Like the majority of pets in this fast paced world of convenience items, your pet has probably been fed a commercial diet for most of its life to date.  Commercially manufactured foods are filled with additives, sugars, preservatives, dangerous chemicals, etc. In addition, perhaps your pet has been sick for a while and has been given antibiotics or medicine. Now you are going to start feeding a fresh, raw, "natural" diet. 

During the transition and for a short time period afterwards, you may notice that your pet becomes sick.  All pets react differently to the new diet depending on their age, health, and how long they were given commercial diets. Your pet's symptoms may range from non-existent, to mild to severe.  Some symptoms you might notice are:  diarrhea, vomiting, itchy skin, oozing skin, ear infections, eye discharge, anal gland problems, etc.  These reactions are the body's way of ridding itself of accumulated toxins.

Do not be alarmed if you notice some of these things happening to your pet at first.  This is a classic example of something that must get worse before it can get better.  The body is healing itself from the inside out. Once the detoxifying process is concluded, these symptoms will disappear and you will have a healthier, happier pet. The symptoms should not last more than 2 weeks, provided your pet is relatively disease-free at the beginning.  Pets with histories of health related problems may experience longer episodes of detox.  If these detoxification symptoms should persist or become violently worse it is important to seek the help of your holistic veterinarian.  

During the detox time, it is also important to bathe your pet weekly or even more often if the skin is badly infected.  Bathing is a good way to clean the skin and wash the toxins away.  Use a mild, gentle, shampoo and remember to rinse very well. 

Always keep fresh, pure drinking water available.  

The following information is from Dr. Pollak's article titled "Healing Episodes" (also sometimes referred to as Healing Crisis).  It covers the detoxification process well:

"Upon switching to a more nutritious diet, physical and behavioral improvements can be dramatic or gradual depending on the state of the animal's health.  Severe nutritional deficiencies and toxic states have been known to mimic almost every known disease in veterinary medicine.  In chronic conditions, some developing over several generations, improvement in health can take months or years.  A pet's ability to respond to high protein diets may require the individual animal "transitioning" through periods of purification or detoxification.  Malnutrition and the toxic condition of the animal fed commercial diets can result in the inability to digest and assimilate basic food components of the fresher, more wholesome type we are describing here.  The body will sometimes expel these accumulated poisons during periods of diarrhea, hair loss, or scaling of skin.   These periods are known as Healing Episodes.  Though these situations are not necessary, they are not uncommon.  The body will cleanse itself of these toxic agents before it can assimilate more healthful nutrients to regain a higher state of balanced health.

During these Healing Episodes, the animal's immune system continues to react to remaining toxins and poisons until a more gentle, balanced diet can complete the transition to a more resilient internal state.  These periods, during which time the animal can have diarrhea, loss of some of its coat, and appear transiently sick, are really signs of a more vital life force finally shedding disease more completely.  The situation is an important sign indicating a transitioning to a state of greater Wellness.  The frequency, intensity and duration a Healing Episode is totally dependent on the individual animal's health, nutritional state, age and breed.   Each animal will react differently during the transitioning to a more nutritious healthier diet.  Not always will there be signs of purification.  We can rest assured that as long as the animal is clear eyed, bright and full of energy of life, these periods (should there be any) will quickly pass and the need for medical intervention is almost never.  As concerned pet owners seek out these more wholesome natural food sources, we can anticipate occasional brief detoxification episodes. Finding professional or lay support that understand the process of Healing Episodes will help make the transition for the owner easier and less filled with fear and doubt."