Reducing Antimicrobial Use in Scottish Dairy Farms

Funded by the Scottish Governments Rural Development Fund
(Knowledge Transfer and Innovation Fund)

Final report submitted by SAC Consulting, the lead organisation for this project.
Project lead: Lorna MacPherson, Dairy Consultant, SAC Consulting
E-mail: lorna.macpherson@sac.co.uk

1. EXECUTIVE SUMMARY

It is current practice for dairy farmers to dry cows off and administer intra-mammary antibiotics to reduce the incidence of mammary infections during the dry period and in early lactation, but this practice could be adapted to significantly reduce the prophylactic use of antibiotics and the risk of antimicrobial resistance. Selective Dry Cow Therapy (SDCT), where cows only receive a teat sealant and no antibiotics at drying off, is already being discussed between processors, veterinarians and their farmer clients. However, it has not been fully adopted by all milk producers and has only been made compulsory for some farmers on retailer aligned contracts.

The aim of this project was to set up groups of dairy farmers throughout Scotland who were keen to reduce their antibiotic usage through the practice of SDCT. Their herd’s somatic cell count (SCC) data and clinical mastitis data was monitored to assess the impact of SDCT and to determine whether there was any detrimental effect on udder health.

This project was supported by the University of Edinburgh as the academic partner, Zoetis as the industry partner with expertise in teat sealants and milk processor Müller who were keen to encourage responsible use of antibiotics. All farmers involved in this project were selling their milk to Müller. Ultimately the project aimed to reduce the use of antibiotics at drying off, increase farmer engagement and build confidence in SDCT.

Over a two-year period, significant volumes of data were collected from 17 farms in Aberdeenshire and Ayrshire on drying off treatment (which cows were dried off with or without antibiotics) and clinical mastitis records. Individual SCC data was accessed via milk recording records for each cow over the calving period to assess the dry period performance and whether cows on SDCT were at greater risk of calving in with a high SCC or mastitis. Based on SCC data, dry period protection rates and dry period cure rates were assessed and compared to standard industry targets. The main key performance indicators for farmers to monitor when practicing SDCT are:

• Dry period protection rates (target 90%).
• Dry period cure rates (target 80%).
• Clinical cases of mastitis rates (target less than 30 cases/100 cows/year).
• Mastitis rate of dry period origin (target less than 1 in 12 cases occurring within the first 30 days of lactation).
• Less than 10% of cows calving in with a high SCC.

Throughout the project, there were six discussion group meetings organised in both areas, where project updates were given to farmers to present results and create discussion on SDCT, how well it was working and reasons as to why some farms were not achieving targets for dry period performance and mastitis rates. Key speakers were also brought in to discuss various factors affecting udder health, preventing and treating mastitis and key focus areas for making SDCT a success (nutrition, milking efficiency and breeding).

The conclusion was that SDCT did not pose a risk to udder health and that there is no reason to give cows antibiotics at drying off if there is no evidence of udder infection during the last three months of lactation. This finding is back up by research (by AFBI, published in 2019) and administering antibiotics to low SCC cows can actually increase the risk of coliform mastitis (Bradley et al, 2010). There was little difference in the risk of mastitis in the first month of lactation between cows on SDCT and those receiving antibiotics at drying off. However, heifers calving for the first time were a significant contributor to mastitis in early lactation on some farms. This information provided the farmers with a focus to reassess heifer management in late pregnancy and their introduction into the milking herd and what they could do to reduce mastitis in this group of animals.

There was clear evidence that the project benefited the participating farmers. Several made changes to their milking and drying off procedures, helping them achieve better results. A reduction in antibiotic usage was a key outcome, with a cost-saving to the business as well. Greater engagement and discussions with their vets resulted, with vets appreciating the data analysis and reports to discuss with their clients.

Reducing Antimicrobial use in Scottish Dairy Herds has been a successful project, despite the initial challenges in recruiting farmers. By the end of the project, 15 out of the 17 participating farms were drying off over 50% of their cows without antibiotics, representing a significant reduction and a cost saving to the business. In fact, one of the project farmers is now drying off 90% of his cows without antibiotics very successfully and sees no detrimental effect on udder health and mastitis. None of the participating farmers have stopped SDCT which in itself gives reassurance to the rest of the industry that the practice is working.

Key findings were disseminated through a conference in Lanarkshire held at the end of the project to discuss the results and out of the number of farmers that attended, 87% were practicing SDCT. These messages will live on with the farmers involved and industry influencers, and messages from the project will continue to be delivered to dairy farmers in the years to come at future farmer meetings and consultancy advice delivered by SAC Consultants and SRUC Veterinary Services.

