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In the Matter of Milk

From rumors of hormones in milk causing early puberty in girls to lurking residues of antibiotic and cancer-causing agents, milk's wholesome reputation has been rattled in recent years — giving rise to the organic milk sector and leading some consumers to ditch dairy milk altogether. Are the alarms based in fact or fiction?

Antibiotic Use among Dairy Herds

The topic of antibiotics in dairy production reflects concerns about general overuse of antibiotics in livestock. According to a recent World Health Organization report on antimicrobial resistance, half the countries in the world may mass-administer antibacterial drugs to food-producing animals.

In the U.S., antibiotics are not used as preventive guards against illness or to boost growth or milk production in dairy cows, according to Tom Overton, PhD, professor of dairy management at Cornell University. If a dairy cow is sick, a veterinarian might administer antibiotics — but only for specific infections and when other means of managing the illness don't work. "The percentage of cows who might need antibiotics at any one time is very small, typically 2 percent or less of the herd," says Overton.

And since milk from cows taking antibiotics cannot be sold, farmers have an economic incentive to avoid using antibiotics unless absolutely necessary. "On our farm, if a cow is sick or is being treated with antibiotics, she is moved to a separate group," says Heidi Wells, RD, LD, a private practice dietitian whose family owns a dairy farm in Kansas. A cow that falls ill is relocated from the healthy "A" group to the "B" group. Cows in the "B" group are milked while on antibiotics, but their milk is discarded. After the cow finishes her course of antibiotics and returns to good health, her milk is tested after each milking session. Only after there is no evidence of antibiotic residues in her milk will she move back into the "A" group.

Farmers are typically careful about this because the financial repercussions are hefty. Every tanker truck of milk that arrives at a dairy processing plant is tested for antibiotic residue — accounting for about 99 percent of the milk produced in this country, according to Sebastian Cianci with the U.S. Food and Drug Administration.

A tanker of antibiotic-laced milk can be traced back to the farm of origin, which must pay for not only its own wasted milk, but also for the milk from any other farms in that load. Repeat violations jeopardize the farm's ability to sell milk at all.

In 2013, the National Milk Drug Residue Data Base, a voluntary industry reporting program, found that 99.987 percent of bulk milk from tankers tested negative for residues of 10 different groups of drugs, including antibiotics, and 100 percent of all pasteurized fluid milk and milk products were negative for drug residues. Still, while milk in America may be antibiotic-free, critics say dairy farms use practices that potentially promote anti-bacterial resistance, particularly since dairy farms are where disease-susceptible calves typically are raised for veal.

"Calves may be given a medicated milk replacer that contains sub-therapeutic doses of antibiotics in an effort to stave off scours (diarrhea)," says Stacia Clinton, RD, LDN, New England regional director of the Healthy Food in Health Care program, adding that considerations beyond antibiotic residue in food include a potential emergence of antibiotic-resistant bacteria, which can be passed through direct contact or even through animal waste, dust or dirt in the air and through water streams.

"There is no legislation requiring farms to disclose prophylactic use of antibiotics unless there is a prescription from a veterinarian," says Clinton. "The real issue is about transparency."

Hormones and Milk Production

"There are six anabolic hormones, including progesterone, prostaglandins and oxytocin, that may be used to maintain healthy reproduction and lactation cycles [of dairy cows], under the care of a licensed veterinarian," says FDA'S Cianci. No steroid hormones are approved for production purposes in dairy cows — although commercial milk sold in the U.S. is fortified with vitamin D (calciferol), which functions primarily like a steroid hormone.

Arguably the most widely known hormone associated with dairy foods is recombinant bovine somatotropin, or rbST. A synthetic form of the natural protein hormone bovine somatotropin already produced in cows, rbST helps mammary glands take up more nutrients from the bloodstream, thereby producing more milk (approximately one gallon per day more than a cow not given rbST).

