Ask The Vet

Runaway Bull

Heifers he didn't want bred yet, and a runaway bull, created problems for one reader. (Progressive Farmer photo by Joel Reichenberger)


We had a bull break in with a group of heifers. We had seen several cycling already but were not ready to breed them. Our veterinarian advised us to wait at least five days and give all of them Lutalyse. Why do we have to wait to work them?


When a cow ovulates, a structure forms at the ovulation site that is called the corpus hemorrhagicum (CH). It takes about five days for this structure to evolve into the corpus luteum (CL). The CL produces progesterone—we call it the pregnancy hormone.

Prostaglandins like Lutalyse or Estrumate, or those naturally produced by the cow lyse (or destroy) the CL, causing progesterone levels to decrease and the heat cycle to restart.

So, yes, you should wait at least five to seven days from when the bull was removed to make sure any cow accidentally bred has a mature CL on which the Lutalyse can act.

While Lutalyse is labeled to induce abortion up to 100 days and Estrumate up to five months, I advise treating the cows as early as possible. This is easier on the cow and essentially eliminates any complications that might follow from an abortion.