Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
If one makes a vow to do good act, he has to fulfill his vow as he had intended. Hence, if you had the intention of distributing the sheep among the poor and needy, then you have to fulfill exactly what you had intended. If you had intended to feed the sheep to your relatives and family members, you may eat from it as you are a member of your family unless you had excluded yourself at the time of making vow.
If your vow was a general one, without any specification, it is handled as Sadaqah (charity), i.e. it is given to the poor and needy. You should not eat from that unless the custom in your area is that a person eats from the animal or food that is made for the poor to fulfill a vow. Then according to the culture you may eat from that food.
It is better to hide the supererogatory Sadaqah (alms), but it is permitted to make it public. Allah Says (interpretation of meaning): {If you disclose your Sadaqât (alms-giving), it is well, but if you conceal it, and give it to the poor, that is better for you……}[2:271].
The scholars are of the opinion that if making Sadaqah publicly leads to some legal benefit and the person does not fear feelings of showing off, then doing so is lawful.
Therefore, we advise you to be sincere in your intention, and not to give any attention to the whispers of Satan, who wants to prevent you from good deeds and make you sad.
As long as you want to hide your Sadaqah and do it secretly then continue this practice and do not heed your negative feelings.
Allah knows best.