2. PROJECT DESCRIPTION

This project was based on encouraging dairy farmers in Scotland to reduce their antibiotic usage at drying off by practicing SDCT, where suitable cows (low SCC with no evidence of udder infection) are given an internal teat sealant only, instead of the standard practice of administering antibiotics and teat sealant (antibiotic dry cow therapy or ADCT). However, there are concerns that this practice could lead to more mastitis and cows calving in with a high SCC (which would indicate udder infection), which would ultimately cost the business more money in veterinary treatment, reduced milk sales and possibly loss of bonus in milk hygiene quality.

The project aimed to gather data on SCC and clinical mastitis records from herds practicing SDCT to assess the impact on udder health, compared to cows on ADCT. Data was gathered over a two-year period and regularly analysed to look at the effect of SDCT and to highlight where potential improvements could be made on farm to reduce risks to udder health. The project ran from December 2016 to December 2019.

This project involved collaboration with local vet practices, expertise from SAC Consulting vets and support from Müller, one of the major milk buyers in Scotland. Other areas of expertise were provided by the University of Edinburgh and Zoetis, a global animal health company.

Success was determined by whether there was a reduction in antibiotic use, and no negative consequences of increased SCC or clinical mastitis cases post-calving and a cost saving to the business. Information was collected over a two-year period from farms to provide a significant volume of data on which to gauge success and effectiveness of SDCT.

On-going discussion group meetings allowed those involved in the project to discuss progress and results with other farmers and how successful their dry cow treatment was. It was hoped that at the end of the project, those involved would continue to practice SDCT and the results would also encourage other producers to implement SDCT.

At the start of the project, SCDT was generally being practised at low levels and was not widespread. It has often been met with resistance on the uptake due to the lack of established protocols for decision making and concerns about udder health. This project intended to instil confidence in dairy farmers that SDCT is effective and does not increase the risk of mammary infections during the dry period and early lactation.

3. PROJECT AIMS AND OUTCOMES

Project aims and how they were achieved

1. Identify groups of dairy farmers who are willing to implement SDCT and work with SAC Consulting and their vets and share their data and experiences with the group. Müller would be closely involved in this initial part of the project by helping establish these groups and encourage producers to take part.

• A farmer meeting to launch the project was held in Aberdeenshire, Ayrshire and Dumfries-shire with follow up phone calls and farm visits to recruit farmers for the project. Only farmers that were supplying their milk to Müller were invited to these meetings.
• Two groups of farmers (Ayrshire and Aberdeenshire) were established. Dumfries-shire was also targeted through two on-farm meetings about the project but there was little enthusiasm and buy-in from the local farmers on this subject, despite good attendance and positive feedback from some farmers who attended the meetings. There were many reasons for this; some farmers were already involved in meetings with Tesco and Co-op who were making SDCT compulsory. Other farmers were already doing SDCT and were closely involved with their vet practice on monitoring progress and did not want to be involved in another group about the same subject.

2. Establish criteria on which to based decisions on which cows to use SDCT on. Each farm will likely have slightly different criteria or thresholds, given the history of SCC data and mastitis incidence in the herd but these can be established on an individual basis along with veterinary advice.

• Selection criteria was discussed with the farmers involved in the project but early on it became clear that the farm’s vet was the most appropriate advisor to recommend what cows get antibiotics at drying off or not. Many of the farmers already had discussed this with their vets and had a policy in place for selecting cows for SDCT. It was found that as time went on, some farms relaxed their selection criteria so that more cows could be dried off without antibiotics as their confidence in the procedure grew.

3. Aim to reduce antibiotic use at drying off by 50% in herds and monitor the response in herd and individual cell counts and mastitis incidence within the first 100 days of lactation.

• Herd performance was monitored through individual SCC and mastitis incidence in the first month of lactation and not the first 100 days for two reasons – the likelihood of an infection originating from the dry period is greatest in the first month of lactation as opposed to the first 100 days. Also, the time required for data analyses would have been considerably longer.
• By the end of the project, 15 out of the 17 participating farms were drying off over 50% of their cows without antibiotics.

4. To discuss the SDCT strategies and outcomes of the project with the farmers through organised meetings and farm visits.

• There were six discussion group meetings held in both areas throughout the project where results to date were discussed, along with a guest industry expert to provide expertise on subjects related to cow health and management to reduce mastitis and help make SDCT a success.
• Project farmers received regular visits and reports to discuss progress. An example report is shown in annex 1.

5. Dissemination of the outcomes of the project to the wider dairy community and highlight the key findings though an open conference at the end of the project and produce articles in the national press.

