Selective dry cow treatment (SDCT) is very topical right now. SDCT has become the normal situation in some other countries. The alternative, blanket dry cow therapy – treating every quarter of every cow with intramammary antibiotics – has been recommended by the National Mastitis Council for years.
Any time veterinarians and farmers make changes to what they do, it is good to see how those changes worked out for others who made the same or similar changes. Because of new regulations on how antibiotics are used, many dairy farmers in the Netherlands started a widescale switch to SDCT in 2013.
Recently, researchers in the Netherlands published a retrospective evaluation on the impact on udder health after the switch to SDCT. They tracked milk quality data from 2013 to 2017.
The researchers were able to access the test day somatic cell count (SCC) data for almost all cows in all herds in the Netherlands. They were able to look at whether there were changes in the herd’s udder health (that would affect bulk tank milk) and whether there were changes in individual animal’s udder health broken out by parity, heifers versus cows.
The researchers looked at the average bulk tank SCC and at the percentage of high SCC cows (>250,00) and heifers (>150,000) in the herd. They looked at the number of cows and heifers that moved from low test day SCC to a high SCC on subsequent tests in that lactation.
They also looked at whether there were more than 25% of heifers and cows in a herd that had a high SCC in the first 60 days fresh as a way to investigate the impact of the dry period on udder health.
Finally, they looked at the number of herds that had more than 25% of cows that had had high SCC on the last two tests before drying off and on the first test in their next lactation. This was considered a way to look at the risk of mastitis during the dry period.
The use of antimicrobials for dry cow treatment decreased by 36% between 2013 and 2015 and remained at the new lower level through 2016 and 2017. This decrease in dry cow treatment did not have a large impact on most of the measures of udder health. Amongst the udder health indicators that the researchers investigated, five of the six improved between 2013 and 2017. The only indicator that showed a worsening of udder health was in the number of herds that had more than 25% of cows with high SCC after the dry period. This was most evident between 2013 and 2016.
So widespread adoption of SDCT did not seem to have a detectable impact on the udder health in most herds.
These are interesting findings and represent the largest study on the impact of SDCT. The researchers did note that these types of retrospective studies need to be interpreted with caution. There are many things that can change over a five-year period that could also affect the national indicators of udder health not just the wider adoption of SDCT.
There were two major changes that could have been expected to impact many herds between 2013 and 2017. One was a change to EU dairy quota in 2016 and the second was to environmental requirements for manure management in 2017. Both may have affected measures of udder health if they led farmers to change how they selected cows for removal from their herds.
Another finding of the study was equally interesting. There were herds where the farmer decided that rather than use selective dry cow treatment, they would not use any antibiotic dry cow treatment at all. In those herds, all the individual and herd udder health measures got worse. It illustrates that SDCT leads to better udder health than completely eliminating dry cow treatment with antimicrobials.
Dr. Robert Tremblay is a veterinarian for Boehringer-Ingelheim and lives near Guelph.