Selecting and managing replacement heifers can be a hot topic between beef cattle producers. There are a myriad of ways to select and manage heifers, and most producers have a system they are comfortable with. These systems can be quite variable from producer to producer, however, so I wanted to highlight some data from our Show-Me-Select Replacement Heifer Development Program (SMS) database to perhaps provide some guidance on this topic.
In general, research has shown replacement heifers born early in the calving season have the following advantages: they conceive early in the breeding season, they tend to have early born calves, their heifer calves tend to conceive and calve earlier, and their steer calves tend to have higher value carcasses. Managing heifers to calve early in the calving season programs them for productive lives including producing older, heavier calves and more calves during their lifetime.
One key aspect of successfully getting replacement heifers bred is their reproductive status at breeding. This is determined by reproductive tract scoring (RTS). Heifers are examined and scored based on reproductive maturity on a score of 1 to 5. RTS 1 is infantile, RTS 5 indicates a heifer has cycled and is reproductively mature. In the SMS program, this exam is done between 30 and 60 days prior to the start of the breeding season.
Our SMS database from 2010 through 2024 has data on slightly over 81,000 head of heifers. At the pre-breeding exam, approximately 2.5% of these heifers had a RTS of 1 or 2, meaning they had not yet reached puberty. It is interesting to note that the RTS 1 and 2 heifers had an average pre-breeding weight of 658 and 709 pounds respectively. RTS 3, 4, and 5 weighed an average of 772, 812, and 834 pounds respectively. We know RTS is influenced by age, nutrition and genetics, so any single or a combination of these factors could be the reason for the 176-pound difference in pre-breeding weight between the RTS 1 and 5 heifers.
The goal of keeping replacement heifers is for them to become pregnant. An earlier review of the SMS data base showed pregnancy to a fixed-timed artificial insemination (FTAI) protocol for RTS 1 heifers was 4%. RTS 2 had a FTAI pregnancy rate of 27%, 48% for RTS 3, 52% for RTS 4 and 53% for RTS 5. Nearly 43,000 heifers were included in this analysis.
Two clear points emerge from these data. If a producer really wants to emphasize selection pressure on reproduction, do a RTS exam before the start of the breeding season and cull RTS 1 and 2 heifers. This can save development costs on heifers that have a small chance of becoming pregnant during the breeding season.
Secondly, pay attention to the pre-breeding weights of heifers. A goal is to have heifers somewhere around 60% of their mature weight at breeding. If mature cows weight 1,400 pounds, 60% is approximately 840 pounds, so this should be your target weight at breeding. There are a variety of ways to get heifers to this target weight. If you have a large weight spread in your heifer selection pool, it would be cost effective to split the group into a heavyweight and lightweight group and feed accordingly in order to achieve the target weight at breeding.
If you have additional questions on heifer selection or management, contact me at schmitze@missouri.edu or by calling the Pettis County Extension Center at 660-827-0591.
