Sunday, October 26, 2014

What makes a hoof resistant to heel warts?

The dam of 179HO63  Needle Lane Ohlman *RC  is now over six years old, and has crossed the 100,000 pounds actual lifetime production mark with her fifth annual calving.   This cow has never had a heel wart and also has never needed her feet trimmed.    She lives in a 300 cow freestall barn year-round, and lots of her stablemates have chronic heel wart infections.    

Why is she different?      Luck, you might say.    But according to her breeder, Lorne Ruesink, you can make your own luck—through careful genetic selection and compensating mating.    Lorne is a longtime user of the “aAa” breeding guide, which places significant emphasis on mobility and foot/leg structure.   He is also a student of genetics and pedigrees, with a long memory for trait patterns.

Lorne’s 50 cows live within his neighbor’s 300 cow operation, where Lorne acts as herdsman.   Since he moved them there, he has been able to compare the results of his “aAa” use against the linear mating his boss contracts from a major AI stud.    Heel warts and slow fertility are a major problem for the owner’s cows, but increasingly Lorne feels he has avoided those problems.

The key difference between “aAa” and linear mating is that the analyzed cows get stronger, while the linearized cows get frailer.    Lorne has concluded that analyzed cows have stronger feet – deeper hoofs with harder horn walls to protect the soft inner sole—and they distribute their weight more properly on the entire hoof, instead of landing on heels or toes, which leads to abrasions that give warts a start.

But still—a cow who has made five calvings and never had a hoof problem?    Sound genetics is also at work here.     This quality in the dam makes us hopeful for a similarly strong foot on the daughters of her son, “Ohlman RC”  [still available for sampling].     Just to calve annually five times and average 3885 pounds above high-indexing herdmates (which she has done so far) is an exceptional cow today, given the average Holstein “Productive Life” is only 29 months.     When you examine the details of her pedigree, you find that her sire and closer maternal grandsires were all bulls whose dams made above- average lifetime productions and had pretty consistent reproductive histories.    

When some cows avoid what afflicts most others, their difference could be genetic

There are a lot more “genetic” traits in cows than we have the consensus to measure so far.    The kind of hoof that resists heel warts can be identified, and the sires of cows with above average resistance to foot infections could be summarized (just as is now done for Somatic Cell scores).     Thinking that the only “genetic” traits are “milk” and “type” has led the industry to some costly situations.     When you wish to look deeper into the causes of some chronic and costly herd problems, it is always important to ask the question, “Could this problem we face be caused by ignoring something genetic?”
Taking  a  second  look  at  foot and leg traits  and  mobility qualities

For three decades, the debate has been “straight” or “set” hocks, then it became “side view” or “rear view”.    Meanwhile, dairymen continue to keep hoof trimmers busy, and spend millions on treatments for heel warts and lameness—still culling cows for being unable to walk.     Mobility of high production cows remains a big issue.

Do we really evaluate foot and leg traits correctly?

Increasingly, when buying semen, Holstein dairymen just look at the Foot and Leg Composite (FLC) and skip the linear detail.    No one can decide if a straight leg is better than a set leg, and everyone is assuming that a steep foot angle measurement equates to a deeper heel (which it does not).   The front two legs are ignored totally (as well as the front end that positions them and requires their support).

Linear measurement obscures the controlling traits to functional mobility

In the research and design of foot and leg traits, many of the structural elements that affect mobility did not prove to be linearly measurable—so were left out of the equations for “genetic value”.   Of the noted structural elements, thurl position and loin strength, plus the weight-carrying front legs, are observed to be key elements in a cow’s ability to properly support her weight under motion, and get up and down in stalls with relative ease.     Just because you cannot “measure” them is no excuse for ignoring them.

The impact of the thurl joint

The “thurl” is the fusing point of the pelvic base, and acts as the joint/socket for the hind leg attachment. 
When the thurl has a “central” position in the side pelvic view, you will see the hind leg stays under the cow (regardless of degree of set) and helps to support the weight of the rear end.    When the thurl has a “square” (rearward) position in the pelvis, you will see hind legs angled behind the cow, which puts an increasing level of stress on the loin/spinal column and produces tension in the stifle muscles.   This can lead to the cow losing her ability to get up and down in free stalls.

Beyond this, the thurl can look “high” in flat rumped, and “low” in peaked-rumped cows.    That cow with a high thurl and flat rump often has a low hip, a weak loin, and will stand on her heels.   That cow with a peaked rump and low thurl, will stand stiffly, on her toes, with hind legs too close to the udder.   In each case, what would be more desirable is a relaxed stance, with the weight distributed evenly on the entire horn of the hoof—thus neither “flat/wide” nor “peaked/narrow” proves to be desirable.

Hock angle is a “two way” trait  (so is foot angle)

A hind leg needs a “shock absorber”.    The material used is cartilage and tendon—which cushion bones in movement and control the extent of movement.   The three leg joints—thurl, hock, and pastern—work best if they each carry part of the “shock” load—otherwise you will see swelling in the afflicted joint, or injuries that require veterinary or hoof trimming intervention.    “Too set” or “too straight” are both bad.

Some cows lift their hoof as they walk—others drag their toes as they shuffle.   No matter the foot angle, if the cow can control her hoof movement, she will maintain functional mobility and avoid the abraided heel that makes it so easy for the heel wart virus to invade the soft tissue of the heel and sole.
     Why do we totally ignore the front end legs and feet?   (They are carrying half the weight)

The rear skeleton of the cow (pelvis and hind legs) and the front skeleton of the cow (head, chest and ribcage) are not connected by the spinal column.     What holds the cow’s body together is muscle and the cartilage structures between bones, plus the tendon structures in all joints.    The animation of their body depends on oxygenation of the muscles by the heart and lung action, and neural signals sent by the brain across the nerves that radiate from the spinal column to contract or retract muscle movement.

If front legs are poorly positioned or too fine/small to carry the load, there will be an impact on overall mobility of the cow.     Thus a narrow focus on hind leg traits is not adequate to total function.

     Why do we totally ignore the back line (chine, loin, pelvic ridge) ?
A critical part of cow mobility is a continuously level spine to avoid abrasion or pinching of nerves by the movement of cervical bones.    Roached loins, sloped rumps, low/flat loins, square thurls under high pins, all of these imbalances bend the spine—lead to pinched nerves and loss of back muscle strength.

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