Hoof wall cracks are divided into two categories – vertical (sand cracks) and horizontal. If a crack goes clear through the hoof horn, it causes pain and lameness.
Paul Greenough, DVM and professor emeritus in Saskatchewan’s Western College of Veterinary Medicine (WCVM), has studied hoof cracks for many years. In that time, he’s examined the feet of thousands of cattle in western Canada and says dry conditions are probably the biggest predisposing factor.
Meanwhile, Jan Shearer, Iowa State University professor and Extension veterinarian, says vertical wall cracks are much more common in beef cattle than dairy cattle, but horizontal cracks are common in all cattle.
Cracks that run parallel to the coronary band often represent a benign physiological change that creates disruption of hoof-horn formation, Greenough says. Rings around the hoof are normal because the hoof wall grows at different rates during various seasons and physiological reasons, however the growth rings occasionally become cracks.
“The hoof horn is like a history book,” Greenough says. “You can see what happened to the animal at any given time during the past 12 months. Some growth lines become deep horizontal grooves, which means something happened to that cow. If a cow had a retained placenta, difficult calving, or a long period of really bad weather or some other stress, you may see a deep groove in the hoof wall.”
Shearer adds that every time a cow calves, she undergoes a period where hoof growth slows or stops.
“A physiological change is affected by hormones and metabolism as she goes from non-lactating to lactating,” he says. “Interruption of hoof-horn growth creates a horizontal groove, or a growth arrest line, which is associated with calving,” he says.
Seasonal changes are another factor in growth rate. This may be partly nutritional (when feed is plentiful, with green grass), or due to longer hours of daylight. “Growth rate is affected by physiological factors. Some of these things aren’t well understood, but people need to realize that not all horizontal rings are indicative of cattle disease,” Shearer explains.
Some rings, for instance, are associated with extreme changes in nutrient level, balance or availability. “With horizontal growth arrest lines, we sometimes see a true hardship groove – an extremely significant or deep horizontal groove – which we associate with something beyond normal physiological changes,” Shearer says.
Greenough says a nutritional glitch, disease or some type of shock causes the horn to stop growing. When horn formation resumes, a full-thickness crack sometimes develops.
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“Severe disruptions in hoof-horn formation create ridges and grooves,” Shearer says. In the most extreme cases where the fissure is deep enough to create a full thickness defect in the wall, this lesion is called a ‘thimble’.”
When a deep crack gets down to the level of the corium – the sensitive “quick” underneath – the fragment below the crack may become separated from the hoof wall above it. “As this fragment (thimble) is growing down the foot, a deep crack may become painful because every time that fragment moves, it pinches the underlying corium tissues,” Shearer says. The fragment must be removed or the cow will be in constant pain and won’t travel, he adds.
Fewer than 1% of dairy cows develop vertical wall cracks (sand cracks), but up to 64.5% of beef cows get vertical cracks, Shearer says. More than 80% of these cracks occur on the outside claw of the front foot. The inside claw is slightly larger, and bears most of the weight, but there is more movement and strain on the outer claw.
Greenough says 27% of all mature beef cattle in Saskatchewan have a sand crack; incidence can be as high as 65% in some pedigree herds. These cracks also are more common in heavy and older animals. And, size of the foot in relation to the weight of the animal plays a role.
“We don’t know why most cracks appear on the outside claw of the front foot, but this may be due to the weight and conformation of those particular animals that puts additional stress on that claw. There is a genetic component, but actual causes are far from clear; there are probably several contributing factors,” Greenough says.
“Some people think cracks are related to the fact that front feet have a steeper angle than the hind foot and are subjected to more stress. Yet dairy cows have the same steep angle in the front feet, and don’t get vertical cracks,” Shearer adds.
Based on the numbers, there seems to be a breed predisposition to wall cracks, Shearer says. For instance, some family lines, in any breed, have more tendency to crack. And, in certain herds, the cows that develop vertical cracks are often related.
“Other factors associated with vertical cracks include vitamin and trace mineral deficiencies,” Shearer says.
Dry, brittle feet may be prone to cracking. “We see brittle feet in dry regions,” Greenough says. “The moisture content of hoof horn is probably a factor. The outer layer of the hoof is waterproof, but this protective layer wears off in sandy environments allowing moisture to evaporate through the hoof wall.”
Chris Clark, DVM and an associate professor of large animal medicine at WCVM, studied the causes of hoof cracks for his master’s degree project.
“We didn’t come up with complete answers, but did discover that the water content of hoof horn varies considerably throughout the year on western Canadian prairies. In summer, the moisture content of the hoof is close to optimal. But as cattle go through winter, the hoof dries out,” he explains.
In the cold, dry climate, feet are not exposed to water, because snow is dry, not wet, he explains.
“Humidity is extremely low here in winter. We took hoof samples of cattle in February, when it’s typically -30°C. As the hoof wall dries out, it becomes brittle and less pliable. Heavier cattle probably have more force on their feet, and brittle feet may crack,” Clark says.
One factor he investigated was whether long toes made claws more susceptible to cracking, due to added strain.
