The economic impact of duration of antibiotic treatments for mastitis
It rarely pays to extend antibiotic treatment for mastitis beyond label directions.
Much of what we think we known about how to treat mastitis is based on protocols that were developed decades ago when most mastitis was caused by contagious bacteria such as Streptococcus agalactiae and Staphylococcus aureus. Most Michigan dairy producers have done a great job in controlling these pathogens and bulk tank SCC values in Michigan are among the best in the world. While the continued decline in bulk tank SCC is a great indication that subclinical mastitis is increasingly controlled, the incidence of clinical mastitis remains stubbornly high on many farms. Even in herds with low SCC, it is not unusual for about 25-35 % of the cows to have at least one case of clinical mastitis each year. Treatment decisions about those cases can have a significant economic effect. We recently collected disease and treatment data on 40 larger WI dairy farms that contained about 53,000 lactating cows. On these farms, 34% of the cows experienced a case of clinical mastitis and about 70% of those cases were treated with commercially available intramammary antibiotics. The direct costs of mastitis treatments (drugs and milk discard) averaged $147 per case of which 74% was accounted for by milk discard costs. The farms had considerable variation in treatment costs which was primarily based on how many days they administered antibiotics. The duration of treatment for FDA approved intramammary antibiotics ranges from 1.5 to 8 days and few cases likely benefit from treatments beyond that on the label.