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Sow Dentistry 101

Illinois study reveals sow dental problems, raises new questions about impact on culling rates. In a first-of-its-kind study, Illinois swine veterinarian E. Wayne Johnson has taken on the challenge of learning more about teeth condition in cull sows. Johnson, also a graduate student working with swine behavior specialist Stanley Curtis at the University of Illinois, has examined the teeth of scores

Illinois study reveals sow dental problems, raises new questions about impact on culling rates.

In a first-of-its-kind study, Illinois swine veterinarian E. Wayne Johnson has taken on the challenge of learning more about teeth condition in cull sows.

Johnson, also a graduate student working with swine behavior specialist Stanley Curtis at the University of Illinois, has examined the teeth of scores of sows in two packing plants, as well as conducted on-farm dental exams on gestating sows.

Benchmarking Dentition

At the outset, Johnson believes it is important to understand that pigs do not have their full set of teeth until they are nearly two years old.

And, it is important to realize the purpose of the incisors, premolars and molars, and the complications that arise when the deciduous (baby) teeth are retained, and when teeth are chipped or fractured, and the consequences of periodontal disease in sows.

Johnson's baseline studies help identify how widespread teeth problems are in breeding stock and what causes the damage, and, hopefully, provide some solutions.

He references a L.E. St. Clair photo of a sow's skull (redrawn as Figure 1) to show a full set of sow teeth. Table 1 also shows when pig teeth come in (erupt) during their lifetime.

The third incisors (I3) and the canine (C) teeth are present at birth. These are the “needle teeth” that many clip at birth. “If you don't clip them, they fall out somewhere around 3 months of age. If they are clipped, the root stub can be retained for several months or longer,” explains Johnson.

The incisors and most of the pre-molars erupt within three months. These teeth are much like baby teeth in humans. Most are replaced with permanent teeth by the time pigs are 8 to 20 months of age.

“As the dentition table below shows, the first molar tooth (M1) doesn't come in until it's 4-6 months of age. There's a period in a pig's life when that tooth carries the load, and because there aren't any baby molar teeth, M1, M2 and M3 have to last for the pig's whole life,” he says.

This is important to recognize, he continues, because “pigs are 18-24 months old before they get their full complement of molars and they come into wear.” Sows are considered “mature” when all molars have erupted.

“Figure 1 shows a fairly mature animal. The incisors (I1-3, bottom jaw) are designed as scooping teeth; upper teeth are poorly developed and hardly exist at all. The last molar (M3) is just barely coming in,” he says.

“Pigs don't chew their food much,” Johnson explains. “They just get the feed in their mouths and crunch it down with their molar teeth, then kind of wallow it around in their mouths and get it lubricated enough so they can swallow it.”

Cull Sow Study

Johnson examined the heads of cull sows delivered from herds in the Southeast, Midwest and Canada to slaughtering facilities in Momence, IL, and Des Moines, IA. Initially, sow skulls were taken to the laboratory where he drew pictures to document where teeth problems were occurring, much as a dentist marks a diagram of human teeth during an exam.

“After doing that a few times, I had categorized the scope of the problems, then developed a scoring system so I could rapidly score them,” he explains.

Scores reflect incisor wear, molar wear and incisor loss using a subjective five-point scale. Higher scores reflect an increase in severity. Scores of 3-4 were considered “significant.”

Broken, sharp and jagged teeth creating cheek/lip abrasions, and lacerations and abscesses of the gums, lips and cheeks were also recorded.

Tartar levels and presumptive gingivitis were scored, with scores of 2-3 considered to be significant.

Keeping in mind that only cull sows were assessed, and no history on the 82 sows examined was available, about 85% showed significant dental lesions presumed to cause pain or local tissue reaction. More precisely, 63% had molar wear, 62% had incisor wear, 34% had lost incisors and 85% had more than one of these conditions.

“Normally, the deciduous incisors are lost before a permanent tooth erupts,” Johnson explains. “Retention of one or more deciduous incisors often project at abnormal angles, increasing the vulnerability to periodontal disease and tooth breakage.”

Johnson found 15% had retained deciduous incisors.

Over half of the sows examined had significant tartar and gingivitis, which is associated with recession of the gum line and root exposure of the teeth, especially the molars.

Abscesses were found in 4% of the sows, often forming periodontal pockets and resulting in tooth loss.

See adjoining photos and descriptions (page 23) of some of the teeth problems found in Johnson's sample.

What's Causing the Damage?

Some speculate that “bar-biting” causes M1 failure, but the problem exists in sows without anything to bite, including pastured sows. Teeth grinding is another possibility.

Johnson plans to videotape and study how sows interact with the fronts of different gestation stalls. Sows will face horizontal and vertical bars, straight and angled fronts (one severe, another moderate).

“We think that that will give us some idea whether the stall design and the sow's interaction with her environment is a factor,” he says.

Tartar buildup, gingivitis and periodontal disease with gum regression and root exposure are major contributors to tooth loss. Abscesses are common.

Johnson used a dentist's periodontal probe to measure receding gums. The probe measures 3.5 mm to the base of a black mark and 5.5 mm. to the top of the black mark. Johnson says the probe went well below the 5.5 mm. mark in some sows. Bacteria get down in the periodontal cavities and erode the bone that anchors the tooth.

