The Dry Period, Dry Cow Therapy and Culling
After each lactation, dairy cows require a dry period which is sufficiently long to allow the udder tissue to repair and rejuvenate. Many of the milk producing cells are removed and replaced again before the next calving. Areas of damage are repaired, and this period provides us with the best opportunity to remove chronic udder infections by using dry cow antibiotics. Culling can be used at this time to remove the cows that have irreparably damaged udders and those that are unlikely to be cured of udder infections.The dry period can be thought of as a factory shut down and refit. The worn out and damaged tissues are repaired and replaced. As this process requires approximately six weeks to be completed, ideally cows should be provided with a minimum of six and preferably eight weeks from dry-off to calving.
Dry cow therapy (DCT) has been a crucial part of mastitis control for over a decade. The intent of dry cow therapy is to administer high doses of antibiotics into the udder that persist for the much of the dry period (20 to 70 days depending on the preparation) and kill mastitis bacteria. The prolonged time of exposure to antibiotic and the formulation enhance penetration and give an increased chance of curing infections embedded deep in the udder. Dry cow therapy has also been shown to reduce the number of infections developed during the dry period by promoting the formation of the keratin plug that seals the teat canal.
Over the years different dry cow therapy programs have been promoted. There are two basic programs, Strategic and Blanket DCT. A guide to assist you determine how you treat your herd is available here. Selective DCT only treats selected cows with dry cow antibiotics. The cows that are treated are the ones that have the greatest likelihood of being infected, for instance cows with a cell count above 250,000 and cows that have been treated for clinical mastitis. Strategic therapy works well when the level of infection in the herd is low and the risk of cows acquiring new mastitis infections is low. Blanket Therapy involves treating all cows in the herd, irrespective of their infection status.
Traditionally blanket therapy has been advocated in herds that have a high BMCC and/or high rate of clinical mastitis. However, many farmers with very low rates of mastitis have decided to continue to blanket treat their herd, thereby keeping the level of mastitis low. A majority of the recipients of last years VDIA Milk Quality and Cell Count awards used blanket dry cow therapy and attributed some of their success to this policy. Further, recent research from Holland has shown that the farms that repeatably produced low cell count milk treated all cows in their herds with dry cow antibiotics at drying off and had done so for a number of years.
Culling cows for mastitis and high cell count can be the only way of eliminating chronic infections from the farm. However, it comes at the cost. Culling cows with chronic infections helps protect the healthy, young cows which are the future of the herd. Culling alone seldom solves farm mastitis problems. Failure to prevent new infections will mean that other cows take their place at the top of the mastitis culling list. Culling should be reserved for removing cows from the herd who are unlikely to be cured by other means, or who are going to be a continual problem.
Cows that should be considered for culling include:
- Older high cell count cows
- Cows that have had three or more cases of mastitis
- Cows with high cell counts for two consecutive lactations
- Cows with damaged or deformed udders
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