I have entered your mare’s dietary information into our ration evaluation software, MicroSteed, to see how well the combination of forages, grains, and supplements are meeting her requirements. From what I see in the current diet, there appear to be sufficient calories, but it may be lacking a little in phosphorus and selenium, both of which will most likely be remedied as you make the changes in diet for upcoming parturition and lactation. The only nutrient deficient is sodium, which is probably not a problem if you have free-choice salt available to the mare.

Because you are feeding such a small amount of concentrate (a handful), you may want to consider using a ration balancer, which would provide the nutrients without a lot of extra calories. A ration balancer is better at fortifying a ration with protein, calcium, and phosphorus than a typical vitamin/mineral supplement that is only fed in ounces. If you decide to use the balancer pellet, you will want to phase out the product if you increase the concentrate feed, as described next.

With parturition pending, if the mare is at a good weight, you will probably not want to increase the amount of concentrate feed until the last 30 days of pregnancy and risk the mare gaining too much weight. You were not specific as to which concentrate you are feeding, but it is wise to choose a feed that is labeled for broodmares. Then, during the last 30 days (310-340 days) of gestation, gradually bring her up to a couple of pounds of the feed or whatever the minimum feeding rate is for that feed. This way, when she foals and her caloric needs increase exponentially to meet the needs of lactation, it will not be as much of a shock to her digestive tract to be consuming larger quantities of a concentrate feed.

If the mare is a really easy keeper and does not need all the extra calories from a concentrate feed even during lactation, it is possible to keep her on the ration balancer at 2-3 lb (0.9-1.4 kg) per day.