Why does the Torah insert the words "la'Shor ha'Echad"?
Menachos, 91b: Based on the fact that the moment ia calf is born it is called a 'Shor', it teaches us that, as opposed to a sheep, where the Nesech of a lamb is different than that of a ram, the Nesech of a bull is no different than that of a calf. 1
Why does the Torah insert the word "la'Ayil ha'Echad"?
Menachos, 91b: To teach us that, although the Nesech of a lamb differs form that of a ram, once it becomes a ram, there is no difference between the Nesech of a two-year old sheep and a one of three years.
What is the definition of "Seh"?
Rashi: A "Seh" 1 is a lamb or a kid-goat in its first year.
Refer to 15:11:151:1.
Why does the Torah insert "O la'Seh ba'Kesavim O ba'Izim"?
Menachos, 91b: To teach us that, although the Nesech of a lamb differs form that of a ram, there is no difference between the Nesech of a female lamb and a ewe, 1 or between the Nesech of a kid-goat and a he -goat.
See Torah Temimah, note 22.
QUESTIONS ON RASHI
Rashi writes that a 'Seh' is in its first year. But in Bechoros, he explains that even after that it is still called a Seh?