Milk production and mastitis research in Ireland

Ireland has a rich tradition of dairy farming. With over 16,000 commercial dairy farmers supplying milk to approximately 30 milk processing cooperatives (Central Statistics Office, 2024), it contributes significantly to the Irish economy. Most farms in Ireland operate a spring calving system (where cows calve between February and April and are dried-off between November and December), with a number of herds producing milk during the winter months. The average herd size according to the last survey was 92 cows (National Farm Survey, 2023) and comprised of mostly owner-operated farms, with family as the most common source of help around the farm. The above mentioned factors contribute to a significant workload for farmers in specific times of the year, coinciding with times in the cow’s productive cycle when they are most at risk of acquiring new infections (i.e. shortly before and after calving and shortly after drying-off).

Teagasc is Ireland’s agriculture and food development authority. It is the national body providing integrated research, advisory and education services to the agriculture and food industry and rural communities. Within the research directorate, the mastitis research programme comprises, one Research Officer, 3 PhD students, 1 Technologist and soon 1 Post-doctoral researcher. The objectives of the programme are to generate evidence around mastitis prevention and treatment, and the diagnosis, pathogenesis and immunology of mastitis. Additionally, the programme aims to contribute evidence to the development of national guidelines for mastitis prevention and control and reducing antimicrobial use in Ireland.

Current challenges

In January 2022, a regulation on veterinary medicinal products from the European Union came into effect in Ireland (European Parliament and the Council of the European Union, 2019). The regulation states that antibiotics should not be used as a preventive measure. In practical terms, this means that it is no longer permitted to have a “blanket” approach to antibiotic use at dry-off (where traditionally all quarters of all cows were treated with antibiotic to cure existing infection and prevent new ones during the dry period). This has resulted in a large shift in practice in the country where up to the year 2019, based on antibiotic sales data, almost 100% of the cows would have received antibiotic dry cow therapy (1). The indicators for 2023 suggest that currently just under 88% of cows would be receiving antibiotic dry cow therapy based on sales data (Animal Health Ireland, 2025, personal communication). The average bulk milk tank somatic cell count (SCC) for Irish dairy farms fluctuates around 180,000 cells/mL, with many farm experiencing marked increases at the beginning and end of the lactation season. This “seasonal” variation is more than likely due to an increased rate of new infections (2), especially at the beginning of the year which represents early lactation for most cows in these seasonal calving herds.

It is estimated that approximately 56% of herds conduct regular milk recording (where SCC information is obtained) 4 times in the lactation on average, with roughly 78% of the cows in the country recorded in 2024 (Irish Cattle Breeding Federation, ICBF, 2025). This means that many farmers might not have information on SCC to make informed decisions around mastitis management and dry-off treatment. When compared to other European countries, Ireland is behind in this regard with Germany, for example, conducting regular milk recording on 85% of the herds (ICAR, n.d.; ICBF, 2011).

According to Irish research, most subclinical infections are caused by Staphylococcus aureus, a contagious bacteria spread from cow to cow, mostly during milking. Internationally, many herds have dealt with contagious mastitis, with environmental pathogens as the most common cause. One hypothesis for this difference in Irish herds is the lack of culling of chronically infected cows. A study in 21 commercial herds in Ireland found that infection at dry-off ranged from 10% to 39%, with an average of 18% (3). Therefore, many Irish farmers have to deal with high levels of subclinical infections at the end of lactation. In the case of clinical mastitis, the causes are more varied, with Streptococcus uberis, Escherichia coli and S. aureus as the main type of bacteria causing these cases (4). Farmers are therefore faced with several challenges that could present an obstacle for the successful implementation of non-antibiotic dry cow therapy (selective DCT).

Mastitis research

The current scenario around antibiotic use has fuelled Teagasc’s mastitis programme research in recent years. Initially, we conducted studies to evaluate the impact of selective DCT on infection levels and SCC. The research evolved to investigating common practices that are implemented by farmers conducting selective DCT, exploring risk factors associated with early lactation SCC, clinical mastitis and mastitis in first lactation cows.

