Milk Quality on Organic Dairy Farms

Introduction

Organic farming is a management system that requires the integration of cultural, biological and mechanical practices that foster the recycling of resources, promote ecological balance and conserve biodiversity (AMS--National Organic Program, 2002). Administration of antibiotics, hormones, growth-promoters and most synthetic medications are prohibited in animals producing organic food and fiber. However, these treatments cannot be withheld just to maintain the animal's organic status. Animal welfare must come first. However, if an animal receives a prohibited substance, that animal must be removed from organic production forever.

Organic rules elsewhere in the world differ from the United States regulations. Organic livestock production in the European Union (EU) is governed by EU Regulation 1804/99 and went into effect in 2000. Individual EU member states may have more stringent rules for their countries. EU organic regulations require that animals on organic farms have more living space, regular outdoor access and be fed a diet relying heavily on forage although there is an allowance for up to 5% of the feed to come from conventional sources until 2008. Prophylactic use of antibiotics (e.g., blanket dry cow treatment) is prohibited, but antibiotics may be used for treatment of disease as long as withdrawal times are prolonged (usually twice the label recommendation).

In 2006, Canada adopted its own organic standard (CAN/CGSB-32.310-2006); prior to that date, most Canadian certifiers used the U.S. organic standard.  The Canadian standard is a blend of European and U.S. regulations. Antibiotics are permitted for emergency use only. Milk must be withheld but the animal can retain its organic status.

The European Picture

As in the U.S., bovine mastitis is a major concern for dairy farmers, both conventional and organic. Little has been published regarding milk quality and udder health on organic dairies in the U.S. More information is available from the European Union, but their organic standards differ from that of the U.S. in that restricted antibiotic use, coupled with extended withholding times, is allowed.

Several studies of milk quality and udder health on European organic farms are summarized in the table in Appendix 1.  Bulk milk Somatic Cell Counts (SCC) do not differ tremendously between organic and conventional dairies.  Bennedsgaard et al. (2003) evaluated cow health and milk quality on Danish conventional, long-established organic farms (before 1990), moderately old organic farms (converted prior to 1995), and newly converted organic farms and concluded that the longer a herd is managed under organic production, the better its milk quality.  Nauta et al. (2006) categorized farms in the Netherlands in a similar manner and evaluated health and milk quality in first calf heifers.  In contrast to the Danish study, first calf heifers on long established organic farms had relatively poorer milk quality than newly converted or conventional farms.

Multiple studies report that clinical mastitis treatments are fewer on organic dairies than on conventional dairies; however, most studies evaluated clinical mastitis rates based on number of treatments recorded by the dairy farmers.  Many European countries require that all antibiotic treatments be recorded in a national database but none to date require the recording of alternative botanical and homeopathic treatments.  These latter treatments predominate on organic farms (Weller and Cooper, 1996), so clinical mastitis may be underestimated on organic farms.

Milk Quality on U.S. Organic Herds

No formal studies have studied milk quality on US organic dairies in depth, although a few authors have included limited milk quality data in publications.  Tikofsky, et al. (2003) reported, in a study on antimicrobial susceptibility of Staphylococcus aureus, that bulk milk SCC for organic farms in New York averaged 273,000 cells/ml, while bulk milk from similarly sized conventional herds included in the study averaged 559,300 cells/ml.

In a survey on management practices and antibiotic usage, Zwald et al. (2004) surveyed 99 conventional farms and 32 organic farms and classified farms according to six SCC levels. Eighty-five percent of organic farms had bulk milk SCC less than 400,000 cells/ml; 53% had bulk milk SCC less than 300,000 cells/ml (see Figure 1).

Figure 1. Somatic cell count levels on conventional and organic farms. Source: Zwald. A.G., P. L. Ruegg, J. B. Kaneene, L. D. Warnick, S. J. Wells, C. Fossler and L. W. Halbert. 2004. Management practices and reported antimicrobial usage on conventional and organic dairy farms. J Dairy Sci. 87: 191-201.

