According to recent studies comparing the nutritional value of meat from wild animals and meat from domesticated animals, wild animals have less total fat than do livestock fed on grain and more of a kind of fat they think is good for cardiac health.


(B) wild animals have less total fat than livestock fed on grain and more of a kind of fat thought to be


(C) wild animals have less total fat than that of livestock fed on grain and have more fat of a kind thought to be



Doubt- Why is "that of" not used for Comparison in this question. 



That’s a good doubt that you have asked. I see that there’s a gap in your understanding of Comparisons.


Let me try to explain it using the given sentence. 

 

This sentence has different parts. Let’s look at all of them



According to recent studies comparing the nutritional value of meat from wild animals and meat from domesticated animals,



 studies comparing the nutritional value of-

  • meat from wild animals
  • Meat from domesticated animals

Maintains parallelism 



What is the result of the study?

Wild animals have less total fat than? Than livestock fed on grain.


We could use “that of” if we were comparing some feature of wild animals to the same feature of livestock. 


For ex-


The tail of wild animals is longer than that of livestock. ( A hypothetical example, of course :D )


“That of” replaces “tail” 


Look at another sentence-


My friend eats more food than I (do).


Here, the comparison is between who eats more food.


Similarly,


wild animals have less total fat than livestock fed on grain.