Most international research has shown no negative impact of treating low SCC or uninfected cows with an internal teat sealant (ITS) alone. Internal teat sealants are usually bismuth nitrate based products meant to act as a physical barrier during the dry period, therefore preventing infections during this time. Controlled studies in Ireland conducted in research and commercial dairy herds, showed that low SCC cows (<200,000 cells/mL) treated with ITS alone had higher SCC in the following lactation and higher levels of intramammary infections compared to cows treated with antibiotic plus ITS (5; 6). At first, an explanation for these results were that using a SCC cut-point of 200,000 cells/mL could have resulted in low sensitivity to detect infections given the bacteria causing infections in Irish herds. However, from the commercial herds study, apparent new infection rate over the dry period (uninfected at dry-off and infected at calving) was much higher in the cows treated with ITS alone compared to the antibiotic plus ITS cows (5). This was surprising given the preventive nature of ITS. The hypothesis was that a high level of infection at dry-off combined with S. aureus being the most common source of infection would have played a role. Alternatively, cows could have acquired infections very early in the lactation due to lack adequate mastitis management. Finally, a potential explanation would have been that the dry-off procedure itself, if not done hygienically enough could be introducing infections.

Further studies in Ireland showed that, from a convenience sample of 21 commercial herds conducting selective DCT, the SCC cut-point that maximised the sensitivity (Se) and specificity (Sp) was 65,000 cells/mL, with still moderate levels of both (72.5% and 75.1% for Se and Sp, respectively, 7). This was based on data from the last milk recording of the lactation, which was conducted 30 days before dry-off on average. That study also showed that, for this group of farmers that had been conducting selective DCT for a number of years, the average SCC at the last milk recording of the lactation was 55,000 cells/mL for cows treated with ITS alone at dry-off (7). Given the infection level in Irish herds, it would be sensible to consider lower SCC cut-points to assign cows ITS alone at dry-off.

A follow-up study (3) used milk recording data and a questionnaire with the 21 dairy farmers to identify cow-level as well as farm-level factors associated with SCC. Cows that had a milk yield > 15 kg at the last milk recording and dried with ITS alone were associated with a higher SCC early in the subsequent lactation compared to similar yielding cows treated with antibiotic plus ITS. Longer dry periods (average 84 d in the study by 3), older cows and cows with a higher SCC at the last milk recording of the previous lactation also had higher SCC in the following lactation. At the farm-level, farmers cleaning the cubicles twice per day had lower SCC cows compared to farmers doing this just once a day (3). Therefore, trying to lower milk yield towards the end of lactation, continuing to implement management practices to prevent new infections (even in late lactation) and maintaining clean housing facilities would be beneficial for farmers to achieve lower SCC in early lactation, are factors that have been supported by other research (8; 9).

Grid used for assessing cubicle cleanliness in study by Millar et al. (unpublished), adapted from Robles et al. (2021) (11). Each square is marked as dirty or clean and then an overall score is assigned based on the number of “dirty” squares. Image on the right show a typical cow housing facility in Ireland. 

Finally, a study presented at the National Mastitis Council (NMC) regional meeting, showed the importance of the dry-off procedure in terms of cleanliness and infusion technique (10). We investigated the effect on SCC of a “best-practice” dry-off procedure versus the “standard” dry-off procedure (normal procedure carried out by farm staff) in cows treated with antibiotic plus ITS or ITS alone (see appendix for steps in the procedures). We found that cows dried-off with the “standard” dry-off procedure and ITS alone had significantly higher SCC in the first 30 days of the following lactation compared to cows treated with ITS alone and dried with the “best practice” technique. This highlighted the importance of cleanliness and technique when drying-off cows and how this could explain the high new infection rate in cows treated with ITS alone in the study by Clabby et al. (5).

Images on top show some steps (partial insertion technique, pinching of base of teat for infusion of ITS and a small remnant of ITS visible from outside the teat after infusion) of the “best practice” dry-off procedure presented at NMC.

Best practices for selective dry cow therapy

The “best practice” procedure for selective DCT include:

1. clip udder and tail hair before procedure;
2. use of new (clean) pair of gloves;
3. apply teat disinfectant and allow 30 s of contact time;
4. clean and dry teats with individual paper towels;
5. disinfect teats with cotton wool soaked in methylated spirits (one per quarter) starting from front to rear quarters;
6. use 70% alcohol wipes as a final disinfection step and to check for residual dirt;
7. partially insert the nozzle (both from the antibiotic and the ITS), do this from rear to front quarters;
8. massage the antibiotic (for cows receiving antibiotic) up the gland without touching the teat ends;
9. pinch the base of the teat and apply the ITS;
10. ensure the ITS remains in the bottom of the teat and covers the teat canal (some should be visible from the outside of the teat);
11.  apply teat disinfectant.

