Malbim: Rachamim is always for a person; it hurts one to see another perish or afflicted. Chemlah and Chus can apply to other matters. Chus is when he needs the matter [and does not want it to be lost]. Chemlah is even for something that he does not benefit from it; he decides that it is improper to destroy it, and better to preserve it. Hashem did not forbid Rachamim or Chus on Amalek, for they are innate feelings that can arise in the heart. Chemlah is through thought - he thinks that the command to destroy them was improper. This is a great sin, due to weak Emunah!

Rashi: They are the healthy ¹ animals. We do not find like this word elsewhere. I say that it is like Meshanim, like Kesef Mishneh (Bereishis 42:12), i.e. double; they had twice as much meat and fat [as regular animals]. The same applies to "u'Far Sheni Sheva Shanim" (Shoftim 6:25).

Radak citing Targum Yonasan: The letters are reversed; this is like Shemenim (fat).

Radak #1: They are yearling lambs.

Radak #2: They were born second from the womb.

Malbim: They are the intermediate [of the cattle]; they are not as good as Meitav.

Radak citing Targum Yonasan: They are animals that people fattened; ha'Meshanim are fat by themselves, from grazing.

Radak: They are sheep above one year old.

Malbim: They are the intermediate [of the flock]; they are not as good as Meitav. ¹

Radak: It is flock, like "l'Regel ha'Melachah" (Bereishis 33:14). Anything that a person engages in is called Melachah, whether a craft, farming or shepherding.

Rashi: It is like Nivzah; the Mem is secondary (superfluous).

Radak: There are two extra letters. ¹ The same applies to "Matla'ah" (Mal'achi 1:13. It is like La'ah (weary).)

Ha'Kesav veha'Kabalah (Shemos 1:11): V'Names is like v'Nim'as (with an Aleph, i.e. despised).

Radak: We find like this - "Ru'ach Gedolah v'Chazak" (Melachim 1 19:11). The feminine refers to the Melachah, and the masculine to the Inyan (the flock).