1 Feb 2022
Emma Fishbourne
Job Title
Image © Ehrecke / Pixabay
Although its implementation is dependent on context, numerous benefits to selective dry cow therapy exist – particularly in the use of internal teat sealants – by reducing the risk of intramammary infections including mastitis and, therefore, the need for antibiotic treatment, while also reducing economic losses for dairy farmers.
The challenge for veterinary professionals is to work with farmers – and each other – to educate clients on the benefits and processes of selective dry cow therapy.
The clinical decision to implement selective dry cow therapy is complex and entirely farm dependent.
Some reluctance remains to implement it among vets and farmers alike, and this article aims to address some common concerns and reiterate the role internal teat sealants can play in UK dairy herds, helping to reduce the use of antibiotics on farms while benefiting cow health.
When I first started in cattle practice in the early 2000s, internal bismuth teat sealants in the UK were relatively new and were advised for cows that had a low probability of an existing mammary infection, as an alternative to antibiotics, in preventing new intramammary infections over the dry period.
I was fortunate that my more experienced boss was aware of the importance of maintaining sterility during infusion of the sealant, so we were able to encourage clients to switch to selective dry cow therapy.
We had clients who had encountered negative experiences with internal teat sealants, where cows had become severely ill or had died following administration, but through education we encouraged them to try them again and explained why they had experienced problems previously.
Although internal teat sealants have been around for many years, it’s only recently (with the drive for a reduction in antibiotic usage in the dairy sector) that farmers and vets have been forced to implement selective dry cow therapy on farms.
This has led to a huge reduction in antibiotics usage, but has also thrown up some valid questions and concerns from vets and farmers.
While most farmers are implementing selective dry cow therapy on an individual cow basis, discussion has taken place over whether further reductions can occur if cows are selectively dried off on a quarter basis – but not much literature appears to be currently available.
A study to explore how vets in the UK rationalised their prescribing decisions for mammary treatments at drying off (and the barriers and motivators they perceived to implementing selective dry cow therapy) was conducted via face-to-face interviews (Higgins et al, 2017). This study found rationale was different for vets at different stages of their career.
Assistants felt they were often struggling to gain the trust of farmers, despite numerous studies reporting that vets are farmers’ most trusted advisors.
Trust of the farmer is vital in the context of selective dry cow therapy, but distrust over the use of teat sealants is common – likely due to historical and severe adverse reactions that have been reported.
The study identified that to facilitate change to selective dry cow therapy, initiatives were required to alter the vets’ perceptions of the risks associated with switching, and that senior vets needed to take a leading role to facilitate farms to implement selective dry cow therapy. Senior vets were also of great benefit in helping less-experienced colleagues gain a farmer’s trust. The study also highlighted that less experienced vets may lack knowledge and confidence in their own abilities.
The majority of the vets interviewed for this study were proactive in their approach to responsible antibiotic use and stated a preference for selective dry cow therapy. Interestingly, also acknowledged in this study, on most farms the decision taken by more senior vets often resulted in blanket antibiotic treatment, even when this decision differed from their personal preference.
The study concluded that this may be a way of managing risk and uncertainty, protecting themselves and their relationship with their client, and animals, against possible unwanted outcomes.
Fear over adverse reactions when using internal teat sealants alone featured highly in the thoughts of many of the vets interviewed for this study, and one vet stated a personal preference for blanket antibiotic dry cow therapy because mistakes were less likely to happen.
Vets in the UK retain responsibility for the outcome of a treatment, but delegate control for its administration. Ultimately, it is the choice of the vet whether to prescribe antibiotics, but a conflict of interest exists as vets have concerns over losing clients. The study concluded that vets must work together to promote switching to selective dry cow therapy where appropriate (Higgins et al, 2017).
A study in Ireland identified barriers and facilitators among Irish farmers to implementing selective dry cow therapy. Barriers included a fear of increasing mastitis incidence, infrastructure limitations, peer influence and a lack of preventive advice.
The authors suggested that building farmer confidence by using a graded approach to selective dry cow therapy could help overcome the fear of it, and that regulatory pressure, high standards of hygiene on farm and targeted use of veterinary consults facilitated the switch to selective dry cow therapy.
Education of farmers was suggested to highly motivate them in the future uptake of selective dry cow therapy (Huey et al, 2021).
The benefits of selective dry cow therapy are numerous, and an abundance of peer-reviewed articles support its use.
We know that clinical and subclinical mastitis are major concerns for dairy producers, with the potential to cause significant economic losses each year. These losses occur through the cost of treatment, reduced milk production, reduced milk constituent quality, decreased fertility and increased culling or death (Bradley, 2002).