While there are environmental benefits to increased milk production per cow — fewer cows are needed to produce a given quantity of milk, resulting in less feed, manure and methane gas — European and Canadian bans on both rbST itself and products from cows treated with rbST strained trade agreements with the United States in the 1990s. This, coupled with boycotts by consumers and retailers, led some manufactures to voluntarily label their products as "rbST-free." Today, the USDA estimates less than 9 percent of cows were treated with rbST in 2010.

Controversy about rbST use in milk production have ranged from whether it increases cows' risk of mastitis, an infection of the mammary glands (it doesn't, according to a 2014 meta-analysis published in the Journal of Dairy Science), to its potential effect on human health.

All milk — conventional or organic — contains very small quantities of bST, and cows treated with rbST are within tiny variations of the natural bST hormone. There is no test that can differentiate between naturally occurring bST and rbST in milk, and most of it is denatured through the pasteurization process. Like a vast majority of proteins, bST and rbST break down into individual amino acids and peptide fragments during digestion. Hormonal activity is destroyed, rendering bST and rbST biologically inactive in humans. Even if the hormones survived digestion, because they are bovine forms of somatotropin and are speciesspecific to cows, they are not recognized by any human cell receptors.

Another criticism hinges on studies that have shown milk from rbST-treated cows to have slightly higher levels of the hormone insulin-like growth factor, known as IGF-1. How this hormone might affect cancer risk is unclear; early studies found a relationship between blood levels of IGF-1 and colorectal, prostate and breast cancers, although later studies either have not confirmed these findings or have found weaker relationships.

But drinking milk from cows treated with rbST likely would not affect IGF-1 levels in a person's blood anyway, according to Overton, since it would be degraded in the digestive tract. Even if it were absorbed intact, it's estimated that an adult would need to drink the equivalent of more than 39 gallons of milk per day to equal the amount of IGF-1 that's naturally secreted in a person's GI tract, says Overton.

Patty Lovera, assistant director at consumer advocacy group Food & Water Watch, disagrees — saying research indicates most IGF-1 actually survives digestion since it binds to casein, the main protein in milk, and may be absorbed into the human bloodstream with it. "The initial concerns we had about rbST and IGF-1 levels are still concerns. The issue of rbST among the public has receded somewhat because of the reduction in how widely it's used by dairy farmers, not because there is any new evidence of its safety," Lovera says.

Healthy Farm Management Practices

The average cow makes about 2,500 gallons of milk a year, says Overton, but this can vary significantly among cows. While rbST can boost milk production, it is just one tool — and not the most important one — that dairy farmers use. "[It] is not a magic substance that automatically increases milk production," says Overton. "If a cow isn't healthy or doesn't eat a good diet, rbST will not override those factors to help increase her milk. In fact, if you examine the data from 1993 (when rbST was introduced) to today, you will not see a huge blip skyward in milk production. Cows in the U.S. continue to increase production because of genetic improvement and other factors that relate to the quality of management in many areas of the dairy farm."

Wells' family farm, which has a milking herd of 165 cows, does not use rbST because there was not a great enough increase in milk production to warrant its expense compared to other ways they care for their cows. Proper animal husbandry is the biggest piece of the milk production puzzle — and nutrition plays a significant role, according to Wells. An animal nutritionist visits monthly to monitor and optimize the feed ration for their cows. Dry, comfortable bedding and a relaxed environment are also important. "It may sound funny, but cows really do sense nervousness and tension," says Wells. "When you are gentle and calm in the milk barn, the cows stay calm, making it easier to express milk."

Clinton agrees, saying that changes in animal production methods could help reduce the need for use of antibiotics and added hormones such as rbST in the first place. "With topics like these, if you look at them singularly — in this case, only within the milk and dairy industry — they may not seem like much of an issue," says Clinton. "But we really need to examine all facets in an approach that is systemic and comprehensive in order to have a full picture."

Contributing editor Kerry Neville, MS, RD, is a nutrition communications consultant based in Seattle.

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