Introduction
When a dog dies, its body systematically begins to shut down. The cessation of life functions does not occur all at once, but instead happens progressively through a series of orderly and predictable stages. Understanding the sequence in which a dog’s bodily systems fail can provide pet owners insights into what to expect during the dying process.
The first things to stop functioning when a dog dies are the higher-order centres in its brain that control consciousness and cognition. As oxygen levels deplete, the cerebral cortex responsible for awareness and thought is impacted within seconds. Shortly after, the subcortical structures governing vital functions like respiration and heartbeat begin to fail. Within minutes, breathing and circulation shut down, which starves the organs of oxygen. The brain itself can survive only for a few minutes without an oxygen supply.
Following closely behind brain death, the dog’s heart stops beating and lungs cease activity. Kidney and liver function deteriorates quickly thereafter. The digestive system is generally the next to stop. Even cellular metabolism and immune responses can persist for hours after clinical death, but will eventually cease as cells die from oxygen starvation. Skin and muscles are the last systems to expire post-mortem.
Understanding this orderly shutdown sequence provides insight into the gradual process of passing that pets and their owners experience. Recognizing which functions fail first can also help identify signs that a dog is dying. By appreciating how the body progressively slows down and ceases activity, we can better prepare for our dog’s final moments.
The Brain
The brain is one of the first organs to shut down after cardiac arrest in dogs. Brain function and consciousness are lost almost immediately when the heart stops beating and blood flow to the brain ceases (https://pubmed.ncbi.nlm.nih.gov/2768903/). Within minutes, lack of oxygen causes irreversible brain damage.
One study induced brain death in dogs using high voltage electrical current to the head. This resulted in immediate onset of isoelectric electroencephalogram, indicating complete loss of brain function (https://pubmed.ncbi.nlm.nih.gov/8914628/).
Another study examined brain blood flow after inducing brain death in dogs. They found blood flow to the brain dropped dramatically within 30 minutes and brain function could not be restored (https://www.sciencedirect.com/science/article/pii/0883944192900334).
The brain requires constant oxygenated blood flow and is rapidly affected when circulation stops. It is one of the first vital organs to fail after cardiac arrest in dogs, with loss of consciousness and brain death occurring within minutes.
The Heart
When a dog dies, the heart is generally the first major organ to stop functioning. This is because the heart requires a constant supply of oxygen and nutrients carried in the blood in order to pump properly. As a dog dies, the brain signals the heart to slow down and eventually stop beating altogether. This leads to cardiac arrest, meaning the heart stops pumping blood effectively [1].
Once the heart stops beating, blood pressure immediately drops to zero as blood is no longer being pumped through the arteries and veins. Deprived of oxygen and nutrients, the heart muscle quickly becomes damaged beyond repair. Ventricular fibrillation may occur, which is uncoordinated quivering of the ventricles rather than pumping. The result is circulatory failure, as all bodily organs are starved of blood flow [2]. This rapidly leads to cell death and organ failure across the body.
Lungs
When a dog dies, the lungs are one of the first organs to stop functioning. The primary role of the lungs is to transfer oxygen into the bloodstream and remove carbon dioxide. Once the dog’s heart stops beating, the lungs no longer receive blood flow and can no longer transfer oxygen (Matsuyama et al., 2023).
Studies show that within minutes after cardiac arrest, the lungs become heavy and congested as fluid leaks into the airspaces (Fonkalsrud, 1976). This pulmonary edema causes the lungs to fill with fluid and lose their ability to oxygenate blood. As a result, the blood oxygen levels start dropping dramatically after death.
In canine transplantation research, studies show that ligating the pulmonary artery after 15 minutes of reperfusion leads to complete loss of lung function as it can no longer oxygenate blood (Okazaki et al., 2006). This demonstrates how rapidly lung function ceases after interruption of blood flow.
In summary, the lungs are one of the first vital organs to stop functioning after death in dogs as they require constant blood circulation to transfer oxygen. Within minutes after the heart stops, the lungs become flooded with fluid and unable to oxygenate blood.
Kidneys
The kidneys are two bean-shaped organs in the abdomen that filter waste products from the blood and produce urine. At death, the kidneys stop filtering blood and producing urine. According to a 2020 study published in PMC, acute kidney injury is common in dogs with chronic kidney disease (Source). As the kidneys fail, toxins build up in the bloodstream leading to symptoms like vomiting, diarrhea, weakness, and weight loss.
