Heat Synchronizing Heifers
By Judy Brener
(From The BueLIngo World - January-March 1993)


Since starting our BueLingo herd, we have tried to have our yearlings calve as a group a month before the rest of our cows. We have found that many two-year old cows have trouble conceiving a second calf. We hope to give them more time to recover before breeding them again, and by keeping them separate, they can be watched more closely. We are trying to accomplish this by using heat synchronization and AI breeding. Other advantages include a more uniform calf crop because their ages are closer together and a lessened workload because of a shorter season. Because we use AI we can increase our herd’s blood-lines and match cow/bull traits. We have found that dairy cow heat synchronization techniques and heat detection patches were not 100% reliable with beef cows.

For the 1991 breeding season we tried heat synchronizing twenty heifers using two prostaglandin injections eleven days apart and a heat detector patch. The medication costs and the patch came to about$11/head. Out of the 20, we detected heat in 10 which were bred using Al. All 20 were then turned out with a clean-up bull. We had 15 calves born within the first 30 days (75%) and all 20 conceived a second calf in 1992. Although this method was mostly successful, we felt it involved too much handling.

Before 1992 we investigated and decided to use the 37 day Colorado system of heat synchronization in beef cows. Thirty of our heifers were fed 0.5 mg/head/day of MGA in their grain for 14 days. After the MGA was withdrawn many of the heifers were noted to be “riding;” an expected but sub fertile heat period. Sixteen days after the MGA was withdrawn, each heifer was injected with prostaglandin and given a heat detector patch. The medication costs and the patch came to about $7/head. Our original plan was for the heifers to also receive their spring vaccinations and to be wormed at the same time to avoid extra handling. Our veterinarian suggested waiting for at least 45 days after breeding because he felt that any added stress could affect breeding success.

After 48 hours, five heifers showed signs of heat and were bred with AI. Thirteen more were bred at 72 hours. The remaining 12 were AI’d after 96 hours. In the last group, six still were not showing signs of heat, but were AI’d anyhow. They all were given a quiet pasture for themselves and a clean-up bull was added after a week.

Pregnancy checks this winter indicated all had conceived, but at least three would be later than the others. The first calf from this group was born 273 days after AI’ing and within the next 12 days we have had 15 more. For us this was simple and successful. We intend to use it again.

37 Day Colorado system
  • 14 days – 0.5 mg/head MGA fed
  • 16 days – wait
  • Prostaglandin Injection
  • 1-7 days – heat detect & breed

Editor’s Note: Since this article was written several other methods of heat synchronization have been developed. Most breeding services have advice on these at their web sites.