Hi J B,
This is an interesting question and I’ll give you my thoughts. When two complete and balanced foods are mixed the resulting mixture is complete and balanced. However, feeding for weight loss is a special situation, a complete and balanced food, when fed to achieve weight loss, may not meet nutrient needs.
This is because nutrient levels in foods are tied to an assumed average intake. Because a caloric deficit is needed to achieve weight loss, weight loss foods need to be fortified with nutrients so that when feeding fewer calories a dogs nutrient needs are met.
In this situation you are asking if feeding a presumed fortified with a non fortified food will meet the dogs needs. To answer that you’d need to know the nutrient levels of each food to calculate the levels in the resulting mix, factor in the amount being fed and then compare to needs.
To add to the puzzle is that the nutrients in the vitality formula to support senior health will be being fed at a lower level which may or may not affect outcome.
You said your dog weighs 83 lbs. How much of the vitality formula is she eating a day? What other calorie sources are consumed? Treats, Supplements, dental chews etc. In my experience, Hill’s feeding guidelines are well calculated and so if currently she is consuming an amount at the higher end of the feeding recommendations I’d simply cut back to the lower range and trim other sources. If however she is already consuming at the lower end of the Vitality feeding range, and you would need to feed less than the recommended amount of that diet to achieve weight loss I’d consider switching completely over to a weight loss formula
Finally, Hill’s has a vet support service and you can ask your vet to contact Hill’s, discuss your particular dog, and get customized feeding advice.