• A conference in Lanarkshire and attended by 45 people was held to discuss the project results, which were backed up by the keynote speaker Dr James Breen (University of Nottingham and Evidence Based Veterinary Consultancy), one of the UK’s leading experts on the subject of mastitis and udder health.
• Articles to highlight the key messages from the project have been published in the main farming press: British Dairying (November 2019), Farmers Weekly (December 2019) and Scottish Farmer (December 2019) amongst others.
• Key messages have also been made available to farmers through the Farm Advisory Service (FAS) in various Milk Manager News editions and a summary report on the FAS website accessible via: www.fas.scot/livestock/dairy-cattle/effect-selective-dry-cow-therapy

Through their involvement in the project, farmers became more aware of the incidence of mastitis in their herd and especially mastitis originating from the dry period. This helped focus them to look at areas of housing, environment and management practices that they could alter to help improve udder health, lower SCC and reduce mastitis cases. Some of the changes implemented included changing udder preparation routine in the milking parlour, where they dried off cows and hygiene practices at drying off to reduce the risk of introducing infection into the udder. As a result, the number of cows being dried off without antibiotics on many farms increased as time went on, as the farmers grew in confidence that the procedure was not detrimental to udder health.

There were several vets from local practices who received regular progress reports on their dairy clients that were involved in the project and they also attended some of the discussion group meetings. The vets appreciated this information as many said they did not have the time to provide such in-depth data analysis and it gave them information on how cows on SDCT compared against those receiving antibiotics at drying off. The project also provided free bacteriology testing to identify the main bacterial cause of mastitis. This information helped vets provide more specific advice on how to help tackle mastitis and how farmers could improve on their dry period performance (as monitored by SCC).

The project enabled a significant amount of data from the Aberdeenshire farms to be provided for a BSc Agriculture Honours project dissertation for an SRUC student (Rachel Foley, who graduated in 2018) based at SRUC’s Edinburgh Campus. This provided the student (who came from a beef farm) with the opportunity to learn more about the challenges of dairy farming and the topical subject of antibiotic use and SDCT. Her dissertation helped her achieve a 2:1 degree and after graduation Rachel went to New Zealand to work on a dairy farm for a year.

4. LESSONS LEARNED

Challenges

In the first two years of the project there was still some resistance to the uptake of SDCT in the industry, going by discussions with farmers not involved in the project at meetings. However, by the end of the project, the general feel was that resistance is reducing as Müller (and other milk buyers) are more closely scrutinising antibiotic usage and either recommending or making SDCT compulsory on a proportion of the herd. SDCT has certainly become more common practice and is more likely to be the norm in many herds, with those not doing SDCT being in the minority.

Some of the reasons for poor uptake of SDCT by farmers at the beginning of the project were as follows:

• There is still resistance to the uptake of SDCT with concern over cow health and the possible risk of increased mastitis and deaths from severe mammary infections shortly after drying off without antibiotics. Any increase in mastitis rates will negate any cost-saving to the business of not giving antibiotics at drying off. Also, treating a cow with mastitis will likely increase her antibiotic use which will be greater than the antibiotics giving routinely at drying off.
• Not all farmers milk record and therefore do not have records on individual cow SCC on which to base decisions on which cows should not receive antibiotics at drying off.
• Farmers will only start SDCT if their vet is fully supportive of this practice and recommends it for their herd. In some instances, vets are advising farmers not to practice SDCT for several reasons: e.g. herd SCC, high level of mastitis in the herd, poor dry cow accommodation where the risk of infection is increased etc.
• Some vet practices, particularly in Ayrshire (the most heavily dairy populated county) are very proactive in the area of SDCT and are already holding meetings on the subject, often in conjunction with animal health companies. This means that farmers have already attended meetings on this subject and are not keen to be part of another discussion group. This is also the case with the aligned Müller contracts (farmers whose milk goes to Tesco or Co-op). These farmers are under more pressure to reduce antibiotic usage and are more likely to already be doing SDCT with support from their vet. In addition, they are also involved in meetings with Tesco and Co-op on this subject and are not wanting to be involved in another group where there will be several meetings on the same subject.
• SDCT is currently not a requirement by Müller (for non-supermarket aligned suppliers) and it is not clear whether it will be compulsory in the future. Until farmers are told they must practice SDCT (or face some sort of penalty), some are not keen to do so if not being forced into it.

Impacts

The project was very successful in bringing together various people in the dairy industry (farmers, milk processors, vets and animal health representatives) to look at the impact of SDCT on udder health. The audience at the closing conference in Lanarkshire was an excellent example of what the project had achieved over its three-year run, with farmers in the audience sharing their experiences and successes (one farmer is now drying off 90% of his cows without antibiotics very successfully and sees no detrimental effect on udder health and mastitis rates in early lactation).

