Bovine Reproduction: Improving Pregnancy Efficiency in Your Herd

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During your annual pregnancy check of your cows, you might wonder why so many of them are open.  Some of you may not be terribly worried about your current pregnancy rate, but did you know that increasing your pregnancy rate from 87% to 95% can increase your profits by $127/calf?  A single mating between a fertile cow and a bull will result in a live calf 60-70% of the time.  Most calf losses occur during very early pregnancy (by day 14) and the cow cycles through again normally. Using a 65-day breeding season, cows that cycled in the first 3 weeks of the breeding season can re-cycle by day 42 in the event that they lose an early pregnancy from the first mating and again by day 63 if they lose a second pregnancy.  95% of cows that have 3 opportunities to get pregnant (65-day breeding season) will give birth to a live calf.

The mathematics demonstrate the importance of having most of your herd calve early in the breeding season so they have multiple opportunities to get pregnant before the breeding season ends.  Because a bovine pregnancy lasts 283 days, a cow/heifer must rebreed within 82 days to maintain a yearly calving interval.  The average length of time before a cow starts cycling after calving is 40-60 days.  Therefore, if cows start calving 30-40 days after the start of calving season, it is unlikely that they will be cycling at the beginning of the breeding season.  First calf heifers take an average of 80-100 days to start cycling after calving.

How do I get my cows to calve early in the breeding season?

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In order to obtain higher pregnancy rates, it is important for your herd to be “front end loaded,” meaning 65% of your cows are calving in the first 20 days of the calving season.  To ensure that your cows will be cycling, mature cows should have a minimum body condition score of 5 on a 9-point scale at the beginning of the breeding season.  The pregnancy distribution that is currently in your herd is likely the pregnancy distribution that you will see the following year.  Mature cows generally calve at the same time of year every year, and it is very difficult to move them ahead.  Therefore, a heifer replacement program is necessary to improve your pregnancy distribution and take steps toward having a herd that is “front end loaded.” Because a bovine pregnancy lasts 283 days, a cow/heifer must rebreed within 82 days after calving in order to maintain a yearly breeding interval.  If the breeding season starts on the same day as the previous year, the breeding season will start 63-82 days postpartum and end 123-142 days postpartum for cows that calved in the first 20 days of the calving season.

Heifers should have a body condition score of 6 out of 9 at the beginning of the breeding season.  Most heifers reach puberty at 13-15 months of age.  As stated above, first calf heifers take 80-100 days to start cycling following calving.  If you bred your heifers at the same time as your cows the year before, they must rebreed within 82 days to maintain a yearly calving interval, and the majority of them will be unable to do that.  In this case, some of your heifers may have 1 or 2 opportunities to be bred during the breeding season, but will not get a full 3 breeding opportunities and this will increase the proportion of cows calving toward the end of your breeding season. Therefore, it is necessary to start the breeding season of your heifers 42 days prior to your mature cow breeding season to ensure that your heifers will be cycling at the same time as your cows during the next breeding season.

Another important element to improving your pregnancy distribution is culling cows or heifers that are not getting bred in a timely fashion and replacing cull cows with fertile heifers.  You will not achieve desirable profits or pregnancy efficiency in your herd by continuing to feed and invest in animals that are not reproductively sound.

Why can’t my cows get bred at the beginning of the breeding season?

The reason for low pregnancy rates in the first 20 days of the breeding season include: inadequate numbers of females having fertile estrous cycles at the beginning of the breeding season, the bull was unable to deliver adequate amounts of fertile semen to the reproductive tract, or a number of infectious and non-infectious causes prevented or ended the pregnancy (toxic plants, genetics, environmental stress, bacterial disease, viruses, fungi, yeast, venereal disease, the list goes on).  It is very important to have your veterinarian evaluate the herd in these instances to better determine the cause of low pregnancy rates in your herd.  There are several disease, husbandry, or nutritional factors that need to be assessed in order to implement change.  It is also important to have a breeding soundness exam performed on your bull annually before the breeding season.  New bulls should also be tested for Tritrichomonas foetus.

Summary

In other words, to have a herd that is truly “front end loaded,” the heifer breeding season has to be started 42 days prior to your cow breeding season.  Using a replacement heifer program such as this could take up to 5 years to change your pregnancy distribution to 65% in the first 20 days and increase your pregnancy rate up to 95%.  While it may take a few years, as stated above, studies have shown that increasing a herd pregnancy rate from 87% to 95% can increase the total earnings/calf by $127.

Pregnancy efficiency is vital to beef cowherd profitability.  The best way to do this is by having a high percentage of your cows calving in the first 20 days for the calving season, and having a relatively short breeding season.  In order for this to happen, your cows and heifers need to be cycling at the beginning of the breeding season, your bulls need to be fertile and physically able to mate cows, and no diseases are causing pregnancy loss.  Nutrition, male and female reproductive soundness, genetics, and husbandry can all negatively impact your pregnancy.  Allow your veterinarian take an active role in helping to manage your herd to ensure the highest pregnancy rates and increase your profits.

Resources

1. Bob L. Larson, DVM.  Kansas State University  “Cattle Reproduction: What we want/expect.”  MVMA Convention 2013

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