Canine Anatomy, Physiology, and Species Appropriate Nutrition
January 2023
Canine professionals offer varying opinions regarding species appropriate nutrition for the domestic dog. Taxonomy includes the domestic dog in the order Carnivora, along with other primarily carnivorous mammals. (1)(2) However, the domestic dog does have the ability to utilize a limited amount of plant material. A basic understanding of canine anatomy and physiology will determine the ideal diet for the domestic dog.
Eyes
The position of the eyes is relative to whether a mammal is prey or predator. The eye position of prey is side facing, the eyes are set on the sides of the skull, which allows the prey a wider range of view for protection from predators. The eye position of the domestic dog is forward facing, the eyes are set on the front of the skull, which allows the dog to focus on prey while hunting. (3)
Dentition
Dentition refers to the number, type, and arrangement of teeth. The dentition of an herbivore includes flat premolars and molars, which function to grind plant material. The dentition of the domestic dog includes long pointed canines, which function to hold prey firmly in the mouth, as well as pointed premolars and molars, which function to tear flesh and crush bone. Carnassials are the largest and most powerful teeth, these are only found in carnivores, such as the domestic dog. (4)
Temporomandibular Joint
The temporomandibular joint connects the lower jaw to the skull. The temporomandibular joint of an herbivore has a wide range of motion, allowing for a side-to-side action, which functions to grind plant material. The temporomandibular joint of the domestic dog has a limited range of motion, allowing for a scissor-like action with a strong bite force, which functions to hold prey firmly in the mouth, as well as tear flesh and crush bone. (5)
Taste Receptors
Taste receptors are responsible for the sensation of taste. The tongue of a vertebrate that consumes large amounts of plant material holds many taste receptors that are sensitive to bitter, which function to protect the vertebrate from consuming toxic plant material. The tongue of the domestic dog does not hold many taste receptors that are sensitive to bitter, the dog requires less bitter taste receptors for the reason that flesh and bone is generally not toxic. (6) Instead, the tongue of the domestic dog holds many taste receptors that are sensitive to umami, which is described as a meaty flavour. (7)
Salivary Glands
The salivary glands secret saliva into the mouth. The saliva secreted from the salivary glands of a mammal that consumes large amounts of starch contains amylase, the enzyme responsible for starch digestion. The saliva secreted from the salivary glands of the domestic dog contains little to no amylase, the dog does not require large amounts of salivary amylase for the reason that flesh and bone does not contain starch. (8)(9)
Stomach
The stomach is a muscular organ that acts as a reservoir. The stomach of a ruminant herbivore is complex, consisting of multiple chambers, allowing for optimal digestion and fermentation of plant material. (10) The stomach of the domestic dog is simple and digestion is monogastric, the stomach consists of one large chamber, allowing for the consumption and digestion of large prey. (11)
Gastric pH
Hydrochloric acid is secreted into the stomach to control gastric pH. The gastric pH of an herbivore is significantly less acidic than the gastric pH of a scavenger, such as the domestic dog. A less acidic gastric pH is ideal for the digestion and fermentation of plant material. A more acidic gastric pH is ideal for the digestion of flesh and bone, as well as neutralizing pathogenic microorganisms from consuming decomposing carcasses. (12)
Small Intestine
The length of the small intestine is relative to the amount of plant material consumed. The small intestine length of an herbivore, such as the cow, can measure up to 49 meters, which allows for increased time for digestion and fermentation of plant material. (13) The small intestine length of the domestic dog can measure up to 5 meters, which allows for the quick passage of easily digested flesh and bone. (14)
Caecum
The caecum is a muscular organ located at the beginning of the large intestine that acts as a reservoir. The caecum of an herbivore, such as the cow, can measure up to 73 cm long and 24 cm wide, allowing for additional digestion and fermentation of plant material. (15) The caecum of the domestic dog is short and narrow with no significant function for the reason that flesh and bone are easily digested. (16) Excessive fermentation in the gastrointestinal tract of the domestic dog can lead to gastric dilatation-volvulus, a potentially fatal condition commonly referred to as bloat. (17)
Gut Microbiome
Gut microbiome refers to the microbial population inhabiting the gastrointestinal tract. The gut microbiome of a mammal that consumes large amounts of plant material inhabits microbes that produce cellulase, the enzyme responsible for cellulose digestion. (18) The gut microbiome of the domestic dog does not inhabit microbes that produces cellulase for the reason that flesh and bone does not contain cellulose. (19)
The eyes, dentition, temporomandibular joint, taste receptors, salivary glands, stomach, gastric pH, small intestine, caecum, and gut microbiome all determine the ideal diet for the domestic dog is primarily flesh and bone with a limited amount of plant material.
References
1. https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=726821#null
2. Aspinall, O'Reilly (2004) Introduction to Veterinary Anatomy and Physiology, Elsevier; p3
3. Aspinall, O'Reilly (2004) Introduction to Veterinary Anatomy and Physiology, Elsevier; p67-68
4. Aspinall, O'Reilly (2004) Introduction to Veterinary Anatomy and Physiology, Elsevier; p109-111
5. Aspinall, O'Reilly (2004) Introduction to Veterinary Anatomy and Physiology, Elsevier; p108
6. https://academic.oup.com/mbe/article/31/2/303/1000231?login=false
7. Case, Daristotle, Hayek, Raasch (2011) Canine and Feline Nutrition: A Resource for Companion Animal Professionals - 3rd Edition, Mosby Elsevier; p46
8. https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/full/10.1002/pmic.201700293
9. Aspinall, O'Reilly (2004) Introduction to Veterinary Anatomy and Physiology, Elsevier; p111
10. https://bio.libretexts.org/Courses/Hanover_College/Comparative_Anatomy_and_Physiology_of_Animals/02%3A_The_Digestive_System/2.02%3A_Digestive_Systems
11. Aspinall, O'Reilly (2004) Introduction to Veterinary Anatomy and Physiology, Elsevier; p113-114
12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4519257/
13. https://jemds.com/data_pdf/sreeknathc.pdf
14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7152060/#:~:text=It%20is%20approximately%201%20to,57%2D1%2C%20A
15. https://jemds.com/data_pdf/sreeknathc.pdf
16. Aspinall, O'Reilly (2004) Introduction to Veterinary Anatomy and Physiology, Elsevier; p118
17. Aspinall, O'Reilly (2004) Introduction to Veterinary Anatomy and Physiology, Elsevier; p113
18. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8865330/
19. https://vetnutrition.tufts.edu/2017/10/digestive-enzyme-supplements/?fbclid=IwAR16tAuRt5mSinfEWjsneCnixi21lgl-cE09rCE2C0hFrnSDxIURROp0Aus