Most of the participating farmers were extremely bought in to the project, as they appreciated the need to reduce antibiotic usage due to the threat posed by antibiotic resistance to both livestock and human health.

We have had great feedback that the project made a meaningful impact on the farmers that were most engaged with the project. For example, Bruce Mackie from Rora Dairy, Peterhead who spoke at the conference said that taking part had given him the impetus to stop using dry cow antibiotic tubes. “Three years ago we were tubing 75% of the dry cows with antibiotics and now it is less than 25%, with no health or yield issues and no change to the bulk somatic cell count”.

Following one of the discussion group meetings, the key speaker (Colin Lindsay, Independent Vet from Veterinary Consultancy Ltd) visited Joe and Moira Davidson of Tarbothill Farm, Aberdeen to discuss the problems they were having with mastitis. On the back of his advice they changed their pre-milking routine (started using a pre-dip to clean and disinfect teats before milking and changed to using individual wipes as opposed to using one cloth kept in disinfectant to minimise cross-contamination of bacteria between cows before milking). These changes resulted in a reduction of the bulk tank SCC and reduced the number of mastitis cases in the four months following these changes. The farmer said, “the cell counts have dramatically improved, we are now averaging consistently low 100s whereas before we were between 150 and 200 so here we can definitely see the benefits.”

Through their participation in the project, some farmers have changed their procedure for drying off cows and have focussed more attention on the importance of hygiene at drying off. For example, they no longer dry off during milking time when the herd is being milked. There is more focus now on taking time over the drying off procedure (where cleanliness/hygiene must be top priority), with this process being carried out after the whole milking has been completed. This allows more time and closer attention to be paid to the procedure to make sure it is carried out as aseptically as possible and is not being rushed, minimising introduction of infection to the udder.

Another change is that some farmers have moved away from using the disinfection wipes that are supplied with teat sealants for disinfecting teats. The gold standard is to use cotton wool soaked in surgical spirit, which all vets advocate as being best practice.

At the start of the project it was clear that there were many farmers (who did not take part) who were wary of doing SDCT and were not going to implement it unless forced to do so. There was concern about the effect it could have on udder health, SCC and mastitis rates. However, throughout the course of the project this opinion appeared to change. As time went on there were farmers who were initially sceptical, who eventually started to practice SDCT.

The perception is that this project has played a major part in raising awareness of the need to reduce antibiotic use in dairy herds and that this can be done successfully through SDCT. Towards the end of the three-year project there were more and more farmers doing SDCT and those not practicing SDCT were seen to be in the minority. Farmers are much more receptive of SDCT now and it is now becoming more the norm. This is in part due to increased awareness through the project but also due to increasing pressure from their milk buyer (especially if on a supermarket aligned contract), discussions with vets and farmers and on-going information in the press regarding SDCT and the need to reduce antibiotic usage. In addition, certain antibiotics are now prohibited for use (3rd and 4th generation cephalosporins and fluoroquinolones) unless they can be justified under veterinary advice and so this has all lead to a greater uptake of SDCT. There were 23 farmers who attended the conference at the end of the project, out of which only three were not practicing SDCT (13%).

The project has highlighted the following main KPI’s for farmers to measure when implementing SDCT and provided data for discussion with their vet and areas for improvement. It is fair to say that some vets did not have the time or were less proactive in looking at this information for dairy farmers and this project provided in-depth analysis that they had not received elsewhere.

• Dry period protection rates (target 90%).
• Dry period cure rates (target 80%).
• Clinical cases of mastitis rates (target less than 30 cases/100 cows/year).
• Mastitis rate of dry period origin (target less than 1 in 12 cases occurring within the first 30 days of lactation).
• Less than 10% of cows calving in with a high SCC.

The majority of farms greatly reduced their antibiotic usage at drying off throughout the project which has provided a cost saving to the business. The cost of this is in the region of £8-10/cow depending on which antibiotic is being used (say £9/cow on average). With most farmers drying off at least 50% of their cows without antibiotics and an average herd size of 228 cows in the farms involved, that is a saving of £1026/year.

5. COMMUNICATION & ENGAGEMENT

Discussion Group Meetings

Six discussion group meetings were held in both Aberdeenshire and Ayrshire over the three years. The topics and speakers are listed below:

1. Dry cow housing and environment. Jamie Robertson, Livestock Management Systems Ltd.
2. Treatment of mastitis. Alastair Macrae, Royal Dick School of Veterinary Studies.
3. Control of environmental mastitis. Colin Lindsay, Veterinary Consultancy Ltd.
4. Maximising milking efficiency. Dan Humphries, Advance Milking.
5. Breeding for mastitis resistance. Mike Coffey, SRUC.
6. Nutrition and management of dry cows for enhancing immunity. Hefin Richards, Rumenation Nutritional Consultancy.

