You can choose to accept the scientific studies or choose to believe the opinions on internet blogs
For example:
New feeds from genetically modified plants: substantial equivalence, nutritional equivalence, digestibility, and safety for animals and the food chainLivestock Production ScienceVolume 74, Issue 3, April 2002, Pages 223–238
A Aumaitre, Karen Aulrich, A Chesson, G Flachowsky, G Pivad
One huge advantage of GMO feeds is that we get more nutritional yield per acre. This means that the exploding world population can be fed with existing farm land as opposed to forcing people to live in high density leaving sufficient land for food production for our ever increasing population.