Properly managing dry cows can have a huge influence on whether or not a cow gets mastitis during the next lactation. Chronic subclinical infections (present at dryoff and after calving) and new infections (developed between dryoff and calving) both cause higher rates of subclinical and clinical mastitis during the next lactation.
The dry period
Cows are more susceptible during the first three weeks of the dry period and immediately before calving. Reasons for greater susceptibility during this period include:
Mastitis develops when exposure to bacteria exceeds the ability of the teat end defenses to prevent bacterial infection. Risk factors for the development of mastitis during the dry period are similar to those during lactation.
Since we will no longer forestrip and predip, there is greater growth of and exposure to bacteria on teat skin and in the streak canal. The streak canal becomes shorter during the dry period, and the development of a physical barrier to infection (keratin plug in the streak canal) takes time. There’s a strong association between the failure to develop a keratin plug and the development of clinical mastitis.
- More gland pressure that fosters milk leakage and leads to easier entrance of bacteria through the teat canal;
- Reduced local immune response; and
- Lack of flushing effect of milking on bacteria present in the mammary gland.
What you can do
Some cows simply are at greater risk of developing mastitis. It is important to identify potential risk factors for the development of mastitis during the dry period and right after calving so you can put in place strategies to reduce the impact of those infections on production during the next lactation.
A cow’s age is one of the most important risk factors for developing both subclinical and clinical mastitis. The mastitis history in the previous lactation is another very important risk factor for development of clinical mastitis in the next lactation. Quarters that had at least one case of mastitis during the lactation before dryoff are also more likely to have a case of mastitis in the next lactation, as compared to quarters of cows that did not have mastitis previously.
The presence of persistent subclinical mastitis during the dry period results in lower production and poor colostrum quality.
Our advice is
Continue to use dry cow antibiotic treatment for all quarters in all cows. Manage the dry cows’ environment to reduce exposure to environmental mastitis organisms. Using internal teat sealants is a good option for many herds.
In some cases, it makes sense to dry off quarters. Using selective dry cow therapy can be very effective when carefully applied in selected herds. If you have controlled subclinical mastitis in your herd to a bulk tank somatic cell count of less than 200,000 cells/ml and are able to monitor active quarter infections with use of California Mastitis Tests (CMT) and culturing, then your herd may benefit from selective therapy. Selective therapy, when applied effectively, can decrease antibiotic usage without increasing mastitis.
How you house and handle cows right after calving is at least as important as what you do during the dry period. Strive to not overcrowd during this critical period.
A good rule of thumb is to not calve cows in areas that you would not feel comfortable lying down in yourself. Do not use the same milking unit to milk cows with mastitis and those that are recently fresh.
It is likely that management of these cows is specific to each herd, and you should discuss appropriate protocols for dealing with these cows with your veterinarian.