Data Collection and Analysis

Data collection from the project farms was ongoing over the three-year project lifetime, with all farms in Aberdeenshire having two years’ worth of data and between one to two-years’ worth of data in Ayrshire. Data was collected and analysed by the project team on an on-going basis and was presented at each of the six discussion group meetings to update the farmers on progress and findings.

Monthly information collected:

• • Bulk milk somatic cell count (monthly test figures from Müller).
• • Mastitis records
  • Cow number (to include heifers)o Date of when case was diagnosed
  • Quarter(s) affected
  • Pathogen type (if tested for)
  • Was cow on SDCT or ADCT at previous drying off?
• Cows dried off in the month
  • Cow number
  • Date of drying off
  • Milk yield at drying off (if recorded, if not used yield at last recording to investigate whether this was a factor increasing the risk of a cow calving in with a high cell count)
  • Whether the cow was on SDCT or ADCT

From this information the data was analysed to investigate the following:

• Dry period protection rate (cows ending their lactation with a low SCC and calving in with a low SCC).
• Dry period cure rates (cows ending their lactation with a high SCC – indicating udder infection – and calving in with a low SCC).
• Influence of SDCT on bulk tank SCC.
• Effect of milk yield at drying off (or last recording) on dry period protection rates and cures rates in cows on SDCT and ADCT.
• Clinical mastitis incidence in cows on SDCT and ADCT.
• Incidence of mastitis of dry period origin (occurring within the first 30 days of lactation) in cows on SDCT and ADCT.
• Effect of lactation number on mastitis cases.
• Length of dry period and effect on dry period protection and cure rates.

An example of the two reports produced for farms on a regular basis are provided in Annex 1.

Final Seminar

A final seminar held at the Radstone Hotel, Larkhall in Lanarkshire was organised for the end of the project, to highlight the outcomes as well as main messages to help reduce antibiotic use and inform the audience that SDCT is not detrimental to udder health. The keynote speaker (Dr James Breen) confirmed the findings of the project through his own (and others) research and on-farm experience. This event was attended by 45 people; made up of farmers, vets, consultants and those working in the dairy industry (e.g. feed and animal health representatives). This was a very well received event, with an extremely positive response and excellent follow up by the press.

Farm Advisory Service Engagement

A project update with initial findings was published in the January 2018 issue of Milk Manager News, which is a Scottish Farm Advisory Service funded publication. Another article was published in March 2019 edition with more detailed findings. A final article detailing the conclusions of the project were reported on in the January 2020 issue of Milk Manager News.
This information is available to all dairy farmers and industry representatives through the Farm Advisory Service website.

6. KEY RESULTS & RECOMMENDATIONS

Results

• There was no significant difference in dry period protection rates (cows being dried off with a low SCC and calving in with a low SCC) between cows on SDCT (82%) and those on ADCT (84%). Industry target is 90%.
• As anticipated, more cows with a high SCC at drying off getting ADCT were cured during the dry period (79%) compared to only 74% in the SDCT group. This result shows the benefit of the responsible use of antibiotic dry cow therapy when used to target those cows that had evidence of udder infections at drying off.
• There was a huge variation between farms in their dry period performance rates (see table 1). The best performing farm was using SDCT in 75% of the cows at drying off. Conversely some farms had poor dry period performance even in cows that were on ADCT, indicating that there were areas for improvement e.g. better housing environment and management of dry/transition cows. Seven farms achieved the 80% target for cure rate in both SDCT and ADCT cows.

Table 1. Dry Period Performance in the Best and Worst Farm.

	Dry Period Protection Rate		Dry Period Cure Rate
	SDCT	ADCT	SDCT	ADCT
Best Farm	91%	93%	84%	87%
Worst Farm	66%	71%	61%	64%

*49 cows with a high cell count prior to drying off were accidently dried off with teat sealant only

 

• Bulk tank SCC were not negatively affected by drying off cows without antibiotics so there was no danger of the farm’s SCC running into penalty levels on hygiene quality. These findings were backed up by research carried out by Dr James Breen.
• Many cows had high milk yields at drying off (>25 litres), which was a concern for risk of calving in with a higher SCC and mastitis. The effect of milk yield at drying off was investigated as a risk factor associated with dry period performance. Two farms provided data on milk yield on the day of drying off. There was little difference in dry period protection rates between the SDCT and ADCT group when yield was less than 25 litres at drying off. However, when cows were dried off giving more than 25 litres, the cows on SDCT had slightly lower protection rates than cows on ADCT. These findings are backed up by research which shows that the higher the yield at drying off, the greater the risk of a new intramammary infection during the dry period.
• There were fewer mastitis cases of dry period origin in cows on SDCT compared to those on ADCT, and the total number of mastitis cases was significantly higher for cows on ADCT. This is to be expected as these are the problem (or high SCC) cows more likely to have chronic recurring udder infections, which would sporadically result in clinical mastitis. When expressed as a percentage, mastitis cases of dry period origin out of the total number of mastitis cases was slightly higher for cows on SDCT, but the biggest risk was for first calving heifers.

