Gastric dilatation-volvulus (GDV), in the dog-world commonly called bloat, remains an enduring concern for all owners of at-risk breeds. Despite numerous studies on this horrible disease, a definitive cause has yet to be identified. This has left owners of susceptible breeds with a ‘shopping list’ of potential causal factors along with recommendations of how to avoid them, for example avoiding feeding from a raised food bowl.
Over the last couple of years several really interesting papers looking at GDV have been published, so the purpose of this article is to pull together the latest scientific thinking on causes and prevention. We hope that this article will help owners of at-risk dogs to review their current knowledge and understanding of GDV and, if necessary, update and correct the steps they currently take in their dog’s day-to-day management to help reduce the chances of the disease.
Update on the epidemiology of GDV
To begin, we start with a celebration of ‘big data’. Unless isolated and cut off from main-stream society, our modern lives are shaped by the information collected about us, regardless of whether we like it or not. From the decisions made by governments about housing and tax policy to the points we collect on our Tesco Club cards (other retailer loyalty cards exist), we are being watched and counted. But it’s not all bad; big data has come of age in the veterinary profession too in the form of the VetCompass Program. VetCompass collects and makes available for research clinical data about pets from veterinary practices all over the United Kingdom (VetCompass, 2017).
A recent study used the VetCompass database to tell us what the current prevalence, risk factors and survival rates are in the UK for dogs diagnosed with GDV (O’Neill et al., 2017). The researchers had available to them the clinical records for 77,088 dogs treated at 50 different emergency care clinics. This makes it the largest study of GDV in dogs ever undertaken. Of this population, 462 were diagnosed with GDV. This gives us a number of 0.64% for the prevalence of GDV in the UK, that is, approximately 6 in 1,000 dogs.
Overall, less than half the dogs (49.7%) that got to the vets alive actually survived and were sent home. This is because they were too ill at that point and 88.5% of these dogs were euthanased. However, of those dogs that were fit enough when they were admitted into the veterinary clinic to undergo surgery, nearly all of them (80%) survived and were sent back home.
These statistics highlight the importance of owners recognising the seriousness of the problem and getting their dogs to the vets as quickly as possible. Time is the killer, not GDV itself, given that 8 out of 10 dogs that were well enough for surgery survived.
In relation to chances of survival, the study reveals more. Over half the dogs (51.1%) that could walk into the veterinary practice survived. Survival fell to 21% for dogs that were collapsed and unable to walk when they reached the vets. In addition, blood lactate levels were an important indicator for chances of survival, dogs with lower lactate levels had a better chance. What lactate indicates is discussed below. The authors of this study do urge caution for dogs owners in relying on these 2 indicators in isolation of other clinical data, however.
In terms of breed, Great Danes, Akitas and Dogue de Bordeaux came out as the top three, followed by Irish Setters and Weimaraners. Breeds represented less commonly were Bassett Hounds, Rhodesian Ridgebacks, German Shepherd Dogs, Dobermans, Boxers and Labradors.
The dog’s age was also a factor. Risk of GDV started to increase at 3 years old and continued to rise up to 12 years old. It then decreased through to 15 years old where numbers of cases were negligible. This of course was because big dogs have shorter live-spans than smaller dogs and very few live to that age. Dogs between 9 and 12 years old were 10 times more likely to develop a GDV than dogs less than 3 years old. Finally, more neutered male dogs were affected than entire female dogs.
The researchers of this study do point out that there are some limitations in the data presented above (O’Neill et al., 2017). The first is that, because the clinical data was collected from 50 different veterinary clinics for an acute emergency admission, some data was missing. There was a lack of previous history for many of the dogs because the practices were exclusively out-of-hours emergency clinics (Vets Now) that cover other day clinics in their areas. Furthermore, because Vets Now are exclusively out-of-hours clinics, they may not represent those veterinary practices that handle their own out-of-hours cover. However, given the number of dogs involved here, the researchers are confident that the data presented is a very good representation for GDV in dogs in the United Kingdom.
