Dry cow therapy with a non-antibiotic intramammary teat seal - a review
© The Author(s) 2004
Published: 1 July 2004
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© The Author(s) 2004
Published: 1 July 2004
Dry cow antibiotic therapy is used to eliminate existing intramammary infections and to prevent new infections in the dry period. It is implemented as part of a total management system known as the 'Five-Point Plan' for mastitis control. Recent public concerns over the widespread prophylactic use of antibiotics, coupled with an increasing interest in organic farming, have lead to a re-evaluation of the treatment of cows at drying-off. As a result, attention has focussed on the use of novel alternatives to antibiotic therapy at the end of lactation. One such therapy involves the application of a non-antibiotic bismuth-based intramammary teat seal designed for use in cows with low cell counts at the end of lactation. Like the keratin plug that forms naturally in teats of cows that have been dried-off, teat seal forms a physical barrier to invading pathogens. To date, a number of independent studies have shown that teat seal is as effective as traditional dry cow antibiotic products in preventing the occurrence of new infection during the dry period in cows with somatic cell counts of ≤200,000 cells ml-1 at drying-off. This paper reviews the efficacy of teat seal in preventing dry period mastitis in both conventional and organic dairying systems.
Mastitis continues to be one of the greatest problems faced by the dairy industry. Over 137 different organisms have been identified as being causative agents of bovine mastitis, including bacteria, viruses, mycoplasma, yeasts and algae . However, most of the mastitis cases in the UK and Ireland are caused by one of the following bacterial pathogens: Escherichia coli, Staphylococcus aureus, Streptococcus uberis, Strepococcus dysgalactiae and Streptococcus agalactiae . Mastitis continues to be the most economically important disease of dairy cattle, due to the expense of antibiotic treatment, along with the associated costs of decreased milk production and decreased fertility or, in cases where antibiotic treatment is ineffective, culling or death . Indeed, mastitis is believed to be the most common cause of death amongst lactating cows, with a death rate of 0.6% . Overall, clinical mastitis has been estimated to cost the UK dairy industry £168 million annually  and the worldwide costs have been estimated to be $1.5 to $2.0 billion per annum .
Although about 20 to 35% of clinical mastitis cases are of unknown aetiology , it is widely accepted that bovine mastitis is mainly bacterial in origin. It can be classified as contagious or environmental . In the former case, it is caused by organisms such as S. aureus, Strep. dysgalactiae and Strep. agalactiae, which are all adapted to survive in the udder, causing subclinical infections. Environmental pathogens such as Strep. uberis or enterobacteriaciae like E. coli are not welladapted to survive within the udder and, instead, they multiply rapidly following invasion, evoke a swift immune response and are eliminated .
The advent of antibiotics in the 1940 s led to hopes that mastitis would be eradicated quickly and easily. However, it was not until the 1960 s, following the introduction of a 'Five-Point Plan' developed initially in the UK , that any success was achieved in the control of clinical and subclinical mastitis . The plan suggested that control of the disease could be achieved by using the following five strategies:
Routine maintenance of milking machines.
Post-milking teat disinfection.
Rapid identification and treatment of clinical cases.
Routine whole herd antibiotic dry cow therapy.
Culling of chronically infected cows.
More recently, EU milk hygiene directives imposed strict limits on the somatic cell count (SCC) of bulk tank milk and they have ensured that the guidelines laid down in the Five-Point Plan are followed, improving milk quality and production [2, 6]. While there have been enormous improvements in milk quality, recent evidence suggests that the frequency of mastitis due to environmental pathogens or to minor pathogens like coagulase-negative staphylococci and Corynebacterium bovis is increasing rapidly [24, 20]. These data, allied with increasing consumer fears over the widespread and often indiscriminate use of antibiotics, have lead to the conclusion amongst many people working in the dairy industry (including those engaged in research on mastitis) that a re-assessment of existing treatments and development of novel treatments are essential, if current standards are to be improved or even maintained.
Several factors have conspired to ensure that mastitis has not been completely controlled to date. Firstly, in the dairy industry emphasis is often placed on breeding cows for increased milk production . A negative correlation exists between milk production capacity and resistance to mastitis; this is attributed, in part, to the increased metabolic stresses associated with the synthesis and secretion of milk . The nutritional status of the cow is also an important factor in determining susceptibility to infections: deficiencies of selenium, copper, zinc or vitamin E levels can predispose the cow to infection . Milking machines are often the cause of problems, as they can induce changes in the width of the teat duct, increasing the risk of colonisation of the teat duct and new intramammary infections . Invasion by environmental pathogens such as Strep. uberis and E. coli almost certainly occurs at or soon after milking or if there is any teat damage. Surprisingly, even though animal husbandry practices have improved greatly, there has been no reduction in the number of environmental infections. Probably the greatest problem in treating mastitis is the plethora of pathogens that can cause mastitis - if protection or immunity is enhanced against one pathogen, it doesn't protect against another .
