Mastitis is important to consider when selecting cows to cull because those with persistent infections pose a real threat to young, healthy animals and the whole enterprise.

Although smart culling rarely solves a serious mastitis problem on its own, in conjunction with a sound day-to-day prevention program it is a key part of good mastitis management.

Cows with persistent infections are prime candidates for culling. The hard part is identifying exactly which cows in the herd have persistent infections. Two groups to consider are:

• Cows with multiple clinical cases  in one lactation
• Cows with high cell counts for two lactations despite receiving Dry Cow Treatment during the last dry period

Specifically, cows that have had three or more clinical mastitis cases in one lactation should be culled. These cows are easily identified if you keep stock treatment records as part of a factory quality assurance program. 

It is more difficult to identify cows that have no obvious signs of mastitis but have persistent subclinical infections. Most cows will be cured over the dry period with Dry Cow Treatment.  So if you have cows with peak cell counts above 250,000 cells/mL for two lactations despite having Dry Cow Treatment in the period between, they should be seen as persistently infected cows. 

Don’t be tempted to focus on cows with very high cell counts in one season alone because many will cure if treated with Dry Cow.

Culling is an important tool in mastitis control but it is an expensive option if the wrong cows are removed. Take time to assess and identify the animals in which infection has persisted.

Countdown Farm Guideline or Technote
Farm Guideline Introduction, 15

Keywords
Cull, persistent infection, clinical cases, cell counts