A large private organic dairy in the Western U.S. recently analyzed two years' of bulk milk SCC tests (n=3,359 bulk milk samples) for its herd of 4,000 Holstein cows. Bulk milk SCC averaged 270,525 cells/ml (range 100,000 – 964,000 cells/ml; median=100,000 cells/ml) (Velez and Melendez, 2006).

Finally, a study compared milk quality from four different milk processors in Maine over a ten-month period. Dairies shipping to the organic processors averaged an SCC of 283,000 cells/ml; farms shipping to the four conventional processors averaged 207,000 cells/ml, 313,000 cells/ml, 322,000 cells/ml and 416,000 cells/ml (Kersbergen and Schivera, 2006).

Also as a part of the previous study, 46 organic farms were surveyed. Sixty-seven percent of organic farmers employed the California Mastitis Test (CMT) regularly to evaluate milk quality; the majority of these producers did not use the CMT when they were conventional. Eleven percent of farms regularly participate in a DHIA cell counting program.

Once problem quarters are identified, 60% of farms milk them separately with a quarter milker and feed that milk to calves or discard. Eighty-five percent of organic respondents used iodine based pre-dips and post-dips and 90% used individual paper towels.

Udder Health Management on Organic Dairies

The National Mastitis Council's (NMC) Ten Point Plan has been advocated for years to help producers achieve and maintain high milk quality. However, U.S. organic farming methods preclude the use of dry cow antibiotic treatment, as well as lactational antibiotic treatment under any circumstances. Therefore, intensely monitoring udder health for the early detection of new mastitis cases, as well as proactively adapting management strategies are essential for organic dairies. An adaptation of the NMC plan, for farmer education, is provided below.

Eight Steps to Better Udder Health

1. Set Farm Specific Udder Health Goals

These will vary from farm to farm depending on the challenge facing the farm, the certifying agency, and producer philosophy. Realistic, achievable goals for the majority of farms are:       

• 0% Streptococcus agalactiae (Strep ag) and 0% Mycoplasma.
• <5% Staphylococcus aureus.
• Bulk tank SCC < 200,000 cells/ml.
• Fewer than 5% new infections each month.
• 5-7% or less chronic infections.
• 2-3% clinical mastitis.

If contagious mastitis is present in a herd planning to transition to organic dairy production, all efforts should be made to identify, treat, and/or cull infected animals prior to transition. Strep ag is a highly contagious mastitis: even a few cows infected with Strep ag in a small herd (<30 cows) can cause bulk milk SCC to exceed the regulatory limit. Strep ag responds well to antibiotic treatment, so it is best to eradicate it before you begin to ship organic milk. 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 use in large numbers of animals. 

A suggested management plan is:

• Culture composite milk samples from all lactating cows in the herd.
• Identify (colored legbands) all cows infected with contagious mastitis (Strep ag, Staph aureus, Mycoplasma).
• Cull older lactation, high SCC, open, and/or clinical animals.
• In freestall operations, group contagious mastitis cows in separate pen and always milk this group last.
• In tiestall or stanchion operations, segregate contagious mastitis cows to one area of the barn and always milk last or with a unit designated just for use on contagious mastitis cows.
• Prevent transmission during milking: wear gloves, apply post dip well (1% iodine is recommended), use single service towels (no common rags or sponges).
• Continually culture dry cows and heifers and segregate if positive.
• CMT cows weekly and hold out of tank when high.
• Control flies in barn.
• Manage yard areas to minimize contact with mud, manure, and moisture.
• Provide clean, dry bedding in loafing areas.
• Ensure that adequate amounts of bioavailable selenium, vitamin E, and other trace minerals are included in the ration for all stages of lactation.

