Use and limitations of alternative feed resources to sustain and improve reproductive performance in sheep and goats

In tropical, semi-arid, and arid areas, animal production is increasingly reliant on supplemental feeding, especially during energetically expensive reproductive seasons. The cost of many traditional feeds restricts their use in many countries, and producers are turning to alternative feed sources. These feed sources may supply the energy and protein requirements for reproduction, but can contain plant secondary compounds that affect various components of the reproductive cycle. In this article, we outline the intake requirements for reproduction in both sexes of sheep and goat, highlighting the importance of timing, as well as quantity, of supplementation on reproductive performance. We investigate examples of various alternative feedstuffs that have been studied throughout the world, such as willow cuttings, lupin seed, feed blocks, and alternative pasture species. We then review what is known about the effects of these feeds on reproduction in sheep and goats, from the well known estrogenic effects to some positive effects from feeds containing condensed tannins.