Wednesday, July 4, 2012

Dairy Cow Hock Lesions

When you think lameness, you rightfully focus on feet.  But look up two feet and pay closer attention to the tarsal joints, better known as the hocks.  They could be telling a revealing story that could potentially shed some light on management problems on your dairy.  Hock lesions are preventable by focusing on cow comfort, proper foot trimming, and genetic selection.

You can look across your dairy herd and observe cows with varying degrees of hairloss, ulceration, and swelling of the hocks.  Closely scrutinize both sides of the hocks because even though the majority of lesions are located on the outside area, lesions can also be find on the inside region.  Greater than 95% of your herd should possess hocks with no lesions.  No more than 5% should have hocks with signs of hairloss.  Though difficult to achieve, especially in facilities with freestall design flaws or maintenance problems, no cows should have evidence of hock swelling and ulceration.

The majority of hock lesions are associated with cow comfort problems.  A hock lesion typically starts out as hairloss from rubbing, friction, and shearing forces on hard surfaces.  As the friction or trauma persists, either an ulcer or hygroma will form or a bursa, or fluid-filled sac, will develop to protect the joint from trauma.  With continued and repeated trauma, the bursa may become infected, turning into an abscess or burst into an ulcer/hygroma. 

The majority of hock lesions are created by freestall design flaws and poor maintenance (lack of grooming or bedding).  A lack of bedding, exposing hard surfaces such as poor or outdated mattresses or freestall bases, will increase risk.  Freestalls assumed to be deeply bedded may be poorly groomed or compacted resulting in a greater incidence of hock lesions.  Hard, course, or rough bedding, particularly recycled drywall products or sawdust resembling tree bark, is extremely abrasive on mattress surfaces and should be avoided.  Freestall design resulting in diagonal lying where the rear legs drape over the rear curb will create hock lesions, particularly on the inside area of the lock. 

The design flaws and poor maintenance issues mentioned result in excessive restlessness while the cow is lying in the freestall.  More frequent leg movements, combined with the weight of the cow and shear forces increase the risk for the development of hock lesions.  Crushing soft tissue injuries in cows can occur in 6 hours if lying on hard, unforgiving surfaces. 

To prevent hock lesions resulting from freestall design flaws and poor maintenance, deeply bed the freestalls with a minimum of 4” of bedding.  If diagonal lying is an issue, deeply bedding will help, however, you will likely need to analyze length of the bed, the ability for the cow to lunge forward, the height of the brisket board and distance from rear curb, and neck rail height and distance from the rear curb.  Groom and add bedding frequently to decrease compaction.  If compaction is an issue particularly with lime, consider adding sawdust in order to add a “fluff” factor.  Avoid very course bedding. 

Swelling of the hock joint is associated with trauma or arthritis.  The greatest risk for trauma or arthritis occurs in overcrowded pens, facilities with poor footing conditions, and narrow alleyways.  Awareness of the cow’s time budget is also critical.  Overtaxing the time budget and increasing the time standing will place increased stress on the joints escalating the risk for trauma and arthritis.  During a 24-hr period, a cow should spend no more than 2.5-3.5 hours outside the pen including travel to and from the parlor, holding pen standing time, and actual milking.  Daily lock-up or management rail time should not exceed 1 hour in order to prevent overtaxing the time budget.

Leg conformation and degree of set to the hock are critical factors that increase the risk for hock arthritis.  Cows that are sickle-hocked (excessive set to hock), post-legged (excessive straightness to hock joint), or cow-hocked (hocks pointing toward each other) are at greater risk for arthritis.  The angle extremes place excessive forces over areas of the joints not designed to handle the weight.  To compensate, the cows develop arthritis.  In some cases, corrective hoof trimming can alleviate a degree of the condition.  Therefore, the hoof trimmer may need to see the “at risk” cows more often.  Culling problem cows and using sires that transfer correct foot and leg traits will lead to progress. 

Take a moment and observe the hocks of the cows in your herd.  If over 5% of your cows possess any hairloss, swelling, or ulceration, critically analyze and focus changes on cow comfort, corrective hoof trimming, and genetic selection.  Remember, if the cow loses her legs, you lose the cow.

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