How to Supplement Protein for Cats

1 How to Supplement Protein for Cats

Protein metabolism

How does protein work in a cat? First, a diagram shows protein metabolism in the cat.

After hydrolysis in the stomach and small intestine, a small part is absorbed directly by the small intestine; the rest goes to the liver, where after transamination and deamination it enters the urea cycle.

All this needs liver enzymes, which the cat cannot regulate; liver enzymes stay active, breaking down a fixed amount of protein into energy over a fixed time.

The enzymes of the urea cycle (which expels the toxic element ammonia) are also uncontrolled by the cat and can’t change activity with protein intake.

This trait greatly boosts the cat’s ability to clear ‘nitrogen waste’ but also weakens its ability to retain nitrogen.

In the 2016 ‘Nutrient Requirements of Dogs and Cats,’ the authors reported: on a protein-free diet, the cat’s urinary nitrogen excretion was the highest among the studied omnivores (pig, rat, dog).

Moreover, the urea cycle always involves amino acids (hydrolyzed protein); lack of protein stalls or even stops the cycle.

A stalled urea cycle can threaten the cat’s life.

Protein quality

Of course protein varies in quality; the key is how many essential amino acids it provides and in what amounts.

High-quality protein provides suitable ratios and higher levels of essential amino acids that the cat uses fully, with little waste.

Poor-quality protein, after digestion and breakdown, yields many non-essential amino acids the body can’t use well, and metabolizing them overloads the kidneys.

Protein quality is usually shown by digestibility (PDCAAS); closer to 1 means better protein.

How much protein a cat needs

To judge if a food meets protein needs, NRC gives a reference:

Crude protein concentration (E) and essential amino acid nitrogen (T) as a percentage of total amino acid nitrogen (E:T)

If crude protein is moderate, the E:T range is wide and meets the cat’s needs

If crude protein is very low, E:T must be high to meet needs

If unclear, see NRC’s concrete numbers

Protein should reach 50g/1000kcal ME, including 1.93g/1000kcal ME arginine, 0.85g/1000kcal ME methionine+cystine, and 0.1g/1000kcal ME taurine.

Is more protein always better?

The answer is yes: high-quality protein and meat are easiest for cats to digest; single-source protein foods—one high-quality meat—are the ideal diet.

Then why do some cats get diarrhea on high-protein food? Mainly two reasons:

1. Too many meat types make the protein source complex; the gut can’t tolerate it

2. Allergy or intolerance to some ingredient in the formula

In the wild, over 50% of a cat’s body energy comes from protein; its main calorie source is protein—so how could more protein be bad?