Dry Off Treatment	Total Number Mastitis Cases	Number of DP Cases in 1st month of lactation	% DP cases
SDCT	651	127	19.5
ADCT	1107	140	12.6
First calving heifers	301	82	27.2

 

• Research at the University of Nottingham by Dr James Breen backed up the findings of the SAC Consulting project, showing that there is no benefit in treating low cell count cows with antibiotics at drying off, and that cows treated with a teat sealant only are at no greater risk of calving in with a high cell count or more likely to have mastitis in early lactation.

Recommendations

• Hygiene at drying off is crucial to the success of SDCT and preventing mammary infections in the early part of the dry period. The gold standard is to disinfect clean teats with cotton wool soaked in surgical spirit. There are several other recommendations to follow during the drying off procedure (order of teat disinfection and order of teat sealant insertion) but most successful farmers take their time to dry off cows and do not carry out this procedure at normal milking time. They recognised it is an important task requiring care and attention to detail and treated it as such.
• Try to avoid overstocking dry cow facilities. Some farms did find when stocking densities increased in the dry cow pen that there were more cows calving in with a high SCC or mastitis in early lactation. Aim to provide 1.25m2 per 1000 litres of herd average production.
• Look at the management of heifers into the dry cow group and milking herd. Heifers contributed significantly to mastitis in the first 30 days of lactation and are under more stress in the pre-calving period than cows. Look at ways to minimise stress on heifers at this critical time.
• • Review results regularly in conjunction with your vet and see whether there is scope to relax selection criteria (e.g. increasing from a maximum SCC of say 150 to 200 under which cows do not receive antibiotics at drying off). Base this on bulk tank SCC, clinical mastitis data and bacteriology to identify the main mastitis causing organisms on your farm. This will allow more cows to be dried off without antibiotics, further reducing cost to the business.
• The above recommendations were summed by Dr James Breen at the conference. He said, “The most cost-effective way of preventing new udder infections during the dry period is to minimise the risk by using a teat sealant and pay careful attention to hygiene at drying off. The dry cow housing environment can also have a significant effect on the infection risk during the dry period. There is a place for antibiotics in cows with high cell counts but they should never be used routinely.”

7. CONCLUSIONS

Reducing Antimicrobial use in Scottish Dairy Herds has been a successful project, despite the initial challenges in recruiting farmers. The amount of data generated was a huge task to analyse and draw conclusions from, but the findings are very positive for the industry. They are reassuring to farmers currently not doing SDCT, in that with attention to detail in the drying off procedure and good dry cow management, SDCT can be a success and not detrimental to udder health.

The farmers involved in the project were very positive about doing SDCT and were very interested in their results and how they could improve further. It has given them confidence in the procedure to carry on and reduce antibiotic use even further at drying off.

The project has enabled significant knowledge transfer to the wider Scottish agricultural industry, where key messages have been drip fed through farm meetings, press articles and an industry seminar. This project has had a positive effect on the farmers involved, local vet practices, the operational group and the industry.

In conclusion, SDCT can work very well and it is possible to achieve industry targets for dry period performance with high rates of SDCT. Although there was a slight increase in clinical mastitis cases immediately after calving for those cows on SDCT, heifers contributed the most to mastitis cases in the first month after calving on many farms, and so their management and introduction to the herd must be carefully managed to minimise stress and reduce the risk.

8. REFERENCES

Bradley, A.J., Breen, J.E., Payne, B., Williams, P. and Green, M.J. (2010). The use of Cephalonium– containing dry cow therapy and internal teat sealant, both alone and in combination. Journal of Dairy Science 93, 1566-1577.

Craig. A. 2019. Promising early results at AFBI on the use of selective dry cow therapy. [Online]. Available from: https://www.afbini.gov.uk/news/promising-early-results-afbi-use-selective-dry-cow-therapy [Accessed 11th February 2020].

