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Dry cow therapy: A prescription for success

Julia Hollister for Progressive Dairy Published on 26 August 2020

Mastitis can spell disaster for dairy farmers. This potentially fatal mammary gland infection is the most common disease in dairy cattle in the U.S. and worldwide.

But a treatment – dry cow therapy – has proven to be effective.

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“Blanket dry cow therapy is a management practice implemented in the late 1960s as part of the five points plan to control mastitis,” said Fernanda Ferreira, population health and reproduction specialist at University of California – Davis. “The main objective was to treat infections that have low cure rates if treated during lactation and to prevent new cases of mastitis during the dry period.”

Speaking before a crowd at the Golden State Dairy Management Conference earlier this year, the DVM said advancements in management, nutrition and milk-management practices have put many herds in a position in which some cows are healthy at dry-off and are at low risk of infection during the dry period. This is an opportunity to reduce the use of antibiotics in dairy production systems, which may also be an economic opportunity for dairy farmers.

Selective dry cow therapy (SDCT) is a management practice that is being proposed as an alternative to blanket dry cow therapy (BDCT). The rationale behind it is that modern dairy herds have a lower prevalence of contagious intramammary infections and overall better milk quality. This means there are cows that do not benefit from antimicrobial use at their dry-off, and therefore, an opportunity to reduce use of antimicrobials exists. This may reflect not only an economic opportunity but also a reduction in overall antimicrobial use in food animals.

This practice has proven to be successful, and when combined with improvements in herd management, nutrition, facilities and cow health, it has led to a substantial decrease in national bulk tank somatic cell count (BTSCC)levels and improved milk quality in the U.S.

Economic analysis can help veterinarians, dairy farmers and managers to make better-informed decisions about their dry-off management practices. It can help answering questions such as, “Is it economically feasible to implement SDCT?”, or “What would be the overall cost of mastitis in my herd if I implement SDCT?” Therefore, the objective of the preliminary analysis was to evaluate the costs of mastitis around the dry period (CMDP) if SDCT is implemented in California herds.

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“CMDP considers all the costs associated with labor, antibiotics and teat sealants that are used to dry off cows, as well as costs associated with clinical and subclinical cases of mastitis of the subsequent lactation of cows (antibiotic use, labor, milk losses, discharged milk),” Ferreira said. “The idea of this analysis is that if there are cows that do not benefit from receiving antibiotics at the dry-off, there is an opportunity to save money there. However, there might be an elevated risk of mastitis in the next lactation, and therefore, we must evaluate the overall costs considering these risks.” 

Ferreira obtained milking testing data from 376 herds and a little over 1.5 million lactations (2009-2017) from cows with subsequent lactation information. Her team looked at the last test-day somatic cell count (SCC) and the SCC in the next lactation, up to 50 days in milk (DIM). These were the records used to estimate infection and cure risks for subclinical mastitis around the dry period, considering that all these herds use BDCT.

Ferreira selected a total of 9,986 cows from parities one to eight, with subsequent lactation information and looked at their last SCC before dry-off and the cases of clinical mastitis in the next lactation. With this data, she was able to estimate, using regression, what would be the infection risk of clinical and subclinical mastitis for large California herds based on the last test-day SCC.

The first step of the analysis was to understand the new infections and cure risks of mastitis around the dry period throughout the year in California. Overall, these are seasonal, with the greatest risk of infection happening during wet winters. Regardless of the month, there are at least 50% of all primiparous (given birth only once) cows enrolled at the Dairy Herd Information Association (DHIA) testing with a last test day SCC below 50,000 cells per milliliter, and 25% of multiparous cows with a last test day SCC below 50,000. Twenty percent of all California herds have annual weighted average BTSCC below 143,000 cells per milliliter. These results show promising opportunities to implement SDCT in California herds.

Ferreira simulated three 1,000-cow herds (varying their BTSCC) and assumed a 35% cull rate, labor costs of $12 per hour, teat sealant cost at $2 per tube, antibiotics for both lactating and dry cows as $3 per tube, and milk price as $19 per hundredweight (cwt). If a cow has an episode of high somatic cell count (greater than 200,000 cells per milliliter), she has subclinical mastitis, and each case lasted on average of 85 days, resulting in milk losses of 1.9 pounds of milk per day. Feed costs were 28 cents per kilogram. If a cow has a case of clinical mastitis during her subsequent lactation, a cost of $217 per case resulted.

The next step was to estimate what the risks of clinical and subclinical mastitis would be if cows were not treated with antibiotics. Antibiotics were always combined with teat sealant, and if antibiotics were not used, teat sealants were still used.

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“Our results have shown that, under the current conditions, there is an opportunity to implement SDCT in herds, even in the ones considered high BTSCC,” she said. “In a herd with average BTSCC, the least CMDP would be achieved if only primiparous [cows] with last test day SCC above 107,000 cells per milliliter were treated, and multiparous with last test day SCC greater than 57,000 cells per milliliter. This would mean that only 23 percent and 77 percent of the first and multiple dry period cows would be treated. The CMPD for these two groups of cows would be 33 dollars and one cent and 55 dollars and 90 cents, respectively.”

Compared to a BDCT strategy for that same herd, a SDCT strategy represents less $3.06 and $1.26 per cow. In low BTSCC herds, these differences would be $4.49 and $1.91 less per cow per year.

If teat sealant by itself is as effective as teat sealant plus antibiotics (0% penalty), the difference in the CMDP would be $11.41 and $11.01 less per cow per year for first and multiple dry period cows, respectively. A 100% penalty resulted in very minor differences, less $1.73 and $0.75 per cow per year in their CMDP.

“Despite not being a significant decrease, and susceptible to variations in milk price and other inputs prices, these reductions may represent an economic opportunity in well-managed herds,” Ferreira said. “These results demonstrate that there is an economic opportunity in implementing SDCT in large herds. We advise that herd-level analysis looking at the risk of clinical and subclinical mastitis risks should be done and used for economic evaluations.”  end mark

PHOTO: Staff photo.

Julia Hollister is a freelance writer based in San Francisco, California. 

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