Focus on Feet
Wet feet may be okay for ducks but moisture can lead to cows on the limp

Providing dry footing for your herd may be one of the keys to promoting healthy hooves. One group of researchers has been looking into the notion that environmental conditions on some farms may be causing changes to feet that make cows more prone to foot ailments.

Previous work has shown that the thickness of the soles of cows' feet varies. It's theorized that thin soles provide little protection for the foot's internal structures, so claws with thin soles are prone to bruising from hard flooring. Lack of protection can also lead to damaging other parts of the foot.

For example, laminitis, a specific type of lameness, can occur when blood circulation to the germinative, or growing, layer of the sole is reduced. Interference with circulation reduces the oxygen and nutrient supply. The result is production of abnormal and weak sole material.

This weak sole is then prone to further damage from pinching between the toe bones and floor. It's strongly suspected of causing sole ulcers in the lateral claws of dairy cows' hind feet.

Not only is this abnormal sole material structurally weak, it lacks a protective coating. Without the coating, the sole material becomes more porous and can absorb more moisture. Soles with higher moisture levels are more likely to be thin and less protective. They may be thin because wet soles are softer and wear down faster. This could potentially become a big lameness problem if your cows spend a lot of time on hard floors or have to walk on uneven surfaces.

Scientists still have to work out many of the links in this chain of theories, although they're close to proving some. In particular, there's some proof emerging for the relationship between sole thinness and moisture content.

In a recent study, Florida researchers looked at the moisture content differences of the sole horn in cows with soles of either thin or normal thickness. They examined the hind feet of 16 cows with normal soles and 26 with thin soles. These cows lived on the same farm in the same environment, ate the same feed and were otherwise healthy. They were housed all the time in a sand-bedded freestall barn and walked on cement alleyways scraped twice daily. They were milked twice daily and cleaned before milking with water sprayers in the holding areas. They walked through a return alley regularly flushed with parlour water for cleaning.

By ensuring all cows were housed and managed the same way, the researchers could concentrate on the sole thickness as the major factor influencing sole moisture content.

They determined thin-soled cows had a toe length {the length of the dorsal or top hoof wall) of the outside claw of less than 7.5 centimetres. Those with a toe length longer than 7.5 cm were predicted to have soles of average sole thickness. The researchers backed up this method of determining sole thickness with ultra- sound tests to produce an actual sole thickness measurement.

To measure sole moisture, they took a paring of sole from the same area of each of the four rear claws on the cows' hind feet. The sole was weighed, then dried for 48 hours and re-weighed. The difference in the two weights was the amount of water lost.

The comparison between thin and normal soled animals showed claws with thin soles had a higher moisture content. Overall, the soles of the rear claws had more moisture than the front claws. Thin rear soles had the highest moisture content of all.

This research supports the theory that the claw that experiences the most lameness in dairy cows-the lateral, or outside, claw of the hind foot-is the most likely to have thin, moist soles.

To prevent the soles of a cow's feet from deteriorating, we need to start considering management, housing - and cow factors that can affect sole moisture content and risk of wear. There's still much work to be done in. this area but some information is already available.

Other research has shown flooring type affects the sole's moisture content. Cows on slatted floors had soles with a higher moisture content, at 29 per cent, than those housed in tie stalls at 22 per cent. Although liquid can drop through slat openings, exposing cows' feet to the moisture held in manure on top of the slats still presents more of a risk for thin soles than housing animals in drier tie stalls. Research still needs to be done to find out whether scraping slats would counteract the problem, and determine the sole moistures of cows in scrape-alley barns.

There's also speculation that rear claws may have a higher moisture content when cows lack stall comfort. Under these conditions, cows spend more time perching-their front feet high and dry in the stalls, their hind feet mostly in alleyways exposed to manure and urine.

When excessive perching occurs, not only do cows have moist, thin soles on the rear claws; they increase the load and pressure the rear feet have to bear.

How long does it take for sole moisture to be affected? Do changes occur after short or long-term exposure? We still need to find answers under practical circumstances. However, preliminary research has shown that when claws were submerged, water intake was maximized after 48 hours. So far, it seems even short-term exposure of a few days can start to influence the moisture content of the sole, and increase the risk of thin soles and internal foot damage.

Looking at changes in the sole of the foot that predispose cows to lameness will continue to be an active research field. Looking at the sole itself is only one facet. We also have to look at other factors, including the interaction of sole characteristics with flooring type, flooring finish, the time cows spend on the floor, stall design, trimming frequency, feeding programs and ration content. The goal is finding the best combination of factors to keep cows free of lameness, so they can fulfil their production capability and reproduce without problems.

In practical terms at this stage, it's fair to assume sole moisture and sole thickness vary among lame and non-lame cows. When clusters of lame cows occur or lameness is chronically present at too high a level, we should look at sole thinness as one factor that can increase the risk of foot ailments. Finding ways to keep feet drier, especially among dairy cows housed all the time, may be the ticket to thicker soles, fewer problems and lameness-resistant cows.

Keeping herd's feet healthy can solve other problems

The widespread appearance over the last 10 to 12 years of digital dermatitis, or strawberry foot, has drawn attention to lameness as a problem, but may have distracted veterinarians and dairy producers from other important and common lameness problems.

Lameness causes cow discomfort. Common sense tells us lame cows eat less, milk less, and conceive less. Research backs this up. Moreover, the way lame cows behave may also make them prone to further lameness.

Research in one herd looked at 165 cows graded from non-lame to very lame. The lame cows at fewer meals per day (20) than lame cows (30). Ultimately, both groups had the same dry matter intake per day, but the lame cows had to eat bigger meals to meet their requirements.

Providing a ration that carries enough fibre in every bite to offset the diet's high energy content is the aim and intent of feeding a total mixed ration. Lame cows may miss this benefit if they slug feed because they go to the bunk less frequently. By the time the lame cows get to the bunk, the non-lame more aggressive cows have already sorted the feed and eaten the good stuff. Nutrition may not be as balanced as planned for either the lame or the non-lame cows.

Right behind lameness, in the frustrating problem category, producers and vets cite poor reproductive performance as a major bottleneck. It turns out that the two are closely related.

A study of a large Florida herd looked at 65 cows that had lameness diagnosed within 30 days of calving. Their reproductive performance was compared to 130 non-lame herdmates that calved during the same period. Among these cows, 31 percent of the lame cows were culled before any reproductive event such as a heat or breeding was recorded. During the same period, only 5% of the non-lame cows were culled.

Among the lame cows that remained, ovarian cysts occurred at three times the rate of non-lame animals, and the lame cows were only half as likely as their herdmates to conceive during the 480 days they were followed. Non-lame cows were almost four times more likely to conceive at first service.

Lameness hurts many areas of animal health important for efficient milk production. When we deal with problems such as low dry matter intake, low milk production and poor reproductive performance, we have to be careful not to underestimate the impact of lameness. It's often difficult to improve production and reproductive performance until lameness problems are solved.

The main paper cited was Moisture content, thickness and lesions of sole horn associated with thin soles in dairy cattle by SR van Amstel, JK Shearer and FL Palin. Journal of Dairy Science 87:757-763. 2004.

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