There are two strategic times to use a bot dewormer. One is during early spring just before bot larvae leave the horse's stomach. The other is in late fall, after a killing frost and after all bot eggs have been removed from the horse's coat. The other four times, you can also use ivermectin or you can choose from other dewormers, paying close attention to their effectiveness against strongyles, which are the biggest parasite threat to your horse's health. 

The easiest and most effective way to deworm your horse is to use paste dewormer in a tube. Most equine dewormers are either a low-volume dose (about 6ml.) or a high-volume dose (about 20ml.). Most ivermectin products are a low-volume dose. Low-volume dewormers are easier to administer: There is less to insert in the horse's mouth so there is less chance for mess and waste, and the smaller syringes are easier for small hands to operate one-handed. Dewormers should be at a low room temperature when administered. If they are too cold, they can be stiff and difficult to dispense from the tube. If they are too warm, they won't stick to the horse's tongue and palate well. Check the expiration date on the dewomer box or tube to be sure it is fresh. Clean any food out of your horse's mouth so that your horse does not mix the dewormer with the food and spit it out. If you are working alone, you can hold the lead rope and the cheek portion of the halter with your right hand and clean out the mouth with your left hand. Insert your fingers at the corners of your horse's lips and enter the interdental space where there are no teeth. Often just the presence of your fingers will cause your horse to begin moving his tongue and jaw and drop any hay wads he has hidden in the recesses of his mouth. Other times you will have to reach into the safe zones to remove wads of feed. To further clean your horse's mouth, flush it out with warm water. Remove the needle from a 60 cc plastic syringe and fill it with warm water. Hold the lead rope and the cheek piece of the horse's halter with your left hand. You may find you have more control if you slide your hand over to the noseband instead. Insert the syringe full of water into the corner of your horse's mouth between his teeth and his cheek. Then angle the syringe across toward his tongue and depress the plunger, releasing the water into his mouth. You may need to flush with two or three syringes of water if your horse's mouth was particularly full of food. Wait a few minutes in order to let him work all the water out of his mouth before you proceed. The dewormer won't stick to a very wet tongue or palate. 

If you are using a low-volume dose dewormer, adjust the syringe to the proper dosage according to your horse's weight. Remove the cap from the syringe. Use the same basic procedure to administer the dewormer as you did for flushing the mouth. With the halter or noseband in your left hand and the syringe in your right, insert the tube at an upward angle between the horse's premolars and cheek. Turn the syringe into the mouth cavity. If you are deworming a horse that opens his mouth and works his tongue right away, you'll be better off applying the dewormer to the roof of his mouth. If you apply it onto a busy tongue, he will likely spit it out as soon as you apply it. If you are using a high-volume dose dewormer, adjust the syringe to the proper dosage according to your horse's weight. Lock the ring into position so when you depress the plunger, it will stop dispensing at the desired dosage. If you are deworming a quiet-mouthed horse, insert the large tube just a few inches. Turn the dewormer tube inward and dispense the product onto the tongue. If the dewormer was at low room temperature, it will dispense easily. It is always a good idea, but especially if you are using a high-volume dose, to hold the horses head up for a minute so the dewormer has time to dissolve in his mouth. If some dewormer has ended up on your horse's lips, wipe it off with a damp cloth.