By Debbie James

A switch from blanket antibiotic treatment at drying off to targeting only cows that need it has cut antibiotic use at a Welsh dairy farm by more than a third.

Drying off has traditionally involved using intramammary antibiotics across all cows to treat and prevent new infections developing during the dry period.

But many milk buyers are now setting new standards on the use of antibiotics in dry cows, including requiring farmers to put strategies in place for adopting selective dry cow therapy (SDCT).

Neil and Diane Evans, who run a high yielding flying herd of 180 Holstein Friesians on an all-year round calving system, had been tubing all cows at drying off with antibiotics until they trialled SDCT as part of a Farming Connect project.

“Antibiotics cover a multitude of sins, you know you are safe if the cow has had antibiotics at drying off, but the world moves on,’’ says Mr Evans, of Holebrook Farm, Wrexham.

Holebrook Farm is a Farming Connect focus site and, as such, a trial was put in place to study the effectiveness of SDCT in the herd.

Rhys Davies, Farming Connect dairy technical officer for north Wales, who designed and oversaw the project, said Mr Evans had previously considered implementing SDCT but was nervous about taking the leap.

During the trial, which began in March 2018, Mr Evans was supported by his veterinary practice, LLM Farm Vets, to assess cell count records and to select cows suitable for SDCT.

“Full monthly recording data, together with accurate mastitis treatment records, are essential when reviewing somatic cell counts (SCCs) during current and previous lactations,’’ Mr Davies explained.

To work out which treatment to apply to individual cows, clinical mastitis samples are collected from the cows and analysed at LLM’s laboratory. The results identify the mastitis-causing pathogens.

The farm’s vet Sarah Hampson, who led a Farming Connect workshop on SDCT at Holebrook Farm, says testing establishes which treatment approach is needed.

SDCT was ruled out in cows with a lactation average SCC of more than 100,000 cells/ml, or those that had a case of clinical mastitis in the latter stages of her lactation.

Mrs Hampson recommends a cautious approach to SDCT, especially when it is first implemented.

“It is selective for a reason. In cases where there have been disasters it has been when farmers have gone straight in without checking individual mastitis levels.’’

If in any doubt, use antibiotics, she adds.

“If there is infection and you are only using sealant you will put a plug on the infection.

“SDCT should not be used in cows with staph aureus, until the cause has been addressed.’’

For the trial at Holebrook Farm, every cow treated with dry cow antibiotic was also given a sealant and cows with low cell counts had a sealant only.

Teat end scoring was carried out on all cows at drying off – any animals with teat damage or warts were treated with both antibiotic and sealant regardless of SCC values.

Average infection rates in the next lactation show minimal difference in cell count between cows on sealant and those with antibiotics.

On average, of the cows given sealant alone, 76 per cent experienced a cell count drop and 24 per cent a cell count rise.

Of those administered antibiotic dry cow therapy, 72 per cent had a cell count drop and 28 per cent a cell count rise.

According to Mr Evans, the only freshly calved clinical case of mastitis treated was a cow that had been given dry cow antibiotics.

“As you would expect, the cows selected for antibiotic dry cow therapy had a significant drop in cell count and shows the value of treating udder issues in the dry cow period,’’ says Mrs Hampson.

Dry cow antibiotic tube use between March and August 2018 reduced by 39.5 per cent – the equivalent of tubing 28 fewer cows with 112 dry cow tubes – compared to the same period in 2017.