Boyd’s Bible Dictionary:
(high-bullock). Red heifers sacrificial (Num. 19:10). Frequent source of metaphor (Judg. 14:18; Isa. 15:5; Jer. 46:20; Hos. 4:16).
Concise Bible Dictionary:
Heifer
A young cow, which is several times alluded to as “three years old,” as if that was the age when they began to be broken in for labor (Gen. 15:9; Isa. 15:5; Jer. 48:34). They were not usually offered as sacrifices; but it was appointed that one should be slain when an unknown murder was discovered in a field, to put away the guilt of shedding innocent blood (Deut. 21:1-9). Various symbolical references are made to the heifer. Samson called his wife a heifer with which others had plowed to discover his riddle (Judg. 14:18). Egypt was like a “very fair heifer”; and Israel was a “backsliding or untractable heifer,” though it had been taught and loved to tread out the corn (Jer. 46:20; Jer. 50:11; Hos. 4:16; Hos. 10:11).