The researchers say this is the first study showing that goats’ milk carrying elevated levels of lysozyme, a protein found in human breast milk, can successfully treat diarrhea caused by bacterial infection in the gastrointestinal tract. Human diarrheal diseases claim the lives of 1.8 million children around the world and impair the physical and mental development of millions more and these findings offer hope that genetically fortified milk could eventually help prevent such diseases.
In the study, researchers fed young pigs milk from goats that were genetically modified to produce higher levels of lysozyme, which occurs naturally occurs in the tears, saliva and milk of all mammals. Although lysozyme is produced at very high levels in human breast milk, the milk of goats and cows contains very little lysozyme, prompting the effort to boost lysozyme levels in the milk of those animals using genetic modification.
Because lysozyme limits the growth of some bacteria that cause intestinal infections and diarrhea and also encourages the growth of other beneficial intestinal bacteria, it is considered to be one of the main components of human milk that contribute to the health and well-being of breast-fed infants.
Jim Murray, UC Davis professor of animal science and vet med population health and reproduction, photographed at the Dairy Goat Research Facility. Credit: Joe Proudman / UC Davis
Pigs were chosen for this study as a research model because their gastrointestinal physiology is quite similar to humans, and because pigs already produce a moderate amount of lysozyme in their milk.
Half of the pigs in the study were fed pasteurized milk that came from the transgenic goats and carried greater amounts of lysozyme -- 68 percent of the level found in human breast milk. The other half of the pigs were fed pasteurized milk that came from nontransgenic goats and thus contained very little lysozyme.
The study found that, although both groups of pigs recovered from the infection and resulting diarrhea, the young pigs fed the lysozyme-rich milk recovered much more quickly than did the young pigs that received goats' milk without enhanced levels of lysozyme. Overall, the pigs fed the lysozyme milk were less dehydrated, had less intestinal inflammation, suffered less damage to the inner intestines and regained their energy more quickly than did the pigs in the control group. And, the researchers detected no adverse affects associated with the lysozyme-rich milk.
“Many developing parts of the world rely on livestock as a main source of food,” said James Murray, a UC Davis animal science professor and lead researcher on the study. “These results provide just one example that, through genetic engineering, we can provide agriculturally relevant animals with novel traits targeted at solving some of the health-related problems facing these developing communities."
The lysozyme-enhanced milk used in this study came from a transgenic line of dairy goats developed in 1999 by Murray, co-author Elizabeth Maga and their colleagues to carry the gene for producing human lysozyme in their milk.
Published in PLoS One (no citation info yet)
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