Horse Dung is a byproduct item in Rust used in farming and was introduced via the Farming 2.0 update. Players may only acquire it by feeding rideable horses and… ‘collecting’ it after a few moments. It is then only useful as fertilizer, created by placing horse dung into the Composter.
Fertilizer serves two potential purposes. It is used to improve the ground quality of both the Large and Small Planter Boxes. Alternatively, it can be harvested and sold directly to Bandit Camp at a rate of 3 Scrap per 2 fertilizers.
For more information regarding horse dung, fertilizer, and its assorted uses in plants, check out our extensive Farming guide.