In the ever-changing landscape of the pet food industry, various commercial pet food formats have emerged in response to consumer demands and attempts to optimize nutrition. The effects of processing conditions, especially heating temperature and duration, on pet food digestibility remain a critical area of exploration. In a recent study conducted to address this gap, University of Illinois Urbana-Champaign researchers conducted an experiment to determine the amino acid digestibility and nitrogen-fixed energy values of different formats of pet food. The scientists published their results in the Journal of Animal Science.
The study compared four distinct pet food formats: frozen raw, freeze-dried raw, fresh and extruded dog foods. Diets from well-known brands such as Hill’s Science Diet, Just Food for Dogs, Primal Pet Foods, and Stella & Chewy’s were subjected to precision-fed cecectomized and conventional rooster assays. The diets selected are Chicken and Barley Recipe, Chicken and White Rice Recipe, Chicken Formula, Chicken and Sorghum Hybrid Freeze-dried Formula, and Chicken Dinner Patties.
Amino Acid Digestions
- The freeze-dried raw showed the highest, while the extruded showed the lowest amino acid solubility.
- Lysine digestibility was significantly higher in freeze-dried raw and frozen raw compared to extruded.
- Threonine digestibility is higher in freeze-dried raw than extruded.
Reactive Lysine:Total Lysine Ratio
- Ratios ranged from 0.93 to 0.96, with freeze-dried raw, frozen raw, and fresh diets maintaining a consistently high quality profile.
Truly Metabolizable Energy
- Frozen raw showed higher true metabolizable energy than freeze-dried raw, fresh, and extruded.
- HFD showed higher true metabolizable energy than fresh and extruded.
- Freeze-dried raw showed higher true metabolizable energy than extruded.
The findings of the study emphasize the significant effect of diet processing on amino acid digestibility and actual amounts of energy intake. Interestingly, the freeze-dried raw, hybrid freeze-dried raw, frozen raw and fresh diets outperformed the extruded diet in terms of higher amino acid digestibility coefficients and greater actual energy intake values. . However, the study acknowledges that other factors, such as ingredient composition and macronutrient composition, may also influence these results.
For pet food industry professionals, these findings underscore the importance of considering processing conditions in the formulation of pet diets. While the study provides important insights, it also highlights the need for further research.
“More research in dogs is needed to test the effects of the format on food palatability, digestibility, stool quality, and other physiologically relevant outcomes,” wrote the authors of the study.
Roosters help study protein digestibility of pet food
A surgical procedure, similar to a human appendectomy, makes roosters an effective and efficient model for the digestive systems of dogs and cats, aiding pet food nutrition research. The method, called the precision-fed cecectomized rooster assay, allows Kelly Swanson, PhD, University of Illinois – Urbana-Champaign animal nutrition professor, to compare the digestibility of chicken feed with raw, steamed and retorted chicken.
“We and others in the pet food industry not only evaluate the protein quality (amino acid profile) of ingredients, but use the cecectomized rooster assay to assess amino acid digestibility,” he said in a previous article. “Knowing both protein quality and digestibility is necessary to accurately formulate diets and ensure dogs/cats are meeting their needs.
“Although the current study only tested specific ingredients, one could use this assay to test complete diets that have been processed in different ways,” he said. “If done that way, one can compare how extrusion compares to retort, pasteurization, freeze-drying, etc. It can also be used to test kibble diets made with chicken meal versus fresh chicken.”
Other methods of evaluating pet food protein and amino acid digestibility have drawbacks compared to the cecectomized rooster assay. For example, estimates of digestibility using fecal analysis are inaccurate because bacteria and other microorganisms, or microbiota, in the large intestines of dogs and cats alter the results, Swanson said. The cat and dog microbiota also consume some of the nutrients in the animal’s food, masking the true digestion of the pet’s food.
“In addition to avoiding the bias provided by the large intestinal microbiota, the cecectomized rooster assay allows one to test individual components,” he said. “This is not possible in dog or cat studies where complete diets must be fed, and the substance in question is only a proportion of the diet.”
Also, in vitro studies of nutrient digestibility cannot match the cecectomized rooster assay, Swanson said. In vitro lab experiments focus on specific ingredient categories, such as soy or chicken-based proteins, so those methods are not accurate for other ingredients. This makes it increasingly difficult to test novel pet food ingredients.
“Therefore, we believe that the cecectomized rooster assay is the best choice for testing the amino acid digestibility of new protein sources or those subjected to different processing conditions,” he said.
Effects of cecectomized rooster assay on birds
For decades, scientists have used the cececomtized rooster assay as a model of not only dog and cat digestion, but also humans and animals. Although there are differences between the anatomy and metabolism of mammals and birds, biologists have found that the cececomtized rooster assay provides a good estimate for the digestion of dogs, cats and other animals.
Roosters themselves experience few health issues from the surgery to remove their two cecums, or ceca, Swanson said. Roosters require a short recovery period before the study begins, after which the birds can be housed and cared for like other roosters in animal research facilities.
“In terms of animal welfare, the rooster assay is a good example of the 3R’s of research: reduction, replacement and refinement,” Swanson said. “It replaces the need for work on dogs and cats, is a refined and precise method, and requires a small number of animals (four or five birds per tested substance) because of its accuracy.”
