Added Fat Improves Horse Behaviour

flaxseed oil Has a 41 ratio of omega 3s to omega 6s making it an ideal choice
Chia seeds Has similar omega 3 to omega 6 ratio as flax
Canola oil 10 percent omega 3s and relatively low in omega 6s. Also contains monounsaturated fatty acids no harmful impact on inflammation
Rice bran oil Only 1 percent omega 3s less than 50 percent omega 6s and high in monounsaturated fatty acids
Copra meal and coconut oil Not a source of omega 3s and omega 6s but rather medium chain fatty acids which may be beneficial when added to an omega 3 source
Soy lecithin Only 4 percent omega 3s but also contains choline a helpful component of neurotransmitters
Soybean oil Only 7 percent omega 3s and mostly omega 6s less desirable choice
Corn oil No omega 3s and higher in omega 6s than soybean oil poorest choice.
How Much?
I prefer to limit fat intake to no more than 10 percent of the total calories though some athletes are fed levels as high as 20 percent. For the lightly exercised mature 1100 lb 500 kg horse the National Research Council recommends a minimum total diet of 20 Mcals per day to maintain body condition. Ten percent would be 2 Mcals per day from fat. One cup 8 fluid ounces or 240 ml of oil will meet this requirement. It weighs 240 grams and at 9 kcalsg provides 2 16 Mcals. 
How to Add?
When adding any amount of oil to your horses feed start with a small amount say one tablespoon or 15 ml. Most horses do not like oily feed but more important it takes several weeks for the horses cells to become accustomed to metabolizing more fat.
Summary
Short attention span spookiness reluctance to work excessive sensitivity and alertness to surroundings irritability and hot behaviours can be reduced by adding fat to the diet. Fat is high in calories so limit the amount you feed based on the horses weight and his caloric need. Omega 3s need to be in balance with omega 6s so choose oils carefully. And finally build up to desired intake by starting slowly and increasing over four to six weeks.