Excellent herd reproductive performance is one of the most important factors to maximizing herd profit. Table 1 shows how much net return per cow increases with increasing pregnancy rates. The reason is that improving pregnancy rate affects many areas of the dairy. These are the reasons higher pregnancy rate improves herd profit:
- Keeps days in milk (DIM) in the optimum range. Ideally DIM should be 150 to 170. Lower DIM means a higher percent of cows are in early lactation resulting in higher milk production. For every 10-day reduction in DIM, milk production will increase 1.2 to 1.7 pounds per cow per day. Whole herd feed efficiency will increase because of the higher milk production.
- Less reproductive culls. Culling cows because they do not become pregnant in a timely manner is the biggest reason for culling in most herds. Decreasing the number of cows culled because of reproduction allows producers to cull more cows for low production.
- Increases in the number of calves born. This results in more bulls to be sold. The extra females improve replacement option flexibility such as culling low genetic heifers or increasing whole herd cull rates.
- Less over-conditioned cows at calving resulting in lower incidence of transition cow disorders.
- A lower percent of cows with a high number of days dry.
Every herd should set a goal of having a pregnancy rate of 20% or greater. Many herds are achieving pregnancy rates of 23 to 25%. By understanding the factors that affect pregnancy rate we can examine our records and develop a plan for improvement. Pregnancy rate is simply the percent of cows eligible to be bred that actually get bred multiplied by the conception rate of those inseminations in any 21-day period of time. A 21-day period is used because that is the average length of a cow's estrus cycle.
Here is an example:
- Fifty open cows are eligible to become pregnant (beyond the voluntary waiting period)
- Thirty cows actually are inseminated (30/50 = 60% submission or service rate)
- Twelve of these cows become pregnant (12/30 = 40% conception rate)
- For this 21-day period, the pregnancy rate is 12 pregnant cows/50 eligible cows or 24%
- Another way to calculate the pregnancy rate is 60% x 40% = 24%
First let's examine the factors that affect service rate. The list is not very long. The biggest factor is how fast cows are bred after the end of the voluntary waiting period. Improved heat detection or a timed AI program will increase this. The reason timed AI programs often improve pregnancy rate is that 100% of cows are bred shortly after the end of the voluntary waiting period. The next biggest factor is the ability to identify and re-inseminate open cows rapidly. The best herds have systems in place that identify open cows through estrus activity at the first estrus cycle following insemination. Some herds do frequent herd checks to identify open cows and re-enroll them in a synchronization program. It is difficult to achieve high pregnancy rates without re-inseminating open cows in a timely manner.