If you see your dog to vomit, suffering from diarrhea or frequent loose motion or if the dog refuses to eat and drink, it is documented evidence of some degree of dehydration, so measures should be taken to prevent the dog's condition from worsening. A dog can get dehydrated due to vomiting and diarrhea. Without water, dogs can quickly become dehydrated and suffer serious health issues. Dehydration may occurs when the body is low on fluid.
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SYMPTOMS OF DEHYDRATION:
• A dehydrated dog's gums will feel STICKY (DULL) and DRY. Normal dog's gums will always feel SLICK (slippery), reflective and WET to the touch.
• Dehydrated dog's skin will lose elasticity. Dehydrated dog will not have the degree of skin elasticity (if you pull and relese the skin at the scruff of the neck/shoulder, it will flatten out immediately for the normal dog; but in case of dehydrated dog it will lose its elasticity and take long time to flatten; skin does not snap back into place immediately. The longer it takes the dog's skin to flatten, the more severe the dehydration).
• Dehydration may also show the sign of Lethargy, Depression & Sunken eyes of the dog
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You may take the following actions to prevent and treat dehydration:
1. Encourage and allow your dog to drink plenty of water or salt water
2. Offer unflavored mixed food with water in a 50-50 mix. If vomiting persist, offer broth ice cubes to the dog as this will enable the dog to take slowly, preventing additional vomiting.
3. If the dog refuses to drink or unable to drink, use a large liquid oral syringe to feed the dog. Give about 1/4 cup of ORS or oral saline every 20-30 minutes for eight hours.
4. Offer salt mix (table salt) beef broth or watery chicken broth to the dog. If the dog able to eat well, feed the dog salty wet food or add slight hot salty water to the dog's dry food and allow the dog's to digest and absorb the water, food.
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If you see your dog to vomit frequently, having diarrhea or loose motion and refuses to eat, notice it to the veterinarian who will inject intravenous saline or subcutaneous Ringer’s solution injection.
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http://petcare.suite101.com/article.cfm/causes_and_cures_for_dehydration_in_dogs#ixzz0rSv7UdMo
http://petcare.suite101.com/article.cfm/causes_and_cures_for_dehydration_in_dogs
http://ezinearticles.com/?How-to-Prevent-Your-Dog-From-Dehydration-and-Other-Effects-From-a-Lack-of-Fluids&id=3534578
http://www.natural-dog-health-remedies.com/dog-dehydration.html

Dog dehydration is a very common problem in dogs and it affects puppies, overweight dogs and older dogs of any breed and size. In order to detect dehydration in dogs it is very important to notice the loss of any skin elasticity by pinching the back of the dog's neck. In younger dogs the skin generally falls back in place but in the case of older dogs there is the presence of excess body fat. Obese dogs lose body elasticity faster and many people often mistakenly think that their dogs are dehydrated due to this sole reason.

You can check for heavy panting and dry and sunken eyes. There are symptoms of vomiting and diarrhea. You will also notice some lethargic behavior in your pet. Your pet may also vomit frequently and have dry gums and mouth. In order to rehydrate your dog you must ensure that your dog drinks plenty of water in small amounts. Excessive drinking may result in your dog vomiting the water. You should bring the dog to a shaded area if you are out in the heat. You should not give the pet any dry food to eat so that he does not block his throat. You can also hydrate him by mixing electrolysis in his water to drink. If your animal does not want to drink water you should add broth to his water so that he drinks the water.