Out California Way (movie, 1946)

Newcomer Monte Hale is tying to just get a job in western films when he meet young Danny McCoy and his sister Gloria. Danny is trying to get his horse, "Pardner" into films. Monte sings a song and "Pardner" does some tricks and a casting director notices. Monte gets a singing-cowboy role and the horse gets a bit, but there is an accidental explosion, engineered by western star Rod Mason, who is jealous of Monte, and the horse is badly scared and blows his lines.