It contains a blood vessel and a nerve, so avoid cutting it

Clipping nails with no consideration will most likely lead to cutting the quick. How do you avoid doing this? For dogs with clear nails, the quick is visible and you should only trim the white or the tip of the nail. When you start getting close to the pink, you should stop.

Most people when cutting nails try to cut directly across the dog’s nail (as in the diagram below).

3. Watch for aggression
Some dogs absolutely hate having their nails cut, especially if they had a traumatic experience with it at some point. If you can successfully trim one or two nails, you'll likely be fine. If the dog is attempting to attack you when trimming, it may be necessary to take them to a professional groomer. Another option is to use a Dremel tool instead of clipping, which allows you to grind down the end of the nail instead of cutting it off. Some dogs prefer this.

Shiny, healthy nails; moist, uncracked pads

Almost anyone who has trimmed a dog’s nails has probably had the unfortunate experience of cutting too close -- and it hurts! A normally healthy dog will not bleed to death when that vein inside their nails is cut or broken. It can be quite intense when the blood does start to flow, fast and furious, but a healthy animal will have the proper coagulation that will stop the flow in due course. There are ways to stop it, products made for the same purpose as when a man cuts himself shaving. One such product is called Quik Stop, made with a styptic powder that basically cauterizes the wound and burns the vein closed. When cutting a dog's nails, I always have a small open pot of the powder ready beside me in case it is needed. It can cause a tiny bit of heated pain to the animal, so avoiding cutting the quick would be the best method, but that is not always possible. Just do not panic and in so doing panic the animal.

Clipping a Dog's Claws (Toenails)

My dog is almost two years old and he always had a problem with clipping his nails. Recently it has be getting harder to clip them because he runs away, moves his paw, anything really to not get his nails clipped. I don't want to accidently cut his nail in the wrong spot because he is moving so much! I have tried treats, doing one nail a day and giving lots of good boys and treats after, doing it when he is calm but nothing is working. He never had any bad experinces from cutting his nails. I have no idea what to do!! please help because his nails are getting long. thanks.

Fear of nail cutting | Cesar's Way

The most common reasons for avoiding nail trims are that 1) the owner is afraid of “quicking” the dog, or 2) the dog fusses and creates bad feelings around the procedure. Nail cutting becomes an event surrounded by angst and drama. For very active dogs, who run all day long on varied surfaces, cutting nails may not be necessary. High mileage wears them down naturally (Photo: Normal Toenails). But among city or suburban dogs, who are lucky to get a mile or two walk daily, excessively long toenails are more common than not.
A: Since individual dogs vary a great deal in their reactions to tranquilizers, I'm not in favor of their use at home without the direct supervision of a veterinarian. Few dogs enjoy nail cutting but most, with training, will learn to allow their nails to be cut without a major struggle.