Survey links digital dermatitis, on-farm practices
KIMBERLY – The results of a survey for the presence of digital dermatitis (hairy heel warts) on dairy farms in east central Wisconsin were outlined in a presentation by Kewaunee County agriculture agent Aerica Bjurstrom at the Extension Service's semi-annual farm management update for agribusiness professionals.
With the help of a summer intern, Outagamie County had the most herds among the 45 that were scored during the project in 2016. Fond du Lac and Kewaunee counties had the next highest participation while Brown, Calumet, Manitowoc, Waupaca, and Winnebago counties had at least two herds that were surveyed.
Conducted in large part by Extension Service agents, including Bjurstrom, the survey checked 11,817 cows for evidence of the infection.
The group of 45 herds consisted of 15 small ones (22 to 115 cows), 19 medium sized ones (70 to 590 cows), and 11 large herds (850 to 6,200 cows). Of the 45 herds, the 15 with tie-stall housing had 917 cows in the survey while the 30 with free-stall housing had a total of 10,900 cows that were checked.
All of the cows in the small herd group were scored along with 84 percent in the medium group, and 43 percent in the large herds. Bjurstrom participated in the scoring of 1,500 cows in one herd in her home county.
Digital dermatitis history
Bjurstrom noted that digital dermatitis (DD) was first positively identified in Italy during 1974. Within a decade, it had arrived in the United States and then spread rapidly in this country during the mid 1990s, she observed.
According to the latest information, DD is found on 70 percent of all dairy farms in the United States, including 95 percent of those with at least 500 cows, Bjurstrom indicated. Cows with the infection, which is most prevalent on the back feet, are at risk for decreased milk production, lameness, and lower fertility, often making them candidates for involuntary culling, she stated.
In addition to the presence of already infected cows in the herd, contributors to a new case of DD are wet conditions, poor foot hygiene, and poor management of footbaths, Bjurstrom indicated. Genetic susceptibility, low heel height, early lactation periods, and high milk production are other high risk factors for an infection, she added.
Prevalence of DD
On dairy farms, it is common for 5 to 37 percent of the cattle to be considered as lame, Bjurstrom reported. Of those cases, 10 to 40 percent are directly attributable to DD, she said.
Dairy scientists refer to DD in three different stages or designations, Bjurstrom pointed out. They are M0 (no signs of lesions), M2 (acute or active lesions), and M4 (a chronic non-active lesion that can nonetheless serve as a source of other infections). She emphasized that there is no way to cure cows which have DD.
Despite the national statistic which indicates that 95 percent of dairy herds with at least 500 cows have a DD presence, the 2016 east central Wisconsin survey found that the large herds had the highest portion of M0s (82.9 percent) and the lowest presence of M2s (1.1 percent) while the large and small operations had a similar presence of M4s, Bjurstrom reported.
Of the 11,817 cows that were checked, 212 had an active M2 case, 2,014 were identified as M4s, and the remaining 9,591 were M0s. The highest percentage of M2s was 27 – in herd which once had 50 percent M2s, Bjurstrom noted.
To keep the M4 category cows from infecting other cows, the frequent use of footbaths is prescribed, Bjurstrom stated.
She stressed that this advice was borne out in the survey, which found that the 11 farms not using a footbath had the highest M2 frequency of 6.9 percent while those using a footbath one to three times a week had an M2 rate of 3.1 percent and those using a footbath four to seven times a week had the lowest M2 rate of 1.7 percent.
To be effective, Bjurstrom urged that the footbaths be long enough (10 to 12 feet) to force cows to place their feet in the brine at least two or three times during each trip.
This means placing two of the typical 6 foot, 9 inch fiberglass units (cost of about $580 each) end to end, she said. “Don't skimp on the footbath design.”
A copper sulfate solution is the most popular choice for the footbaths on the surveyed farms, Bjurtrom indicated. Following in popularity are pre-mixes and a solution that also contains Formalin.
Hoof trimming practices
The frequency of hoof trimming stood out as another variable in the statistics compiled for the survey, Bjurstrom continued.
The operations with bi-weekly hoof trimming had both the lowest percentages of M2s (1.1) and M4s (16) while those with bi-monthly or quarterly trimming had 5.3 and 3 percents of M2s respectively along with a 24 percent average rate of M4s for both. The herds (mostly the smaller ones) with less frequent hoof trimming had 7 percent M2s and 18 percent M4s.
While Bjurstrom endorses the more frequent hoof trimming that helps to identify DD infections and trends, she cautions that the treatment of M2s is sometimes overdone. She said the footwrap bandage which accompanies the treatment need be applied so it will stay on for only up to one hour rather than for a couple of days.
In a subgroup of the eight herds in the survey with the lowest DD rates, it was noted that all of them keep hoof health records and used a professional trimmer (one of which was in-house trained), Bjurstrom pointed out.
Other frequent practices in those herds were trimming on set schedule, trimming up to three times per month, using a footbath at least three times a week, and regular lameness scoring, she added.
By using some of the same equipment and apps that were used in the survey, farmers can perform their own analysis of DD presence in their herds, Bjurstrom suggested.
For details on that, contact her by e-mail to firstname.lastname@example.org or Fond du Lac County dairy and livestock agent Tina Kohlman at email@example.com.