Are the replacement heifers ready for the fall breeding season?
By: Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist
Fall-calving herds will be breeding replacement heifers in late November. Now is the time to make certain that those heifers are ready for the upcoming breeding season.
Immunize the heifers. Ask your large animal veterinarian about proper immunizations for yearling replacement heifers. Replacement heifers should be immunized for respiratory diseases such as IBR and BVD. The heifers should receive this vaccination at least one month before the start of the breeding season. This would also be a good time to include other reproductive disease protection that may be recommended by your veterinarian. Examples of other immunizations that should be considered include leptospirosis and campylobacter (sometimes called vibriosis).
If a set of scales is available, weigh the heifers. There is time to make adjustments to the supplementation being fed to the heifers to insure that they meet the target weight at the start of the breeding season. To be certain that a high percentage of heifers are cycling at the start of the breeding season, they must weigh a minimum of 60% of their mature weight (Davis and Wettemann). See OSU Research Report 2009. If these heifers will eventually grow into 1200 pound cows, then they must weigh 720 at the beginning of the estrous synchronization and artificial insemination (or bull turn-out if natural breeding is used). Calculate the weight gain needed between now and the start of the breeding season to see if additional energy is required to achieve the desired weight gain.
Some producers may choose to grow heifers at a lower rate and attempt to breed them at 55% (or lower) of their estimated mature weight. In this scenario, about twice as many heifers need to be raised, synchronized and inseminated in order to assure that adequate numbers are bred in a timely manner to meet the future needs of the herd. All of the heifers need to be pregnancy checked about 60 days after the breeding season so that non-pregnant heifers can be marketed as soon as possible.
Many small cow calf operations will not have scales available to monitor weight gain. The next best evaluation tool is to monitor body condition of the heifers. If all of the heifers are in a body condition score of 6 (based on the 1 to 9 BCS system) then they should meet the desired target weight. With adequate summer forage available this year, heifers should need only a small amount of protein supplement (1 to 2 pounds of high protein (about 40% protein) supplement per head per day) to maintain adequate body condition going into the breeding season.