Globally, food-producing animals consume 70 to 90% of genetically engineered (GE) crop biomass. This review briefly summarizes the scientific literature on performance and health of animals consuming feed containing GE ingredients and composition of products derived from them. It also discusses the field experience of feeding GE feed sources to commercial livestock populations and summarizes the suppliers of GE and non-GE animal feed in global trade. Numerous experimental studies have consistently revealed that the performance and health of GE-fed animals are comparable with those fed isogenic non-GE crop lines. United States animal agriculture produces over 9 billion food-producing animals annually, and more than 95% of these animals consume feed containing GE ingredients. Data on livestock productivity and health were collated from publicly available sources from 1983, before the introduction of GE crops in 1996, and subsequently through 2011, a period with high levels of predominately GE animal feed.
Source: Prevalence and impacts of genetically engineered feedstuffs on livestock populations
The data mostly consists of livestock production values, not toxicology or histopathology, and very poor model organisms (broiler chickens) were used for the vast majority of the data. Finally, it is deceptive to promote this study as a “long-term analysis of safety”, considering the shortened lifespans of the animals in question and the lack of any medically useful data.
Everyone was worried about pesticides, so we created GMO crops that allowed for less/no pesticides. Out of this movement grew fear over GMO crops, and a push to go back to organic and non-GMO foods, which require the same pesticides we wanted to get rid of to be put back into use.
With respect to Bt-crops, this is true. By inserting the Bt cry genes into a crop, the plant can now produce its own insect-specific pesticides and no longer need to be sprayed with other agents. This has obviously led to outcry from people, who believe that ingesting Bt toxins may be harmful to humans (though there is no evidence of this). However, one needs to realize that there are over 40 “organic” pesticides that are approved for organic farming that use Bt toxins as the main ingredient.
The main relevant mechanism for harm discussed about Bt is not about its ability to cause direct harm to humans like it does insects, but that it has an adjuvant effect similar to cholera toxin. When tested in the presence of digestive helminths, cholera toxin and Bt can both still register an allergic response to a previously unknown allergen. This wouldn’t be a major concern for most of the human population, since the adjuvant effect is decreased if you’ve already been exposed to a certain allergen, but it does create some concern about an increase in food allergies in children, who may be exposed to the adjuvant in formulas or even in breast milk from a mother who has ingested a GE product. This hasn’t been extensively tested, but relevant research backs it up and it’s really the only mechanism for “harm” imaginable.
People who want organically grown food many times do not want any pesticides used on them. The tradeoff here is a lower yield and less “perfect” crops. People willing to accept a higher price and using crops that may look a little weird in one way or another (not the “perfect” shape, color, etc.) can get all of these things without using pesticides.
The truth about GMOs is that nothing is universally true about all GMOs. If you’re concerned about safety to your health or the environment, you need to address each GMO strain individually since they each have their own positives and negatives. Lumping them all into one category and labeling it “good” or “bad” is a huge logical misstep and entirely misses the point of why it might be helpful to regulate and/or label these things. Really, that sane logic applies to anything.