A frequent problem we see in reviewing herd records is a difficulty getting nursing, two-year-old heifers bred back for their second calf. Excellent research over the past decade or so shows that improving body condition score (BCS) in these heifers before they deliver their first calf is the most important factor in getting them bred back.

The first question we get when suggesting an improvement in precalving BCS to 6.5 is, “Won't that make the calves bigger and increase calving difficulty?”

Body Condition Is Key

Table 1 illustrates that while the birth weight may increase slightly (some studies show no difference) in first-calf heifers when the precalving BCS is improved, calving difficulty remains the same.

This study of 240 first-calf heifers in three states not only showed the “non-issue” of dystocia, but also points out how important pre-calving BCS is to the rebreeding rate.

Only 56% of heifers calving in a BCS 4 were rebred after a 60-day breeding season, while 96% of heifers in a BCS 6 were rebred in the same time frame.

Table 1. Body condition score (BSC) and reproductive performance of first-calf heifers
Body weight @ calving 744 825 933
Calf birth weight 64 67 71
Dystocia score 1.2 1.2 1.2
Percent showing heat
by days in rebreeding season
20 days 42 54 63
40 days 56 80 98
60 days 74 90 98
Percent bred back
by days in rebreeding season
20 days 27 35 47
40 days 43 65 90
60 days 56 80 96

Another way to improve total herd fertility is to breed heifers for a shorter period of time than you breed your cows. When heifers are bred for only 30-42 days (as opposed to 65 days for cows), the possibility of late-calving heifers is eliminated.

In our experience, a late-calving heifer has two fates in the herd — she continues to be a later-calving cow or she becomes an open cow. Neither option is positive for your herd.

As we examine the economics of breeding heifers for a shorter period of time, it becomes obvious why it's better to have her open as a yearling rather than as a two-year old.

To illustrate this point, examples A, B and C in Table 2 are simplistic scenarios that can occur with heifers retained for breeding.

Weight-Age Link

A basic factor often overlooked is that weaning weight mostly depends on the age of the calf. This puts even more of a premium on early calving.

When a shortened breeding season for heifers is first mentioned as a way to improve herd fertility, owners generally respond with a blank stare. The objection is typically: “A shorter breeding season equals fewer heifers bred, so how does this help our fertility?” After going through the economics, however, it totally makes sense.

Table 2. Scenarios for heifers retained for breeding
Example A
Data $
750-lb. open heifer value $600
Heifer calves first week of calving season
Heifer is rebred to calve 3/2002
Weaned calf weighs 500 lbs.
Value of cow $800
Value of calf $475
Total expenses 5/1/01 to 9/20/02 ($425)
Profit $250
Example B
Data $
750-lb. open heifer value $600
Heifer calves last week of calving season
Heifer is open
Weaned calf weighs 350 lbs.
Value of open cull cow $360
Value of calf $400
Total expenses 5/1/01 to 9/20/02 ($425)
Profit (loss) ($265)
Example C
Data $
750-lb. open heifer value $600
End of 42-day breeding season
Pregnancy check day — heifer found to be open
Heifer implanted and placed in feedlot for 90 days
Heifer weighs 1,175 lbs. and sells to slaughter for $825
Total expenses 5/1/01 to 11/1/01 ($195)
Profit $30

If your calving season is too long and/or not enough calves are born in the first 42 days (goal is 88%) of the calving season, these proven practices can help improve your herd's fertility.

Reference: Spitzer, JC, Morrison DG, Wettermann RP, Faulkner, LC. 1995: “Reproductive Responses and Calf Birth and Weaning Weights as Affected by Body Condition at Parturition and Postpartum Weight Gain in Primiparous Beef Cows.” Journal of Animal Science 73:1251-1257.

Mike Apley, DVM, PhD, is an assistant professor of beef production medicine at Iowa State University in Ames. W. Mark Hilton, DVM, is a clinical assistant professor of beef production medicine at Purdue University in West Lafayette, IN.

Fertility Builders

Here are some additional measures we suggest to improve heifer fertility:

  • Have your herd health veterinarian perform reproductive tract scoring on heifers 30-60 days prebreeding.

  • Vaccinate heifers with a modified-live IBR-BVD-Lepto vaccine at least 30 days prebreeding. This should be part of a comprehensive vaccination program in which this is not their first exposure to this vaccine.

  • Choose high-fertility, crossbred heifers for replacements.

  • Use a synchronization program to get more heifers bred the first few days of the breeding season.

  • Breed heifers 14-21 days before breeding cows so heifers have more “lag time” between calving and rebreeding.