As cows near the end of lactation their milk quality changes i.e. levels of lactose decrease and SCC increases. Milk from low-producing cows may cause processing problems for some dairy products. Cows producing less than 9 L/day may have an elevated somatic cell count even if uninfected. They may contribute to a higher bulk tank SCC (especially in seasonal herds), even though their milk volume is low.
Udder infections during the dry period can be minimised by events at drying-off. The aim is to shut down milk secretion and seal the teat canal as rapidly as possible – this sealing usually takes about two weeks. Research has shown that virtually all new infections occur in quarters where the teat canal has not sealed.
Intermittent milking provides an on-going stimulus to produce milk and impedes teat sealing. In the lead up to drying-off if the frequency of milking is changed e.g. ‘skip-a-day’ or ‘once-a-day’ milking, mastitis risk is greatly increased.
During the first two weeks after drying-off, it is also important to minimise the number of bacteria that contaminate the teats.
Teat dipping after the last milking ensures complete coverage of the teat by disinfectant and reduces the number of contagious mastitis bacteria present on the skin.
To reduce the number of environmental mastitis bacteria, areas where cows lie should be as clean as possible. There should be no bare ground or heavy manure on outdoor pads and housing should be clean. Outbreaks of E. coli mastitis have been recorded in situations where cows lie in wet conditions in the first few days immediately after drying-off. These infections may be very severe (often fatal) and can be challenging to treat.