Animal Laws greatly vary around the world and often contradict one another.
International Laws that affect animals tend to be related to the shipment of livestock, animal welfare issues, and the protection of wildlife.
The Georgetown Law Library has a good guide to help locate information on animal law in the context of international and foreign law.
The International Law Library at Cornell has a good site about international law in general.
The American Society Of International Law has a branch on their site devoted to Wildlife Interests. The purpose of the Wildlife Interest Group is to contribute to the objective of conserving endangered wildlife species by helping to strengthen international wildlife treaty regimes, regional accords and national legislation that implements international treaty regimes. The group's efforts focus on scholarship and public education.