The USDA-NAHMS survey Dairy 2014 presented a series of abstracts at the Joint Annual Meeting of the American Dairy Science Association and the American Society of Animal Science, held this week in Orlando, Fla. One entire Monday morning session was devoted to the data analyzed in the study so far, featuring more than a dozen abstracts on calves, which we described in “USDA-NAHMS provides update on dairy farm practices at 2015 ADSA,” and bulk tank sampling and dry off procedures, which we will describe below.

The NAHMS team surveyed bulk milk tanks and milk filters pairs from a large sample of farms in 17 states during March through July 2014. The analysts from the USDA-ARS-NEA Environmental Microbial and Food Safety Laboratory in Beltsville, Md., then tested the samples for Campylobacter spp., Salmonella Dublin, and Salmonella and Listeria monocytogenes, pathogens found in the environment but also killed by proper pasteurization.


Campylobacter spp. was found on a portion of the 231 farms sampled, but more in larger operations, and more frequently in the west region of the 17 states sampled. 91.3% of those Campylobacter spp. were jejuni, with a small number of of C. lari, and C. coli. In total, just over 24% of surveyed farms had enrichments of Campylobacter spp.

Salmonella Dublin

Salmonella Dublin was detected using 230 samples of bulk tanks, estimating that 8% of herds had antibodies present. However, 39% of farms with 500+ cows had Salmonella Dublin present, while just 2.1% of medium (100-499 cows) and 1% of small (30-99 cows) farms showed signs of the pathogen. Interestingly, herds that raised cattle offsite (20.6% positive) and especially those that commingled heifers (28% positive) showed higher risks. Farms without contact from other cattle showed only 3.2% positive sampling for Salmonella Dublin.

Salmonella and Listeria monocytogenes

Using 234 bulk tank samples and 396 milk filters, NAHMS saw 18.6% of operations positive for Salmonella, though the majority were the non hazardous types of Salmonella. Listeria spp. was found on 20% of farms, while the newsworthy L. monocytogenes was found on 3% of operations. Both were down from 28.1% and 7.1% in the 2007 study, respectively. A significant presence of either pathogen can point to health risks for raw (not pasteurized) milk.


Dry-off done by mostly by schedule, not milk

Using face-to-face interviews, USDA’s NAHMS team worked with the University of British Columbia and Colorado State University to conduct face-to-face interviews about farm operations in 2013. The average dry period was 57.1 days, according to the surveys. Farmers were asked whether cows were dried off by a set date or pounds of milk. 98.8% of farms dried off at least some cows on schedule, while 81.3% of operations based on a low milk production level. 

Just over 88% of cows were dried off on a schedule, making the remaining 11.9% of cows dried off cows based on a minimum milk production measure. In addition, 73.6% of herds simply stopped milking at least some or all of their cows, while 47.5% of operations gradually dried off at least some or all of their cows by milking less per day. Gradual dry-off only represented 10.2% of cows while the other nearly 90% were abruptly tried off.

Intramammary antibiotics are used on 80.3% of farms, and 93% of cows were treated. The top administered was Cephapirin benzathine (ToMORROW® - Boehringer Ingelheim Vetmedica) on 31.6% of cows. 

As the session ended, presenter Jason Lombard, D.V.M., noted that blanket dry treatment may go away due to public pressure on antibiotic use. However, Pamela Ruegg, a University of Wisconsin Veterinarian and mastitis researcher, noted that Cephapirin benzathine is one of the longest-used dry-treatment antibiotics and resistance has remained flat through decades of use.

Other dry-off stats: 

  • 15% of farms perform a California Mastitis Test at dry-off
  • 65.7% switch the quality or energy of the ration
  • 10.9% restricted access to feed  before dry-off
  • 3.9% restricted to water before dry-off
  • Alcohol pads were used on 90.3% of farms before dry-treatment.
  • Internal teat sealants were used on 37.3% of farms, with external sealants of on 14.5% of farms
  • Average cost of antibiotics and sealants is $13.09/cow