By: Alvaro Garcia, SDSU Professor & Dairy Specialist
Most dairy farmers have long recognized that feeding raw milk to calves is not exempt of health risks. Of the U.S. dairy farms only 25.6% feed raw milk to their calves (APHIS 2007). Dairies with more than 500 cows are rapidly adopting pasteurization with 30.7% of them already doing it. The reason has been the understanding of the role pasteurization played in history as a process to increase milk safety both in cattle and humans.
In the late 1800 tuberculosis in the U.S. decimated both cattle and human populations. At the time 70 to 90% of urban inhabitants were infected, and almost 80% of those died from the disease. Unpasteurized cow’s milk was a very common cause of tuberculosis, typhoid fever and salmonellosis. Unpasteurized cow’s milk caused nearly 25% percent of all food-borne outbreaks during that time. Public outcry demanded solutions to the high children mortality. In 1882 commercial pasteurizers were developed with the first U.S. milk pasteurizing plant opening at Sheffield Farms Dairy in New Jersey in 1891. In 1892 the "Pasteurized Milk Laboratory", funded by the Straus family, opened in New York offering free of charge "purified milk" (pasteurized) to indigent mothers. In 1897, encouraged by the results obtained in New York, the U.S. Health Department set chemical milk standards, and required milk shop dealers to obtain permits. Chicago became the first major American city in 1908 to pass a law that required commercial milk pasteurization. . Initially introduced to prolong milk shelf life, pasteurization led to the full control of bovine tuberculosis (TB) transmission to humans.
Scientists discovered later on, that the tuberculosis bacterium was not the only pathogen present in milk, and that it could contain other bacteria such as brucella, E. coli, salmonella, and listeria. Alice C. Evans (1881-1975) a USDA microbiologist discovered in 1918 that brucella, the bacterium which caused "undulant fever", the disease with which she was personally affected, could be found in milk. Other bacteria sometimes found in raw milk have resulted in recent outbreaks. In a recent E. coli outbreak for example which occurred in Tennessee in November 2013, nine children became ill after drinking raw milk. Five of the nine children, all younger than seven, required hospitalization, and three developed a severe kidney problem known as hemolytic uremic syndrome. Listeria monocytogenes is less frequently found compared to other bacteria however it is feared for its relatively high fatality rate. The health risks are particularly severe among the young, elderly, pregnant women and those with compromised immune systems.
Between 1993 and 2006 a total of 20 states reported 121 outbreaks caused by contaminated dairy products. Of these 73% involved non-pasteurized products and were caused by bacteria (CDC). The bacteria identified in raw milk or non-pasteurized dairy products outbreaks were: Campylobacter (54%), Salmonella (22%), Shiga-toxin producing Escherichia Coli (13%), Brucella (4%), Listeria (4%), and Shigella (3%). The MN Department of Health recently published an extensive (one decade) report on non-outbreak gastro-intestinal infections associated with raw milk (Robinson et al. 2013). Main causative agents were: Campylobacter, Salmonella, Cryptosporidium, E. coli O157, and E. coli non-O157 with Campylobacter accounting for 77% of the cases. Results of this report concluded that sporadic illnesses associated with raw milk consumption far outnumber those reported as outbreaks by the Center for Disease Control (CDC). It also concluded that laboratory-confirmed infections are 25 times greater than reported outbreaks and that 17% of Minnesotans that consumed raw milk became ill during the duration of the study. Campylobacter is the most common intestinal pathogen in Minnesota, with a yearly median of 903 cases between 2001 and 2008. In one of the biggest outbreaks of campylobacter bacteria seen nationally, raw milk from a Pennsylvania dairy sickened 148 people in four states in January 2012 (CDC).
Milk has become safer today than in the past as a result of better understanding of bacteria, improvements in cattle health, and the development of hygienic milk handling practices. However, the best we can do is just to reduce, not eliminate the risk of contamination. A cow producing 80 pounds of milk excretes nearly 100 pounds of wet feces, and no matter how careful dairy farmers are they cannot guarantee milk to be free from bacteria. Not only does bacteria come from feces but also from infected udders (mastitis), dust, rodents, insects, dirty milking equipment, etc. Quickly, cooling raw milk in sanitary storage containers such as a bulk tank helps preserve it and minimize the growth of these bacteria to a certain extent. Once we drink it however, bacteria enter an environment (our digestive system) abundant in nutrients and optimum temperature for their growth. A fight then ensues between the body cells and the pathogens. The body of a healthy adult might remember previous similar challenges (immunity) and be prepared to fight. However young children don’t have this acquired memory within their body cells (immunity), and the elderly have lost it or it’s weakened. After extensive studies on food and its safety, pasteurization was developed to protect the end consumer from harmful and sometimes fatal microorganisms that may haphazardly reach the food chain, while simultaneously protecting humans and young calves from unwanted diseases.