Gingivitis, common in dogs, frequently develops general disease in the body. “A dog with a bad tooth will often develop kidney or liver problems,” he explains. Plaque infected with bacteria develop and circulate in blood vessels and the heart. It's the same bacteria that were found in the rotted sow teeth, he says.

Nutritional Factors

Johnson thinks diets fed to replacement gilts should be studied, too. Molar development is of less concern in market animals than replacement gilts. Are replacement gilt candidates being fed a normal finishing diet or a developer diet during the critical 4-6 months of age when permanent molars are erupting, he wonders.

“There is some evidence that people who have certain diets have better teeth — even in terms of hardness,” he explains. “One of the things that has been shown to improve hardness is molybdenum.” Boron is another mineral that deserves consideration. Calcium-phosphorus balance should also get a second look, he adds.

Johnson also hopes to study whether vitamin C deficiency could be contributing to periodontal disease in sows, as it does in people. He admits that it's difficult to demonstrate a significant effect of the vitamin. Still, pigs with ample glucose in their bloodstream are capable of making their own vitamin C. Johnson thinks it's possible that thin sows (those in a negative energy state) could develop a vitamin C deficiency.

There are no restrictions on vitamin C supplementation, but it's expensive — $2 to $3/ton for the recommended amount. “That's not so much on a per sow basis, but with large numbers of sows, say 5,000, that's $15,000 a year,” he notes.

On-Farm Study

To better understand any correlation between teeth condition and culling rates, Johnson evaluated the oral condition of 53 live sows, Parities 1 through 10, in a commercial herd.

Sows were snared and scored. Later, the number of cull sows with good teeth vs. bad teeth was compared.

“Molar wear had a significant effect on culling,” reports Johnson. “Sows with bad molars were 17 times as likely to be culled as those with good molars. Even when adjusted for age, sows with bad molars were nine times as likely to be culled.”

This sample was statistically too small to make any definitive projections about the impact of teeth on culling levels, says Johnson, “but we do know that those with bad teeth tended to be culled.”

In all, Johnson has consulted with four commercial herds and all had problems with molar wear and broken teeth, confirming the fairly widespread problem he'd seen in his packing plant work.

Taking the Next Step

Recognizing the problem is the first step to solving it. “When I first started looking at these sows in the packing plant, I felt so dumb,” Johnson admits. “I've worked in the industry for over 20 years, and I wasn't aware that this was going on.”

Realistically, producers and veterinarians aren't going to catch sows and examine their teeth with a periodontal probe. Therefore, the advice given by your dentist also fits here — prevention is the best solution.

Studying sows' interaction with their environment and taking a closer look at nutrient requirements as they pertain to dental health may yield some solutions.

“Remember, if the first molar comes in at 4-6 months of age, that tooth is already developed by the time a gilt is placed in the gilt pool. That means we would have to adjust a late-nursery, early-grower diet to have any effect,” he says.

“Or, as is the case with people, genetics may affect teeth quality. Maybe that's a part of the longevity formula, too,” he adds.

“In herds with high cull rates, maybe we should be doing sow slaughter checks, looking at the reproductive tracts, but also looking at the heads and teeth, because there seems to be a lot of pathology, or disease, there,” says Johnson.

“We know that culling rate and mortality rate are too high, and the longevity is too short in our industry,” he continues. “It appears that bad teeth are associated with higher culling rates. This should be a part of the sow longevity research, and I think it is important that pork producers recognize that. It should be on their radar screens.”

Figure 1. Dentition in Hogs

Porcine Dental Eruption Table
Tooth Deciduous Permanent
Incisor 1 2-4 week 12 months
Incisor 2 2-3 months 16-20 months
Incisor 3 Pre-birth 8-10 months
Canine Pre-birth 9-10 months
Premolar 1 5 months 12-15 months
Premolar 2 5-7 weeks 12-15 months
Premolar 3 and 4
upper 4-8 days 12-15 months
lower 2-4 weeks 12-15 months
Molar 1 4-6 months
Molar 2 8-12 months
Molar 3 18-20 months

A Plethora of Problems

To give producers a better picture of what's happening inside sows' mouths, Illinois researcher E. Wayne Johnson reviews a set of teeth maladies he has found:


Severe incisor wear and breakage; the alveolar bone loss is replaced by connective tissue; the arrow shows the retained deciduous incisor (RDI).


Retained deciduous incisors (arrows) have caused permanent incisors to slip behind the “baby teeth” and forced them to come in at odd angles; the permanent incisors were cracked and a repetitive motion has caused them to gradually chip away. Eventually, the bone will be replaced with scar tissue and a pad will develop.


Broken incisors were examined in live sows and found to be painful. Bacteria gets into the socket, causing the bone to recede, which is replaced by scar tissue. Note bone loss and cratering.


This broken tooth was stuck through the sow's gum; this sow probably quit eating, so the producer culled her.


This very bad tooth had hair and tooth fragments poked into the cavity. Hair is the most common item found in periodontal pockets.


Perforation of the lower lip was fairly common in the culled sows. The broken teeth are so jagged that they pierce their lips. Healing at the margin of the upper wound indicates this is not a new injury.


This mature sow (three molars present) shows severe wear and failure of M1. “This is difficult to understand,” says Johnson. “Why are these sows wearing their teeth out chewing feed that's already ground?”