Masechet Chulin, a derivative of the word chol, translates as “The Secular Tractate”, and stands in contrast to the first two masechtot of seder Kodshim, those of Zevachim and Menachot, which deal with the laws of animal and grain sacrifices, respectively. With Jewish thought of the view that everything has the potential for holiness, masechet Chulin is a relative term. In fact, it is specifically by elevating the “secular” that we reach the highest level of holiness. It is the laws of shechita, the opening theme of masechet Chulin, along with the laws of forbidden foods and forbidden sexual relations, that comprise Sefer Kedusha, the fifth of the 14 books of the Rambam’s Mishne Torah.
Shechita serves not as an actual mitzvah, but as a matir, a necessary prerequisite to enable one to eat meat. There is no biblical requirement to eat meat (save for the korban Pesach—but such slaughter is one of the zevachim, sacrificial animals, not chulin) and hence, there can be no requirement to shecht animals. Nonetheless, our Sages did establish a bracha before shechita. Yet as the Taz (Yoreh Deah 1:17) explains, this is not a bracha on a mitzvah, but a birchat hashevach, a bracha of thanksgiving—thanksgiving to G-d for enabling us to become sanctified through the most mundane and animalistic act we do, that of eating. Interestingly, the Taz compares this to birchat eirusin, the bracha of the first part of a Jewish wedding. The Taz argues that there is no actual mitzvah to get married; rather, getting married is a preparatory stage to the mitzvah of having children.
An animal that was not shected properly becomes a nevelah. In addition to dying of natural causes, there are five ways in which the shechita can be invalidated, rendering the animal a nevelah. They are shehiyah, pausing in the middle of the shechita; derasah, pressing the knife down on the neck as opposed to moving the knife back and forth; haladah, having the knife completely covered by the animal, effectively rendering small knives “treif”; hagrama, making a cut outside the prescribed neck area; and ikkur, tearing either the esophagus or the trachea, this being the reason the knife must be totally free of any nicks.
An animal that is destined to die within 12 months—either by disease, or having been attacked by another animal (or human)—renders the animal a treifah, the subject matter of the third and fourth chapters of masechet Chulin. While today there is no practical difference between a treifah and a nevelah, the latter conveys ritual impurity whereas the former does not—something most important during Temple times.
The fifth chapter of masechet Chulin delineates the parameters of “otto v’et b’no,” the prohibition to slaughter a mother animal and her child on the same day. This law has less to do with cruelty to the animals themselves and more with preventing the development of callous character traits. The Torah grants permission to slaughter an animal and eat its meat, but to kill two generations of an animal family on the same day is something we must avoid.
A similar idea may be seen in the mitzvah of kisui hadam, the obligation to cover (part) of the blood of a slaughtered animal. Blood is life, and to let the blood remain exposed displays a certain insensitivity to life. As the blood of sacrifices must be sprinkled on the altar, thereby sensitizing us to the fact that all life is a gift from G-d, there is no obligation of kisuei hadam on sacrificial animals.
The seventh perek of masechet Chulin discusses the prohibition of eating the gid hanashe. This mitzvah does apply to sacrificial animals (as well as non-sacrificial ones), perhaps because the prohibition to eat the gid hanashe is the result of Yaakov’s struggles in facing his adversaries, whether external or internal. It was this struggle that led him to become Yisrael, and the Beit haMikdash is where we go to recharge ourselves so we can better face the struggles of life.
The eighth chapter discusses the prohibition to mix meat and milk which, biblically speaking, only prohibits the cooking of kosher meat with kosher milk. Yet once cooked, it is prohibited not only to eat but to derive any benefit from the mixture, thus prohibiting one from selling, or even feeding one’s dog, meat and milk. Eating meat (or fowl) and milk that was not cooked together is “only” rabbinically prohibited.
The 10th and 11th chapters discuss the gifts that must be given to the kohanim from each slaughtered animal, namely the shoulder, the cheeks and the maw; and the mitzvah to give the kohen the first shearing of one’s sheep. These mitzvot, the Mishna makes clear, are applicable even after the destruction of the Temple.
The 12th and last chapter of masechet Chulin discusses the mitzvah of shiluach haken, the mitzvah to send away the mother bird if one would like to take the baby chick. The Mishnayot of Chulin conclude with the beautiful teaching, "and if, by such an easy mitzvah, one that costs just about an issar (a few pennies), the Torah says ‘So that it be good for you and you will have length of days’ (Devarim 22:7), how much more so [is one to be blessed with length of days] for the more difficult mitzvot of the Torah?”
 This should not be compared to, say, the mitzva of tzitzit, which obligates one to put tzizit on a four cornered garment. By specifically purchasing such a garment and putting on tzizit—something all observant men do—we do fulfil a mitzva. Rather, it is to be compared to the giving of a get, where clearly there is no mitzvah to get divorced but rather, if one wants to divorce one must follow specific procedures. If one wants to eat meat, one must follow the specifics of shechita.
 The agricultural gifts, i.e., trumah (and maasarot to the Levi) and Challah, are discussed in seder Zeraim. Due to the fact that these laws were of no practical significance after the destruction of the Temple and never in Babylonia, there is no Gemara on these tractates and hence, no Daf Yomi. As to why, then, seder Kodshim dealing with the Temple ritual does have Gemarot, please see here.