The scale of the job she is doing
A mare in the first months of nursing is feeding two horses on one mouth. Milk production climbs steeply after foaling and peaks while the foal is still small enough to look harmless, and the energy, protein and minerals leaving her body in milk each day far exceed anything pregnancy demanded. Mares that are underfed in this window milk at the expense of their own bodies, losing topline and rib cover while the foal still grows — for a while. Feeding the lactating mare well is feeding the foal, protecting the mare and setting up her next breeding season all at once.
Forage stays at the center
Her ration is built on forage first: as much good-quality hay or grazing as she will eat, offered so she is rarely standing at an empty rack. Quality matters more now than at any other time — leafy, early-cut forage carries the protein and energy density that stemmy, late forage cannot, and a mare milking hard on poor hay will eat to her gut's capacity and still fall behind. Where pasture is good, grazing does much of the work; where it is not, hay quality is where the money belongs.
Adding concentrate, gradually and divided
Most lactating mares need a concentrate feed on top of forage, chosen for breeding stock and introduced or increased in steps over days, never in a single jump — her gut microbes need time to adjust, and abrupt changes risk colic in exactly the horse you can least afford to have ill. Divide the daily amount into at least two, preferably three, smaller meals; a mare's stomach is small for her size, and several modest feeds are digested better and safer than one large one. Follow the condition of the mare, not the calendar, when deciding how much: a mare holding her weight needs no increase, whatever the foal's age.
Protein, minerals and the water nobody budgets for
Milk is mostly water, and a lactating mare drinks strikingly more than a dry one — her water must be clean, plentiful and never allowed to run dry, freeze over or foul, because her intake and her milk fall together. Protein quality matters for milk production, and calcium and phosphorus leave in milk in quantity, so a feed or balancer formulated for lactating mares earns its place over a generic ration. Salt available freely encourages the drinking she needs to do.
Read the mare weekly
Stand back once a week and score her honestly: ribs felt easily under a smooth cover is the target, a visible ribcage and a sharpening topline mean the ration is behind her, and a mare gaining fat is being fed for a job she is not doing. Adjust in small steps. As the foal grows, starts on creep feed and nurses less toward weaning, taper her concentrate down gradually in step with his independence, so her milk dries up comfortably and her condition arrives at weaning where you want it.
When to bring the vet in
A mare losing condition despite generous feeding, a hot, swollen or painful quarter of the udder, milk that looks abnormal, or a mare off her feed and dull should be seen by your veterinarian promptly — a milking mare's problems quickly become the foal's problems too.
Her stepped-up ration stays on track when it lives in KinsLe's Care Teams: each of the mare's daily meals can be an assigned duty for the yard, marked complete with a timestamp, so her feeding never depends on one person's memory.