 

9. ANNEX 1 – Example reports

SDCT Project Update – Farm A

Selective Dry Cow Therapy	Teat sealant only. 211 cows with complete data
Previous Lactation	Calving Status	Description	Numbers	Percentage
Uninfected	Uninfected	Protected	174	83%
Uninfected	Infected	New Infection	27	13%
Infected	Uninfected	Cure	7	3%
Infected	Infected	Failure	3	1%
Antibiotic Dry Cow Therapy	Antibiotic and teat sealant. 187 cows with complete data
Previous Lactation	Calving Status	Description	Numbers	Percentage
Uninfected	Uninfected	Protected	69	37%
Uninfected	Infected	New Infection	8	4%
Infected	Uninfected	Cure	88	47%
Infected	Infected	Failure	22	12%

Pre-calving status is classed as:
Infected – one out of 3 recordings has a cell count >200
Uninfected – all last 3 cell counts are <200

Post-calving status is classed as:
Infected – first recording after calving is >200
Uninfected – first recording before calving is < 200

Dry Period Protection Rate (target 90%)
SDCT - Of the cows that got teat sealant only, 87% (174 out of 201) maintained a low cell count into the next lactation.

ADCT - Of the cows that received antibiotic and teat sealant, 90% (69 out of 77) maintained a low cell count into the next lactation.

Dry Period Cure Rate (target 80%)
SDCT - Of the 10 cows that were dried off with a high cell count 7 (70%) calved down with a low cell count. Note small number of cows so not too concerned about this being below the 80% target.

ADCT - Of the 110 cows that were dried off with a high cell count 88 (80%) calved down with a low cell count.

These figures have been very consistent over the 2-year period, with cows on SDCT being just a few % points lower in dry period protection rate. The lower dry period cure rate percentage is perhaps to be expected in cows on SDCT. Generally, in the ADCT group both targets are being met:

Reporting dates	SDCT	ADCT
Dry Period Protection Rate
1.3.17 - 30.4.18	86%	90%
1.3.17 - 31.7.18	83%	92%
1.3.17 - 31.1.19	85%	91%
1.3.17 - 31.3.19	87%	90%
Dry Period Cure Rate
1.3.17 - 30.4.18	75%	81%
1.3.17 - 31.7.18	50%	80%
1.3.17 - 31.1.19	70%	79%
1.3.17 - 31.3.19	70%	80%

Mastitis from 1st April 18 to 31st March 19

• Over the last 12 months (1st April 18 – 31st March 19) there were 129 cases over an average of 309 cows so clinical case rate is 42 cases/100 cows/year.
• Over the last 6 months (1st Oct 18 – 31st March 19) there were 82 cases over an average of 315 cows = 52 cases/100 cows/year. Assuming the incidence of mastitis cases does not change over the next 6 months, the clinical case rate will have increased.
• Out of the 129 cases, 114 of these cases were repeats in the same quarter (10.9%). AHDB Dairy target for mastitis re-occurrence rate is less than 10% of the total number of cases so this is just about on target.
• 19 cases occurred within the first 30 days of lactation indicating they were of dry period origin (19 out of 129 cases = 14.7%).
• 10 of the 19 cases of dry period origin occurred in cows that were on SDCT at the end of previous lactation. 5 were in cows that were on ADCT at the end of previous lactation. 4 were in heifers (no dry off treatment).

Milk Yield of Cows at Drying Off

SDCT Cows
Milk yield at drying off ranged from 2 to 36kg.

Recordings for 50 cows giving over 25kg of which:

• 43 out of 53 cows maintained low SCC into next lactation (Dry period protection rate 86%).
• 7 cows had dry period new infection (L-H) 14%.
• There were 0 cows with high cell count before drying off.

Recordings for 141 cows giving under 25kg of which:

• 131 out of 151 cows maintained low SCC into next lactation (Dry period protection rate 87%).
• 20 cows had dry period new infection (L-H) 13%
• 7 out of 10 cows had dry period cure (H-L) 70%
• 3 cows had failure to cure (H-H) 30%

ADCT Cows

Milk yield at drying off ranged from 2 to 35kg.

