It Doesn’t Take Much
במדבר יט,ב: וְיִקְחוּ
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ךיֶלֵּא פָּרָּ ה אֲדֻמָּּה תְּמִימָּה אֲש ֶר אֵּין־בָּּהּ מוּם אֲש ֶר לֹא־עָּלָּה עָּלֶיהָּ עֹל :
Baal HaTurim notes that the word על is missing the letter Vav. This teaches that the Red Cow did not need to have drawn the yoke, in order to be rendered invalid. It is sufficient for the yoke just to have been placed on its back to become disqualified.
Regarding the Red Cow any burden placed on cow renders it invalid. This rule is derived from the על (yoke) but written without the Vav, can be read “upon”, that anything placed on it is as if it is a yoke. Anything necessary for the animal’s comfort (such a blanket to keep away the insects) is not considered a burden.
This is in contrast to the prohibition of working with an ox and a donkey, which is only forbidden if they actually worked together (and not just if the yoke was placed upon them together).
