Pigs were the original truffle hunter, however, dogs have largely replaced pigs in the truffle hunting world.
Pigs are attracted to the pheromones that truffles release, due to the similar compounds that mirror testosterone found in pigs (which is why we think of it as an aphrodisiac), and would therefore, naturally hunt for them.
However, due to the extreme excitement of the pig, and their erratic digging method, they end up destroying the environment and eating those precious truffles.
Due to the environmental impact, pigs have been banned in Italy for truffle hunting since 1985.
Dogs have been introduced, because they can be trained to find the exact location of the truffle, do not disrupt the ecosystem, and are not attracted to it.
The preferred breed for a truffle hunting dog in Italy is the Lagotto Romognolo, however any breed can become a truffle hunter, and other breeds commonly used are pointers and braccos.