Adapted with permission from: Mendenhall, K. (ed.) 2009. The organic dairy handbook: a comprehensive guide for the transition and beyond. Northeast Organic Farming Asociation of New York, Inc., Cobleskill, NY. (Available online at: http://www.nofany.org/organic-farming/technical-assistance/organic-dairy, verified 18 July 2012).
Milk quality can mean many things to many people. Consumers expect that their milk will have a consistent appearance, pleasant taste, and last a week or more in their refrigerator. According to the Pasteurized Milk Ordinance (PMO), Grade A milk has a Somatic Cell Count (SCC) of less than 750,000 cells/ml and a standard plate count (SPC) of less than 100,000 colony-forming-units (cfu)/ml and is free of added water and harmful residues above a designated tolerance limit. These are the minimum standards. Organic processors are willing to pay for high quality so there is opportunity for dairy producers to increase their milk check substantially by focusing on udder health and limiting mastitis on their farms. Many processors are reluctant to receive milk that is consistently greater than 400,000 cells/ml.
In a healthy udder, somatic cells are epithelial cells from the lining of the mammary gland and some types of white blood cells. A healthy gland should have cell counts less than 100,000 cells/ml and typically, counts are much lower than that (less than 25,000 cells/ml).
When bacteria invade the gland, the few white blood cells normally present send out an alarm to the rest of the body and recruit thousands of additional white blood cells from the blood stream to come into the mammary gland to fight infection. Infected glands have SCCs greater than 250,000 cells/ml and often the counts reach into the millions. If all goes well, these white blood cells kill the invading bacteria and the SCC of the gland decrease to less than 100,000 cells/ml within 30 days. We can estimate the number of infected quarters in a herd and the impact on production from the bulk milk SCC (see Table 1).
|Bulk Tank SCC||Percent infected quarters in herd||Percent production loss|
|Source: Britt, J. 1987. Herd linear scores versus bulk tank sampling. Proceedings of National Mastitis Council Annual Meeting. Orlando, FL.|
Regularly monitoring SCC at both the herd and individual animal levels provides you with valuable information to help manage milk quality and improve profitability. Monitoring will help you detect new infections so that appropriate therapies can be administered early in the course of the disease. Monitoring chronically infected cows will help you identify those for culling, early dry off, or candidates for potential nurse cows. You can also follow SCCs after administering therapies to determine whether the treatment was successful. There are many ways to monitor SCC on farms and they vary in terms of cost, ease of use, and reliability of information (see Table 2).
|Cell Counting Option||Cost||Accuracy||Limitations|
|Monthly DHIA testing||$0.80 to $1.50 per cow per month||Excellent||• Only gives SCC for the cow for that single day
• SCC can fluctuate day to day
|Cow-side direct cell counting||• $300 to 3,000 for initial unit
• $1.50 per cow per test
|Very good to adequate||• More expensive devices have better accuracy|
|California or Wisconsin Mastitis Test (CMT/WMT)||• A few cents per test||Fair||• More accurate for very high cell counts
• Can be difficult to read for SCC< 1,000,000 cells/ml
|Electrical conductivity||• Hand-held unit: $300–400
• In-line monitor: thousands
|Highly variable||• Best used for early detection of clinical mastitis
• Reliability for chronic or subclinical mastitis is limited
Several factors affect bacteria counts in raw milk: cleanliness of the cow’s teats and udder, udder infections (mastitis), cleanliness of milking machines, and milk storage and cooling. Excessive bacteria counts impact shelf life, flavor, and increase the risk of foodborne diseases (e.g., Salmonella, Listeria) in the milk supply. Pasteurization effectively kills a majority of the bacteria in milk, but it does not sterilize milk. Thus, when milk has extremely high bacteria counts, a portion of bacteria can survive the pasteurization process and be present in the final product.
Mastitis-causing bacteria may increase bacteria counts in raw milk. These are usually bacteria in the streptococcus family (Streptococcus agalactiae, Streptococcus uberis, and Streptococcus dysgalactiae) and infrequently, E. coli. The majority of bacteria issues in raw milk are related to poor cleaning or improper cooling of milk.
Dairy producers can ensure that their milk has low bacteria counts by adhering to the following practices.
The Standard Plate Count (SPC), also known as the Plate Loop Count (PLC), is the most common bacterial count done on raw milk and is the only bacteria count that has a legal limit in the Pasteurized Milk Ordinance (PMO). Other tests include the Lab Pasteurized Count (LPC), Preliminary Incubation Count (PIC), and Coliform Count (CC). Farmers use these tests to diagnose causes of high bacteria counts from the cows, poor cooling, or poor cleaning.