During the dry period (i.e., the time between the last milking of one lactation and calving at the start of the next), the mammary gland undergoes a series of changes that influence the cow's resistance to bacterial infection. Even the length of the dry period can affect udder health . Additionally, it is well known that the presence of infection during the dry period can have profound effects on cow health and productivity after calving, often resulting in decreased milk yield and milk of poor quality from the infected quarters. Dry period infections may have persisted from the previous lactation or they may be new infections acquired during the dry period. Indeed, new infections during the dry period have been shown to occur at up to 10 times the rate of new infections during lactation, with E. coli or Strep. uberis being the most common causative agents. However, clinical mastitis is rare during the dry period, probably due to high concentrations of lactoferrin and leucocytes in the mammary gland at this time. Nonetheless, while dry period infections may not present as clinical cases during the dry period, there is a high risk that subclinical cases will become clinical after calving .
The use of antibiotics for the treatment of mastitis in the 1950 s led to the development of dry cow therapy . It is used to eliminate existing intramammary infections (IMI) and to prevent new infections during the dry period . Ideally, dry cow therapy will achieve high initial concentrations of antibiotic throughout the udder, resulting in a swift kill of existing pathogens, followed by a prolonged period of release of the antibiotic to prevent new infections . The antibiotic should then be readily milked out following calving. While normally very effective, dry cow antibiotic therapy has some disadvantages, including the appearance of residues in the milk when treated cows calve. As a result, milk is normally withheld for a period of time following calving, with concomitant economic losses . Additionally, there is mounting concern over the indiscriminate overuse of antibiotics, as it may contribute to the alarming increase in resistance to antibiotics that many microorganisms have evolved . Such claims have been fiercely debated. Even after 30 years of use, resistance to cloxacillin has not been detected in bovine isolates of S. aureus . Regardless of the concerns, or their veracity, dry cow antibiotic therapy remains a cornerstone of mastitis treatment.
Limiting therapy to infected cows or to infected quarters (selective dry cow therapy) is one method by which the use of antibiotics is reduced [9, 10]. However, several investigations have shown that the incidence of new intramammary infections increases when uninfected dry cows are left untreated. A recent study by Berry and Hillerton  compared the effects of dry cow treatment and no treatment on the incidence of new IMIs and clinical mastitis within two low-cell-count herds and two herds undergoing conversion to organic farming. They demonstrated that there was a significant reduction in the incidence of clinical mastitis during the dry period in cows that had been treated with an antibiotic when compared to untreated cows . In addition, there were also significantly more IMIs present at calving in the untreated groups in all four herds. Fifty per cent of new infections that occurred at calving were caused by S. aureus, a microorganism that is particularly difficult to treat effectively with antibiotics . Thus, it appears that antibiotic treatment is necessary during the dry period, unless new alternatives can be developed [1, 2].
Number of new intramammary infections (IMIs) over the dry period and at calving in udder quarters of untreated cows (negative control) and of cows treated with a dry cow antibiotic (positive control), teat seal, or teat seal plus antibiotic (Adapted from )
Teat seal + antibiotic
Total quarters treated
New dry period clinical IMIs
New IMIs at calving
Total new IMIs
% of quarters infected
A similar independent study . was undertaken in the UK where the efficacy of a dry cow antibiotic containing cephalosporin was compared to teat seal. The cows chosen for this study did not have any sign of clinical disease, had four functioning quarters, and had been free of anti-inflammatory and antibiotic treatment for at least 30 days.
Additionally, the selection process specified a SCC level of ≤200,000 cells/ml and freedom from clinical mastitis in the preceding lactation. Using these criteria, 605 cows were selected for the study: of these, 252 were infused with teat seal (Cross Vetpharm Group Ltd., Ireland) and 253 with a long-acting antibiotic preparation (250 mg cephalonium, Cepravin Dry Cow, Schering Plough Ltd. UK).
Number of IMIs acquired during the dry period, listed by causative organism (Adapted from )1.
No of quarters = 928
No of quarters = 940
All major pathogens
All minor pathogens
New infections in sealed teats and in unsealed teats of non-lactating cows after inoculation with 1,200 cfu S. dysgalactiae.
No. of new infections
% new infections
Incidence of clinical mastitis in the dry period and new infection status at calving in seven dairy herds (Adapted from 3]).
