Risk of infection during the dry period

Mastitis pathogens

The majority of clinical mastitis cases soon after calving are due to infections acquired during the dry period, more specifically during the transition phase. The risk is not evenly distributed during the dry period. The bovine mammary gland becomes more susceptible to new infections at both the beginning and end of the dry period.

 

A major risk factor associated with infection during the dry period is the failure to develop a functioning keratin plug

  • 50% of teats were still open 10 days after drying off (Williamson et al. 1995. NZ Vet J 43 (6) 228-34)
  • Cows with a higher milk yield have a slower rate of closure.
  • The use of the antibiotic DCT increased the rate of development of a functional keratin plug
  • There is no important breed predisposition for teat closure

References

Bradley and Green 2004. The importance of the nonlactating period in the epidemiology of intramammary infection and strategies for prevention. Vet Clin Food Anim 20:547-568

The impact of the dry period on clinical mastitis

The peak of clinical mastitis during early lactation can be mainly attributed to the dry period. Infections acquired during the dry period have the ability to remain quiescent within the udder, subsequently causing clinical mastitis early in the next lactation.

Selection of a dry cow therapy with extended activity against gram negatives could result in 53% reduction in clinical coliform mastitis in early lactation, compared with a DCT with no gram negative activity (Bradley and Green. 2001. J Dairy Sci 84(7)1632-9). This confirms the importance of the dry period in environmental mastitis epidemiology.

The probable reason why animals do not develop clinical mastitis during dry period, although infection is very common, is that the mammary environment is not fit for bacterial growth.  High lactoferrin and leucocyte concentrations prevent rapid multiplication, but not infections from occurring. 

References

Bradley and Green 2004. The importance of the nonlactating period in the epidemiology of intramammary infection and strategies for prevention. Vet Clin Food Anim 20:547-568

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