Rating: 
Hill’s Prescription Diet Z/D dry dog food is not rated due to its intentional low meat therapeutic design.
The Hill’s Prescription Diet Z/D product line includes two dry dog foods, each designed to prevent “adverse reactions to food and claimed to meet AAFCO nutrient profiles for adult maintenance.
The following is a list of recipes available at the time of this review.
- Hill’s Prescription Diet Z/D Low Allergen
- Hill’s Prescription Diet Z/D Ultra Allergen-Free
Hill’s Prescription Diet Z/D Low Allergen dry dog food was selected to represent both products in the line for this review.
Hill's Prescription Diet Z/D Low Allergen
Dry Dog Food
Estimated Dry Matter Nutrient Content
Ingredients: Dried potato product, hydrolyzed chicken liver, potato starch, soybean oil (preserved with BHA, propyl gallate and citric acid), hydrolyzed chicken, lactic acid, powdered cellulose, calcium sulfate, dicalcium phosphate, glyceryl monostearate, iodized salt, choline chloride, vitamins (vitamin E supplement, l-ascorbyl-2-polyphosphate (source of vitamin C), niacin, thiamine mononitrate, vitamin A supplement, calcium pantothenate, biotin, vitamin B12 supplement, pyridoxine hydrochloride, riboflavin, vitamin D3 supplement, folic acid), calcium carbonate, potassium chloride, minerals (ferrous sulfate, zinc oxide, copper sulfate, manganous oxide, calcium iodate, sodium selenite), dl-methionine, taurine, preserved with mixed tocopherols & citric acid, rosemary extract, beta-carotene
Fiber (estimated dry matter content) = 3.4%
Red items when present indicate controversial ingredients
| Estimated Nutrient Content | |||
|---|---|---|---|
| Method | Protein | Fat | Carbs |
| Guaranteed Analysis | 21% | 16% | NA |
| Dry Matter Basis | 21% | 16% | 55% |
| Calorie Weighted Basis | 18% | 34% | 48% |
The first item in this dog food is potato product, a dried residue of the potato processing industry consisting primarily of potato pieces, peelings and culls.
Potato product is equal to corn in energy value yet contains 50% more protein.1
The second ingredient is hydrolyzed chicken liver, organ meat that’s been chemically broken-down into its component amino acids. Hydrolyzed proteins are considered hypoallergenic.
The third item lists potato starch. Potato starch is a gluten-free carbohydrate of only modest nutritional value to a dog.
The fourth item lists soil oil, red flagged here only due to its rumored (yet unlikely) link to canine food allergies.
However, since soybean oil is high in omega-6 fatty acids and contains no omega-3′s, it’s considered less nutritious than canola or flaxseed oils.
What’s worse, this oil is preserved with butylated hydroxyanisole (a suspected cancer-causing agent) and propyl gallate (a potential reproductive toxin).
This specific oil – especially preserved the way it is – should not be considered a quality component.
The fifth ingredient lists hydrolyzed chicken, another chemically processed meat item notable for its hypoallergenic qualities.
The sixth ingredient lists powdered cellulose, a non-digestible plant fiber usually made from the by-products of vegetable processing. Except for the usual benefits of fiber, powdered cellulose provides no nutritional value to a dog.
From here, the list goes on to include a number of other items.
But to be realistic, ingredients located this far down the list (other than nutritional supplements) are not likely to have much of an effect on the overall rating of this product.
With two notable exceptions…
First, we find no evidence of probiotics, friendly bacteria applied to the surface of the kibble after processing.
And lastly, we also note the minerals here do not appear to be chelated. And that can make them more difficult to absorb. Non-chelated minerals are usually associated with lower quality dog foods.
Hill’s Prescription Diet Z/D Dry Dog Food
The Bottom Line
Even though this is a prescription product, we continue to limit our judgment to the estimated meat content of the recipe as well as the apparent quality of its ingredients. And nothing else.
Our ratings have nothing to do with the accuracy of claims made by the manufacturer as to this product’s ability to effectively treat or cure a specific health condition.
So, to find out whether or not this dog food is appropriate for your particular pet, you must consult your veterinarian.
With that understanding…
Judging by its ingredients alone, Hill’s Prescription Diet Z/D appears to be a below-average dry dog food.
But ingredient quality by itself cannot tell the whole story. We still need to estimate the product’s meat content before determining a final rating.
The dashboard displays a dry matter protein reading of 21%, a fat level of 16% and an estimated carbohydrate content of 55%.
As a group, the brand features an average protein content of 20% and a mean fat level of 15%. Together, these figures suggest a carbohydrate content of 57% for the overall product line.
And a fat-to-protein ratio of about 72%.
Below-average protein. Below-average fat. And above-average carbs when compared to a typical dry dog food.
Yet when you consider the plant-based protein-boosting effect of the dried potato product, this is the profile of a kibble containing only a limited amount of meat.
Bottom line?
Hill’s Prescription Diet Z/D is a potato-based dry kibble using only a modest amount of hydrolyzed chicken liver as its main source of animal protein. However, due to its intentional no meat prescriptive design, this dog food is not rated.
Those looking for a wet product from the same company may wish to visit our review of Hill’s Prescription Diet Z/D canned dog food.
A Final Word
This review is designed to help you make a more informed decision when buying dog food. However, our rating system is not intended to suggest feeding a particular product will result in specific health benefits for your pet.
For a better understanding of how we analyzed this product, please be sure to read our article, “The Problem with Dog Food Reviews”
Remember, no dog food can possibly be appropriate for every life stage, lifestyle or health condition. So, choose wisely. And when in doubt consult a veterinarian for help.
Have an opinion about this dog food? Or maybe the review itself? Please know we welcome your comments.
Notes and Updates
07/19/2010 Original review
05/09/2012 Last Update
The Dog Food Advisor publishes independent reviews to help pet owners make better choices when shopping for dog food.