The deal is expected to be finalised in the first half of 2013, Sanofi said on Thursday. Financial details were not disclosed.
Dosch's animal health business sells more than 86 products destined for livestock and pets, including medicines and feed supplements.
"The acquisition of Dosch's animal health division will be a significant milestone for Merial and give us a strategic platform for our development in the Indian market," Merial Chief Executive Jose Barella said in a statement.
Animal health is one of the businesses Sanofi is focusing on to drive growth after the loss of its top-selling drugs to generic rivals.
The animal health market in India was valued at more than 350 million euros in 2012 and is experiencing annual double-digit percentage growth, according to Sanofi data.
India is home to the world's largest herd of cattle and buffalo, second-largest herd of sheep and goats, and has the world's fifth-largest poultry population.
The country is also the world's largest milk producer.
Shares in Sanofi, which have risen around 26 per cent since the start of 2012, were trading 0.5 per cent higher at 71.51 euros at 1149 GMT, slightly outperforming the CAC 40 index, up 0.1 per cent.
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