Final answer:
The valid conclusion that follows from the premises provided is that all mustangs are animals, as this is determined by deductive reasoning.
Step-by-step explanation:
The valid conclusion from the premises 'all mustangs are horses' and 'all horses are animals' is that all mustangs are animals. This conclusion is deduced by combining both premises in a transitive manner. Since mustangs are a subset of horses, and horses are a subset of animals, it logically follows that mustangs must also be a subset of animals. This type of reasoning is known as deductive reasoning, a process where the conclusion is a logical result of the premises.