766. Farm Animals on Chol HaMoed

104:20 We do not breed animals on chol hamoed because one doesn't suffer a loss if he waits until after yom tov. (If one may miss a window of opportunity, some permit it and others are stringent - Mishnah Brurah 536:6.)

104:21 One may not place a chicken on eggs on chol hamoed in order to hatch the chicks. If one placed her before yom tov and she ran off, it is permitted to return her within three days; after three days, one may not return her even if means that he will lose the eggs. (The Pri Megadim is unsure if "three days" means three days on the calendar or 72 hours - Shaarei Tziyon 536:9.) Placing a different chicken on the eggs is prohibited even within the three days. (Even the idea of permitting labor on chol hamoed to avoid a loss has its limits - MB 536:11. If the original chicken died, one may rely on the lenient opinion to place a different chicken on the eggs if failure to do so will result in a significant loss - Bi'ur Halacha 536:4 s.v. meisa harishona.)