21 September 2016

4 minute read

North America

“When we're using selective dry cow therapy programmes, we want to use antibiotics to treat quarters with known intra-mammary infections, so really the difficult part of implementing a selective dry cow therapy programme is to find the appropriate method to identify cows that have active infections and will benefit from the use of antibiotics in those quarters,” said Dr Ruegg.

There are three methods to consider:

1. Review the history of the cow: Has she had previous cases of clinical mastitis, and what is her monthly somatic cell count history look like?
2. Perform individual quarter tests right before dry off, such as the use of a California Mastitis Test or the use of an individual quarter somatic cell count test.
3. Try to identify active intramammary infections by either collecting a milk sample for culture or for the use of a molecular test such as PCR testing.

Try to identify active intramammary infections by either collecting a milk sample for culture or for the use of a molecular test such as PCR testing.

“None of these methods are perfect but that doesn't mean that some herds can't successfully use these to use a selective dry cow therapy programme,” she said. “What you have to decide on your own individual herd is what your level of risk management is and is your herd really an appropriate herd to be able to use one of these methods and reduce the amount of antibiotics you use, or would your herd benefit more from continuing to use blanket dry cow therapy.”

Research on Selective Dry Cow Therapy

The purpose of the study was to compare the use of blanket dry cow therapy in every quarter of every cow to selective dry cow therapy (no dry cow therapy in low somatic cell count (SCC), low risk cows). Four herds were used in Ohio. The study evaluated each cow based on their somatic cell count and clinical mastitis history in the last 90 days, and only cows with low SCC were enrolled in this randomised clinical trial with half receiving blanket dry cow therapy and half of did not.

The study results showed:

• No overall effect on milk yield
• SCC was 16 per cent greater in those low SCC quarters that did not get dry cow therapy
• There were big differences between herds in the effect of reducing the amount of dry cow therapy that was used. In some herds, the use of dry cow therapy in every quarter of every cow was extremely beneficial, while in other herds, cows did fine with the use of selective therapy. The take-home message from this study is, not all herds should use selective dry cow therapy programme.

The question to think about is, which herd are you?

Another study performed in Holland with almost 1,700 cows from 97 randomly selected Dutch herds. Within those 97 herds, the researchers looked at the last DHIA SCC of each cow, and cows that had low SCC were enrolled in the study.

In enrolled cows, two-quarters received dry cow therapy and two-quarters did not, so this is a quarter level study that reduced antibiotic usage by about 85 per cent.

“The conclusion of the study was that the risk of clinical mastitis was actually increased in the quarters that did not get dry cow therapy and the SCC was slightly increased in quarters that did not get dry cow therapy. We can conclude that not every herd is appropriate for this type of programme. In some herds, every quarter of every cow should get dry cow therapy. Randomly applied, this type of programme doesn't seem to be effective,” said Dr Ruegg.

Another study was conducted in Canada, and they enrolled about 16 herds and about 700 cows. They had very rigorous selection criteria both for the herds and for the cows. All enrolled herds had to have bulk tank cell count of less than 250,000, and the cows had very serious eligibility criteria:

• Low SCC in the last 90 days of lactation
• No clinical mastitis in the last 90 days of lactation
• CMT test was performed on all of the cows at dry off

Half of the screened cows met their eligibility criteria to fall into the study to evaluate selective dry cow therapy and the other half of the cows received blanket dry cow therapy and a teat sealant to every quarter of every cow.

In this particular study, they evaluated a number of outcomes:

• Intramammary infections at calving
• Clinical mastitis in the next lactation
• SCC for the first 180 days of lactation
• Milk yield in the first 180 days of lactation

“They had outstanding results using a selective dry cow therapy programme with absolutely, no negative impact on either milk quality or milk yield,” said Dr Ruegg.

Based on the research, the use of selective dry cow therapy randomly to herds decreases antibiotic usage effectively but it also increases mastitis. Reducing antibiotic usage at the end of lactation isn't appropriate for every herd.

“Selective dry cow therapy, when carefully applied in selected herds, clearly can decrease antibiotic usage without increasing mastitis, without decreasing milk quality and for some herds, it can be quite an appropriate programme,” she said.

To view Part One in Dr Ruegg's Dry Cow Therapy series, click here.

Sarah Mikesell, Senior Editor

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