In early December, Wayne County Extension held a milk quality workshop. Part of that workshop involved a panel discussion with milk processors. The central message that came across loud and clear is that milk quality is a driving factor regarding milk processing and marketability of dairy products.
Milk processors are looking for, and expect, high-quality milk from dairy farms.
Somatic cells
There are several measurements that are used to help define milk quality, but the most common measurement is somatic cell count (SCC), which refers to the number of somatic cells in a milliliter (ml) of milk.
Somatic cells, primarily white blood cells, are a defensive mechanism to help prevent and defend against an infection. Somatic cell count is an important measure because it correlates directly with mastitis.
Costly disease
Mastitis is defined as inflammation of the mammary gland, usually caused by a bacterial infection. Mastitis is a costly disease for dairy producers. Dr. Ben Enger, a mammary physiology and mastitis researcher in the OSU Department of Animal Science and located at the OARDC campus in Wooster, says that mastitis is a two-billion-dollar disease in the United States.
The Federal Grade A Pasteurized Milk Ordinance limit for grade A milk is 750,000 somatic cells/ml, while the international milk export standard is 400,000. However, the reality for our dairy farms is that milk processors are looking for milk from herds with SCC at 200,000 or less. This was verified by our panel of milk processors as well. Where do they get this number?
Lower quality milk
Research indicates that milk from an uninfected udder contains less than 100,000 somatic cells per ml. SCC’s above 200,000 indicates an inflammatory response; there is some level of infection or recovery from an infection. The bottom line for milk processors is that high SCC milk is lower quality milk.
During our milk quality workshop, Dr. Ben Enger said that the term milk quality is used to refer to the aggregate of undesirable changes that occur in milk collected from mastitic glands. Those undesirable changes include increased pH, more whey protein and nonprotein nitrogen, less fat, less lactose, less casein, reduced cheese yield, longer processing times, poor cheese curd characteristics and poor shelf life. The poor shelf life is explained by blood components and enzymes found in milk as part of the defensive response to inflammation.
Milk quality improves as the farm manages for low SCC. Managing for low SCC depends upon understanding mastitis, and the pathogens that cause mastitis.
Recognizing mastitis
According to Dr. Enger, the clinical or visible symptoms of mastitis may not start until SCC is in the 800,000 to one-million range. Those clinical symptoms include flakes or clots in the milk, swollen udder quarters, fever, loss of appetite and lethargy. However, sub-clinical mastitis, with no visible symptoms, but with milk SCC elevated above 200,000 is 15 to 45 times more common than clinical mastitis. An important component of mastitis management is identifying mastitis as either contagious or environmental. This identification is necessary to develop treatment and management strategies.
Types of mastitis
Contagious mastitis is transmitted from cow to cow or from quarter to quarter. Most frequently this happens in the milking parlor, and there are a couple of primary staph and strep bacteria responsible.
Environmental mastitis is the result of infection organisms in the cow’s physical environment. Providing cows with a clean, dry environment in the barn is important to managing environmental mastitis. The organisms responsible are different than the contagious bacteria.
Often, the organisms responsible for environmental mastitis do not respond to antibiotic treatment. Environmental mastitis cases may self-cure with a healthy immune response. For that reason, antibiotic use should not be the automatic default treatment option for all cases of mastitis.
Basics of milking. Dr. Luciana da Costa, OSU Extension dairy veterinarian specializing in milk quality and mastitis also presented at the December milk quality workshop. Attention to milking procedures, proper maintenance and use of milking equipment and use of records are management practices that can lower the incidence of mastitis and result in higher milk quality.
The basics of a milking routine are strip, pre-dip, clean and dry (with individual towels or paper) and post-dip. Dr. da Costa strongly recommends the use of clean, disposable gloves worn during milking. She encourages farm managers to cultivate an attitude of continuous improvement in the milking parlor. The odds of a quarter acquiring a new Staph aureus infection are increased by 2.4 times when producers believe they are already doing enough to manage mastitis.
Producers need to pay attention to milking equipment. Milking clusters should hang evenly and over milking avoided to prevent teat end damage that leads to increased mastitis infection rates. Maintain equipment to provide the recommended vacuum, and change inflations and hoses as recommended by equipment dealers.
Keep records
Records can be used to identify trends as well as some potential management practices that need more attention. For example, is the mastitis problem more prevalent in younger or older cows? If the issue is with first lactation cows, look at heifer raising programs. If mastitis is more prevalent in older cows, examine the dry cow program and/or milking procedures.
Look at what is happening with SCC over the course of a lactation. If SCC is highest in early lactation, look at your dry and fresh cow management practices. While SCC numbers normally increase somewhat over the course of lactation, if that increase is greater than normal examine milking procedures and the housing environment.
More information about mastitis management is available at the National Mastitis Council website at www.nmconline.org/.
