Several studies have demonstrated that using antimicrobial dry-cow-therapy and/or an internal teat sealant can reduce the incidence of new intramammary infections during the dry period and in early lactation.
For a large number of farms, using some form of dry-cow-therapy and/or teat seal has become common practice at dry-off and is an industry standard recommendation as part of mastitis management. --> DairyNZ has some great resources that we have linked for you here <--
Some extension advice is tailored towards reducing farm working expenses. This makes the cost-benefit of any treatments at dry-off (or any other time) fairly important. This has lead some to wonder if treatment at dry-off (e.g. dry-cow therapy and/or teat seal) could be removed entirely for some cows?
This week's summary is about a study that was designed to provide information from a veterinary practice to a farming group on not treating cows at dry-off when they are wintered on fodder beet.
Teat sealing at dry-off was associated with a reduction in the incidence of clinical mastitis compared with no treatment at dry-off
Teat sealing at dry-off was associated with a reduction in the proportion of cows with SCC greater than or equal to 200,000 cells/ml compared with no treatment at dry-off
The cows used in this study were "low-risk" cows that did not have clinical mastitis or a history of high SCC. Results from this study should be used for discussion purposes, treatment of cows at dry-off should be decided at an individual farm or cow level under veterinary guidance.
For 4 herds located in the South Island, the use of internal teat sealant at drying-off resulted in a reduction in the incidence of clinical mastitis between dry-off and ~80 days after calving compared with cows that had no treatment at drying-off.
Half of the cows were assigned to the “control group” where no treatment was applied at dry-off. The other half of the cows were assigned to the internal teat seal group “ITS group” where an internal teat sealant was infused into each quarter at dry-off by trained farm staff under vet supervision.
After being dried-off cows were fed a maintenance diet for ~one week while being monitored for signs of clinical mastitis before being transported to their winter grazing of fodder beet, kale and ryegrass straw.
As their calving dates neared, cows were transported back to their home farm ~2 weeks before calving.
Farm staff were given guidance on detection and appropriate recording of clinical mastitis cases (so everyone was on the same page to ensure the data collected could be used in the experiment). Animals that were suspected of having clinical mastitis had a milk sample taken before treatment to be analysed for microbiology.
Average length of the dry period was 70 days, the shortest was 32 days and the longest was 140 days.
Within the 30 days from drying-off, 32 cases of clinical mastitis were diagnosed and between 30 days before calving and 84 days after calving, 77 cases were diagnosed.
Approximately 75% of the clinical mastitis cases had milk samples collected for bacteriology. Strep uberis was the most common bacteria found in the samples (70%; 58/83), followed by staph aureus (7.2%; 6/83).
Importantly, there were no differences in the type of pathogen detected between cows in the 2 treatment groups.
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Probability of being diagnosed with clinical mastitis
The authors used their data to predict the probability of clinical mastitis occurring for a variety of scenarios.
Their ‘base’ cow was the most common group in their study - Friesian-Jersey (FJ) crossbred aged 4-8 years.
For such a cow with a dry period between 30 and 80 days, without teat seal treatment (control), the probability of her having clinical mastitis was 12%. For the same cow that instead was teat sealed at dry-off, the probability was 7%.
This is illustrated in the figure below, the blue circle represents the untreated cow with a 30 to 80 day dry period and the purple circle represents the teat sealed cow with the same dry period length. The black lines on the figure (called error bars) show the 95% confidence interval for each estimate.
If the dry period was longer, the probability of getting clinical mastitis either increased or decreased depending on the treatment at dry-off.
For example, the same FJ cow aged 4-8 years with a dry period between 81 and 140 days if not teat sealed she had a probability of getting clinical mastitis of 21% (blue triangle), if treated with teat seal at dry-off this probability was 5% (purple triangle).
Somatic cell count
At the first herd test, 16.6% (134/808) of all the cows studied had a SCC greater than or equal to 200,000 cells/ml.
Approximately 20% of the cows left untreated at dry-off had SCC greater than 200,000 cells/ml whereas, only 13% of those teat sealed cows had SCC greater than 200,000 cells/ml at first herd test after calving.
As with the probability of being diagnosed with mastitis, the authors predicted the probability of having a SCC over 200,000 cells/ml for the same FJ, 4-8yo cow that had a dry period between 30 and 80 days and calved 70 days before the first herd test.
A cow that did not get teat sealed (control) had an 18% probability and the teat sealed cow had a 12% probability of having 200,000 somatic cells/ml at first herd test.
Based on these values it would appear that using teat seal at dry-off lowered the probability of having a SCC greater than 200,000 cells/ml at first herd test. Although the 95% confidence bands are fairly large and there is considerable overlap indicating there was no difference between treatments.
So what should I do?
Removing treatments at dry-off in an attempt to save costs are unlikely to result in a large amount of savings, especially compared with overall farm working expenses. Further, the risk of new mastitis cases are uncertain and the costs involved (financial and welfare) are also uncertain.
Importantly, the cows were selected for this study based on not having had clinical mastitis in the lactation or a somatic cell count greater than 100,000 cells/ml at any herd test. In other words these were “low-risk” cows with no history of mastitis. Cows that had previously had clinical mastitis or those that had higher SCC were not used in this study. Therefore, any recommendations on whether to teat seal or not is not applicable to these cows, only to low-risk cows.
Further, we at The AgriSciencer are not here to tell you what to do or what not to do, we are here only to share information in an easily digestible format. If you plan on changing up your drying-off protocol based on this research, we strongly advise you to chat with your vet. Drying off advice should be specific to your farm and probably even specific to each cow. As always, use our platform for discussion and leave the important decisions to conversations with the experts.
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Bates AJ, Saldias B. 2018. Effect of treatment with an internal teat sealant at drying-off in cows wintered on forage crops in New Zealand on clinical mastitis and somatic cell counts. New Zealand Veterinary Journal. 66(2):64-71.