Reference for Rosh Hashanah 51:4
<big><strong>גמ׳</strong></big> שפיר קאמר רבי יוסי ורבנן כל השופרות אקרו שופר ואקרו קרן דפרה קרן אקרי שופר לא אקרי דכתיב (דברים לג, יז) בכור שורו הדר לו וקרני ראם קרניו
SAID R'JOSE: ARE NOT ALL SHOFARS CALLED 'KEREN' AS IT SAYS, WHEN THEY MAKE A LONG BLAST WITH THE RAM'S KEREN [HORN]?<span class="x" onmousemove="('comment',' Josh. VI, 5. This is identified by the Talmud with the shofar mentioned in the same verse (when ye hear the sound of the shofar) .');"><sup>4</sup></span> <big><b>GEMARA: </b></big>R'Jose was surely quite right. What can the Rabbis reply? - That all shofars are called both shofar and keren, whereas that of a cow is called keren but is not called shofar, as it is written, His firstlin bullock, majesty is his, and his horns [karnaw] are as the horns of a re'em.<span class="x" onmousemove="('comment',' Deut. XXXIII, 17. We see here that the horn of a bullock is called keren. rp rua');"><sup>5</sup></span>