Dr Anna Lavery and Dr Aimee Craig

Agri-Food and Bioscience Institute

 

The use of antibiotic dry-cow tubes has long been standard practice on many farms. However with improvements in both milking hygiene and cow genetics, average herd somatic cell count (SCC) has decreased over the last two decades. Consequently, this may provide an opportunity for many farms to reduce antibiotic use at drying-off. Selective dry-cow therapy (SDCT), as the name suggests, involves being more selective about which cows are treated with antibiotics, and limiting this to those that are ‘high risk’. While there is no agreed approach to identify cows that are ‘high risk’, this is often based upon milk SCC levels above 200,000 cells/ml, together with the cows’ mastitis history during the months prior to drying-off. Cows considered ‘low risk’ receive no antibiotic treatment and are dried-off using teat-sealant only.  A blueprint to identify ‘high’ vs ‘low risk’ cows is one area being examined in a major research project entitled ‘STrategic AntiMicrobial use in Dairy, Beef and Lamb Production’ (STAMP), involving the Agri-Food and Biosciences Institute (AFBI), in partnership with AgriSearch, Animal Health and Welfare Northern Ireland, LMC and Farm Vet Systems. This project is co-funded through DAERA’s Research Challenge Fund. 

 

AFBI research

A two year study implementing selective dry-cow therapy at drying-off, and involving almost 400 cows, has recently been completed within the dairy herd at AFBI Hillsborough. In this study cows were considered to be ‘high risk’ if they had a SCC greater than 200,000 cells/ml during any of the last three monthly milk recordings prior to drying off, or had more than one case of mastitis during the 3 month period prior to dry-off. These ‘high risk’ cows received intramammary antibiotic treatment at dry-off together with teat sealant. Cows identified as ‘low risk’, namely those with a SCC of less than 200,000 cell/ml during the three milk recordings prior to drying-off, and with no cases of mastitis during the 3 months prior to dry-off, were considered not to need antibiotics at drying-off. However in order to evaluate this practice, these ‘low risk’ cows were allocated to one of two treatments; i) Conventional dry-cow therapy (DCT): treated with intramammary antibiotics and teat sealant, or ii) Selective DCT: treated with teat sealant only.

 

Preliminary results indicate that neither milk yield nor milk composition in the first 3 months post-calving were affected by treatment at drying-off (Table 1).  However , during the three milk recordings post-calving, cows considered ‘high risk’ at dry-off had an average SCC of 219,000 cells/ml. In contrast, ‘low risk’ cows dried-off using conventional DCT had an average SCC of 75,000 cells/ml, while ‘low risk’ cows dried-off using SDCT had an average SCC of 80,000 cells/ml (Figure 1). Preliminary results also show ‘high risk’ cows had on average 0.6 cases of mastitis per cow in the subsequent lactation, while ‘low risk’ cows dried-off using SDCT had a similar incidence of mastitis post-calving as ‘low risk’ cows dried-off using conventional DCT (0.2 cases of mastitis per cow). These findings suggests that SDCT can be adopted with ‘low risk’ cows with no negative implications for udder health or performance during the subsequent lactation. In addition, a SCC of <200,000 cells/ml and no mastitis  during the 3 months prior to dry-off appeared to be an appropriate basis for selecting ‘low risk’ cows in the AFBI herd.

 

Lowering antibiotic use is a key tool to enhance goals within a ‘one health agenda’ which aims to achieve optimal health for people, animals and the environment. For that reason, as the dairy sector works towards a reduction in antibiotic use, there will be increasing pressure for farmers to adopt SDCT on their farms. To ensure success with SDCT it is important to consider the following points:

 

  • Selection criteria: Making decisions on whether to adopt SDCT on your farm, and which individual cows to dry-off without the use of antibiotics, requires good information on your herd, and on individual cows. In general SDCT is not advised on farms with high bulk tank SCC (an average bulk tank SCC of greater than 200,000 cells/ml indicates that SDCT may not be appropriate on a farm). In addition, participation in milk recording will be required in order to identify the SCC of individual cows. Furthermore, excellent health records will be required to identify the mastitis history of each cow during the current lactation. If you are thinking of adopting SDCT, this decision should be made in consultation with your vet, who will help you develop an individual cow selection criteria that is specific to your herd.
  • Hygiene: While good hygiene at drying-off is critical at all times, it is especially so if you are not using an antibiotic so as to avoid introducing bacteria into the udder. Working with your vet to develop a step-by-step protocol to follow at drying-off will reduce the risks.

If you would like to adopt selective dry-cow therapy on your farm, speak with your vet who can provide additional information and help to develop an appropriate plan at drying-off.

 

Table 1. Average daily milk yield and milk fat and protein content (%) for ‘high risk’ cows which received antibiotic plus teat sealant, and for ‘low risk’ cows subject to either SDCT (teat sealant only) or conventional DCT (antibiotic plus teat sealant). 

 

High Risk

Low risk

(SDCT)

Low risk

(conventional DCT)

Milk yield (kg/day)

41.7

39.3

40.3

Fat (%)

3.9

3.9

3.9

Protein (%)

3.3

3.3

3.3

 

 

Figure 1: Average somatic cell counts (‘000/ml) during first three milk recordings post-calving for ‘high risk’ cows that received antibiotic plus teat sealant, and for ‘low risk’ cows subject to either SDCT (teat sealant only) or conventional DCT (antibiotic plus teat sealant).