Ask three researchers and you will likely get three opinions, ranging from feed particle size and feeding patterns to genetics and health issues.
Gastric ulcers and their cause have been studied for more than 30 years. "Today, we know that gastric ulcers continue to be widespread and aren't going away," says Robert Friendship, DVM, Ontario Veterinary College, University of Guelph, Guelph, Ontario. "They remain a hidden problem. The cases we do see are the tip of the iceberg."
A gastric ulcer forms when bile and digestive juices move from the stomach's acidic end to the neutral esophageal area that has no natural protection from stomach acids. Lesions associated with gastric ulcers can develop within 24 to 48 hours after a triggering event.
"Research shows that gastric ulcers in pigs are not the same as gastric or stress-related ulcers in humans," says John Deen, DVM, University of Minnesota. "In fact, they are analogous to acid-reflux disease in humans."
At slaughter, up to 80 percent of pigs will show some ulceration, he notes. The majority of those are healed lesions, but several are fresh. "The ulceration progresses from the roughening of cells to deep-cell erosion that results in bleeding out," notes Deen.
"We recognize that while fine feed grinding, expander technology and pelleting all improve feed efficiency, increase nutrient digestibility and decrease waste secretion, they also play a role in increasing the formation of gastric ulcers," says John Hancock, Kansas State University animal nutritionist. "It becomes a balancing act between feed conversion and possible ulcer production."
Gastric ulcers first came to the forefront in the 1970s, as pork production moved to indoor finishing and fine-particle-size diets to improve feed conversion.
In the past, feed particle size was much larger such as shelled corn, notes Friendship. This large particle size required more mixing and time to pass through the animal's stomach, tying up gastric juices and rarely leaving the stomach without some type of food in it.
"At slaughter, we will see pigs with lots of ulcers and large amounts of scar tissue with the esophagus nearly closed off," notes Friendship. "These pigs have managed to make it to slaughter weight, but how long did it take them and how much gain was lost without any visual symptoms?" he questions.
"Within the last six to eight years, gastric ulcers have become a real issue, with herds reporting 10 percent pullouts or more," notes Hancock.
In the last 30 years, the emphasis has been on selecting genetics for lean carcass value and feed conversion. By choosing animals with low backfat levels, the industry has inadvertently selected for picky eaters, and those hogs are more prone to gastric ulcers, says Friendship.
The following factors have been implicated with developing gastric ulcers:
Feed particle size: Less than 700 microns encourages ulceration.
Poor environment: Inadequate ventilation and overcrowding pigs, for example.
Respiratory disease: A respiratory disease outbreak can trigger an outbreak of gastric ulcers.
Genetics: European genetics with low backfat. Ulcer heritability is equal to many carcass traits.
You can often pinpoint a time frame when gastric ulcers are likely to flare up in a herd. "They seem to become a concern every few years during the summer," notes Deen.
Lack of feed intake is a critical component in developing lesions, say Deen and Friendship.
"Anything that allows the animal's stomach to empty and remain empty can play a role in ulcer development," notes Friendship. "Empty feeders, illness and decreased food consumption due to heat or the environment, are all factors."
Another thing researchers can agree on is that a respiratory disease outbreak will trigger an outbreak of gastric ulcers.
"Today's pigs are being pushed to the edge with feed formulations, crowding and ventilation issues," says Hancock. "They perform well until a disease or management factor tips the scales against them. Gastric lesions are one of the secondary results."
There also appears to be a connection between ulcers and tail and ear biting. "It's like the chicken and the egg question," notes Hancock. "I'm not sure if the ulcers or the biting come first, but there is definitely a connection."
While there isn't a vaccine or proven method to prevent ulcers, management protocols have been developed with varying levels of success.
One that's gaining recognition is interval feeding. "It focuses on giving animals some kind of relief from the intense, finely ground feed ration by switching to a coarse-ground mash for a specialized period of time in the growth cycle," notes Hancock. "For instance, the relief diet can be fed in the early finisher for one to two weeks. Some herds are able to pinpoint rough spots, and try a coarser feed grind during those times."
The optimum particle size for a swine diet is considered to be 700 microns. The relief diet, however, features particle sizes less than 500 microns for corn and wheat, and sorghum particle size at less than 300 microns. Using a roller mill for feed grinding helps maintain feed efficiency while avoiding fine, powdery feed.
On the sow side, Hancock recommends using the coarse-ground mash during the gestation period to give sows some relief after the high-energy, finely ground lactation diet.
"In some sow herds, mortality is a real problem," notes Deen. "We're seeing sows consuming high levels of feed top-dressing; and for sows suffering from esophageal ulcers, the stress of farrowing is a major insult point often resulting in death."
Research into adding buffers to the diet has shown little success. "We've tried alkaline salts and clays as buffers as well as antibiotic spiking, but it has not produced a real definitive reduction in ulceration," says Hancock.
At this time, the experts say, the best gastric ulcer prevention is management, including:
Keep animals healthy.
Keep feeders and waterers maintained and working properly.
Provide proper ventilation for the age of the pigs.
Provide cooling systems in summer to improve the animals" appetites and feed consumption.
Know the Signs of Gastric Ulcers
Gastric ulcers in pigs appear to be on the rise. Do you know what to look for in your herd?
A combination of clinical signs and post-mortem observations provide an accurate diagnosis of gastric ulcers.
Here are clinical signs, categorized as peracute, acute and chronic.
Death or collapse of apparently healthy pigs.
Very pale carcass, due to hemorrhaging.
Animals are weak and wobbly on their legs.
They are anemic, with increased respiration.
Animals have pale skin.
Pigs appear to be dehydrated.
Teeth grinding due to stomach pain.
Animals lie down and fidget, trying to find a comfortable position.
Tail and ear biting.
Bloody, tarry looking feces. Vomiting may also be noted.
Animal is generally anorexic, with normal temperature.
Animals with intermittent appetites and possible weight loss.
Weak animals may be misdiagnosed as pneumonia in growing pigs.
In some cases the esophageal entrance becomes narrow and a stricture occurs. Pigs vomit shortly after feeding.
Many gastric ulcer lesions are incidental findings on a post-mortem exam with no clinical symptoms.
"Using clinical signs, we can point out pale, poor-doing pigs with tarry stools as likely suffering from ulcers," says Robert Friendship, a veterinarian with Canada's University of Guelph. "But a look at the esophageal area will confirm the findings. Not all pale, poor-doing pigs suffer from gastric ulcers."
Feces should be examined for blood. Necropsies involve the animal's stomach for lesions or ulceration, which will help differentiate gastric ul cers from hemorrhagic bowel syndrome, Eperythrozoonsis, the red stomach worm (Hyostrongylus rubidus) and porcine enteropathy.
By Natalie Knudsen, is a Minnesota-based freelance writer. The article is adapted from Pork's sister publication, Swine Practitioner magazine.