Mastitis poses the highest economic impact on dairy farms from all diseases. This is due to losses in unrealized milk production, treatment costs, increased risk of culling, and discarded milk production.
Fresh dairy cows are at highest risk of getting mastitis with the highest economic impact. During early lactation, fresh cows immune system is depressed with impaired defense mechanisms against infection.
The weeks following calving represent the greatest risk for mastitis in dairy cattle because the numbers of clinical and especially subclinical mastitis during this period determine the udder health and performance during the entire lactation.
The average case of clinical mastitis during the first 30 days of lactation has a total economic cost of $444, including $128 in direct costs and $316 in indirect costs . The biggest part of the cost comes from future milk production loss and premature culling and replacement. Treatment and current milk loss represent relatively small part of the total cost of clinical mastitis.
However, we should not forget the impact of subclinical mastitis which is more difficult to control and represent mainly hidden costs. Each subclinical mastitis possesses a high risk of becoming a clinical.
There are a variety of factors that place fresh cows, including heifers, at risk for udder infection:
- The high new infection rate characteristic of the dry period.
- Metabolic disorders such as Ketosis during transition period.
- Systemic inflammation post-calving.
- Nutritional transition from dry to lactation diets and following acidosis.
Relation between SCC and mastitis
One of the best indicators to assess the risk of mastitis is the SCC measured in bulk milk and individually. A high SCC numbers in bulk milk above 200,000 indicates a subclinical mastitis. Individual SCC is important as few cows with high SCC can affect the bulk milk.
However, if more than 15% of the cows have SCC above 200,000 measures should be taken. In a study  after measurement of 200,000+ SCC in bulk tank milk 11% of the cows developed mastitis. Primiparous cows with a high SCC has a 4-fold higher risk of developing a clinical mastitis than primiparous with a low SCC (below 200,000), while multiparous with a high SCC had a 2-fold higher chance multiparous with a low SCC. Additionally, multiparous with a low CSCC had a 2-fold higher hazard for CM occurrence than primiparous with a low CSCC.
By preventing high SCC after calving approximately 25% of first subsequent clinical mastitis can potentially be prevented. Decreasing SCC below 200,000 lowers the clinical cases from 11% to 7% .
Often lactation mean somatic cell score (SCS) or test-day SCS are used as mastitis indicators. Today regular measurement of bulk and individual SCC can warn the farmer of existing risk of mastitis. Lower SCS results in lower cases of mastitis:
Somatic cell count (SCC) is the total number of cells per milliliter in milk and is the main indicator for dairy cows milk quality. The somatic cells consist of 2% mammary gland cells and around 98% white blood cells – leucocytes that are immune cells, produced by the cows immune system. As SCC in are immune cells their numbers in the milk increase as a response to an immune challenge in the udder. This challenge is usually caused by pathogens and leads to an inflammation – mastitis.
To stop the infection additional immune cells migrate to the mammary gland causing an increase in the SCC accompanied with decreased milk production. The first recruited immune cells migrating into mammary gland are the neutrophils (PMNs) forming an important line of defense. The primary function of PMNs is to engulf, phagocytize, and destroy foreign materials, including invading bacteria. With a properly functioning immune system the infection should be promptly solved with short and transient increase of SCC. However, most of the cows are immunodeficient, especially around calving, drying off, and stress periods when the immune system is suppressed. In those cases, the number of matured neutrophils is limited and insufficient but the bone marrow continues producing large numbers of immature neutrophils that are being mobilized in the inflammation. These immature neutrophils are forming the majority of SCC during a subclinical mastitis being recruited into the mammary gland in increasing numbers but not being able to reduce the pathogens load and causing the infection to transit to clinical mastitis.
High SCC negatively impacts milk production
As an economic impact for the farmer the high SCC is not just related to milk premium or penalty but also directly impacts the milk production. SCC rise as a response to mammary gland infection, causing inflammation and reducing the mammary gland tissue ability to produce milk. Several factors are related to milk losses due to high SCC:
- Milk production reduction for the entire lactation
- Risk of clinical mastitis risk
- Increased culling rates due to high SCC
It is estimated that an increase of SCC in bulk milk over 100 000 results in a milk production decrease.
SCC relation to estimated milk losses.
Strategies to reduce SCC in fresh cows
Cows with very high SCC for prolonged duration of time are advised to be culled. They are more prone to clinical mastitis and fertility problems. Culling, however, should be done smart, according to established breeding program, and in coordination with a vet.
Prevention Through Sanitation and Management
Improving sanitation to decrease mastitis is a key for successful dairy farming and udder health. It is simply keeping the udder clean and free of pathogenic bacteria that cause mastitis. Major teat contamination can be avoided by eliminating mud and preventing formation of ponds around cows walking areas. Keeping dry and clean bedding.
Cleaning and sanitation of the milking machines and the udder before and after milking. Correct vacuum regulation. Higher vacuum levels cause the tits canal to remain open after milking for longer time allowing pathogens to enter the udder.
To reduce SCC also helps to increase the milking frequency. Increasing the number of milkings per day may help to reduce SCC individually or on herd level.
Dry Cows management
Risk of intra-mammary infections is greatest during the early and late dry period. In early dry period cows have remaining pathogens from the lactation but they are not flushed out on daily basis with the milking. Most of the fresh cows mastitis are caused by bacteria remained from the dry period.
To reduce pathogens during dry period cows should be dried off when individual SCC are below 200 000. Cows with higher SCC should be treated before drying-off. If the cows are not properly dried mastitis can occur during the dry period too.
Dry cows should be monitored for signs of mastitis such as redness and swelling in the udder and treated.
Nutrition is involved in maintaining immunity. Inadequate energy and deficiencies affect resistance. Nutrient deficiency may lead to negative energy balance and immunosuppression. Well balanced diets with sufficient nutrients may help supporting well-functional immune system and thus contribute to SCC reduction. We need to have in mind that immune system uses mainly glucose as energy source. Glucose is also the main source for milk production as the mammary gland uses it to synthesize lactose.
Fresh cows are usually in negative energy balance manifested with low blood glucose levels. In those cows, the immune system is compromised and they are more susceptible to mastitis. This explains also why most mastitis cases occur during early lactation.
Strategies preventing negative energy balance and subclinical ketosis may help reduce the risk of early mastitis.
Nutritional strategies preventing acidosis in early lactation may also help reducing systemic inflammation and strengthening the immune system.
Some probiotics and prebiotics supplied with the diet demonstrate beneficial effect on the innate immune system being able to support an adequate immune response leading to stable SCC reduction.