Source: Manitoba Agriculture, Food and Rural Initiatives
A lot of fuss is made in beef management circles about short calving seasons and high conception rates. A 95% conception rate sounds good, but the economic effect of when in the breeding season the cow is bred, and the resulting calf weaning weight once the calf is on the ground is considerable and worth looking at.
It makes sense that calves born early in the calving season tend to have heavier weaning weights than those born later, as they are older at weaning time. On average (assuming a calf growth rate of 2.5 lbs/day) each time a cow is not bred during a heat cycle when she is in the breeding pasture costs about 52 lbs of weaned calf per cow.
Table 1 shows the effect of date of birth within the calving period and the weaned weight of the calf assuming a gain of 2.65 lbs/day from birth to weaning, and that all calves are weaned at 200 days from the start of calving. So what happens if we take this information and apply it to a 100-cow herd? First, we must define some terminology. For ease of understanding, we split the breeding season into 21 day periods (one heat cycle). If your breeding season is 63 days, you have three 21 day periods, and a breeding season of 84 days – four heat periods and so on.
Ideally, we would like to see a calving distribution of 70-20-10. This means that 70% of the cows calved in the first 21 days (day 0-20), 20% in the second 21 days (day 21-41) and 10% in the third 21 days (day 42-62).
If for example the bull is lame or sick for part of the first 21 day period, and unable to breed for part of that period, then does very little in the second 21 day period, but picks up and does the job for the last 42 days, you would expect a calving distribution as follows: 40-10-40-10. Is this a problem? Since all the cows were bred in 83 days, yes – take a look at the economic effect!
Table 1. Calf weights and values by calving period
| Period in Which the Calf is Born | Weaning Weight (lbs) | $/CWT | Value of Calf |
| 0-20 days | 618 | $101 | $624 |
| 21-41 days | 560 | $100 | $560 |
| 42-62 days | 502 | $100 | $502 |
| 63-83 days | 444 | $98 | $435 |
Using the values and prices we calculated in Table 1 and applying them to the herd gives an indication of the economic effect of calving distribution (see Table 2).
A herd with a calving distribution of 70-20-10 had 59,480 lbs of weaned calf valued at $59,912 (using prices as in Table 1). The herd with a calving distribution of 40-10-40-10, even though all the cows got bred in 83 days, only had a weaned calf weight of 54,840 lbs, for a total value of $54,998. You can see that any factor that affects breeding and calving distribution as shown in this example would result in a net economic effect of $4,914.
Table 2. Bottom line effect of two calving distribution scenarios
| % Calves Born in Each 21-Day Period | Pounds of Weaned Calf Produced | Value of Weaned Calves |
| 70-20-10 | 59,480 | $59,912 |
| 40-10-40-10 | 54,840 | $54,998 |
| 25-50-15-10 | 55,420 | $55,485 |
So now that the economic effect of calving distribution is clear, how can the cow herd be managed to ensure that optimum breeding takes place and that we end up with as close to a 70-20-10 calving distribution as possible.
Cows
Nutrition programs and cow condition will have the greatest effect on how soon the cows get settled after bull turnout. Ensure that your cows are getting all the nutrients they require.
Heifers
First calf heifers still have some growing to do and need some extra attention to ensure that they are in adequate condition for rebreeding. Separating the heifers and feeding separately from the main cow herd ensures that the heifers get the nutrients required for growth and rebreeding.
The Bull
Ensure that your bull is physically sound – sound feet and legs, adequate testicle size, etc. Most importantly, ensure that your bull has been evaluated by a professional for breeding soundness (including semen testing).
Ensure proper bull to cow ratio. For example, 15 cows for a yearling and 30 for a mature bull.
Herd Health
The cow herd should be properly vaccinated prior to the breeding season. The most important vaccinations include IBR/PI3/BVD/BRSV. All breeding females should be vaccinated every year. Heifers will require two doses, one at four to six weeks and another two to three weeks prior to breeding. The cows will just need a booster two to three weeks prior to breeding. BVD is the most common cause of infertility/abortions in beef cattle. Consult your local veterinarian for additional vaccinations that may be recommended in your area.
Most importantly, take the time to go over your historical records. If you see a consistent calving pattern that you are not satisfied with take the time to evaluate your program. It can help you stay profitable in tough times!
