The case between road kill that someone for the most part hit on accident and eating meat that has been put their for your consumption is two different things. Are you suggesting that eating the roadkill is the same as eating meat from the supermarket? if so, why?
Sentience is the ability to feel, perceive, or be conscious, or to experience subjectivity. from wikipedia...
sen·tience
1. The quality or state of being sentient; consciousness.
2. Feeling as distinguished from perception or thought.
from http://www.thefreedictionary.com/Sentience
so in that case sentinence is the ability to feel or perceive or be conscious.
A newborn baby can feel so it is indeed sentinent. However, obviously a newborn anything can pretty much feel also so... that newborn sheep is sentinent just as much as that newborn human is also.
Do you not think that if you pinched a newborn it wouldn't cry or if you hit a newborn sheep it wouldn't try to run away from getting hit again? Of course it would. The newborn sheep has a nervous system just like we do. If it didn't then we can state its not sentinent.