Written by: Jacquelyn Prestegaard
Because they are produced primarily for human consumption, the creation of transgenic crops or livestock is one of the most groundbreaking, yet controversial technologies emerging in agriculture to date. While millions of people consume genetically modified plants every day, genetically modified livestock are not yet approved as part of the food chain.
“It will be quite some time before we see transgenic animals commercially available for human consumption,” said Dr. Cecil W. Forsberg, Professor Emeritus of Molecular and Cellular Biology at the University of Guelph.
Forsberg and his fellow researchers have studied a transgenic line of pigs, called Enviropigs, that were genetically altered to secrete the enzyme phytase in their saliva.
The purpose of creating the transgenic pigs was to reduce the need to add expensive phytase supplements in swine diets, which is needed for optimal nutrition. Like humans, pigs require phosphorus (P) in their diet, but most phosphorus in cereal grains is contained in the molecule phytate, or phytic acid, that is indigestible by non-ruminants. Not only is the phytate P largely unavailable to the pigs, but undigested P excreted in manure can pollute aquatic ecosystems.
The Enviropig line of transgenic pigs, also called the “Cassie” line, was identical to Yorkshire pigs, except that the transgene was targeted to the parotid salivary gland. Previous research trials indicated no differences in the carcass or nutrient compositions of transgenic swine.
In an article published in the August issue of the Journal of Animal Science, Forsberg and his research team addressed, “Phytase properties and locations in tissues of transgenic pigs secreting phytase in the saliva.” The study was developed to examine expression of the transgene.
As expected, researchers found phytase “… present at high specific activity in the salivary glands.” More importantly, the phytase was not expressed in major food tissues (skeletal muscle) or in other tissues such kidney, liver, and skin, and compared with salivary glands only very low levels of phytase were detected in these tissues.
“[This] provides a solid basis on which to conclude that the major food tissues of [the transgenic] and conventional…pigs [have] essentially the same composition,” the researchers wrote.
There are no current trials being conducted with the transgenic pigs. Forsberg said studies on the Enviropig might be revived if scientists develop a way to “stack” other beneficial traits in transgenic swine.
In the meantime, government regulations on transgenic animal research are an enormous obstacle. Forsberg said unless there is a monumental breakthrough, such as the prevention of disease through transgenics, he believes it will be many years before transgenic food animals are commercially available.
“The expense for meeting testing requirements is astonishing,” Forsberg said. “Every tissue of a four-legged animal requires extensive research and documentation.”