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Saturday 3 December 2016

Dry Cow Therapy: What’s to consider?

Published 24/11/2016 | 23:42

In recent years dry periods have ranged from two months to nearly five months but from now on most cows will probably be dry for only six to eight weeks.

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There are two potential issues with a shorter dry period.

  1. Bulk tank antibiotic residue failures with long acting dry cow tubes
  2. Less effective cure of sub-clinically (high cell count) infected cows.

The dry period is an important time for the cow to rest and recover from the previous lactation. Nutritionally it is an opportunity for the cow’s body condition to be managed so that she calves down with a body condition score of 3.00 to 3.25 (scale 1 to 5). 

Too thin and she will not milk as well in the next lactation and be less likely to go back in calf on time. Too fat and the cow is at risk of a number of costly metabolic diseases including milk fever, abomasal displacement, metritis etc. all possibly leading to poor fertility later in the lactation.

For the udder, the dry period is both a period of risk and an opportunity to clear up existing infections.

Antibiotic dry cow therapy has two main objectives:

  1. To prevent new infections occurring during the dry period.
  2. To clear up existing sub-clinical infections.

Once a cow is dry for a couple of weeks and the udder has involuted (shrunk back), inhibitory substances, like lactoferrins and immunoglobulins are naturally produced in the udder tissue that further help eliminate underlying  infections and prevent new infections from colonising the udder tissue. The cow also produces a waxy keratin plug that blocks the teat canal producing a physical barrier against the entry of new infections.

Risk of infection & relative persistence of different Antibiotics

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The first risk period of the dry cow period is within the first 1-2 weeks. All dry cow antibiotic therapy products should be effective in protecting against new infections developing in this period.

The second risk period is at the end of the dry cow period, close to calving. It is important to note that not all antibiotics used for Dry Cow Therapy (DCT) persist for the same time in the udder. The diagram below illustrates how long various dry cow antibiotics persist for in the udder. 

It is recognised that the longer an antibiotic persists in the udder, the higher the probability of reducing Staph aureus and Strep uberis infections (two of the most commonly isolated bacteria from mastitis samples ). The diagram also illustrates that even the longer persisting antibiotics used in DCTs will not protect the udder during the second risk period close to and at calving time. 

At this stage the cow relies on natural defences and the keratin teat plug.  Internal teat sealants have been developed to supplement the natural keratin plug and will usually remain present until after the cow has calved down, when they can then be stripped out prior to first milking.

dry cow theraphy 1.PNG  

dry cow theraphy 2.PNG In the past, blanket dry cow therapy with a long persisting antibiotic tube was highly efficacious and safe as cows had longer dry periods. In the post quota era, where shorter dry periods of six to eight weeks will become more common, selection of dry cow tubes with appropriate milk withholding times will become more critical.

Longer persisting antibiotic tubes will deliver better cure rates but will also increase the risk of antibiotic residues being present when cows calve down. The ideal treatment will be long enough to result in a cure of subclinical mastitis and reduction in somatic cell count; and short enough not to run the risk of antibiotic residues once the cow has calved. 

A tube with a dry period recommendation of about six weeks/42 days would therefore be desirable. Scanning for pregnancy is also important so that accurate calving dates are available. Discussion with your vet is critical to review individual cow milk recording results and will allow your vet to prescribe an appropriate dry cow therapy programme. Selective dry cow therapy, where some cows are treated with internal teat sealant only is a possibility where individual cow milk records are available.

dry cow theraphy 3.PNG Key points

Dry Cow tubes have different: minimum dry period and milk withholding times after calving.

In conclusion

  • Blanket antibiotic dry cow therapy is highly efficacious at reducing sub-clinical mastitis
  • Selective dry cow therapy should be discussed with your vet to determine which cows can receive internal teat sealant with or without an antibiotic dry cow therapy
  • Antibiotic dry cow treatments need to persist long enough to allow a cure but not too long to cause antibiotic residue problems
  • An internal teat sealant protects  cows against new infections, particularly at the end of the dry period.

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