Recordings for 41 cows giving over 25kg of which:

• 30 out of 32 cows maintained low SCC into next lactation (Dry period protection rate 94%).
• 2 cows had dry period new infection (L-H) 6%
• 7 out of 9 cows had dry period cure (H-L) 78%
• 2 cows had failure to cure (H-H) 22%

Recordings for 141 cows giving under 25 kg of which:

• 39 out of 44 cows maintained low SCC into next lactation (Dry period protection rate 89%).
• 5 cows had dry period new infection (L-H) 11%
• 78 out of 97 cows had dry period cure (H-L) 80%
• 19 cows had failure to cure (H-H) 20%

Conclusions

• Over the 2-year period, 53% of cows have been dried off without antibiotics and 47% with antibiotics.
• The dry period protection rate is only slightly worse in the SDCT – 87% versus 90% in cows on ADCT and this has been consistent throughout the 2-year period. The SDCT group runs just below the 90% target.
• Cure rates are a good bit lower in the SDCT group at 70% compared to 80% for the ADCT group, which is on target. However, over the 2 years only 10 cows on SDCT had a high SCC before calving and so the 70% cure rate is not a concern.
• Milk yield at drying off is not negatively associated with poorer dry period protection rate in either the SDCT or ADCT group (for cows giving over 25kg at drying off). In fact, in the ADCT group, cows with the higher yield at drying off had a higher dry period protection rate (94%) compared to those giving less than 25kg (89%).
• Cases of mastitis are 42 cases/100 cows/year and this rate has been very similar throughout the 2-year period, so mastitis incidence has not changed, but it is still higher than the industry target of 30.
• Cases of mastitis in the first month of lactation have reduced over the 2-year period.
  • From 1st April 17 – 31st March 18, number of cases in the first month of lactation were 36 out of a total of 145 cases (24.8%).
  • From 1st April 18 to 31st March 19 there were 20 cases in the first month of lactation out of a total of 129 cases (15.5%).
• There are more cases of mastitis of dry period origin in cows on SDCT compared to those on ADCT, both numerically but also as a % of the total cases of mastitis in the two groups.

 

Mastitis Cases of Dry Period Origin Report

Dry Period Origin Mastitis Cases (March 17 – March 19)

Notes:

• Number of cows and heifers calving in month is taken from the calving profile report on CIS.
• Target for cases of dry period origin is <1 in 12 or <8.3% per 30-day period. % of dry period cases is worked out from:

(No. cases in 1st 30 days post-calving each month / total calvings in previous month)*100

No. cases in 1st 30 days post-calving includes cows with mastitis during dry period.

Month	No. of mastitis cases in 1st 30 days post calving	Number of cows/heifers calving previous month	% rate of dry period cases	No. cases in cows on SDCT	No. cases in cows on ADCT	No. cases in heifers
March 17	1	20	5.0	0	1	0
April 17	0	26	0.0	0	0	0
May 17	7	15	46.7	5	2	0
June 17	4	33	12.1	1	2	1
July 17	3	28	10.7	2	1	0
August 17	5	30	16.7	2	1	2
September 17	2	35	5.7	0	1	1
October 17	3	29	10.3	2	1	0
November 17	1	30	3.3	0	0	1
December 17	3	37	8.1	2	1	0
January 18	2	31	6.5	0	2	0
February 18	4	22	18.2	1	0	3
March 18	2	22	9.1	1	1	0
April 18	1	25	4.0	1	0	0
May 18	1	13	7.7	0	1	0
June 18	0	21	0	0	0	0
July 18	0	24	0	0	0	0
August 18	4	25	16.0	2	1	1
September 18	1	28	3.6	0	0	1
October 18	2	22	9.1	1	0	1
November 18	3	46	6.5	3	0	0
December 18	6	40	15	3	2	1
January 19	2	29	6.9	0	2	0
February 19	0	22	0	0	0	0
March 19		23	0	0	0	0
Total	57	676		26	19	12

• In 15 out of 25 months, the % of dry period cases was within the target of <8.3%. Average % of dry period cases over the 25 months is 8.2% so only just within the target.
• Out of the 57 cases of dry period origin, 12 were in 1st lactation animals (21%, no dry off treatment).
• 26 out of 57 cases occurred in cows that were on SDCT at the end of their previous lactation (46%).
• 19 out of 57 cases occurred in cows that were given antibiotic dry cow therapy at the end of their previous lactation (33%).
• During the 25 months of data the numbers of cases of dry period origin and treatment at drying off expressed as a percentage is as follows:

Drying off Treatment	Total number of mastitis cases	Number of mastitis cases within first 30 days	% of mastitis cases within first 30 days
SDCT	109	26	24
ADCT	124	19	15
Heifer	44	12	27

• Based on percentage, the highest incidence of mastitis cases within the first 30 days is in heifers, closely followed by cows on SDCT. As the number of cases in the first 30 days (and their % of total cases) is higher in cows on SDCT compared to those on ADCT, it can be concluded that SDCT is having a detrimental effect on udder health.
• Although there are more cases of mastitis in cows on ADCT compared to those on SDCT, this is perhaps to be expected as these are likely the “problem” cows with higher cell counts. Over the 25 months, 53% of cows were on SDCT and 47% were on ADCT.