Q. Regarding eating meat on Yom Tov, is chicken/turkey considered meat for the purpose of simchas Yom Tov? Is one required to have meat for both the night and day meal or is meat at one of those meals sufficient to “cover” that day of Yom Tov?

A. Poskim disagree if on our days when we don’t consume yet the meat of shlamim, if there still is a mitzva of eating meat and if it is Biblical. Biur Halocho (529: keitzad) maintains that although there is no obligation to eat meat, the mitzva remains. Some assert that the obligation also continues. (Nimukei Orach Chaim 529, Divrei Moishe 1: 11, Darkei Teshuva Y.D. 89: 19, et. al.).

Many Poskim maintain that the mitzva applies only to mammal’s meat and not fowls (See Piskei Teshuvos ibid. n.35). However, leniency is given to the one who for medical reasons may not eat or does not enjoy that or any kind of meat, as the mitzva is the pleasure and enjoyment. The minimum amount to comply with the mitzva is a kezais (about 28 g.)
The mitzva is mainly on the day. Shaarei Teshuva (ibid. 4) maintains that at night it is only a Rabbinical mitzva, Mogen Avrohom (ibid.) insist it is Biblical. Sfas Emes (Suka 48b) opines that the obligation is to eat only once a day, preferably on the day, others disagree.
See questions 1437 and 1438 in regards to the mitzva of simcha on Rosh Hashana.
Horav Shlomo Miller’s Shlit’a opinion is that at least a kezais should be eaten also when possible at night.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a