Short-term acceptance of botanical feed additives by horses: a multidimensional behavioural and consumption analysis

Abstract Background Herbal and algal materials are increasingly used as feed supplements in horses, but their sensory properties may influence whether supplemented feed is readily consumed. This study investigated whether commercially sourced botanical materials differ systematically in short-term acceptance by horses and whether reduced acceptance is expressed through a coherent multidimensional behavioural and consumption-related response. Twenty adult warmblood horses were exposed to 50 dried dietary materials, comprising 49 plant materials and one macroalgal material ( Ascophyllum nodosum ). On each experimental day, 10 g of one material was mixed with 500 g of oats and 50 ml of water and presented at three routine feeding times. Leftover occurrence, pre-ingestive olfactory exploration and completion time among completed trials were analysed using Bayesian mixed models. Model-adjusted material effects were combined using principal component analysis. Results The first principal component (PC1) explained 70.2% of between-material variation and summarised the three response domains as a statistical composite, with higher scores indicating a relatively less favourable behavioural and consumption profile. Ten materials were classified as clearly unfavourable, including Zingiber officinale , Pimpinella anisum and Ascophyllum nodosum , whereas six were classified as clearly favourable relative to the 50 tested materials, not relative to oats alone. Botanical-material-level effects were positively correlated across response domains, and olfactory exploration was associated with higher odds of leftovers (OR = 2.29, 95% CrI 1.28–4.07). The unfavourable end was substantially more reproducible than the favourable end and remained evident across analyses addressing individual-horse influence, prior specification, treatment of incomplete trials, trial position, hypothetical calendar-day-effect scenarios and exposure-opportunity proxies. Conclusions These findings indicate that reduced acceptance of botanical materials in horses is multidimensional and is not adequately represented by consumption time alone. The most robust result was the persistence of a reproducible low-acceptance tail rather than the exact ranking of all tested materials. The findings therefore support targeted investigation of the sensory, chemical and experiential factors underlying reduced acceptance.