Government of India approved Bt cotton hybrids for environmental release and cultivation in 2002. There were reports of mortality of sheep grazing on Bt cotton leaves in Warangal district of Andhra Pradesh in early 2007. These baseless reports are still being used by some anti-GM groups to spread misinformation about GM crops. Genetic Engineering Approval Committee (GEAC) requested Government of Andhra Pradesh in 2007 to investigate the matter. Andhra Pradesh Government informed that Bt cotton samples analysed by four laboratories indicated the presence of high content of Nitrates, Nitrites, residues hydro-cyanide (HCN) and organophosphates which may be common constituents of soil or fertiliser or pesticides used in cotton cultivation and were the cause of animal deaths (GEAC, 2007; http://www.envfor.nic.in/divisions/csurv/geac/geac-jun-78.htm). Since the farmers use significantly lower quantities of insecticides on the Bt cotton crop, nitrates and nitrites could have been the likely toxicants.
There have been no confirmed reports of animal/sheep mortality in the past six years (2008-2013).
Reference: Karihaloo, J. L. and Kumar, P. A. 2009 Bt cotton in India: A status report. Asia-Pacific Consortium on Agricultural Biotechnology, New Delhi, India.