Parity - susceptibility to mastitis pathogens

The effects of age, development, lactation stage and number of lactations

The degree of susceptibility to mastitis pathogens can vary throughout the cow's development and lifespan due to several factors.

There is significant evidence to suggest that contagious mastitis pathogens can be passed via cross suckling, flying insects and infected bedding to the juvenile udders on young heifers. The resultant infections may only become apparent when the heifer calves and joins the herd going through the parlour.

This underlines the importance of monitoring the whole farm environment for any areas of potential mastitis infection, and is one argument for not feeding milk from infected cows to youngstock. It also underlines the potential of cross contamination between heifers and mature dry cows when housed or grazed together. Heifers have specific nutritional requirements and are particularly infected with mastitis-causing pathogens in the last stages of pregnancy and just before calving, and are particularly prone to Summer mastitis.

Older cows, due to the number of lactations they have had, become more prone to chronic mastitis and the risk of clinical disease due simply to having been milked more and thus exposed more to the environmental pathogens that cause subclinical illness and are more likely to have damaged teats or udder tissue in which contagious infection can easily enter and colonise. Older cows also tend to have higher SCCs partly because they display a good immune response. The prevalence of infected quarters increases with age.

Biosecurity is an important consideration for herds that are not closed and flying herds. Newly bought-in cows that are in-milk should have a good Somatic Cell Count history; ideally with no SCC over 100,000, and cows with a SCC history of over 200,000 should be avoided altogether. Any newly bought-in cows should be monitored for three days after purchase by California Mastitis Testing to check for any problem quarters.

The analysis of recorded information on the lactation stage and number of lactations of cows with both clinical and subclinical mastitis can help to define the role of maiden heifers, first and second lactation cows and old cows on the herd's mastitis profile in programmes like the DairyCo Mastitis Control Plan.

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