“We found bigger feet were more prone to cracking, rather than a longer toe. We examined hooves from cows at slaughterhouses – cows that did and did not have sand cracks – and did biomechanical testing of the hoof; we were unable to find a difference. Many theories have been proposed regarding causes, but my final conclusion was that drying was the biggest risk factor,” Clark says.
Cracks and lameness
Cracks almost never penetrate the entire thickness of the wall; they just exist in the outer layer, Clark points out. “The hoof matrix has a crack-diversion mechanism. As the crack penetrates deeper, it’s diverted away from going in a straight line,” he adds.
“The animal’s body responds to a crack by thickening the wall in that area, to protect itself. Often the worst-looking cracks don’t cause lameness. If you cut into a dead hoof, the wall in that area may be 2 to 3 times thicker than normal. If the wall gets very thick, you may also see remodeling of the bone, to accommodate the increased thickening. Some of these cracks persist for years,” Clark says.
“The way the hoof is formed, it’s like reinforced concrete. The hoof wall is made up of tiny tubules that run vertically, like rebar, which is why most cracks form vertically rather than horizontally; it’s the natural cleft between the tubules. But the crack diversion mechanism ensures that the crack doesn’t split inward,” he says.
“Once in awhile, however, the animal goes lame and you may find an abscess at the bottom, or deepest portion, of the crack. In my experience in dealing with lame cattle, the crack itself is rarely the cause of lameness. We see many lame cows, and the owner often thinks it’s due to the crack. When we trim the foot, we often find an abscess somewhere else in the foot, rather than under the sand crack,” Clark says. Usually the crack is incidental.
“Our usual advice is that ‘if it ain’t broke, don’t fix it,’ but if the animal is lame, you need to clean the crack out – grind it out or trim it – to try to get back to healthy horn,” Clark says. “The risk factors for crack formation still exist, however, so even if you get that one cleaned up, the chances of it reforming are high.”
Palpating the area over the crack, as well as the coronary band above it, is required to determine if a sand crack is painful. “If there’s an abscess, it will be hot. We use hoof testers to put pressure over the crack; if she winces, we suspect an abscess and clean it out,” Clark says.
Debriding the area (removing all damaged horn) and draining the abscess will relieve pain and lameness.
“I tell my students to not focus on the sand crack when faced with a lame cow. Look at it like any other foot, and try to find the true cause of the problem – is there an abscess and where is it? If it happens to be in the sand crack, then we deal with the sand crack. In some cases, I’ve tried filling the crack with an epoxy, but I don’t think it really helps in the long run,” Clark says.
Sometimes, limiting the animal’s movement is required, Shearer adds. “If one side of the foot is better than the other, we try to stabilize it and take the weight off the affected claw. We may nail or glue a wood block under the healthy claw. If we get the weight off, the corium won’t continue to be traumatized, and will hopefully heal and start to produce new horn.
“The main objective is to stabilize the two portions of the wall that are loose and moving/pinching. Sometimes, the fragments are wired together,” he says.
“If the foot is overlong, we trim it back, and sometimes can remove the fragment, or a portion, so it won’t be flexing so much. This may provide the cow some relief from movement and pinching until the foot can grow out,” Shearer says.
Nutritional factors in hoof care
“Copper and/or zinc deficiency (and other feed deficiencies) can be a contributing factor in sandcracks,” says Paul Greenough, DVM and professor emeritus in Saskatchewan’s Western College of Veterinary Medicine. Most cows in badly affected herds have horizontal “hardship” grooves as a result of some kind of nutritional stress.
Iron and sulfur inhibit uptake of certain trace elements – including copper and zinc – in the animal. “A problem with hoof cracks may be specific to any given area depending upon climate, soil and multiple other factors, including how the stockman manages his farm and cattle,” he explains.
Mike Mehren, a livestock nutritionist in Hermiston, OR, says hoof cracks can suddenly occur on a ranch, leaving one wondering if something changed in the feed or management. The important thing nutritionally is to ensure a balanced diet that includes all the crucial trace minerals that play a role in hoof health. Chelated minerals are more readily utilized in the body.
Selenium is important to hoof health and strength, but overdose can be toxic.
“With selenium toxicity, cattle can actually lose their feet and tail switch. You might not think excess selenium would be possible in the Pacific Northwest, which is a selenium-deficient area. However, people tend to think that if a little is good, a lot is better.
Suppose you injected selenium, fed a trace-mineral salt with selenium and fed a protein supplement with selenium. Each source might supply 3 mg/day, the maximum legal amount of selenium. But, the combination would provide 9 mg, which might not cause death, but could conceivably, in some instances, cause hoof cracking,” Mehren says.
Vitamins A, D and biotin (one of the B vitamins) play a role in hoof growth, and fatty acids help maintain a waterproof barrier on the outside of the hoof. Many nutrients are important to hoof health, so there isn’t one “magic” ingredient that will solve hoof problems.
“Having a balanced mix of vitamins and minerals seems to bring about a long-term correction of problem in most herds,” Mehren says. “We recommend staying on a year-round mineral supplement, not just during winter. Many ranchers do a good job with minerals in fall and winter, but figure the cattle are okay on green grass and plain salt. If you’re having foot problems, it’s best to continue the mineral program because animals don’t store minerals.”
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