This law, written in Deuteronomy 25:4, had nothing to do with oxen. When an ox is threshing, he is doing beneficial work. Muzzling an ox would be used to punish and tame it, so you shouldn’t punish the ox for doing a good work. Likewise, you shouldn’t punish a servant of the Lord for doing His work. Like Paul said in 1st Corinthians 9:9, “Does God care about oxen?” He meant this law had nothing to do with actual oxen.
Another thing sort of written about oxen was when Jesus appeared to Paul on the road to Damascus, and said to him “It is hard for you to kick against the pricks.” Jesus said this to Paul accusing him of persecuting Him. A prick was a wooden spike that was fixed behind an ox, typically, to break up the ground for tilling. If the ox refused to move, then the prick could be angled upwards to jab at it to make it move. Sometimes, however, the ox would instead kick back at the prick causing more pain.
Jesus said this to Paul, which subtley told him that Jesus had been calling Paul, but instead of answering the call, he used that inner agitation to go after Christians with more fury. As one that was called, I can tell you that it is such an uncomfortable feeling. The call would make one feel restless, uncomfortable in one’s own skin, and a feeling of not being in the right place no matter where they are. Because we are human, we would not answer His call if we felt good.