With dexterous lips and a defiant attitude, any horse can become a picky eater, but it is easy to keep your horse on a balanced, healthy diet no matter what its taste preferences may be.
Check for Oral and Digestive Health
Horses are not generally picky eaters, and when your horse goes off its feed, there is usually a 
reason for the change. Check for mouth sores or injuries, dental problems, stomach ulcers or digestive issues that could make eating painful, and address any health problems that may be affecting how your horse eats. Any condition, even one unrelated to eating, can also change a horse's diet if the animal is in too much pain to eat, so don't overlook any health considerations if your horse's eating patterns change.
Ensure Food Quality
Horses have sensitive tastes, and if food quality degrades with mildew, mold or other spoilage, they can often detect those differences even if the changes may be too subtle for humans to notice. If your horse refuses food that seems fine, double check the feeding trough, storage bins, scoops and other equipment and containers for signs of contamination. Similarly, check that the feed supplier has not changed the food's composition recently, a change picky horses might refuse.
Provide Nutritional Balance
Horses have an innate sensitivity for the nutrition they require, and a horse that seems to be picky about its feed may simply be nosing through to get just the supplements it needs while avoiding fillers. Check the nutritional value of the horse's feed, and make the appropriate adjustments to compensate for the animal's gender, age and physical condition, including breeding status, exercise and seasonal needs.
Moisten Grain
A horse might pick through its grain to get to the special treats it prefers, but if the grain is slightly moistened it will stick together better and encourage better eating. Moist grain will also have a more consistent flavor that can better appeal to a picky horse.
Reduce Treats
If a horse gets many treats during a training session or just for being a friend, it will be less likely to eat its meals properly because it will simply wait for a tastier morsel to be offered. Reduce the treats or eliminate them entirely until after the horse has eaten its feed and the picky eating will be reduced.
Offer Small Meals
Some horses are naturally light eaters and may not finish a large meal all at once. Offering several small meals more frequently can encourage better eating habits without risking that leftover food becomes rancid, contaminated or otherwise unpalatable and unhealthy.
Try Group Meals
Horses can be competitive eaters and will quickly finish a meal if they believe other horses may usurp their portions. Feeding horses together can encourage each animal to eat all the food offered, but be sure none of the horses are overly aggressive feeders when trying this technique.
Be Consistent
Horses don't always appreciate change, and it is necessary to gradually alter their feed if a change is necessary. Always use the same feed bags or containers, offer meals at the same time and feed horses in the same location to stave off picky eating from inconsistent habits.
It is natural for horses to occasionally be picky about their food, but by using several techniques, even the pickiest eaters can be encouraged to enjoy their meals more easily.