I wouldn't use bleach. I would first try to degrease it as much as possible. Simmer (don't boil) it in water with some dawn dish soap for a good while til the grease is gone. You may have to do it several times. Then get you some peroxide from Sally's beauty supply. This is what I use for hog skulls.
http://www.sallybeauty.com/on/demandware.store/Sites-SA-Site/default/Product-Show?pid=SBS-760100&dwvar_SBS-760100_webSize=128.0000+OZAnd this for extra whitening and touch ups
http://www.sallybeauty.com/on/demandware.store/Sites-SA-Site/default/Product-Show?pid=SBS-760140&dwvar_SBS-760140_webSize=128.0000+OZ