2. Implement a Plan to Regularly Monitor Udder Health

This can most easily be done with regular cell count testing through the Dairy Herd Improvement Association (DHIA), but effective monitoring with a strip cup, visual observation, and a CMT test can also achieve goals. Once a month, evaluate the udder health of all lactating animals. Cows with high cell counts on two consecutive DHIA tests or two monthly CMT tests should be cultured so they can be milked last, monitored, managed with an alternative therapy, or culled. Clinical mastitis cases should also be cultured so that intervention opportunities in the environment can be instituted. Semi-annual meetings with your certifier, veterinarian, and nutritionist to evaluate the current mastitis control program and review udder health goals are advised. 

3. Proper Milking Procedures

A proper milking routine should be instituted at all milkings and be followed by all milkers. Cows crave consistency so having a standardized procedure will reduce stress and enhance milk letdown and milkout. Components of a good milking procedure include the following.

• Udder wash/Predip: Teats should be washed or predipped and wiped clean before units are attached. Single use towels should be used on each cow. Do not share towels among cows, as this will spread mastitis.
• Forestripping: Removing 3-4 squirts of milk from each teat prior to milking helps stimulate the milk letdown response. Cows will milk out faster and on-time of the milking unit will be decreased so that damage to teat ends will be minimized. Forestripping also allows you to identify clinical mastitis earlier and also removes milk in the teat end that is higher in bacteria and somatic cells. Forestripping should be done into a cup or into the gutter so that bedding and hands do not become contaminated with milk.
• Gloves: Gloves (either nitrile or latex) should be worn at milking time to reduce the risk of spreading mastitis on hands. Gloved hands are more easily disinfected between cows or when contaminated with milk or manure than bare skin
• Milking order: Cows infected with contagious mastitis should be identified permanently (leg bands) and milked last or with a unit designated just for them at each and every milking.
• Overmilking/machine stripping: It is not necessary to get every drop of milk out of the cow's udder. Leaving the units on the cow when milk flow is low or pulling down on units will damage teat ends: keratin that develops at the teat end and has some natural antibacterial properties will be removed.  Overmilking will also cause eversion of the teat sphincter and development of scar tissue which leads to multiple problems. The teat sphincter and its ability to close between milkings is the first line of defense against mastitis so we must keep teat ends healthy. Scars and cracks that damage teat ends are more likely to be colonized by S. aureus and will increase the risk of mastitis.
• Post milking teat dipping: Attention to the selection and application of post milking teat dip is of utmost importance in herds with contagious mastitis. If an uninfected cow is unknowingly milked after an infected cow, contagious bacteria are deposited on the milk film on the teat surface. There they will multiply and move toward the teat end in an attempt to infect. Applying post milking teat dip to at least two-thirds of each teat will kill bacteria before they have a chance to multiply and spread on the milk film. Teat dips should contain at least 10% teat skin conditioners to maintain udder health and prevent chapping and cracking.

4. Maintain Milking Equipment Regularly

The mechanical milking system should be evaluated by a qualified individual at least twice yearly and dynamic testing should be performed while the system is operating. Vacuum fluctuations, due to liner slips, flooding, inadequate vacuum reserve, and poorly functioning regulators, are likely to force bacteria up the teat end during milking and increase the risk of mastitis. 

Rubber milking liners should be replaced every 1200 cow milkings or every 60 days, whichever comes first. Rubber used longer than this deteriorates and will develop microscopic cracks and ridges that hold mastitis bacteria even through the wash cycle (see Figure 2). Other rubber parts (hoses, tubes, gaskets) should be inspected regularly and replaced when worn.

A.                                    B.

Figure 2. Surface of rubber milking liners. A. Surface of new rubber inflation. B. Surface of rubber inflation after 1200 milkings. Photo credit: DC Engineering UK.

