Performance Trends in Commercial Livestock Populations in the United States Before and Subsequent to the Inclusion of Genetically Modified Feed in Livestock Diets
The first genetically modified (GM) crops were planted in the US in 1996, and by 2000 GM soy and cotton comprised over 50% of US land devoted to these crops. Adoption increased steadily thereafter and in 2013 a total of 93% of soy, 90% of cotton, and 90% of all corn grown in the US were GM varieties. It is estimated that 70-90% of harvested GM biomass is fed to food-producing animals, making the world’s livestock populations the largest consumers of the current generation of GM crops. It has been purported by some that GM feed has deleterious effects on underlying animal health. The US feeds billions of livestock each year, providing a very large uncontrolled GM feeding field data set. Considering that animal health is critical to optimizing production performance and animal production systems are managed to minimize disease, it would be reasonable to hypothesize that if animal feed derived from GM crops had deleterious effects on the billions of animals that have been fed on diets containing predominately GM feed, then animal performance and health attributes in these large populations would have been negatively impacted. To test this hypothesis, data on livestock productivity and health (somatic cell count, % mortality, % post-mortem carcass condemnation) were collated from publicly-available sources for two time periods: 1983-1994 before the introduction of GM crops in 1996, and 2000-2011, a period with high levels of GM feed based on high rates of US adoption and international trade in GM crops. These data on broilers, dairy and beef cattle, and swine revealed improving productivity and animal health trends. Productivity improvements in all livestock species continued in the positive direction they were trending prior to the introduction of GE feed, often at an accelerated rate (P < 0.05), and health parameters also improved over time. Available mortality and carcass condemnation data suggest that these rates actually decreased during the 2000-2011 time period when high levels of GM ingredients would be expected to be present in livestock feed. Field data sets representing billions of observations do not reveal disturbing trends in US livestock health and productivity data. These data are in agreement with the many peer-reviewed, controlled animal feeding studies that have reported no biologically-relevant difference between the nutritional attributes and safety of feed from GM plants as compared to feed derived from conventional crop varieties.
Keywords: Genetically modified, GMO, feed, animal health