Natural mating with estrous synchronization

Producer Question from 2012

Q.  Plan on using the MGA/prostaglandin synchronization method on my heifers. I am considering using my own bulls and natural service. What would be a good bull to heifer ratio and how much is bull overload possible, or is natural service not even recommended? (May 11, 2012)

A.  You can use natural mating with estrous synchronization with the MGA/prostaglandin (PG). Bulls need to go through a breeding soundness evaluation. I would suggest a minimum scrotal circumference 34 cm for yearling bulls. In the experiment that we conducted, we had 40 synchronized heifer using MGA/PG and 4 yearling bulls. We put two bulls in with the heifers at one time. For the first 4 days post PG injection, bulls were rotated every 12 hours and days 5?7 post PG injection, bulls were rotated every 24 hours.

The injection of PG tightens the synchrony and you might expect the majority of the females that respond to exhibit heat 40 to 72 hours post PG. If you do not give the injection of PG the degree of synchrony will be less and cows will come into heat over a longer period of time.

Remember, the first heat post MGA feeding is not fertile.

Dr. Rick Rasby Dr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska–Lincoln, Lincoln, NE