The steps for the “standard” procedure were the normal practice at the farm and consisted of points 2, 3, 4, 5, 8, 9 and 11 of the “best practice” procedure.  Pre and post dry-off disinfection was done with the automatic sprayer from the rotary parlour, and no minimum contact time was observed, whereas in the “best practice” procedure it was done by dipping and observing a minimum of 30 s contact time.

Implications

By conducting the mentioned studies, we have been able to provide local evidence on the impact of selective DCT, management practices that could lower SCC and provide a tested “best practice” drying-off procedure. With the reality of selective DCT and a move away from blanket antibiotic use, the knowledge generated will contribute to the national guidelines, development of training and advisory programmes, and to support improved udder health in Irish dairy farms.

References

1. McAloon, C. I., McCoy, F. and S. J. More. 2021. Trends in estimated intramammary antimicrobial usage in the Irish dairy industry from 2003 to 2019. JDS Commun. 2:271–276. https://doi.org/10.3168/jdsc .2021 -0081.
2. Archer, S. C., Mc Coy, F., Wapenaar, W., and M. J. Green. (2013). Association of season and herd size with somatic cell count for cows in Irish, English, and Welsh dairy herds. The Veterinary Journal, 196(3), 515-521.
3. Clabby, C., Valldecabres, A., Dillon, P., O’Sullivan, K., Arkins, S., Flynn, J., McCarthy, S. and P. Silva Boloña. 2024. The association between selective dry cow therapy, milking routine and dry cow management practices with somatic cell count in early lactation cows from 21 commercial grazing dairy herds. J Dairy Sci, 107: 7106-7120.
4. Keane, O. M., Budd, K. E., Flynn, J., and F. McCoy. 2013. Pathogen profile of clinical mastitis in Irish milk‐recording herds reveals a complex aetiology. Veterinary Record, 173: 17-17.
5. Clabby, C., McParland, S., Dillon, P., Arkins, S., Flynn, J., Murphy, J., and P. Silva Boloña. 2022. Internal teat sealants alone or in combination with antibiotics at dry-off–the effect on udder health in dairy cows in five commercial herds. Animal, 16: 100449.
6. McParland, S., Dillon, P. G., Flynn, J., Ryan, N., Arkins, S. and A. Kennedy. 2019. Effect of using internal teat sealant with or without antibiotic therapy at dry-off on subsequent somatic cell count and milk production. J. Dairy Sci. 102:4464–4475. https://doi.org/10.3168/jds.2018-15195.
7. Clabby, C., Valldecabres, A., Dillon, P., McParland, S., Arkins, S. E. A. N., O’Sullivan, K., Flynn, J., Murphy, J., and P. Silva Boloña. 2023. Evaluation of test-day milk somatic cell count to predict intramammary infection in late lactation grazing dairy cows. J Dairy Sci, 106: 4991-5001.
8. Green, M. J., Bradley, A. J., Medley, G. F. and W. J. Browne. 2008. Cow, farm, and herd management factors in the dry period associated with raised somatic cell counts in early lactation. J. Dairy Sci. 91:1403–1415. https://doi.org/10.3168/jds.2007-0621.
9. Schreiner, D. A., and P. L. Ruegg. 2003. Relationship between udder and leg hygiene scores and subclinical mastitis. J. Dairy Sci. 86:3460–3465. https://doi.org/10.3168/jds.S0022-0302(03)73950-2.
10. Silva Bolona, P. , R. Millar, and T. Donovan. 2024. Effect of dry-off procedure and dry-off treatment on somatic cell count. Proceedings National Mastitis Council Regional Meeting 2024, Ghent, Belgium (August 12-14).
11. Robles, I., Zambelis, A., Kelton, D. F., Barkema, H. W., Keefe, G. P., Roy, J. P., von Keyserlingk, M. A. G., and T. J. DeVries. 2021. Associations of freestall design and cleanliness with cow lying behavior, hygiene, lameness, and risk of high somatic cell count. J Dairy Sci, 104: 2231-2242.
12. Agricultural Economics and Farm Surveys Department. 2021. Teagasc National Farm Survey 2023 Dairy Enterprise Factsheet. Athenry, Co. Galway H65: R718.
13. European Parliament and the Council of the European Union. 2019. Regulation 2019/6 of the European Parliament and of the Council of 11 December 2018 on veterinary medicinal products and repealing Directive 2001/82/EC. Off. J. Eur. Union L 4:43–167.
14. ICBF, Irish Cattle Breeding Federation. 2011. Milk recording National Overview and Plan. Online: https://www.icbf.com/national-overview-and-plan/

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