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Selecting replacement heifers shouldn’t happen at weaning

Jordan Thomas and Carson Andersen for Progressive Cattle Published on 25 August 2020
Replacement heifers

Selection of replacement heifers should happen at pregnancy diagnosis, not at weaning. Not every heifer that gets bred is a profitable investment to retain.

Heifers that conceive later in their first breeding season calve later in their first calving season. As a result, they are more likely to conceive later in the next breeding season or fail to conceive at all. Long-term research efforts have made this clear: Heifers that conceive early in their first breeding season stay in the herd longer, wean more total calves due to their longer productive life in the herd and even wean heavier calves each year.

If she isn’t an early-conceiving heifer, she shouldn’t be considered as a potential replacement. That means replacement heifer selection has to happen at preg check. To drive the point home, we like to refer to the heifer calves you retain after weaning as replacement heifer candidates. That’s all they are at that point: candidates that could potentially join the herd as replacement females. So what, if any, criteria should you use in choosing heifer calves to retain and develop as replacement heifer candidates?

Should all heifer calves get a chance at breeding?

Let’s be honest: The visual appearance of a heifer influences our selection decisions way more than it should. That’s single-trait selection. We need to do better than that. Think through the bigger picture instead of pulling out the biggest, prettiest heifer calves at weaning as potential replacements. Most of us need to retain a certain number of heifers in order to maintain herd inventory and replace culled cows. The more heifers you develop, the more selective you can be about which heifers are retained. Being overly restrictive at weaning and developing too few heifers leaves you stuck with what you get at the end of the breeding period.

The general recommendation to develop a large proportion of your heifer calf crop as replacement heifer candidates is wise. That said, it is also a very rare situation in which every heifer calf should be a replacement heifer candidate. We can easily identify some heifers with low likelihood of becoming pregnant early in the breeding season. Why on earth invest in a development and breeding program for them? We have several opportunities to be more cost-conscious and shuttle heifer calves with poor reproductive potential down a more profitable path.

Should age of a heifer influence whether she should be considered as a replacement heifer candidate?

Heifer calves born early – early in your calving season, not necessarily early in the calendar year – are more likely to attain pregnancy early in their first breeding season. That’s clear from classic research published in the 1970s and observed in the real world every day. Retaining late-born heifer calves as potential replacements just doesn’t pay.

Here is a good rule of thumb: consider developing a heifer calf only if it was born in the first half of your calving season. For example, if you use a 90-day calving season, only consider developing heifer calves born in the first 45 days. That should still be well over half of your heifer calves (if not, we have some other problems to address). This is less of a consideration if you already manage for an ultra-short calving season in your cow herd – for example, something like 30 days. But for more typical herds with calving seasons that are 60 days or longer, you probably do not want to waste time and money developing later-born heifers.

Should reproductive tract scores or pelvic measurements be a deciding factor?

A pre-breeding exam consisting of a reproductive tract score and pelvic measurement can help you avoid unnecessary risks or expenses. Unfortunately, reproductive tract scores and pelvic measurements need to be done closer to the start of the breeding season to be very informative, so a pre-breeding exam is not a tool to screen heifers at weaning. It is, however, a tool to avoid spending further time and money on development and breeding of heifers that aren’t likely to be profitable.

A reproductive tract score is a direct assessment of the pubertal status of a heifer. Your veterinarian will palpate the reproductive tract about four to six weeks before the start of the breeding season, evaluating the size of the uterus and the structures present on the ovaries. In addition to determining whether the heifer has attained puberty, this is a good opportunity to identify any heifers that have already become pregnant or have an abnormality (incomplete reproductive tract, ovarian cyst, etc).

Reproductive tract scoring will have a cost, but the idea is to identify heifers that are poor candidates and avoid incurring additional development, breeding and health costs on these heifers. Many producers also value the information they get about the group. For example, if less than half of the heifers are cycling (reproductive tract score 4 and 5), there may be some nutritional adjustments that can be made.

Pelvic measurements are another screening tool to consider, especially if you have a history of some calving difficulty in your heifers. Hard pulls, cesarean sections and death loss are all risks you want to take out of your program. If your veterinarian tells you to cull a heifer based on an abnormally small pelvic area, do it. It’ll avoid some major risks, and that’s also one heifer you can save further development, breeding and health costs on too.

How short should the breeding season be for my replacement heifer candidates?

The length of the breeding season you should choose for heifers really depends on your goals and your marketing opportunities for bred heifers. If you have a profitable marketing opportunity for later-conceiving bred heifers, by all means, use a fairly long breeding season and generate the maximum number of pregnant heifers possible. Just have a pregnancy diagnosis performed relatively early to accurately determine fetal age among the earlier-conceiving heifers. A nice time point for that is 90 days after the start of breeding. Use that information and be sure all later-conceiving heifers are marketed. Depending on the market and your resources, you might even consider calving those out and marketing the later-calving pairs.

If you don’t have a profitable marketing strategy for later-conceiving bred heifers, here is a wild question: Do you really want a heifer that doesn’t conceive early to conceive at all? If she is more profitable as an open-feeder heifer than as a later-bred heifer, use as short of a breeding season as you can stand. It is a huge benefit to the long-term performance of your cow herd. A 30-day breeding season for heifers doesn’t sound radical to me at all.

Even an A.I. program with no natural service cleanup is something to put a pencil to. There may not be such a thing as “too short” of a breeding season for heifers; it just comes down to the cost structure of your program and your marketing strategy. Short breeding seasons put maximum pressure on your females for fertility as well, but that’s another discussion for another time.  end mark

PHOTO: Being overly restrictive at weaning leaves producers with too few replacement candidates. Instead, producers should consider developing a large portion of their heifers that can later be weeded out. Photo by Lynn Jaynes.

Carson Andersen is a graduate research assistant at the University of Missouri.

Jordan Thomas
  • Jordan Thomas

  • Assistant Professor – State Extension Specialist in Beef Reproduction
  • University of Missouri
  • Email Jordan Thomas

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