5. Evaluate Dry Cow Management

Although dry cow antibiotic therapy is not permitted in organic dairy production, this is still an important time for udder health improvement and rejuvenation of milking tissue. Energy intake should be reduced one week prior to dry off so that milk production is decreased. At dry off, the udder should be milked out one final time and the teat ends dipped with post milking teat dip twice daily for two weeks after dry off. It takes about two weeks for the keratin plug to seal the teat end and prevent the development of new infections during the dry period. Until those plugs form, we need to do our best to sanitize the teat end and prevent contamination by keeping the cow in a clean dry environment. As the cow dries up, changes occur in the mammary secretions that kill bacteria (increases in lactoferrin and alpha-lactoglobulin, increases in antibody levels) and help resolve existing infections. Nutrition of the dry cow is also important especially as she reaches the pre-fresh period. At this time, selenium and vitamin E levels become important for support of the immune and reproductive systems and to ensure the birth of a vigorous calf. The National Research Council recommends that 0.3 ppm per head per day of selenium and at least 1500 IU of vitamin E per head per day be fed. For continued udder health benefits, supplementation of selenium and vitamin E is recommended throughout lactation.

A clean comfortable environment is important to prevent new environmental infections and to prevent teat injuries. When cows are housed inside in winter, stalls should be scraped frequently and sufficient amounts of clean, dry bedding should be available. Pasture environments for dry cows in the summer are generally preferred but wet areas around ponds and streams should be fenced off so that they do not become muddy loafing areas. 

6. Institute Biosecurity and Culling Guidelines

Bringing new animals into an established herd is a risk for introducing many diseases (BVD and Johne's to name a few) besides mastitis into your herd.  Spending a little money up front to ensure the cows entering your herd are healthy may save thousands in disease eradication dollars. As mentioned before, multiple bulk tank samples should be cultured for both the usual mastitis bacteria and Mycoplasma. If this is not possible, new additions should be milked separately and cultured as soon as possible once they are added to the farm. Although farm-raised heifers are generally thought to be safe to introduce, they may also be infected and warrant similar segregation and testing protocols.

As contagious mastitis cows are identified, strategic culling methods should be used to slowly reduce the prevalence in your herd. Milk these cows separately. Place cows infected with contagious mastitis on the "Do Not Breed" list. As soon as possible, remove cows with continued high cell counts or scarred and abscessed bags. For herds with a high prevalence of Staph aureus cows that need to reduce bulk milk cell counts as soon as possible, infected quarters should be identified by culture and dried off to prevent that milk from entering the bulk tank and food supply.

7. Environment

A clean, dry comfortable environment is essential to good mastitis control. Properly sized, maintained and well-bedded stalls will prevent teat damage that may lead to S. aureus mastitis. Contagious mastitis cows should be segregated to one area of the barn so that infected milk that leaks onto bedding does not become a reservoir of potential problems for healthy cows. Since flies have been shown to spread mastitis, in particular S. aureus and A. pyogenes, good fly control is essential for the prevention of mastitis. 

8. Youngstock and Replacements  

Replacement animals are the future of the herd and are a key element in maintaining low bulk milk SCC in herds battling contagious mastitis. If we can keep this group clean and healthy, the farm's financial future is ensured.

Contagious mastitis can be spread to youngstock via two ways when whole milk is fed to calves. Staph aureus and Strep ag bacteria in milk can live in the tonsils and other immune tissues of the mouth for up to two weeks post weaning. If calves are housed together during this period and cross-suckle, contagious mastitis bacteria can be introduced into the juvenile udder and eventually that heifer may freshen with contagious mastitis.  Also, if calves are allowed to roam in the barn, they may nurse from a cow infected with contagious mastitis and then suckle from a non-infected cow thereby spreading mastitis. Even in herds where cross-suckling is not a problem, flies feeding from milk buckets and then on skin and hair, may also spread contagious mastitis bacteria to the juvenile udder. Again, fly control is important.

In herds that have problems with contagious mastitis and are feeding waste milk, a number of preventive measures are recommended. Calves should be separated while on milk and for two weeks after weaning. This is best accomplished via calf hutches but can also be accomplished by tying calves apart. Good fly control is essential during the summer months. If possible, pasteurize milk before feeding to calves. Although this does not sterilize the milk, it will drastically reduce the number of infective organisms. In herds with a known contagious mastitis problem, culture first calf heifers as they freshen. This allows you to identify infected cows early and segregate them.  Alternative therapies which enhance the immune system may have more of an effect if infections are caught early.

