conversion ratio, reduced diarrhoea incidence, enhanced villus morphology and intestinal barrier indicators, increased antioxidant enzyme activity, decreased pro-inflammatory cytokine expression, and improvements in milk yield, milk composition, and egg quality. However, the strength of this relationship depends on species, physiological stage, dietary background, supplementation dose, and study duration. As a natural feed additive, inulin enhances the intestinal health, immunity, growth performance, reproductive outcomes, and lactation efficiency of livestock and poultry, making it a promising option for application in animal husbandry. Based on the synthesised evidence from the studies included in this review, the reported effective dietary inclusion levels of inulin across major livestock and poultry species are summarised as follows. For commercial laying hens, a dietary inulin inclusion of 15 g/kg appears to be a level associated with beneficial responses throughout the production cycle, with consistent improvements documented in laying performance and egg quality parameters. In broiler chickens, 10 g/kg dietary inulin represents a reported effective inclusion level, whether supplemented as a standalone additive or in combination with probiotics, and has been linked to favourable effects on growth performance and intestinal health. In intensive swine production systems, supplementation with 5 g/kg high-purity inulin appeared effective under the conditions of the reviewed studies for weaned piglets, with reported effects of alleviating weaning-associated stress and reducing the incidence of post-weaning diarrhoea. For growing-finishing pigs, a dietary inclusion of 20 g/kg high-purity inulin is a reported effective level associated with improved growth performance and carcass characteristics. In lactating dairy cows, daily supplementation of 200 g of inulin per cow represents a reported effective dosage associated with favourable production outcomes, including enhancements in milk yield and composition, as well as modulation of the ruminal microbial community. In fattening beef cattle, dietary inclusion of 20 g/kg inulin (on a dry matter basis) appeared effective under the conditions of the reviewed studies across feeding regimens, with improved feed conversion efficiency (FCR) and rumen fermentation characteristics observed under both low-concentrate (concentrate-to-forage ratio, C:F = 40:60) and high-concentrate (C:F = 60:40) dietary conditions. Given the inconsistent findings across individual studies and the limited evidence supporting well-defined dose-response relationships, the values summarised above should be interpreted as reported effective supplementation levels or dosage ranges linked to beneficial effects in the included studies, rather than unequivocally established optimal inclusion rates. This paper reviews the physicochemical properties, key physiological functions, and potential uses of inulin in livestock and poultry production, providing valuable insights for its incorporation into animal feed.