Can you use lead bullets on big game animals/?

Yes, you can.  Here is some information about it: LEAD AMMUNITION INFORMATION Hunter Information: Lead can be toxic if ingested. The toxicity depends on the level and frequency of exposure. Lead can have physiological effects. Lead shot is banned in U.S. for waterfowl hunting, but is still used for other purposes. Lead ammunition is still used for purposes other than waterfowl hunting. Wildlife can be poisoned from ingesting lead. People can ingest lead particles from bullets in hunter harvested game animals. Lead particles in venison may be too small to detect by sight, feel or taste.   Risk Reduction Tips: Use non-lead, copper or other high-weight retention ammunition. Liberally trim around the wound channel. Discard meat that is bruised, discolored or contains hair, dirt, bone fragments, or plant material. Use caution when rinsing the carcass to avoid spreading lead fragments. Ground game meat has more lead fragments than steaks and chops. Ask commercial processors not to combine meat from other hunter’s game with yours. Avoid cooking game with acidic substances like vinegar or wine. Practice good marksmanship. Practice clean field handling techniques. Source: 2013 Big Game Rules, page 52