Weather and housing conditions, bedding, and infectious disease may affect the outside surface of the udder and teats. These diseases can affect milking or harbor bacteria (e.g., Staph aureus), resulting in new mastitis cases.
|Disease||Cause||Contributing Factors||Signs||Treatment or Management|
|Mammilitis||Herpes virus||Heifers, winter weather||Blisters, scabs, "wooden teats"||Chlorhexidine teat dips in winter, vaccination|
|Warts||Papilloma virus||Contagious spread at milking||Small, teat colored bump||Surgical removal, vaccination,
|Udder rot||Unknown||Udder edema, mange mites, udder shape||Skin infection between halves of udder or between leg and udder||Scrub with antiseptic soap (iodine or chlorhexidine), dry the area, calendula salve, raw honey|
Mastitis is an inflammation of the mammary gland in response to injury. Usually, this injury occurs via infection by a microorganism, most commonly bacterial, but physical and chemical trauma can also cause mastitis. If contagious mastitis is present in a herd planning to transition to organic dairy production, the farmer should make all efforts to identify, treat, and/or cull the infected animals prior to transition. In established organic herds, contagious mastitis can be more of a headache, but it can be managed with continued effort and monitoring. Alternative therapy regimens usually yield disappointing results and are often impractical for large numbers of animals. More than 100 organisms are capable of causing mastitis in cows and most of these are bacteria. These bacteria may be considered contagious (living primarily in the cow's udder and spreading at milking time) or environmental (living in bedding, manure and mud and infecting cows anytime). See Table 4.
There are two classifications of the degree of mastitis inflammation: clinical and subclinical.
|Contagious Mastitis||Organism||Common Sources||Transmission||Symptoms and Impacts on Milk Quality||Best Management Practices|
|• Infected udders||• Cow to cow at milking time: on inflations and hands||• Very high somatic cells counts
• Decreased milk production
• High bacteria counts
|1. Identify infected cows through whole herd milk culture
2. Milk infected cows last
3. Cull high SCC cows (cull ALL Myco. cows)
4. Wear gloves to milk
5. Post dip
6. Control flies
7. Culture herd replacements
|• Infected udders
|• Similar to Strep ag
• Biting flies
• Cross-suckling by calves
|• Fluctuating somatic cell counts
• Occasionally, clinical mastitis
• Scarring of udder
• May cause gangren
|Mycoplasma species||• Infected udders
• Cows and heifers with respiratory disease
|• Similar to Strep ag and Staph aureus
• Coughing and sneezing
• Calves may be infected by drinking infected milk
|• High SCC
• Decreased milk production in one or more quarters
• Swollen joints
• Coughing and pneumonia
• Calves may have head tilt or ear infectio
|Corynebacterium bovis (C. bovis)||• Teat skin||• Cow to cow at milking||• Occasional clinical mastitis
• Minimal increase of SCC
|1. Post dip with iodine-based teat dip
2. Apply teat dip with a cup
|Environmental Mastitis||Environmental streptococci (Strep uberis & Strep dysgalactiae)||• Bedding, manure, and soil||• Between milkings from environment
• At dry off and during prefresh period
|• High SCC and sometimes high bacteria counts
• Clinical mastitis
|1. Clean cows
2. Clean environment
3. Well-bedded stalls
4. Good premilking teat preparation
5. Well-maintained milking equipment
6. Clean dip cups regularly
7. Good fly control
8. Fence ponds and standing water in pastures
9. Rotate pastures to avoid mudholes from developing under trees
10. Store bedding properly to avoid contamination and moisture
11. Coliform vaccination for herds with E. coli and Klebsiella problems.
|Environmental staphylococci (Coagulase negative staph—CNS)||• Bedding, manure, and soil||• Between milkings from environment||• Mild increase in SCC|
|• Manure||• Between milkings from environment
• More common in summer
|• Acute mastitis: watery milk, hot hard quarter, very sick cow, may cause death|
|Klebsiella species||• Manure, soil|| • Between milkings from environment
• More common in summer
| • Acute mastitis: watery milk, hot hard quarter, very sick cow, may cause death
• Cows that survive will usually have chronic quarters
||• Contaminated water or hoses||• Between milkings
• At milking time from water
• From contaminated mastitis tubes
|• Severe, chronic mastitis|
|Serratia species||• Contaminated teat dip
• Contaminated water
|• Between milkings from environment
• At milking time from contaminated dip cups
|• Chronic mastitis|
|• Soil, dry cow and heifer environments
• Biting flies
|• During dry period
• After teat injury
|• Thick, smelly discharge from swollen quarter|
|• Mud, silage juice, pasture, manure||• Between milkings from environment||• Chronic mastitis
• Cows can shed in their manure
Management of mastitis in a herd should focus on preventing new infections rather than treating infections as they occur. Even in conventional herds where antibiotic treatment is allowed, identifying the risks for new infections and adopting best management to reduce those risks is the key to producing high-quality milk and increasing the profitability of the farm.
Figure 1. Mastitis treatment decision tree.
For specific mastitis treatments, dosages, and additional information, consult with your herd veterinarian or one of the resources listed at the end of this article. When administering medications, administer intramammary infusions with great care so as not to introduce new bacteria into the mammary gland with the medication. Medications should be sterile and packaged in single-use infusion tubes. Proper procures are to dip and wipe the teat, then clean the teat end with cotton moistened with rubbing alcohol, and lastly infuse the quarter. After infusion, dip the teat again.
Remember that all the milk house cleaners, sanitizers and teat dips must be listed in the OSP so they can be reviewed and approved by the certifier prior to use.
This article is part of a series discussing organic dairy herd health. For more information, see the following articles.
This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.