Troubleshooting Reproductive Records to Determine Potential Problems
Part I. The Nuts and Bolts.
by Allen J. Young
Extension Dairy Specialist

Reproductive records can either be the easiest or the hardest to analyze because they are influenced by so many factors such as producer goals, environment, nutrition, inseminator competency, heat detection abilities, disease, and more.

In order to determine what the problem might be, it is necessary to know where to look. This means that you should be looking at numbers which you can control. If you can't control the number, you can't change it. Of all the numbers monitored for reproduction, there are only three that can be directly controlled by the manager: voluntary wait period, heat detection rate and conception rate. All other variables such as days open, days to first service, and, ultimately, calving interval (a number which you can't control directly) are derived from these basic numbers.

The voluntary wait period (VWP) is the point after calving at which you will breed a cow if she comes into heat. Many producers set this value for 60 days, but if cows are on feed, gaining weight and healthy, moving it back to 50 days will provide you with more opportunities to get a cow bred back. Regardless, once you set a voluntary wait period, stick to it! The calculation and interpretation of many reproductive parameters monitored on a dairy are influenced by this value.

Heat detection rate (HDR) is one of the hidden problems on most herds. There are several ways to calculate this number. I have included the two that I use. Equation 1. is calculated for you every month on your herd summary; equation 2. is not. The big difference between the two equations is that one measures what you plan to do (1), the other what you actually did (2). The two values should be reasonably close if you are adhering to your VWP.

1. HDR = (SPC x 21) / ((DO - VWP) + 10.5)

2. HDR = (SPC x 21) / ((DO- DFS) + 21)

In the equations, SPC = services per conception; DO = days open; VWP = voluntary wait period; and DFS = days to first service. The results of these calculations will tell you how many of the potential breedings you actually caught and serviced. Heat detection rates often run as low as 30% or as high as 75%. A reasonable goal is to catch at least 65 to 70% of your breedable cows in heat.

Conception rate (CR) can be affected by many things such as nutrition, sanitation, temperature, timing of insemination, disease, etc. Usually when there is a conception rate problem, it is very evident from the records. The goal here is to maintain at least a 50% conception rate or better (2.0 SPC; CR = 1/SPC).

The following table illustrates how these three control points affect each other. In order to maintain a 12.5 month calving interval for 90% of the cows when conception rate is 50% and heat detection rate is 70%, the voluntary wait period must be set at 51 days. Using the same conception rate, but a 40% heat detection rate, the voluntary wait period would have to be 18 days, a ridiculous goal. Therefore, heat detection must be improved to achieve your goal of a 12.5 month calving interval. Recognize that Days Open is controlled by these there factors. Likewise, the calving interval is just Days Open + 280 days.

Table 1. Voluntary wait period at which breeding must begin in order to have 90% of the cows averaging a 12.5 month calving interval.

Heat Detection
Conception rate (%)
40 50 60 70
  Voluntary Wait Period (DIM)
80 47 57 64 69
70 40 51 59 65
60 31 44 52 59
50 18 34 44 51
40 -1 18 31 40

Finally, it is useful to reemphasize that the goal of any dairy is to get cows pregnant. While that seems like a given, it is important to restate it because sometimes we lose sight of that fact when looking at reproductive records. This value is actually computed for you each month on your herd summary. The calculation is straight-forward and is as follows:

Pregnancy rate (PR) = CR x HDR.

For example: using average values of herds in the U.S., a herd with a 50% CR and a 50% HDR would have a PR of 25%. It is therefore a reasonable goal to have a PR of at least 25%.

Set reasonable goals for a voluntary wait period, heat detection rate, and conception rates. Make a chart of these two indices and plot them each month to monitor your progress toward goal achievement. Post the chart in a conspicuous place where everyone will know what the goal is and how close you are to achieving it. You'll probably find that more people will contribute toward making that goal a reality.

In the next issue we will work through the reproductive records of a herd and show you how to apply the principles discussed to monitor the reproduction of that dairy. If you have any questions about the information in this article, please feel free to contact me at (603) 797-3763. ©