The gemara suggests a kal v'chomer that would result in their being a mitzvah of tzedaka - מצוה להחיותו on animals. Although one may have a mitzvah to feed his own animals, the gemara concludes that there is surely no mitzvah to support the animal (when it is no longer profitable), and certainly one is not obligated to support animals that are not his. The Tosafos HaRosh asks in the name of Rabbeinu Meir, what is the hava amina. There should be an obvious pircha to the kal v'chomer, from the fact that one is not allowed to schecht people, but may schecht animals - this obviously shows that there isn't any mitzvah l'hachayoso on animals. The Tosafos HaRosh responds to this question by saying that the hava amina to make a kal v'chomer would be by animals that one is not allowed to schecht such as a bechor that is mixed with a shor haniskal.
Aside from the actual question of the Tosafos HaRosh, the entire hava amina that one would be obligated to support animals and help them survive seems a little strange. Especially since in the end the mitzvah l'hachayoso only applies to a jew and not a goy.
The Biur Halacha (330:2) writes that one is obligated to help a ger toshav woman give birth because on a ger toshav there is a mitzvah l'hachayoso. He entertains the possibility that the jew can even violate issurei d'rabonon to help the ger toshav give birth because when there is a mitzvah l'hachayoso the rabbonon weren't gozer. Based on this application of the mitzvah l'hachayoso, the mitzvah goes beyond tzedaka, it compels one to actually take care of others and help them through physically challenging circumstances.