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.

Wednesday, October 1, 2014

Do we really grasp what “calving ease” data is telling us?

Dairymen are split somewhat equally on what “calving ease” data means to them.    Some will only use “calving ease” sires, in hopes of avoiding heifer or cow paralysis from oversize bull calves.   Others will avoid using sires with really low “calving ease” %s in a belief that such bulls make small, harder calving cows, perpetuating the problems into the future.

Countries do not agree on how to collect or present the existing data.   In Canada, calving ease is called “percent of unassisted births”—an easy-calving bull is above 87% unassisted births, a hard calving bull is below 84% unassisted.      In the USA, calving ease is called “percent of difficult births”—an easier calving bull is 8% or below, average is 9%, a harder calving bull is 10% or above.     Researchers have found that length of gestation affects calving difficulty, with bulls that sire a shorter gestation length (eg, 6H999 Cole RC, whose c/e is 5% currently) being considered more desirable.

Should you be concerned with “calving ease”?

First—this is more of a Holstein/Brown Swiss issue than a concern of Jersey, Guernsey, Ayrshire, or Shorthorn breeders, where calving ability is a noted breed advantage.    Brown Swiss have the longest gestation length of the major dairy breeds, with Holstein next—so when a calf runs over term in those breeds, calving assistance is expected.      But the Holstein cow tends to produce larger calves than any other cow, regardless of breed of service sire—roughly 7% of mature body weight (Jerseys run about 5% of mature body weight).      So breed differences are a genetic influence on calving ease.

But within breeds, more recent research notes that “percentage of stillborn calves” has also been found to be heritable—a situation where cow fertility genetics overlaps with calving ability genetics.   So the calving ease figures you now read for bulls are 70% “calving difficulty” (a subjective measure) and 30% “stillbirth frequency” (an objective measure) rather than a pure “percent of difficulty”.    Geneticists are assuming that the goal of calving is not just a surviving cow but also a live calf—a better assumption.

Heifers being fed “hot” (high energy) rations in the last trimester of gestation will produce bigger calves given the nutrient diversion to the calf to complete its development.    Much calving difficulty is induced by feeding heifers like steers, prompting weight gain rather than frame development— so what sires you breed them to will have less success in avoiding difficult calvings under “steer feed” nutrition (that pack fat deposits into the pelvic cavity, the udder, and around internal body organs).

Sometimes type selection preferences interfere with calving ease.    The wide, flat “boxcar rump” that is a traditional Holstein standard, finds less favor in most other breeds, who recognize their calving ability comes in part from a “diamond shape” to the birthing channel.    You need thurl and pin width to get the hips out, but first you need pelvic height to get the head and shoulders started.    Both dimensions need to remain in proportion for minimal pelvic interference in birthing.     [This is one of the key areas of the cow physique improved by using the “aAa” breeding guide, instead of linear mating systems.]

Management pressure to breed heifers at earlier ages (to compete with the faster maturity of smaller frame breeds like Jerseys) has produced more heifer calving difficulty.   Heifers are not ready to breed until they are 55% of their expected mature weight.   Thus, if you like 1600 pound cows, do not breed heifers until they weigh 880 pounds—the blanket Holstein recommendation of 700 pounds is assuming you still milk the 1350 pound short-legged smoothies University dairies had in the 1960s.

Genetic   tradeoffs  in  calving ease

Most sire proof lists only show direct “calving ease”—the bull’s ranking as a service sire for birthing.
But in fact, two levels of data are calculated—“direct” and “maternal” calving ease.    The “maternal” rating is an indication of how his daughters are doing for birthing ability.

Exceptions to the assumed rules may prove the rule is defective

What you see across the broad data is a pattern—the lower the “calving ease” direct rating, the higher the “calving ease” maternal rating.    The old saw, “calving ease bulls produce small hard calving cows” is questionable, on the average of the data.    But who wants to milk “average” cows??    The secret is to find “calving ease” bulls whose daughters also calve easily, and produce live calves, for a full lifetime.        

The scoop on calving ease

Calving difficulties have led people to various strategies (breed heifers to Jersey bulls, breed heifers to sexed semen, use only calving ease rated sires) that seem to either raise our AI costs or lower our herd equity value.     Why did this happen?      It relates to the delayed recognition that calving ease was as “genetic” a trait as production or type, and is linked to broader health and fertility issues—such as the rate of still born calves—currently averaging 8% of all Holstein births-- as well as to structural mating issues in the width, length, and proportions of the pelvic rump shape.

One thing for sure—the data does not support some old-timer attitudes like “select for calving ease and you end up with small, narrow, frail cows”.     Increasingly there is recognition that “frailty” is a result of broader selection issues, such as the importance of balancing “sharp” and “round” body qualities in the overall [bull x cow] mating design.     [Programs like aAa breeding guide produce heifers that are more capable of calving unassisted with a living calf—selecting sires to avoid the genetic sources of a lack of vigor in calving, such as using maternal stillbirth rates, add to success in this area.]