Much like Vitamin A supplement the addition of Vitamin D3 is very common in the dog-food industry. With more dogs living indoors and not getting enough sunlight the addition of synthetic Vitamin D has become important supplement for the adsorption of Calcium in animal diets. Below the most common issues with Vitamin d3 has been listed.
Effects: Vitamin D3 helps to promotes the animals absorption of calcium, which is essential for normal development and maintenance of healthy teeth and bones. It also helps maintain adequate blood levels of calcium and phosphorus. With fewer dogs getting access to UV light this becomes an important vitamin when living in the city with a small house dog. Note that 15 minutes of sunlight 3 times a week is normally enough time for the body to make its own source of Vitamin D.
Deficiency: Signs of deficiency of Vitamin D in animals would normally include bone malformations (rickets) such as bowing of the dogs legs, thickening of the joints, and an increased incidence of fractures. You need to see a vet about this.
Stability: Stable in food storage, cooking and processing.
Sources: Vitamin D is only found naturally in animals and animal products. Halibut and cod liver oil, saltwater fish, cheese, yogurt, eggs.