By Kate Kelland LONDON (Reuters) – Massive use of antibiotics in farming poses a critical threat to global public health and should be reduced dramatically to an internationally-agreed target, according to a British government-commissioned review. Agreeing and implementing a global target for agricultural antibiotic use won’t be easy, the review, led by former Goldman Sachs chief economist Jim O’Neill, said, but is vital if life-saving medicines designed to fight bacterial infections are to be kept effective, both for animals and for people. The review suggested that following examples of Denmark and the Netherlands could make a swift, significant difference.