Factors For Bloat
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originally appeared in the "Healthy Dog" section of the April,
Factors for Canine Bloat
Tufts' Canine and Feline Breeding and Genetics Conference, 2003
Jerold S. Bell, DVM
Tufts University School of Veterinary Medicine
Canine bloat, or gastric dilatation-volvulus (GDV), is the
number-one cause of death for several large and giant breeds. If
this painful disorder is not treated within one to two hours, it
Twenty-five percent of bloat cases are caused by gastric dilation.
The stomach fills with gas. The increased pressure compresses both
ends of the stomach, preventing the gas from escaping. But most
cases--75 percent--are due to gastric volvulus, where the stomach
actually twists, crimping and cutting off the inflow and outflow
from the stomach. When the stomach gases cannot get out, they
expand. Affected dogs drool saliva because they cannot swallow.
Also, they cannot belch or vomit, which would help relieve the
mounting pressure from the stomach gases. The pressure causes the
abdomen to become distended. When tapped, the abdomen can sound
like a drum.
The breed with the highest average lifetime likelihood of a bloat
episode is the Great Dane, at 42.4%. Other breeds at higher-than
average risk include the Bloodhound, Irish Wolfhound, Irish
Setter, Akita, standard Poodle, German Shepherd Dog, and Boxer.
Other deep-chested breeds and deep-chested mixed-breed dogs are
also at higher risk.
Dr. Larry Glickman, an epidemiologist at the Purdue University
School of Veterinary Medicine, conducted a controlled study on
canine bloat, beginning in 1994. He followed 1,914 dogs who did
not have a prior history of bloat. Eleven large and giant breeds
were represented in the study. Several risk factors were
identified. The dogs with the greatest risk of developing bloat
have chests that are deep and narrow. This can be evaluated by
measuring the depth and the width of the chest. Then the depth is
divided by the width. The depthto- width ratio reflects the amount
of room there is for stomach movement in the abdomen, behind the
ribcage. The higher the result, the more room there is for
movement. Dogs with more room have a greater risk of developing
bloat. Lean dogs were found to be at higher risk than overweight
dogs. It is hypothesized that this is because fat takes up space
in the abdomen. The lack of fat in the abdomen of a lean dog
creates a basic situation similar to that of a dog with a deep and
narrow chest: A lean dog has much more room in the abdomen for the
stomach to move around than a fat dog. This does not mean, of
course, that overweight dogs are generally healthier than lean
Risk is also higher for older dogs. For large breeds, the risk of
developing bloat goes up 20 percent each year after the age of 5.
For giant breeds, it goes up 20 percent each year after the age of
3. First degree relatives of dogs that have had bloat have a 63
percent greater risk of developing bloat themselves. Dogs that eat
quickly have a 15 percent higher risk of developing bloat. This
may be related to increased swallowing of air.
One traditional preventative has been to raise the height of food
and water bowls, but this was found to actually increase risk by
110 percent. This correlation of risk was verifiable; the dogs of
the breeders in this study did not have close relatives that had
The study also found that fearful, nervous, or aggressive dogs had
a much higher incidence of bloat than did dogs perceived by their
owners as having happy temperaments. Stress can also be a
precipitating factor, and many dogs bloat after recent kenneling,
or a recent long car ride. A slightly higher percentage of males
than females developed bloat.
Several diet-related factors were associated with a higher
incidence of bloat. These include feeding only dry food, or
feeding a single large daily meal. Dogs fed dry foods containing
fat among the first four ingredients had a 170 percent higher risk
for developing bloat. Dogs fed dry foods containing citric acid
and were moistened prior to feeding had a 320 percent higher risk
for developing bloat.
Conversely, feeding a dry food containing a rendered meat-and-bone
meal decreased risk by 53 percent in comparison with the overall
risk for the dogs in the study. Mixing table food or canned food
into dry food also decreased the risk of bloat. During the past 30
years there has been a 1,500 percent increase in the incidence of
bloat, and this has coincided with the increased feeding of dry
dog foods. There is a much lower incidence of bloat in susceptible
breeds in Australia and New Zealand. Feeding practices in these
countries have been found to be less dependent on dry foods.
As for feeding one large meal a day, this can weigh down the
stomach and stretch the hepatogastric ligament, which usually
maintains the stomach's normal position in the abdomen. Dogs that
have bloated were found to have a much longer hepatogastric
ligament; it is thought that this is due to chronic stretching.
This could also explain why bloat risk increases with age.
Several popular theories regarding bloat were not substantiated
during the study. There was no correlation of bloat risk to
exercise before or after eating, as most dogs bloated in the
middle of the night with an empty, gas-filled stomach. There was
also no correlation to vaccinations, to the brand of dog food
consumed, or to the timing or volume of water intake before or
after eating. From the research performed to date, we can list
several factors that, added together, can characterize the typical
dog that develops bloat: a deep and narrow chest; leanness; a
relative that has had a bloat episode; eating quickly; a dry-food
diet; a single, large daily meal; stress; and a fearful, nervous,
or aggressive temperament.
Approximately 30 percent of dogs that develop bloat die or have to
be euthanized. This can be due to shock, to arrhythmia (fatal
irregular heart beats), or to rupture or death of the stomach
wall. Studies have shown that 40 percent of dogs that bloat have
some heart arrhythmia during the bloat episode. Affected dogs
usually receive fluids and shock therapy at the time of treatment
in an attempt to attempt to control this. Emergency treatment of
bloat begins with decompression, or alleviating the gas pressure.
This can be accomplished by passing a stomach tube. If a tube
cannot be passed due to torsion, the use of a hypodermic needle
through the side of the abdomen can help relieve the pressure. If
a dog survives decompression but the stomach is still twisted,
emergency surgery is required to straighten it. Some dogs may also
require removal of a damaged spleen, or a portion of the stomach
wall. Once normal anatomy is re-established, the most important
aspect of bloat surgery is a gastropexy. This procedure "tacks" or
attaches the stomach wall to the body wall and prevents it from
twisting in the future. Studies have shown that 76 percent of dogs
that do not have a gastropexy will bloat again; more than half
will bloat again within three months. Only 6 percent of dogs that
have had a gastropexy have another bloat episode. Dogs that can be
stabilized without surgery should have a gastropexy performed as
soon as possible.
In breeds that are at high risk, many experts recommend having a
preventative gastropexy performed instead of waiting for an
episode of bloat. In pet dogs, this surgery is usually performed
at the time of neutering. In the December 1, 2002, Journal of the
American Veterinary Medical Association, researchers described a
new laparoscopic gastropexy technique. This technique requires
only a small incision on the side of the abdomen.
There is no single, major gene that controls bloat. This is
because dogs do not inherit bloat; they only inherit a
predisposition for the condition. As with other polygenic
disorders, breadth of pedigree normalcy increases the selective
pressure against the condition.
Perhaps the best selective tool against bloat is the chest-depth
to chest-width ratio. Dogs that have lower ratios and whose
littermates have not bloated are the best breeding candidates. If
prospective breeding dogs are compared, and breeders select
against those with high ratios, the prevalence of bloat should
originally appeared in the "Healthy Dog" section of the April,