All shofars are valid except for that of a cow, because it is [called] a keren.  R’ Yose said: But are not all shofars called keren, as it is said: When they make a long blast with the ram’s keren?

The shofar of Rosh Hashanah should be from a wild goat, straight, and [with] a gold-covered mouthpiece, and [with] two trumpets at the sides.  The shofar blows long and the trumpets blow short, for the commandment of the day is with the shofar.