On May 22, 2015, Walmart, one of the largest grocery retailers in the U.S., publicly stated their position on antibiotic use in farm animals. The company stated that “antibiotics should be used responsibly in farm animals” and outlined a specific set of instructions for its producers to accomplish this. Despite the concern about usage of antimicrobials in agriculture, very few studies have described antimicrobial usage in U.S. dairy herds:

• A study examined the use of antibiotics on conventional dairy farms in Michigan, Minnesota, New York and Wisconsin (2004). Based on recall of the previous 60 days preceding the study, 1 to 10 percent of cows received at least one dose of antibiotics during that period.

• Researchers of Pennsylvania and Michigan State University (2005) evaluated antibiotic usage in 113 dairy herds from 13 counties in Pennsylvania. Antibiotics were used to treat clinical mastitis in 14 percent, pneumonia in 3 percent, metritis in 11 percent, foot rot in 16 percent and enteritis in 2 percent of the lactating dairy cows in one year. On the other hand, 10 percent, 7 percent, 5 percent, 3 percent and 8 percent of the dry cows were treated with antibiotics for pneumonia, metritis, foot rot, enteritis and clinical mastitis.

• University of Wisconsin’s researchers estimated antimicrobial drug usage and treatment practices on 20 conventional dairy farms in Wisconsin (2007). Clinical cases treated per year were: 38.5 percent of total cows for clinical mastitis, 3.3 percent for respiratory diseases, 14.5 percent for metritis and 18.9 percent for foot infection.

• According to the “Dairy 2007: Reference of Dairy Cattle Health and Management Practices in the United States” conducted by the National Animal Health Monitoring System (NAHMS; 2007), 2.8 percent of dairy cows were treated with antibiotics for respiratory diseases during 2007, 1.9 percent for diarrhea or other digestive problems, 7.4 percent for reproductive disorders, 16.4 percent for mastitis, 7.1 percent for lameness and 0.5 percent for other diseases. The Dairy 2007 study was conducted in 17 of the nation’s major dairy states, representing 79.5 percent of U.S. dairy operations and 82.5 percent of U.S. dairy cows. State and federal veterinary medical officers and animal health technicians collected data for this report from 582 operations with 30 or more dairy cows. Mastitis was the disease that affected the highest percentage of cows (18.2 percent), and not surprisingly, the highest percentage of cows was treated for mastitis (16.4 percent).

In summary, according to the studies reported previously, the number of antibiotic treatments per cow per year varies depending on the disease or disorder:

• Clinical mastitis: 14 to 38.5 percent of cows
• Respiratory: 2.8 to 3.3 percent of cows
• Reproductive: 7.4 to 14.5 percent of cows
• Lameness: 7.1 to 18.9 percent of cows
• Digestive: 1.9 to 2 percent of cows

Mastitis treatments

A multistate, multi-herd clinical trial conducted on 422 cows from Minnesota, Wisconsin and Ontario (2011) showed that treatments of clinical mastitis with an intramammary antibiotic could be reduced by half without significant differences in days to clinical cure by using culture systems to guide strategic treatment decisions in cows with clinical mastitis. Similarly, University of Minnesota researchers reduced 48 percent of the antibiotic use in dry cows by using a selective dry cow therapy at the quarter level based on culture results.

Successful treatment of mastitis is dependent on early detection and proper diagnosis. The NAHMS 2014 survey, “Milk Quality, Milking Procedures and Mastitis on U.S. Dairies, 2014,” showed 45.4 percent of operations cultured milk from individual cows during the previous 12 months. The dairies were classified as large (500 cows or more), medium (100 to 499 cows) and small operations (fewer than 100 cows). More than half of large operations (56 percent) performed individual cow cultures, compared with about four of 10 medium (44.4 percent) and small dairies (42.6 percent). In this survey, milk was cultured from all clinical cases in 40.6 percent of the dairies (67.6, 33.4 and 33 percent of large, medium and small operations, respectively). The practice of culturing all clinical mastitis cases has improved considerably from the previous NAHMS published in 2007 (the average was 30.3 percent), indicating that selective mastitis treatment is more common among U.S. dairies.

There are increased concerns of treatment-related costs and the economic costs of antibacterial therapy for mastitis. Recent studies in the U.S. have reported that the average treatment cost of a case of clinical mastitis ranges between $50 to $212. The direct costs associated with antibiotic treatment include extra labor, cost of antibiotics and discarded milk. Using an on-farm culture system for strategic identification and treatment of clinical mastitis, Iowa State University researchers reduced the direct cost of clinical mastitis by 65 percent.  

Fernando Diaz is a dairy nutrition and management consultant at Rosecrans Dairy Consulting LLC. Email Fernando Diaz.

Nuria García is a research scientist in food and animal sciences in the Animal Disease Research and Diagnostic Laboratory at South Dakota State University. Email Nuria García.