Most local health food stores will have my two favorite items for calming horses who may be frightened by fireworks.
One is a homeopathic remedy called Aconite , used for fear or terror of sudden things, especially noises. Give your horse about 6-8 of the little pellets on a handful of food or a treat. The first dose can be given in the late afternoon, then give another dose later in the evening just before the fireworks. You can give another dose or two through the evening if you need to; it is very safe. Once the noise has stopped there is no need to continue.
Aconite may not stop every horse from being afraid, but it should settle most of them down at least to a manageable and safe level. Some will be very quiet and relaxed about the commotion.
Next is Rescue Remedy . There are different brand names, but if you ask for Rescue Remedy, this is a Bach Flower, which is a group of remedies for various emotional states. Rescue Remedy is for any stressful situation. Put about 10 drops of the liquid into your horse's mouth or into his water bucket or even the trough.
I would put 10 drops in the water source at the beginning of the day and refresh it with another 10 drops if you fill up the bucket/trough again. Close to the time the fireworks start, you can give a squirt (about 10 drops) directly into your horse's mouth or put it on a treat such as an apple. You can also dilute it in some water and squirt it into his mouth. Repeat the doses 3-4 times during the evening if you need to, or just be sure he has access to his water.
Give these simple things a try and see if your celebration is a bit more peaceful.
Dr. Joyce Harman is a veterinarian and respected saddle-fitting expert certified in veterinary acupuncture and veterinary chiropractic; she is also trained in homeopathy and herbal medicine. Her Harmany Equine Clinic is in northern Virginia. Visit her online shop .