In addition to the nutritional relevance, the use of these ingredients has a significant positive environmental impact due to the reuse of industrial waste. Animal rendering reduces the disposal of by-products and contributes directly to the circular economy and sustainability of the production chain.

However, the quality of these raw materials depends directly on industrial processing, microbiological control, oxidative stability and bromatological standardization. Inadequately processed ingredients can compromise digestibility, amino acid bioavailability, lipid stability, and food safety.

Internationally, entities such as the Association of American Feed Control Officials (AAFCO) and the European Pet Food Industry Federation (FEDIAF) establish nutritional and regulatory parameters widely used by the pet industry. In Brazil, the Ministry of Agriculture and Livestock (MAPA) regulates the inspection, production, transportation and use of ingredients intended for animal feed.

Thus, this bibliographic review aims to robustly discuss the use of animal meals and fats in the diet of dogs and cats, addressing bromatological composition, digestibility, inclusion levels, physiological differences between species, regulation and trends in the pet food market.

Meat and bone meal (MBM) is one of the main protein sources used in the pet industry due to the high content of protein and minerals, in addition to the wide commercial availability.

Its bromatological composition may vary according to raw material and industrial processing, normally presenting:

The protein digestibility of meat and bone meal ranges between 70% and 85%, depending mainly on the amount of bone present and the intensity of the heat treatment.

Studies conducted by Kawauchi (2012) demonstrated that excessive temperatures significantly reduce lysine availability and protein digestibility due to the occurrence of Maillard reactions and structural denaturation.

Meat and bone meal has an important mineral contribution, especially calcium and phosphorus, and is often used in standard and premium foods. However, high ash levels can compromise digestibility and increase fecal volume.

In dogs, inclusion levels typically range between 5% and 20% of the total formulation. In cats, levels tend to be lower due to higher demand for highly digestible proteins and lower tolerance to high mineral contents.

From an economic point of view, MBM has an excellent cost-benefit ratio, being widely used in economic and standard formulations.

Under the regulatory aspect, MAPA establishes strict sanitary controls related to the use of animal by-products in animal feed, especially after international regulations associated with bovine spongiform encephalopathy (BSE).

Offal meal is considered one of the raw materials of greatest biological value used by the pet food industry.

Produced from internal organs such as liver, heart, lungs and gizzard, it has high digestibility, excellent amino acid profile and high palatability.

Its average composition includes:

Offal meal has superior digestibility to meat and bone meal due to the lower mineral content and higher concentration of muscle and organic tissues.

In cats, this ingredient assumes even greater importance due to the natural supply of taurine and high concentration of essential amino acids.

In addition, the liver present in the meal provides important fat-soluble vitamins, especially vitamin A and B-complex vitamins.

In the premium and super premium segments, offal meal often constitutes the main protein source due to the high acceptance by animals and better consumer perception.

Digestibility studies show that diets containing offal meal promote lower fecal volume, higher protein utilization and better fecal score when compared to formulations containing higher levels of meat and bone meal.

Inclusion levels typically range between 10% and 30% in the extruded dry formulations.

Hydrolyzed feather meal is produced through the thermal and hydrolytic breakdown of keratin present in poultry feathers.

Keratin has a structure highly resistant to enzymatic digestion, requiring processing under high pressure and temperature to increase digestibility.

Its average composition presents:

Despite the high protein content, feather meal has limitations related to the unbalanced amino acid profile and lower protein bioavailability.

When properly hydrolyzed, it can achieve digestibility greater than 75%. However, inadequate processing significantly reduces nutritional utilization.

Inclusion levels typically range between 2% and 8% of the total formulation, being used mainly in economical and standard foods.

In premium formulations, its use tends to be reduced due to the negative perception of the consumer and the search for proteins considered of higher biological quality.

Still, from an environmental point of view, feather meal represents an important sustainable alternative for the use of poultry waste.

Blood meal has one of the highest protein contents among the ingredients of animal origin used in the pet industry.

Its average composition includes:

The ingredient stands out mainly for its high concentration of lysine, an essential amino acid often limiting in plant formulations.

However, blood meal has limitations related to low palatability and amino acid imbalance, especially low levels of sulfurized amino acids and isoleucine.

Its use normally occurs at moderate levels, ranging between 1% and 5% of formulations.

Drying methods directly influence nutritional quality. Overly aggressive processes reduce digestibility and cause protein degradation.

In addition, blood meal requires strict microbiological control due to the high biological activity of fresh blood.

Animal fats perform fundamental nutritional, technological and sensory functions in pet foods.

The main sources used include beef fat, pork fat and poultry fat.

Its high energy composition provides approximately 8.5 kcal/g, representing an important source of metabolized energy.

In addition, lipids contribute to:

• absorption of fat-soluble vitamins;
• supply of essential fatty acids;
• maintaining the integrity of the skin and coat;
• improvement of the inflammatory response;
• increased palatability.

In cats, animal fats play an even more important role due to the metabolic requirement for arachidonic acid, a nutrient found mainly in animal tissues.

Inclusion levels typically range between 8% and 20% in dry commercial formulations.

However, lipid oxidation is one of the main technological challenges associated with animal fats.

The formation of peroxides compromises sensory quality, stability and food safety. Thus, antioxidants such as tocopherols, BHA and BHT are widely used by the industry.