Kidney failure is one of the most common causes of death in older dogs. In end-stage kidney disease, the kidneys have lost about 75% of their functioning capacity. At this point, the kidneys can no longer filter waste products effectively. Toxins accumulate leading to severe clinical signs and eventually death if left untreated. However, with proper management and treatment, some dogs can live for months to years after diagnosis of kidney disease.
Digestive System
As the dog’s digestive system begins to shut down, they will lose interest in food and water. The digestive processes start to halt as the organs no longer function properly. According to Agape Pet Services, “As your dog’s digestive organs shut down, they will not experience the sensation of hunger or thirst. Visible weight loss will often accompany this change.”
The dog’s stomach and intestines will stop absorbing nutrients and digesting food. PetMD notes that “Appetite and water intake will gradually decline as the dog’s organ systems begin to shut down. Nausea, vomiting, and diarrhea are also common.” The digestive shutdown leads to gastrointestinal issues like vomiting or diarrhea in the dying dog.
The liver and kidneys are also part of the digestive processes. As they fail, toxins can build up in the bloodstream which may cause vomiting. It’s important to keep the dog comfortable by avoiding feeding difficult to digest foods.
Muscles and Limbs
As the dog’s body shuts down after death, the muscles throughout the body begin to relax and lose functionality. This process starts when the cells run out of adenosine triphosphate (ATP), which is the energy source used by cells for muscle contraction. Without this energy, the muscles are no longer able to contract and relax, leading to a state called rigor mortis.
Rigor mortis begins within 2-6 hours after death and spreads throughout the body over the next 24-48 hours (https://bamganie.com.au/what-to-do-when-your-pet-dies-at-home/). The muscles stiffen due to lack of ATP and become rigid. This rigid stiffening begins in the head and neck muscles, then spreads to the limbs and torso (https://veteriankey.com/estimation-of-time-since-death/). The limbs will be stiff and locked in place once rigor mortis has fully set in.
The onset and duration of rigor mortis depends on factors like the dog’s muscle mass and the environmental temperature. In warm conditions, rigor mortis begins faster but also dissipates more quickly. In cool conditions, it takes longer to begin but lasts longer. Monitoring the progression of rigor mortis can help estimate the postmortem interval or time since the dog’s death.
Skin
After death, the skin undergoes several changes as the circulatory and respiratory systems shut down. One of the most noticeable changes is skin discoloration that occurs as the blood starts to settle and pool due to lack of circulation (Brooks, 2016). This settling of blood is known as livor mortis and causes purplish-red discoloration of the skin in the lowest parts of the body. In dogs, this discoloration typically appears within 1-2 hours after death on the underside of the dog.
Desiccation or drying out of the skin also begins shortly after death as there is no blood circulation to keep the skin moisturized. This causes the skin to become tight, leathery, and discolored brown or black in areas. The skin also takes on a brittle texture as the cells start to die without nutrients and oxygen from the blood (Shedge, 2022). These skin changes continue to progress until the skin takes on a completely dehydrated and mummified appearance.
Cells
When cardiac arrest occurs, blood flow stops abruptly, depriving the body’s cells of oxygen (Cherry, 2014). The lack of oxygen leads to cellular hypoxia, in which cells are unable to carry out aerobic respiration and produce energy. Brain cells are particularly vulnerable, with neuron death beginning just 4-6 minutes after cardiac arrest (NYU Langone Health). Within several hours after the heart stops beating, individual cells throughout the body begin to die from irreversible lack of oxygen.
Conclusion
When a dog dies, its vital systems and functions begin to shut down in a sequential process. The first organs to stop functioning are usually the brain and heart. The brain ceases all activity, including regulation of breathing and heartbeat. Shortly after, the heart stops pumping blood, which contains oxygen, to the rest of the body. Without this oxygen supply, the lungs soon fail as they cannot pull in fresh air to facilitate respiration at the cellular level. The kidneys and digestive system are generally the next to stop, no longer filtering blood or processing food and water. As circulation halts, the dog’s muscles and limbs become rigid from lack of oxygenated blood flow. Skin and cells are the last to lose function as they may still undergo some biochemical reactions for a short time after clinical death. While the order may vary slightly, a dog’s systems essentially shut down in a coordinated cascade culminating in complete organic failure. This systematic shutdown ensures that a dog’s death is usually quick and involves minimal suffering after the loss of brain activity and consciousness.