The mechanics of GDV
GDV is not a single event. Anatomically, it involves 2 distinct processes – volvulus and dilatation.
In young, energetic dogs gastric dilatation as a result of engorgement can be quite common in habitual scavengers that eat rubbish. It is also seen in some dogs that are expert hunters, for example a habitual rabbit hunter can catch and ingest a dozen rabbits on a single walk. In both cases, the stomach becomes hugely distended with a mixture of air and whatever the dog has eaten. In general, these dogs recover without incident, either by vomiting, or simply by digesting what they have consumed.
The dilatation of GDV is a gross enlargement of the stomach by the build-up of gas far beyond the expansion that would normally occur in a scavenger like a dog. The prevailing theory is that this gas is the result of aerophagia, the dog swallowing air while eating or exercising (Davenport et al., 2010). However, a recent study throws doubt on this, suggesting that bacterial fermentation in the stomach is a more important factor (Van Kruiningen et al., 2013).
If volvulus occurs as well (discussed below), depending on the degree of rotation, the stomach contents get trapped as they can no longer be ejected back up the oesophagus as gas and/or vomit. The enlarged stomach also stops the escape of its contents into the duodenum by compressing and closing the duodenum off. Continued bacterial fermentation of the stomach contents produces more gas and at this point the dilatation is unstoppable, eventually the stomach would burst under the pressure. However, long before the stomach reaches this point, it will already be causing serious damage elsewhere.
The stomach shares the very confined space of the anterior abdominal cavity with the liver, pushed up against the diaphragm, the pancreas and part of the spleen. From the heart in the thoracic cavity, the aorta (the body’s primary blood vessel) runs down the length of the body, through the diaphragm and then on down into the pelvis where it divides and supplies oxygenated blood to the dog’s back end and each of the hind legs. Deoxygenated blood is returned back to the heart, and then on to the lungs for re-oxygenation, through the vena cava. Both of these huge blood vessels are suspended just below the spinal column along the length of the body, Where they pass close over the top of the organs of the anterior abdomen, the soft and pliable vena cava is vulnerable to becoming squashed if the stomach becomes grossly enlarged and squeezes up against the other organs around it. This reduces the blood flow back to the heart and this in turn reduces the rate of flow of re-oxygenated out of the heart again to all the organs and tissues of the body. This reduction can be as much as 50% the rate of normal, healthy blood flow.
Another important blood vessel, the hepatic portal vein, is also crushed by dilatation of the stomach. This obstructs blood flow to the liver from the gastrointestinal tract, gallbladder, pancreas and spleen. The net result of these obstructions is that toxic waste products quickly start to build up in the tissues and the cells of the most vulnerable organs including stomach, intestines, pancreas and spleen start to break down and die. Tissue breakdown results is a massive release of toxins into the circulation that causes the blood to start to coagulate (disseminated intravascular coagulation). The end result is multiple organ failure, shock and death.
Volvulus is most commonly a clockwise rotation of up to 360 degrees around the long axis of the stomach (see figures below). Apart from dogs that routinely engorge themselves as described above (more on engorgement vs. GDV later), it is possible that some at-risk dogs can have partial rotations of the stomach of less than 90 degrees that spontaneously resolve themselves without incident. A rotation of greater than 90 degrees seems to be the tipping point for a full-blown GDV to occur. A rotation of greater than 180 degrees blocks off the oesophagus thereby trapping the stomach contents. It is likely that volvulus is the driver of GDV and precedes the dilatation, rather than the other way round (Bell, 2014).
Update on the genetics of GDV
A breed predisposition in some dogs to developing GDV, based on simple observation, has probably been known for as long as veterinary medicine has existed. This strongly suggests a genetic connection which is further supported by the observation that GDV runs in family lines (Glickman et al., 1994, 2000; Schellenberg et al., 1998). Bear in mind that these observations pre-date the mapping of the canine genome, which became available to science in 2004. Since then, thousands of studies have been carried out on just about every imaginable aspect of the dog including appearance, behaviour and disease. To date, no genes have been identified that appear to be directly associated with increased risk of developing GDV. However, absence of evidence does not mean evidence of absence and the search continues.
