Shire Chief Executive Flemming Ornskov will need to dig deeper in his pocket if he wants to win U.S. biotech company Baxalta. Rather than selling out at a premium to a bigger drugmaker, as many investors thought Shire might do, Ornskov is embarking on a risky battle to create the world’s leading rare diseases specialist. The transaction could vault Shire into the top 20 global drugmakers by sales, but hazards include Baxalta’s formidable anti-takeover defenses, as well as the risk that new science could upend the haemophilia market, which accounts for over half its revenue.