Lactation and lactational effects on metabolism and reproduction in the horse mare

Prolactin plays a major role for lactogenesis and for the initiation but not the maintenance of lactation in the horse. While experimentally supplemented or naturally occurring dopamine agonists inhibit the onset of lactation in the mare via a reduction in prolactin release, treatment with dopamine antagonists stimulates lactation. In lactating mares, follicular growth and ovulation are resumed early postpartum and are not prevented by suckling or by the presence of a foal. Lactational anoestrus does not exist as a physiological condition in the horse. Mares are able to meet the increased energy expenditure during lactation mainly by increasing feed intake while mobilisation of body reserves is limited. Plasma leptin concentrations are reduced after foaling. Plasma IGF-1 levels increase in late gestation, reach a maximum at foaling and decrease gradually thereafter. After foaling, LH release increases and reaches levels comparable to non-lactating mares. This increase, together with simultaneously high IGF-1 concentrations, may stimulate the rapid resumption of cyclic ovarian activity within less than 2 weeks after foaling.