The fact remains that there appears to be an association between GDV and the morphology, or shape of at-risk dogs, for example, large, deep-chested dogs. However, shape alone does not account for variations in different family lines within the same breeds of dogs. Another long-standing theory that has been put forward, again based on observation, is an abnormality in the gastrointestinal tract that leads to delayed stomach emptying. However, recent studies do not resolve the question of whether a gastrointestinal abnormality is a cause, or simply the result of GDV (Gazzola and Nelson, 2014).
Temperament, shaped by nature (the genes) and nurture (experience), is another factor. Fearful, or nervous dogs are at higher risk than laid back, playful, relaxed and happy dogs (Glickman et al., 2000). This may explain why GDV is more common late at night and the early hours of the morning where dogs are often on their own and may worry about environmental noises etc. GDV is also more common after a dog has experienced a stressful event, for example fireworks, a visit to the vets a few days earlier, or a stay in kennels. This is logical because fear and chronic stress activate the hypothalamic-pituitary-adrenal axis, which in turn releases stress hormones that permeate throughout the body (for a detailed discussion on the physiology of fear and stress, see another article HERE). Stress hormones have a negative impact on the normal motility of the gastrointestinal tract and stress is known to be an important factor in human inflammatory bowel disease.
In relation to the genetics of GDV, a recent study adds another piece to the puzzle, suggesting a link with inflammatory bowel disease (IBD) in dogs (Harkey et al., 2017). IBD in humans is known to be a genetic disease that causes an abnormality of the immune system. In this study, intestinal biopsies were collected from dogs undergoing surgery for GDV and 60% of these dogs had intestinal abnormalities consistent with canine IBD. Although the number of dogs involved in this study was just 23, what makes it very interesting is a link with another huge study on canine IBD involving 27,463 dogs (Kathrani et al., 2011). Of these dogs, 546 were diagnosed with canine IBD, and what these 2 studies have in common is the breeds of those dogs – Weimaraners, Rottweilers, German Shepherd Dogs, Boxers and Border Collies. Many of these breeds are also high-risk for GDV. In humans, a mutation in several genes have been associated with IBD and Crohn’s disease. Similar mutations in 3 genes (TLR4, TLR5 and NOD2) have been found in dogs with canine IBD (Harkey et al., 2017). Taken together, these studies give researchers interested in canine GDV a promising place to start sifting through the canine genome.
Update on differentiating GDV from food engorgement
As mentioned earlier, dogs are scavengers and, given the opportunity, some will engorge themselves to the point where they develop a gastric dilatation as a result, as discussed above. For both the owner and the veterinarian, gastric dilatation as a result of food engorgement (FE) initially looks the same as the early signs of a GDV, for example bloated abdomen, agitation, restlessness and rapid breathing and heart rate. Both conditions are initially managed in the same way, especially in at risk breeds of dogs. However, unlike GDV, FE has never been studied as a separate condition, so there is little information available to veterinarians and dogs owners about its clinical characteristics and treatment.
One of the main objectives for veterinarians presented with a bloated dog as an emergency is to decompress the stomach as soon as it is deemed safe to do so. The rationale here is to reverse the reduction in blood circulation around the body, as discussed above. This objective currently applies to dogs with GDV and to those with FE, but there is no consensus on whether or not this is the most appropriate course of action for dogs with FE. This is important, because procedures like gastric decompression are not without risk to the patient.
To address this knowledge gap, a new study has now been published that compares the characteristics of FE to those of GDV (Smart et al., 2017). The researchers compared the clinical characteristics and outcomes of 35 dogs with FE and 36 dogs with GDV. All the dogs had been previously treated at the University of Murdoch, School of Veterinary and Life Sciences in Australia, so all the clinical data collected for each of the dogs at the time (e.g. clinical examination, blood test results, X-Ray plates, treatment and follow-up) was available for analysis and comparison. First, the blood results differed between FE and GDV dogs. For example, lactate levels (an indicator of tissue damage and death) did not correlate with the degree of stomach distention measured on the X-Rays.
