Used with the counter 頭 for large animals such as cows, horses, and elephants. The answer is expected to include the counter, e.g. 三頭.
この牧場には牛が何頭いますか。
How many cows are there on this farm?
動物園のゾウは何頭ですか。
How many elephants are there in the zoo?
Used for small animals, fish, and insects, while 何頭 is for large animals.
Used for birds and rabbits, while 何頭 is for large animals.
Compound of 何 (nan, 'what') and 頭 (tō, counter for large animals). The counter 頭 originally means 'head'.