Possible Clues:

• Perhaps llama or alpaca struggling with mink
• Beast of burden, and a hint to 17-, 25-, 36- and 49-Across
• Yak or llama, e.g. (20-Across + 54-Across)
• Mule, for example
• Prospector's mule, e.g
• Llama in Peru, e.g
• Mixture of alpaca, mink, and llama, perhaps
• Wild mink, alpaca and mule maybe
• Mule or llama, e.g.
• Mule or burro