Investors seem to be spurred in part by the interest generated by the huge initial public offering in early 2013 of Pfizer's animal drug division, now called Zoetis. Since then both Aratana and Kindred have gone public, along with Phibro, which develops drugs for livestock, and Parnell, which sells both livestock and pet drugs. Funds like Adage Capital, Baupost, Fidelity and Wellington are investors in one or more pet drug companies.