Mastitis is considered to be one of the most costly dairy cattle diseases, making it highly relevant to dairy farmers. The economic impact of poor udder health cannot be underestimated.
Mastitis is also one of the most common reasons for cows to be removed from the herd. To put this into context, an increase of 100,000 in the milk tank somatic cell count (SCC) equates to a loss of nearly one litre of milk per cow per day. The financial loss per case of mastitis can be up to € 150, with milk loss and replacement making up the majority of the cost (Schroeder, 1997).
Often, mastitis-associated losses are underestimated due to their non-definitive – and often non-clinical – symptoms, such as reduced milk production. Multiple factors contribute to mastitis and elevated SCC, ranging from environmental issues to the milking procedure to poor immune system function. Unfortunately, there is no magical solution that will prevent mastitis problems on-farm.
Causes of mastitis vary from infection to physical trauma. The leading cause of mastitis is bacteria. Yeasts and moulds are sometimes implicated but account for only about 1% of cases. Infectious organisms invade the udder via the teat canal, migrating up through it and colonising the secretory cells. These organisms can produce toxins that damage the milk-producing tissues, which reduces their ability to produce milk. The extent of colonisation depends largely on the cow’s own immune system. The animal’s white blood cells infiltrate the mammary gland and engulf the bacteria, which causes a rise in the SCC. The bacteria can originate from already-infected udders, the environment (including bedding, water and manure) and replacement animals coming onto the farm. Streptococcus spp., Staphylococcus spp. and coliforms are the main culprits for mastitis, resulting in both subclinical and clinical mastitis. For example, Staph. aureus is responsible for so-called “summer mastitis”. Mastitis passed from one cow to another is often termed as contiguous mastitis. Subclinical mastitis usually results from infection from the environment. Interestingly, the primary time for animals to become infected is during the dry period, making adequate dry cow management essential for minimising risk.
The aim of good management is to improve the cow’s own resistance to infection. The first defence is the skin of the udder. Promoting udder and teat integrity by ensuring good hygiene during and after milking (e.g. teat dip or spray), correct functioning of the milking machine (e.g. not leaving the clusters on for longer than necessary) and cleaning udders goes a long way towards reducing the risk of infection. Hygiene and udder scoring are good, practical ways to assess cleanliness, as animals with poor scores can be 1.5 times more likely to have major pathogens isolated from milk samples compared with cleaner animals (Schreiner et al., 2003). Vaccinations are available against certain bacteria (e.g. coliforms). However, the cow’s own immune system is the best vaccination, and proper nutritional management can enhance the response to infection. An optimal supply of minerals and vitamins, as well as taking steps to minimise negative energy balance post-calving, are essential. Producers are encouraged to have a mastitis control plan that includes key areas of management that will be implemented to reduce the risk of mastitis.
Zinc is a crucial component of proteins involved in nearly all metabolic processes, as well as in DNA production. Deficiency can lead to thickened, hardened and cracked skin, especially on the teat end, which can compromise the integrity of the first barrier to infection. In addition, levels of Zn in the blood are known to drop sharply around calving, potentially leaving animals more susceptible to infection. Copper is also involved in the immune system and related enzymes, and Cu supplementation has shown benefits to udder health. Scaletti et al. (2003) noted that dairy cows supplemented with Cu exhibited a less severe infection following an Escherichia coli challenge compared with unsupplemented animals. Use of more bioavailable, organic trace minerals, such as Bioplex and Sel-Plex, can play a key role in cow health, as can support to maintain a healthy immune system.
Mastitis has the potential to significantly reduce the performance, profit and welfare of any dairy operation. Thus, producers should be vigilant in their control plan to try to minimise its impact.