Focus > Dairy herd health - December 2018
The many costs of heifer mastitis
It has been demonstrated that heifers that develop mastitis in the first 30 days after calving produce less milk and are likely to be less profitable over their lifetime. Given the substantial costs associated with rearing heifers until first calving, and given breakeven point is not achieved until the second lactation, it is imperative that mastitis is prevented in the first lactation. In addition to the direct costs associated with a case of mastitis, the effect on longevity in the herd and detrimental effects on production must also be considered and it is, potentially, a significant welfare issue.
Definition
Mastitis is caused by a variety of bacterial pathogens and results in inflammation in the udder, most often caused by bacterial infection. Mastitis can be defined as clinical or subclinical. Clinical mastitis can also be recognised in colostrum. Subclinical mastitis exists without obvious changes in the milk, but there is an increase in somatic cell count (SCC), and relies on indirect tests such as SCC counts on milk records to detect it. It should be remembered, also, that unlike research studies that may evaluate quarter-level infection, most of the proxy measures used for infection is composite cow level SCC. There are many definitions for what constitutes a case of subclinical mastitis, but a widely accepted definition is that of a SCC >150,000 cells/ml for first-lactation animals, at any milk recording, is indicative of subclinical mastitis. This lower threshold is usually accepted for lactation-one animals. In-keeping with the standard threshold of SCC used to determine infection, a threshold of 200,000 SCC/ml can also be used. Even in the absence of visible changes in the milk, bacteria can still be present, causing infection in cases of subclinical mastitis. Heifer mastitis also includes cases where one or more quarters are non-functional in animals in their first lactation. Although it is unusual to see clinical mastitis in heifers before calving, it is possible that heifers develop subclinical infections with mastitis pathogens before calving. It is most common that heifer mastitis is diagnosed after calving when the animal begins milking and either abnormal milk is detected, or an increased SCC. In order for mastitis to develop, bacteria must gain entry to the teat canal via the teat orifice to establish infection and provoke an inflammatory response that results in either clinical or subclinical mastitis. Although many similar pathogens that cause mastitis in adult cows can result in heifer mastitis, pathogens like Streptococcus uberis and non-aureus staphylococcus (NAS), previously known as Coagulase negative staphylococcus, are often involved in heifer mastitis. Other environmental pathogens are also often involved in cases of heifer mastitis. Exposure of the teats to pathogens in the pre-calving environment can result in infection before calving. Some infections may arise from bacteria living on the teat skin as well as from bacteria from the environment that enter the teat and initiate infection. The role of NAS is much debated; and its ability for pathogenicity varies. Some NAS species may result in intramammary infection quite capable of causing both clinical and subclinical mastitis as well as persistent infection. Some are more virulent than others and some more contagious in nature. For example, Staph. chromogenes, Staph. simulans, Staph. xylosus, Staph. epidermidis, Staph. haemolyticus are thought to have a more serious impact on udder health. It is worth noting that identification of NAS and its role in mastitis problems likely requires molecular analysis, this may limit our understanding of the pathogen in commercial farms. The magnitude of the effect of heifer mastitis on an individual animal is influenced by the form of mastitis (clinical versus subclinical), the virulence of the causative pathogen(s) (major versus minor pathogens), the time of onset of infection relative to calving, cure or persistence of the infection when milk production has started, and the host's immunity.
Risk factors
There are several risk factors for heifer mastitis that have been identified but are often farm and region specific. There are studies that show infection of heifer quarters can occur well before calving and the pre-calving heifer must be treated with the same care and hygiene standards as are applied to dry cows. Before considering strategies for control, a threshold for specific intervention must be set; international standards for heifer mastitis are set at a threshold for intervention of 15% of the first calving heifers.
First it must be decided if the problem is specific to heifers, or rather first lactation animals after calving. Records are, therefore, paramount; a herd with high SCC in the adult herd needs a holistic approach to SCC and mastitis control. If the pattern is mainly the heifer/first lactation group affected with either clinical mastitis or high SCC, then control can be targeted at them specifically. This will require good record keeping, including milk recording early enough in lactation to disentangle the effect of the pre-calving/calving period risk from lactation-origin mastitis. An integrated strategy to prevent and control heifer mastitis should include goal setting, assessment of the current farm systems, application of farm-specific interventions and monitoring of outcomes. Again, and very importantly, this will require good records of clinical mastitis cases and a first-milk recording carried out early in the year. Much like most infectious diseases, control relies on both reducing infection pressure and maximising the host response. Some general approaches to heifer mastitis include:
Other farm-specific measures used in mastitis control in heifers include:
There are wide variations between studies and between pathogens making generic advice impossible. In all cases of herds with heifer mastitis problems, risk factors should be investigated and attention to hygiene is f the utmost importance.
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Naqvi, S.A., Nobrega, D.B., Ronksley, P.E. and Barkema, H.W., 2018. Invited review: Effectiveness of precalving treatment on postcalving udder health in nulliparous dairy heifers: A systematic review and meta-analysis. Journal of dairy science.
De Vliegher, S., Fox, L.K., Piepers, S., McDougall, S. and Barkema, H.W., 2012. Invited review: Mastitis in dairy heifers: Nature of the disease, potential impact, prevention, and control. Journal of dairy science, 95(3), pp.1025-1040.
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Compton, C.W.R., Heuer, C., Parker, K. and McDougall, S., 2007. Epidemiology of mastitis in pasture-grazed peripartum dairy heifers and its effects on productivity. Journal of dairy science, 90(9), pp.4157-4170.