While many producers regard young heifers as "uninfected," numerous studies have shown that:
- Heifers as young as six months of age can be diagnosed with intramammary mastitis infections.
- Prepartum heifers have been found to be more than 90% infected with intramammary mastitis prior to freshening.
- Infected animals may carry the infections for a year or more before they are diagnosed with mastitis.
The greatest development of milk-producing tissue in the udder occurs during the first pregnancy, so it is important to protect the mammary gland from pathogenic organisms to ensure maximum milk production during the first lactation and beyond. Animals carrying infections over a long period of time would be in a state of chronic inflammation, which would interfere with maximum mammary tissue development.
Louisiana researchers found that if bred heifers infected with Staph. aureus were left untreated, they produced 10% less milk in early lactation than those receiving therapy. Similarly, research in New Zealand has shown that Staph. aureus mastitis in heifers resulted in significant production losses when mastitis occurred in the first lactation. Those losses carried over to subsequent lactations, even if infected quarters were successfully treated.
A number of studies have been conducted to evaluate the efficacy of intramammary antibiotic therapy prior to freshening first-calf heifers. Clinical cure rates have been encouragingly high - up to 90% for heifers with Staph. aureus infections treated with dry-cow intramammary therapy. Researchers theorize that heifers respond better to intramammary therapy than mature cows because:
- Antibiotic susceptibility testing of various Staph. species from infected quarters in heifers has shown that resistance to commonly used intramammary mastitis therapies is usually low.
- Heifers' lower levels of secretory tissue may result in greater drug concentration in the mammary glands.
- Heifers have less scar tissue and abscess formation in the mammary glands, resulting in better drug distribution and contact with colonized bacteria.
Treating heifers prior to lactation provides the additional advantage of no loss of milk sales due to treatment.
For more guidelines on disease treatment and breeding standards established for Holstein heifers, from six months of age to freshening, see DCHA's Gold Standards II. Always consult with your veterinarian and nutritionist for specific recommendations for your operation.
Source: Nickerson SC, Owens WE. Mastitis Detection, Prevention and Control in Dairy Replacement Heifers. DairExnet. December 2010.
For more information visit Dairy Calf & Heifer Association.