The variable keratin appendages of the forestomach epithelium on both sides of the reticulo-omasal orifice, emerging in early summer and disappearing towards the winter in the moose Alces alces L. were studied. During the study period, droppings of the free-ranging moose were collected randomly for faecal particle size distribution analysis. The morphological distribution, size and abundance of keratin end caps was recorded in moose that had died of various causes, and it correlated with the particle size distribution observed in faeces. The fusiform keratin filter of the reticulo-omasal orifice seems to reflect the forage quality and use. It is suggested that this filter prevents the passage of non-fragmented foliage and twig fragments of excessive size during the period of rapid and non-selective intake of high-quality mature forage and it disappears before the short growing season of easily available succulent vegetation with a high nutrient content.