The era of genetics has brought with it genetic modification of foods, a highly controversial and complex issue. To my knowledge, this issue has largely revolved around the genetic modification of plant foods (such as Monsanto's "Round-Up Ready" seeds where an herbicide resistance gene has been spliced into the wild-type Monsanto soy seed). More recently, genetic engineers have branched out into the world of mammals, and this scientific venture has recently hit the news. Several media outlets have reported on a study published recently by Chinese scientists in the free online journal PLoS ONE. The researchers successfully raised lactating transgenic cattle capable of producing some proteins found in human breast milk (Yang et al., 2011). A short piece from boingboing.net sums up the researcher's supposed motives pretty well, stating, "the researchers claim that this milk would be a suitable substitute for human breast milk, but do not cite any studies or data to directly support this claim" (Doctorow, 2011).
The boingboing article also exposes public misperception of the scientists achievement, as many media outlets have claimed that these cows produce 'human breast milk'. For example, I heard about this story originally from news comedian Stephen Colbert, who stated that the researchers had inserted the gene for human breast milk into a cow. To anyone with a respectable understanding of the complexity of either genetics or milk, this statement is an abomination. There is no single gene for milk production. Even an individual's eye color is determined by multiple genes. Milk is a highly complex substance which, when freshly excreted from the udder, contains many distinct and highly organized parts. These parts include, but are not limited to, a variety of proteins (the structure of each is determined by at least one gene), fat globules (which are assembled inside of udder cells and then pushed out into the milk, a process which must require a multitude of genes), and even living immune cells (each of which contains the entire genetic code of the cow itself).
According to the article on boingboing, "the researchers claim the milk contains lysozyme (an antimicrobial protein), lactoferrin (a protein involved with the immune system) and alpha-lactalbumin" which is a protein found in whey (the liquid portion of milk). The article itself is only concerned with lysozyme, so far as I can tell, so I will focus more on that in a bit. But first, I'd like to point out that all 3 of these proteins are found in both bovine and human milk. These are common milk components, the exact structure of which will likely vary even within species, and certainly varies between species. They have the same name, however, because they are structurally similar and seem to perform the same basic functions.
Alpha-lactalbumin is an interesting case, since it is found in proportionally much higher quantities in human milk than in cow's milk, which is cited by some as being a potential issue in feeding cow's milk to infants (www.alphalactalbumin.com, 2010). Again, the Yang et al. (2011) article itself makes no mention of alpha-lactalbumin contributing to the suitability of their transgenic milk as a substitute for breast milk. They do however state in their discussion section that "the gross composition of milk showed no significant difference between transgenic and non-transgenic cattle" and that "the pattern of the protein distribution in milk from transgenic and non-transgenic cattle was similar". This suggests that the overall ratio of proteins in the milk was not significantly altered, and that this milk is not a suitable substitute for human breast milk.
The researchers' main argument for the superiority of their transgenic milk is the fact that it contains human lysozyme. This argument rests on the assumption that human lysozyme is somehow better than bovine lysozyme. The authors argue this case by exhibiting the results of an experiment comparing the anti-microbial activity of their 'recombinant' human lysozyme to that of commercially available human lysozyme, as well as lysozyme from hen egg whites (that's right, it's in eggs too, as well as your tears and saliva). They found that the human lysozyme had greater antimicrobial activity than hen egg lysozyme. Why they didn't include bovine lysozyme in this experiment could be a mystery, but maybe it has something to do with the fact that some tests have shown bovine lysozyme to have significantly greater antimicrobial activity than human lysozyme (Vakil et al., 1969).
At this point, their argument for the superiority of their milk appears more like a thinly veiled attempt to justify using their time and resources developing the technology to exploit the cow's udder as a "bioreactor for the expression of recombinant proteins" (Yang et al., 2011), or in other words, a machine to manufacture whatever proteins might be commercially profitable. This concept has been in motion for years, as genetically modified bacteria have long been used to produce recombinant proteins (including 'vegetable rennet' used to make cheese). They have simply extended this same concept to the cow's udder. Never mind the fact that the cow is a living, breathing being with a beating heart. Never mind the fact that "incomplete reprogramming of transgenic animals can result in errors in gene expression" (Yang et al., 2011). Never mind the fact that of the 37 transgenic cattle born, "seven calves died within a few hours after birth, and six calves died within 6 months after birth" (Yang et al., 2011), an astonishing 35% death rate within 6 months, whereas a typical dairy herd loses as few as 7.8% within the first full year (Gulliksen et al., 2009). Never mind the fact that of the 24 calves that survived weaning and were deemed healthy by unspecified standards, only 17 expressed human lysozyme and only 4 of those "were lactating normally in the research time" (Yang et al., 2011). Never mind the fact that there is no clearly discernible reason that anyone would want to drink milk with human lysozyme in it. Concerns regarding the well-being of living things can be swept under the rug with a single feeble and poorly translated sentence:
"Of cause[course], the health and welfare of the transgenic animals should be considered" (Yang et al., 2011).
So someday you might start seeing infant formula on the shelf at your grocery store that says "Now with Human Lysozyme!" All I can say is: it's food for thought, not for babies.
Sources Cited
Doctorow, C. (2011). GM Chinese cows express milk with some proteins found in human milk, UK press reports "OMG! Cows give breast milk!". Accessed on 7/8/11 at http://boingboing.net/2011/06/10/gm-chinese-cows-expr.html.
Gulliksen, S.M., Lie, K., Loeken, T., and Osteraas, O. (2009). Calf mortality in Norwegian dairy herds [abstract only]. Journal of Dairy Science 92(6): 2782-2795. Accessed on 7/8/11 at http://www.ncbi.nlm.nih.gov/pubmed/19448012.
Vakil, J.R., Chandan, R.C., Parry, R.M., and Shahani, K.M. (1969). Susceptibility of Several Microorganisms to Milk Lysozymes. Journal of Dairy Science 52(8): 1192-1197.
(Note: Sorry, this one's not available for free online.)
www.alphalactalbumin.com. (2010). Alpha lactalbumin. Accessed on 7/8/11 at http://www.alphalactalbumin.com/alpha-lactalbumin.php.
(Note: Aside from the information on proportions of whey protein to casein proteins, some of the things I read on this website did not seem very reputable to me. More reputable sources suggest that the proportion of whey proteins to casein proteins in human milk varies throughout lactation, but it is well recognized that the proportions are significantly different than in cow's milk, where the proportion of casein proteins is much higher.)
Yang, B., Wang, J, Tang, B., Liu, Y., Guo, C., Yang, P, Yu, T., Li, R., Zhao, J., Zhang, L., Dai, Y., and Li, N. (2011). Characterization of Bioactive Recombinant Human Lysozyme Expressed in Milk of Cloned Transgenic Cattle. PLoS ONE 6(3): e17593.
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