what is estrus
How to Tell when a Cow or Heifer is in Estrus. Estrus is defined as the period where a female (in this case, a cow or heifer) is receptive to a male (or, the bull). Estrous, on the other hand, is the whole reproductive heat cycle that a female goes through, from heat period to no heat period (Proestrus, Estrus, Metestrus, and Diestrus).