We also know that the use of antibiotics in the treatment and control of mastitis has potential implications for public health, via concerns they may contribute to an increased risk of antibiotic residues or bacterial resistance to antibiotics.
Once we look closer at the costs, we can see how selective dry cow therapy could play a crucial role in improving dairy cow health and dairy farm profitability.
The cornerstones of mastitis control have always been the prevention of new intramammary infections and treatment of existing intramammary infections over the dry period; historically, this has been achieved through the infusion of long-acting intramammary antibiotics.
More than 137 different organisms have been identified as causes of clinical mastitis (Watts, 1988), leading to difficulties with specific treatments and prevention.
A reduction in the UK national herd somatic cell count (SCC) indicates that the proportion of cows with subclinical intramammary infections due to a major mastitis pathogen has fallen, reducing the requirement for antibiotic therapy to cure pre-existing infections at drying off, and further supporting the use of selective dry cow therapy.
After drying off, a keratin plug forms naturally in the teat canal, sealing the teat sphincter. The chances for penetration of opportunistic bacteria are massively reduced once it is fully sealed.
The problem is that several studies have frequently identified inadequate natural teat plug formation, with some cows failing to form a teat plug at all. Clearly, this is a major risk factor for a new intramammary infection over the dry period, and farmers want assurances that their cows are protected.
Internal teat sealants, when applied correctly, mimic the natural teat plug of the cow. In the presence of antibiotic dry cow therapy, the sealants have been shown to reduce the risk of acquiring new intramammary infections after calving by 25%.
Internal teat sealants alone reduced the risk of intramammary infections by 73%, compared with untreated cows. The risk of clinical mastitis in lactating cows after calving is also reduced by internal teat sealants alone, and in the presence of antibiotic dry cow therapy, by 29% and 48% respectively (Rabiee and Lean, 2013).
Internal teat sealants administered to heifers pre-calving has also been shown to be effective, reducing new intramammary infections by up to 84% and clinical mastitis by 68% (Parker et al, 2007).
Other studies have demonstrated that treating cows and heifers pre-calving with internal teat sealants significantly reduced the risk of clinical mastitis, and that the benefits were the same when the sealant was used in combination with antibiotics in cows with a history of mastitis (individual SCC of more than 150,000 cells/ml or mastitis in the previous lactation), or when used by itself in cows with no history of mastitis.
The use of an internal teat sealant did not affect the mean SCC of any group at any point, and heifers were randomly assigned a group one month before calving (Laven and Lawrence, 2008).
The efficacy of an internal teat sealant against new, dry period intramammary infections, caused by major mastitis pathogens, has also been demonstrated under UK field conditions in cows with a SCC of less than 200,000
cells/ml and no history of clinical mastitis (Huxley et al, 2002). This study found that, compared with antibiotics, quarters that received the teat sealant had fewer new intramammary infections.
No significant difference was seen in the severity or number of cases of clinical mastitis, and the dry period cure rate was not significantly different. The study concluded that the use of blanket antibiotic dry cow therapy in low SCC cows needed to be questioned and re-evaluated.
One concern with using internal teat sealants is that there may be mis-classification of cows or quarters, and that infusion into cows where a major mastitis pathogen is present at drying off would have adverse effects. Cows are selected for internal teat sealant dry cow therapy on the basis of having three or four individual somatic cell counts of less than 200,000 cells/ml and no history of clinical mastitis.
The probability of them being infected should be very low, but Huxley et al (2002) found that in the UK, 3.2% of these cows still have a major pathogen present, and this is of concern.
Several studies in New Zealand attempted to demonstrate that acute systemic illness and death in cows infused with internal teat sealants appeared to stem from pathogens that were introduced during the process of infusion, rather than exacerbation of existing infections.
However, it should be noted that in New Zealand, Gram-negative infections are relatively rare compared to the UK (McDougall and Compton, 2015).
The barriers to selective dry cow therapy appear to be similar for vets and farmers, but the evidence to support its use is overwhelmingly positive.
Research suggests that some of the fears could be alleviated with education and training of the farmers, to ensure sterility at infusion to prevent the introduction of pathogens.
Studies have been carried out to compare different products and have found them to be equivalent (Rowe et al, 2020). Attempts have also been made to develop models to understand the risk and improve detection of intramammary infection at the end of lactation.
We also must recognise that vets need to work together to ensure they can continue to retain their rights to prescribe antibiotics and preserve their use for future generations.
