sen⋅tient
/ˈsɛnʃənt/ Show Spelled Pronunciation [sen-shuhnt] Show IPA
–adjective
1. having the power of perception by the senses; conscious.
2. characterized by sensation and consciousness.
–noun
3. a person or thing that is sentient.
4. Archaic. the conscious mind.
I would say that deer posses "the power of perception by the senses" and have "sensations" but I do not believe they are "conscious" of these things or have "the conscious mind".
con⋅scious
/ˈkɒnʃəs/ Show Spelled Pronunciation [kon-shuhs] Show IPA
–adjective
1. aware of one's own existence, sensations, thoughts, surroundings, etc
Only we posses the ego concept of "self". Only man is blessed (or is it cursed) with free will. All other living creatures follow the will of their Creator naturally.