You could try bison fat, although I believe bison are, on average, less fatty than other cattle. The USDA (United States Department of Agriculture) forbids the use of hormones and antibiotics in farm-raised bison:

Q: Can hormones and antibiotics be used in bison raising?

A: Antibiotics and growth hormones are not given to bison.

Source: https://www.fsis.usda.gov/food-safety/safe-food-handling-and...