New clinical cases in dry period
New IMI at calving
No. of quarters at risk
No. of new infections
Prevalence of IMI in control (antibiotic only) and treated (seal plus antibiotic) quarters at drying off, 1 to 3 days in milking (DIM) and 6 to 8 DIM (Adapted from ).
IMI present at dry-off
IMI present at 1 to 3 DIM
IMI present at 6 to 8 DIM
(n = 828)
(n = 834)
(n = 812)
(n = 821)
(n = 811)
(n = 809)
Total qts with IMI
% of all qts with IMI
Finally, the proportion of quarters experiencing a clinical mastitis event between drying-off and up to Day 60 of the new lactation was significantly lower (p < 0.05) for treated quarters (5.9%) than for control quarters (8.0%) Thus, in some instances, addition of antibiotic to teat seal may increase its efficacy and safety . The additional protective effect observed by using teat seal plus antibiotic over antibiotic alone may be due to several factors. Firstly, the seal offers a barrier to bacterial entry in the early dry period when the keratin seal may not have formed properly. Secondly, in the late dry period, when the concentration of antibiotic may have fallen below therapeutic levels, the seal persists in its barrier function. Finally, throughout the entire dry period, teat seal provides a barrier against many bacterial species that may be insensitive to the antibiotic being used .
Dry cow therapy was originally developed with the aim of controlling summer mastitis. Its use was rapidly extended to routine use on all cows all year round. More recently, however, the emphasis has changed and in the majority of dairy herds the primary function of DCT is the prevention of new IMIs rather than the treatment of existing IMIs. This is due in part to an increase in organic dairy farming, and also due to attempts to reduce costs in response to lower milk prices. Additionally, in the world of improved milk quality and better udder health one has to question the necessity to treat all cows, irrespective of cell count. Restricted or selective use of dry cow antibiotics would appear to be a good compromise for those concerned about treating cows that do not have intramammary infections at drying-off. Only those cows with an infected gland would be treated, whether in the infected quarter only or in all quarters; in this way, the use of antibiotics would be both targeted and discriminate. Selective dry cow therapy of this type has been shown to be as effective as complete therapy in eliminating existing infections; however, there is still a problem with new infections arising during the dry period. Additionally, selecting treatments at the quarter level proves difficult while infected cows have to be identified quickly, cheaply and accurately. Cell counts, CMT analysis or N-acetyl-β-D-glucosaminidase (NAGase) tests are sometimes used as confirmatory tests. Bacteriological sampling, however, remains the definitive method of identifying infected quarters and, as this method is both time-consuming and costly, it poses a drawback to selective dry cow therapy. To lower the incidence of mastitis in a herd where selective dry cow therapy is practised, it is necessary to cull older infected cows and prevent new IMI in the younger cows. To this end, teat seal provides an attractive adjunct to both selective and blanket dry cow therapy.
Enhancement of teat sealing formulations may be achieved using non-antibiotic additives like bacteriocins, which are proteins produced by some bacteria that have the ability to kill other organisms [22, 23, 27]. Veterinary products used for the treatment or prevention of disease in animals whose tissues and/or products are destined for human consumption may give rise to unwanted or harmful residues. Thus, to maintain consumer confidence, international bodies such as the European Agency for the Evaluation of Medicinal Products (EMEA), Codex Alimentarius and the Food and Drug Administration (FDA) help to evaluate risks and oversee laws relating to the levels and type of residues in milk and dairy products. A non-antibiotic anti-mastitis dry cow formulation containing a bacteriocin derived from a GRAS organism could be of immense benefit to the dairy sector in meeting the rigorous standards imposed by these bodies. Combining the seal with a broad-spectrum bacteriocin provides the physical barrier effect and it localises the anti-microbial inhibitor in the teat sinus. Since the efficacy of the teat seal in preventing mastitis is not dependent on anti-microbial activity throughout the complete mammary gland, then the amount of bacteriocin required per seal treatment will be small relative to antibiotic usage with conventional dry cow therapy. The efficacy of incorporating the bacteriocin lacticin 3147 into teat seal will be reviewed elsewhere (Crispie et al., manuscript in preparation).
Teat seal has been shown to provide a safe, effective alternative to the blanket use of antibiotics at drying-off. Used on its own, teat seal has been shown to be as effective as a long-acting antibiotic in controlling the rate of new infection during the dry period. Importantly, the incorporation of antibiotics or other suitable antimicrobials into teat seal could prevent inadvertent contamination during infusion, thus improving the safety of the product for the untrained user.
dry cow therapy
days in milking
generally regarded as safe
somatic cell count