A new study shows using dry-cow antibiotic treatment on heifers in the third trimester reduces mastitis at freshening.

After caring for heifers for 22 to 24 months and aiding them with their first delivery, it is disheartening to find a mastitis infection at the first milking. However, a 1995 study finds this occurs in 20 percent to 60 percent of all heifers, depending on region of the country and the season of the year.

But, producers don’t have to accept heifer mastitis. A study reported in the April 2001 Journal of Dairy Science, suggests that using dry-cow treatments 180 to 270 days prior to calving can reduce the number of infections. In the study, heifers were checked for mastitis during each trimester. Untreated animals had a 20 percent infection rate throughout their pregnancies with 8.3 percent of the quarters infected at calving. Conversely, infection rates in treated animals dropped below 5 percent immediately after treatment with dry-cow antibiotics and remained low through calving.

The Louisiana State researchers recommend treatment 180 to 270 days prior to calving since this minimizes the chance of new infections occurring after treatment and before calving. Treatment must be 45 to 60 days prior to calving to avoid any residue problems at freshening.

Cost of treatment is easily offset by increased milk production.

On average, heifers that freshen with mastitis produce 5.4 pounds of milk less per day during the first two months of lactation, compared to uninfected animals. That’s about 324 pounds per heifer during the first two months of lactation, or around $42 per animal (assuming a $13 per hundredweight milk price). Estimating the cost of dry treatment at $5 per animal, producers gain $37 per heifer by preventing mastitis.