Related to this, the clinical records showed that, of the 35 dogs with FE, only 9 were treated for shock with fluid therapy. In other words, dogs with FE did not appear to have the degree of reduced blood flow (discussed above) as those with GDV. The reason for this is likely to be that in FE the stomach is not displaced as well, but with GDV it is displaced. In this study only 1 of the FE dogs had surgery to empty the stomach. All 35 FE dogs were only treated with intravenous fluids and analgesic drugs, and all made a full recovery and were discharged from the hospital 12 to 48 hours later. 9 of the FE dogs were followed up over the next 3 years and none of them were treated again for a similar incident. Unfortunately, the researchers did not document the outcomes of the GDV dogs in this study, but one can assume that it was less favourable with those that were well enough having corrective surgery.
Update on preventing GDV in at-risk dogs, gastropexy
In the United Kingdom, nearly all dogs that undergo surgery for GDV also have a gastropexy as the final part of the procedure (O’Neill et al., 2017). Gastropexy is a procedure that anchors the pyloric antrum of the stomach to an adjacent part of the right abdominal wall (see below). Ideally, this achieves 3 important goals – (a) it fixes the stomach in its normal position, (b) it does not interfere with the normal function of the stomach, and (c) it restricts the movement of the stomach thereby preventing the development of a volvulus. Gastropexy is now recommended and has become a routine operation offered to clients with fit and healthy at-risk dogs in order to prevent them from developing a GDV (Allen and Paul, 2014). This is entirely logical given that a definitive cause (or causes) of GDV has yet to be identified, and the procedure itself is considered low-risk in fit and healthy dogs. However, a recent study calls into question the perceived universal reliability of gastropexy in achieving all 3 of the above goals for all at-risk dogs (Tomlinson et al., 2016).
In this study the researchers dug out previously taken CT scans of dogs abdomens obtained over a 6 year period at the University of Liverpool, Small Animal Teaching Hospital. Scans were selected only for dogs that had no signs of abdominal abnormality or disease, and who had normal blood test results at the time. In other words, these dogs were representative of the normal canine population in relation to gastrointestinal anatomy. CT scans are very useful for accurately identifying the positions of anatomical structures and their relationships with each other within the body.
The CT scans of 57 dogs were examined, 37 males and 20 females, ranging in age from 11 months to 12 years old. 17 different breeds were represented,
Labrador Retrievers, English Springer Spaniels, Dogue de Bordeaux, Rhodesian Ridgebacks, German Shepherd Dogs, Bullmastiffs, a Japanese Akita, a Bassett Hound, a Bernese Mountain Dog, a Bulldog, a Dalmatian, a Great Dane, an Irish Setter, a Newfoundland, a Standard Poodle and a Flat Coat Retriever.
The goal of this study was to accurately measure the locations of the pyloric antrum in these dogs. These locations were then assumed to be the normal positions for the breed types. The researchers then compared these locations with the most commonly used standard locations veterinarians use to anchor the pyloric antrum to the abdominal wall in the gastropexy operation. What they found was that the common anchor points being used were significantly different to the normal locations of the pyloric antrum as identified on the CT scans.
The authors are cautious in their interpretation of these results because there are no other studies to compare them with. They suggest that similar studies need to be undertaken on dogs that have had GDV and gastropexy surgery so a comparison of pyloric antrum position, along with long term outcomes for these dogs, can be done. This would help answer the question of whether or not any of the commonly used gastropexy locations where later causing other gastrointestinal problems for the dogs involved.
Update on other causal factors for GDV
Can feeding dry kibble to at-risk dogs cause GDV?