References and Citations

• Agricultural Marketing Service—National Organic Program [Online]. United States Department of Agriculture. Available at: http://www.ams.usda.gov/nop/ (verified 22 Jan 2009).
• Bennedsgaard, T.W., S.M. Thamsborg, M. Vaarst and C. Enevoldsen. 2003. Eleven years of organic production in Denmark: herd health and production related to time of conversion and compared to conventional production. Livestock Prod Sci. 80: 121-131.
• Busato, A., P. Traschel, M. Schallibaum and J. W. Blum. 2000. Udder health and risk factors for subclinical mastitis in organic dairy farms in Switzerland. Prev Vet Med. 44: 205-220.
• Ellis, K.A., G. T. Innocent, M. Mihm, P. Cripps, W. G. McLean, C. V. Howard and D. Grove-White. 2007. Dairy cow cleanliness and milk quality on organic and conventional farms in the UK. J Dairy Res. (ePub ahead of print): 1-9.
• Hamilton, C., I. Hansson, T. Ekman, U. Emmanuelson and K Forslund. 2002.  Health of cows, calves and youngstock on 26 organic dairy herds in Sweden. Vet Rec. 150: 503-508.
• Hardeng, F. and V. L. Edge. 2001. Mastitis, ketosis, and milk fever in 31 organic and 93 conventional Norwegian dairy herds. J. Dairy Sci. 84: 2673-2679.
• Hoerning, B., C. Simantke, and E. Aubel. 2005. Investigations on dairy welfare and performance on German organic farms. Paper presented at Researching Sustainable Systems-International Scientific Conference on Organic Agriculture. Adelaide, Australia. Available online at: http://orgprints.org/4371/ (verified 12 Mar 2010).
• Hovi, M. and S. Roderick. 2000. Mastitis and mastitis control strategies in organic milk. Cattle Pract. 8: 259-264.
• Kersbergen, R.  and D. Schivera. 2005. Organic dairy farming and milk quality. Hoard's Dairyman.
• Nauta, W.J., T. Baars and H. Bovenhuis. 2006. Converting to organic dairy farming: Consequences for production, somatic cell scores and calving interval of first parity Holstein cows.  Livestock Prod Sci.  99: 185-195.
• Roesch, M., M. G. Doherr, W. Schären, M. Schällibaum and J.W. Blum. 2006. Subclinical mastitis in dairy cows in Swiss organic and conventional production systems. J. Dairy Res. 74:86-92.
• Tikofsky, L. L., J. W. Barlow, C. Santisteban and Y. H. Schukken. 2003. A comparison of antimicrobial susceptibility patterns for Staphylococcus aureus in organic and conventional dairy herds. Microb Drug Resist. 9 Suppl 1: S39-45.
• Toledo, P., A. Andren and L. Björck. 2002. Composition of raw milk from sustainable production systems. Intl Dairy J.  12:75-80.
• Velez, J. S. and P. Melendez. 2006. Bulk tank linear score somatic cell count dynamics in an organic dairy farm in Colorado from 2004 to 2005. Proc 1st  IFOAM Intl Conf  Animals in Organic Prod. St. Paul, MN. 200-202.
• Weller, R.F. and P. J. Bowling. 2000. Health status of dairy farms in organic farming. Vet Rec. 146: 80-81.
• Weller, R.F. and A. Cooper. 1996. Health status of dairy herds converting from conventional to organic dairy farming. Vet Rec. 139:141-142.
• Zwald. A.G., P. L. Ruegg, J. B. Kaneene, L. D. Warnick, S. J. Wells, C. Fossler and L. W. Halbert. 2004. Management practices and reported antimicrobial usage on conventional and organic dairy farms. J Dairy Sci. 87: 191-201.

Appendix 1

Summary of European Studies of Milk Quality on Organic Dairies