My excitement about new tools for mastitis prevention during the dry period has not diminished. In fact, with the results we’re seeing, it continues to grow.
A recent review of client records revealed the following:
New infections during the dry period and the percent of mature cows with a first test somatic cell count (SCC) of more than 400,000 have reached unprecedented lows.
In more than 10 years of tracking, we’ve never seen several consecutive months where less than 5 percent of cows freshen with subclinical mastitis.
New dry period infections have dropped from 15 to 20 percent to as low as zero to 10 percent.
Several large herds have achieved an average linear score for mature cows of 2.0 or less. And, this number continues to drop as more clean cows re-enter the milking herd.
Clinical mastitis cases during the first three months of lactation have declined to nearly one-half of the level seen during the same season last year.
Changes are working
So, what sparked the change? These herds all have shortened their dry periods to 30 or 45 days. All animals are housed on clean bedding. All animals receive an internal teat sealant at dry-off. And, all of these herds only use dry-cow antibiotics on animals with a SCC of more than 200,000 on their last test or with a positive CMT test at dry-off.
Field results back up the research showing that teat sealants prevent new infections. So, the question becomes, “Have we cured infections present at dry-off?”
In our client herds, decreased dry-cow antibiotic use has not negatively impacted the cure rate of animals with existing subclinical infections during the dry period. In fact, in most herds, the number of cows that have a positive antibotic treatment response has increased from a range of 60 to 75 percent to 70 to 90 percent. This effect may not be significant, but it does show that decreased antibiotic use has not caused a problem, either.
Shorter dry periods increase the risk for antibiotic residues with early calving. But decreased antibiotic use offsets this.
The one concern with decreased dry-cow antibiotic use is that contagious mastitis — especially Staphylococcus aureus — could accumulate in the absence of blanket dry-cow antibiotics. That’s because infected quarters could have low cell counts when screened before dry-off due to intermittent shedding. Therefore, dry-cow antibiotic use should only be reduced in herds with excellent control practices in place to prevent contagious mastitis.
While all herds had measurable reductions, we believe that incorrect teat-sealant application reduced prevention efficacy for a few. Proper administration of teat sealant is crucial to get good results. However, we have not seen a high incidence of acute coliform infections immediately after dry treatment that would indicate sloppy infusion practices. So, it is possible that these herds are developing new mastitis infections after calving, but before first test. Both herds have slightly higher rates of new infection during lactation.
Of course, this information is only observational. We are not directly comparing the use of teat sealants and short dry periods to traditional practices in a randomized, controlled trial. Is it too early to make recommendations to follow this practice? Not in my herd.
Marquerita B. Cattell is a consulting veterinarian in Fort Collins, Colo.