The prevailing wisdom in the dog world is that dogs at risk of developing GDV should not be fed dry kibble diets. The advice varies from never feeding kibble to limiting its use as just a part of the dog’s diet. Buckley (2017b) took an evidence based look at this question and this is what she found. A total of 6 studies that included looking at feeding dry kibble were found. 4 of these studies were discarded because an inference either way could not be drawn from the results. Of the remaining 2 studies, 1 found that feeding dry kibble did not increase the risk of GDV. The other study found that feeding an exclusively kibble-based diet of less than 5mm particle size increased risk, while feeding kibble of greater than 30mm particle size reduced risk, provided it was fed mixed with some non-kibble food. The author points out that none of these studies give a definitive yes or no answer because of flaws in their design. What can be said with some confidence is that not feeding any kibble at all, dry or moistened, does not increase the risk, neither does using canned dog food or human left-overs. The definitive study to answer this question remains to be done.
Can feeding at-risk dogs from a raised food bowl cause GDV?
As large and giant dogs grow older and stiffer, some can find eating from the floor more difficult. As a result, owners may decide to raise the food bowl onto a stool or chair, or buy a commercial raised feeder, to make things easier for them. However, like the dried kibble question, the current belief is that feeding from raised bowls increases the risk of GDV because it may allow the dog to eat more quickly thereby increasing the volume of air swallowed with the food. This question has also undergone the evidence-based analysis (Buckley, 2017a), where only 2 papers addressing this were identified. One paper answered yes, while the other answered no. In the paper that found no link between feeding from a raised bowl and GDV, there was little information on how the study was actually done, so it cannot be reliably used to answer the question. The other paper was more informative, but there were lots of drop-outs of dogs from the study that could have skewed the results. The results themselves are also confusing in that for large breeds of dogs, feeders raised to less than 1 foot (30cm) increased risk, but feeders raised more than 1 foot did not. For giant breeds, the opposite was found. The risk increased for those fed from a bowl raised more than 1 foot, but not for those fed at less than 1 foot. Taken together, the only thing that can be said with certainty is this – feeding at-risk dogs from floor height does not increase risk for GDV. Again, a definitive answer to this question remains to be established.
Can dogs bolting down their food too quickly cause GDV?
Slow-feeder bowls are often recommended for at-risk dogs, but do they really make a difference? This question has also undergone the evidence based analysis (Buckley, 2016). 6 papers were found that looked at rate of eating as a risk factor. 4 of these papers found no relationship between how quickly the dogs ate and developing GDV. 1 paper found a significant risk, while the other reported an increased risk in large breeds, but not giant breeds. The evidence is therefore inconclusive and the question remains unanswered. However, what can be said with confidence is that using a slow-feeder does not increase the risk of GDV.
The recent research on GDV in dogs adds some really useful insights into this horrible disease, but gets us no closer to a definitive cause, which explains why some veterinarians call it a syndrome. One thing that is certain is this – it is genetic and it is inherited. This means that breeders of at-risk breeds can help by not using family lines where the resulting litters have been shown to be particularly vulnerable.
The most encouraging fact that comes out of all this is that if owners are able to get their dogs to the vets quickly enough, 8 out of 10 dogs that were well enough for surgery survive. (O’Neill et al., 2017). So, time is the killer, not GDV itself.
What still remains unclear is a mechanism to explain why the stomach becomes displaced and rotates in the first place. Does it happen suddenly? Or is it a slower process that may take days or even weeks to occur? Until this question is answered, the best way to prevent at-risk dogs from ever suffering a GDV is gastropexy.
The study discussed above (Tomlinson et al., 2016) leads the way in making this procedure better, with reference to achieving the 3 important goals – (a) fixing the stomach in its normal position, (b) not interfering with the normal function of the stomach, and (c) restricting the movement of the stomach thereby preventing the development of a volvulus.
It’s also worth taking a step back and remembering that GDV is found in other canids like wolves (Hinton et al., 2017). GDV also occurs in humans, monkeys, cats and various types of pigs including guinea pigs (Dudley, 2011). For concerned dog owners, keeping an eye out for research in these species may help answer some of these questions.
© copyright Robert Falconer-Taylor, 2017
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