The reason may be quite straightforward. C ontagious bacteria reside primarily in the udders of infected cows and on the teat skin. Minimizing or eliminating mastitis caused by contagious organisms is best accomplished by a rigid program of post milking teat dipping, treatment of cows as they are dried off and culling of chronically infected cows. As contagious mastitis problems are minimized, environmental bacteria become the primary mastitis concern and unfortunately a high percentage of infections caused by this group are likely to cause clinical symptoms. Critical Periods B ased on results of numerous studies it is clear that around dry-off, calving and early lactation, cows are more likely to develop new infections and a high percentage of the new infections are due to environmental organisms.
Many reasons have been offered, all likely play some role.
Dry cow treatments are ineffective against coliforms. Also, dry cow products do not persist through until calving. Suppressed immunity, cleanliness of dry cow housing areas and physical characteristics such as leaking milk and swollen udders may play a role. Milk fever, ketosis, lameness, fat cows, displaced abomasums also occur more frequently around calving and during early lactation. These disorders likely pre-dispose cows to mastitis problems even though they may not be the primary cause.