1,011. Designating for Use on Yom Tov

Shvisas Yom Tov 1:18

The concept of muktzeh as it applies to yom tov is as follows: if a chicken is set aside for the eggs that it lays, an ox is set aside for plowing, or doves in a coop or produce are set aside to be sold, these and similar things are considered muktzeh and may not be eaten on yom tov. In order to eat these things on yom tov, one would have to designate them beforehand with the intention to eat them. On Shabbos, however, everything is considered designated for use. Just as muktzeh is prohibited on yom tov, something that came into existence on yom tov is likewise prohibited.

Shvisas Yom Tov 1:19

Food may be prepared on weekdays for Shabbos and for yom tov but it may not be prepared on a yom tov for Shabbos or on Shabbos for yom tov. Therefore, an egg that was laid on a yom tov that follows Shabbos is prohibited even though the chicken is designated to be eaten. This is because the egg was finished on the day before, so it would be considered prepared on Shabbos for use on yom tov. The Sages therefore prohibited eating any egg that was laid on any day of yom tov as a preventive measure against days of yom tov that follow Shabbos. The Sages similarly prohibited eating an egg that was laid on any Shabbos as a preventive measure against a Shabbos that follows a day of yom tov.