CSI-Dairy: A cow-side Investigation into escalating SCC and mastitis
By Dave Ohman, DVM
Numerous “culprits” exist on dairy farms, robbing herd performance and injuring the dairy’s bottom line. Identifying and arresting the offender isn’t always easy, and often requires a full investigation, gathering and analyzing evidence on the farm and in the lab. One dairy with new facilities and an emphasis on hygiene faced the mystery of escalating somatic cell counts (SCC) and increasing mastitis problems.
The dairy producer was frustrated. High SCC and clinical mastitis seemed to be getting worse after a larger parlor was built and milking frequency increased to 3X. His hospital pen was full. The bulk tank SCC was approaching a quarter million. Clinical mastitis cases were not responding to treatment and cows were being culled weekly from the 1,700-head Jersey herd due to chronic mastitis. Mastitis cultures were coming back as “environmental,” including Klebsiella sp. The dairy’s focus on improving hygiene, beds and protocol compliance wasn’t working.
An immediate investigation included an analysis of DC305 records, evaluation of all protocols and procedures, as well as parlors and freestalls. Mastitis samples were submitted to the regional veterinary laboratory.
The DC305 records (see Figure 1) showed that 57% of all culls, annualized, were for mastitis (400 cows). The lactating herd had 5.5% new cases per month, with 75% of all mastitis cases being repeats. Of all cows entering the dry period with a SCC of less than 200,000 cells/ml, some 33.7% had a first test greater than 200,000. The mastitis cases clearly carried a pattern of summer initiations.
All parlor equipment was operating according to specifications. Parlor procedures and treatment protocols were satisfactory. Cow comfort and freestall maintenance was good.
One observation did provide an early clue. The flush lanes of the main freestall barns converged in an alley directly in front of the parlor holding pen. All cows moving into the holding pen walked through this area. Furthermore, this alley was in full flush during at least one of the 3X milkings. Often, cows stood in 6-9 inches of flush water as they congregated before milking (see Figure 2). Flush water splashed on the cows’ udders and lower bellies. Since the hospital parlor was accessed via the common flush alley, all hospital cows were exposed to the flush water.
The breakthrough arrived with the laboratory’s culture results. A significant number of cows cultured positive for Prototheca. Previously classified Prototheca cases had been classified as “environmental” mastitis.
An initial entire herd culture of 1,640 cows identified 51 positive Prototheca cases. Subsequent cultures continued to identify positive mastitis cases.
The alga Prototheca is associated with wet environments, and samples of the flush water tested positive for Prototheca. Apparently the flush water was contaminating cows as they entered and left the milking parlor.
A two-pronged approach was adopted: preventing new cases by limiting exposure to contaminated flush water, and identifying and removing all positive clinical cases.
With 3X milkings, changing flush times to solve the problem was considered, but proved impractical. Instead, flush water was physically diverted before the common alley.
A culture media specific for Prototheca was added to the dairy’s culture program. All mastitis cases identified as positive for Prototheca were either culled immediately or segregated in a separate pen. No attempt was made to treat these cows. All fresh cows were cultured, and any Prototheca cases were ultimately culled.
With implementation of the control program, mastitis cases have been dropping steadily. The Prototheca-positive fresh cows, however, did persist for several months following the changes. These cows were likely subclinical carriers.
For the past year, the percent culls for mastitis has been 21%, down from 33%. The percent of repeats has dropped to 33% of total mastitis cases, down from 75%. The bulk tank SCC is around 150,000. New mastitis cases run at 2.4% of lactating cows, and new transition subclinical cases have decreased to 20.9%. Hospital numbers are down to a quarter of the outbreak’s high.
The Prototheca mastitis probably had been slowly building in the herd and had not been accurately identified. The increased exposure to contaminated flush water with 3X milkings instead of 2X milkings could have triggered additional clinical cases. It might have been the proverbial “straw that broke the camel’s back.”
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