More on the first-born animal - figuring out whether you can check for a blemish on yom tov itself. But what a temptation - to blemish your animal so you could have it for yourself (not the way it's supposed to be). Also, an animal that drops dead on yom tov can't be moved. Challah that has been rendered impure likewise has no value on yom tov. What was the status of the animal before it died? The answer to that will have impact on what can be done about both the animal, and the challah (which is known to be sanctified before it became ritually impure). Plus, one can't register to sign up for a not-yet-slaughtered animal, because it will look like conducting business. Rather, divide up the parts before yom tov. And pay the butcher afterwards. Likewise, one can't talk money, even as partnership for the value of meat. A percentage is fine, yes, but not the cost.