By-Products in Pet Food: Good or Bad? The Science vs. the Marketing

What By-Products Actually Are: The AAFCO — see our pet food label guide for how to interpret these standards Definition

AAFCO (the Association of American Feed Control Officials) defines "poultry by-products" as the non-rendered clean parts of slaughtered poultry — including heads, feet, and viscera (internal organs), but specifically excluding feathers except in unavoidable trace amounts. "Chicken by-products" follows the same definition for chicken specifically.

The viscera — internal organs — include:

• Liver
• Kidneys
• Heart
• Lungs
• Spleen
• Gizzards
• Intestines (cleaned)
• Undeveloped eggs

The definition explicitly excludes feathers, hair, horns, hooves, teeth, and hide — the actual waste components of slaughter. When a bag of dog food says "no by-products," it's technically advertising the absence of organ meats. Whether that's a selling point depends entirely on your view of organ meat nutrition — and nutritionally, there's a strong case that removing organ meats makes a food worse, not better.

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9 Dog Foods To AVOID (And The 2 That Are Worth It)

We researched dozens of options, analyzed thousands of verified reviews on Amazon and Reddit, and cross-referenced expert recommendations from AKC breed standards, veterinary journals, and verified Amazon owner reviews. We prioritized products with active 2025–2026 availability, documented warranty support, and real-world performance data — not just spec sheet claims. Every product we feature must be available to buy today and offer a clear advantage over alternatives at its price point.

Why Organ Meats Are Nutritionally Dense

In virtually every traditional food culture in the world, organ meats are prized — not discarded. Foie gras, liverwurst, pâté, haggis, menudo, pajata, kidney pie, sweetbreads, andouille sausage made with intestine, sushi with salmon roe — these are the dishes that command premium prices in restaurants and appear at celebratory meals. The Western preference for muscle meat over organ meats is historically recent and culturally specific. It is not a nutritional judgment.

Here is what the primary organ meats in by-products actually contain:

For Senior Dogs: Wellness Complete Health Senior Dry Dog Food

Liver is arguably the most nutrient-dense food in existence. It is:

• The richest dietary source of vitamin A — so rich that veterinary nutritionists cap liver at approximately 5% of a dog's homemade diet to prevent vitamin A toxicity
• Extraordinarily high in vitamin B12 — one ounce of beef liver provides roughly 988% of the human daily value
• Very high in riboflavin (B2), folate, iron, and copper
• High in quality, highly digestible protein

The concern about liver vitamin A toxicity in homemade diets actually demonstrates how potent it is — you have to be careful not to feed too much because it's too nutritious. That's not a characteristic of filler.

Heart

Heart muscle is one of the richest dietary sources of taurine — an amino acid that is conditionally essential for dogs and absolutely essential for cats (who cannot synthesize it). The research into dilated cardiomyopathy (DCM) in dogs has focused substantially on taurine availability: some grain-free diets with high legume content appear to impair taurine synthesis or absorption in susceptible breeds. Heart in the diet provides taurine directly, bypassing that synthesis pathway.

Beyond taurine, heart is high in coenzyme Q10 (CoQ10), B vitamins, iron, and zinc.

Kidneys

Kidneys are high in B vitamins (particularly B12 and riboflavin), iron, zinc, and selenium. Like liver, they are used in human cuisines worldwide — steak and kidney pie, rognons sautés in French cooking, kidney as a breakfast component in traditional British cooking.

Our Top Pick: Purina Pro Plan Large Breed Adult Shredded Blend Chicken & Rice

Gizzards are high in protein, iron, and zinc. Lungs are lower in nutrients than liver or heart but are still a quality protein source.