What’s wrong with blanket antibiotic therapy at drying off?

Vets at the Zoetis Vets Clinic in Antrim with Aurelie Moralis, Zoetis and Norman Beggs, Udder Health Solutions, Speaker. Photograph: Columba O'Hare
Vets at the Zoetis Vets Clinic in Antrim with Aurelie Moralis, Zoetis and Norman Beggs, Udder Health Solutions, Speaker. Photograph: Columba O'Hare

Just what exactly is wrong with blanket antibiotic therapy at drying off? This was the challenge Norman Beggs of “Udder Health Solutions Ltd” put to veterinary surgeons at a meeting organised by Zoetis.

He explained: “A ‘blanket approach’ whereby every cow receives antibiotic treatment at drying off does not always achieve the objective of controlling clinical mastitis in the herd. Indeed research has shown that administering antibiotic to un-infected cows at drying off can increase the risk of severe acute enterobacterial (i.e. E. coli) mastitis in the subsequent lactation by a factor of 12!”

Apart from this risk, a blanket approach will not meet some of the demands of milk buyers and consumers.

EU Guidelines for the use of Antimicrobials state that systematic treatment of cows with antibiotics at drying off should be avoided and the use of rapid diagnostic tests should be promoted for identifying mastitis causing pathogens in order to minimise the use of antimicrobials in milking cows.

Furthermore, under consideration at the moment is another EU clause which states that antibiotics must not, under any circumstances, be used to compensate for poor animal husbandry.

Regarding milk buyer and consumer demands Norman drew attention to the current extra standards that milk processor, Arla in the UK is demanding. These include the farmer working closely with their vet to ensure that antibiotics are only used for curing or alleviating diseases.

He told the meeting that research suggest that 97% of clinical infections during the dry period occurred in quarters with open teat canals, and that of all the enterobacterial mastitis occurring in the first 100 days of lactation, 52.6% arose in quarters previously infected during the dry period with the same strain of bacteria.

So what is the ideal approach for the farmer and the veterinary surgeon to meet all of the criteria?

Firstly the environmental conditions are crucial – 80% of clinical mastitis cases are caused by environmental pathogens. Norman pointed out that the ideal temperature for the cow (thermoneutral zone) is 4o C, but the thermoneutral zone for humans is 18o C. In an attempt to keep cattle accommodation comfortable for the farmer, ventilation rates are often compromised and the higher temperature and relative humidity increases the viability of environmental pathogens.

Stocking density also has an effect with close-up and freshly calved cows often over-stocked and inadequate feed space or poor feed bunk management causing a decrease in dry matter intake (DMI) leading to poor transition cow management. Hygiene in the environment and at drying off is paramount to help ensure that new infections are kept to a minimum.

Norman also stated that Selective Dry Cow Therapy has been effectively implemented on many mainland UK herds for the past 15 years while maintaining good udder health.

Selective Dry Cow Therapy means effectively distinguishing between infected and un-infected cows at drying off; administering an intramammary antibiotic and internal teal sealant to infected cows while un-infected cows should receive a teat sealant only.

Selective Dry Cow Therapy centres on the decision about whether cows should receive an antibiotic in addition to the teat sealant. Therefore all cows receive a teat sealant and only infected cows receive an antibiotic alongside the sealant. The decision as to which cows should get antibiotic dry cow therapy has to be made at herd level, group level and individual cow level and in conjunction with the farm’s veterinary surgeon.

The most effective criteria for determining infection status are the somatic cell count (SCC) data. The bulk milk tank SCC must be considered in conjunction with the last three SCC from a cow’s lactation and the absence of clinical mastitis in the three months prior to drying off. In cows with a high SCC, i.e. > 200,000 cells/ml, cure is a priority while for cows with a low SCC e.g. < 200,000 cells/ml, prevention is the priority. This threshold of 200,000 cells/ml may be varied according to the bulk tank results. Farmers should seek advice from their vet to determine which threshold is right for their farm.

In order to make an informed decision when determining which groups of cows are eligible for Selective Dry Cow Therapy farmers also need to record clinical mastitis cases and perform bacteriology to understand which pathogens cause mastitis in their herds.

Aurelie Moralis, Veterinary Consultant with Zoetis, outlined the properties of the teat sealant, OrbeSeal®, pointing out that it is a tried and trusted formulation - firstly in that it is licensed for use on its own in uninfected animals and proven to prevent the acquisition of new infections and secondly it contains silica which increases viscosity to create an effective barrier against new infection throughout the dry period. She also emphasised the hygiene techniques needed to ensure success and pointed out that Zoetis has a detailed hygiene instruction for the use of the product.