Pregnancy Rates (Part Two)
Transcript of Select Sires' Reproductive Moment Program
on DairyLine Radio Which Aired Feb. 17, 2005
With Ray Nebel,
Extension Specialist and Professor of Reproductive Management,
Virginia Tech
Ray, we continue our discussion this week on pregnancy rates.
We talked about pregnancy rate last week, and how its value is becoming more and more important because it tells you what is going on in the herd as far as getting cows pregnant. There are two big areas in pregnancy rate.
One is first service pregnancy rate, or how fast we get first service accomplished in getting cows pregnant.
The second one we will talk about is repeat services and we will talk a little bit about resynchronization.
But, if I go back to first service, it was roughly ten years ago that the data first came out on ovulation synchronization, commonly known as Ovsynch. This kind of revolutionized the way we breed cows, at least in the dairy situation, in that we now can set up cows so that first service can occur when we want it to, and we are not depending on the cow to tell us when she wants to be bred. Most people would look at an interval of between 60 to 75 days as when they would program for first service. The pregnancy rate we would expect on first service is usually higher than pregnancy rates on following services, the reason being that there is a higher population of normal cows in the population as a whole. In every herd there is a percentage of cows that is going to be harder to breed, or "hard breeders". If we take a herd of 200 cows, that might be only about 10 percent, or 20 cows. So, at first service we have 180 cows that are pretty much normal and we have 20 problem cows. But, in second service, after we have gotten say 35 percent of them bred, and the pregnant cows are removed from the breeding population, those 20 cows then become a higher percent of the number of cows eligible to be bred (non-pregnant cows). So, we expect second and third service pregnancy rate to be slightly lower because of this effect.[*]
In the first pregnancy rates, the goal is to be between the mid-twenties or mid-thirties, while the overall pregnancy rate that we are shooting for is 20 percent. If we achieve that, then we are doing well.
So, you are talking about the second and third service being lower than the mid-twenties?
That's right. Usually what we see is second and third service to be somewhere around 12 to 15, because now we are dependant on heat detection. On first service it is really a service rate. We are programming for every cow to get bred within a specific time period, so we have got to eliminate heat detection, and it is really service rate times conception rate. Every cow is going to be programmed. For first service, if we get 35 percent of them pregnant, then that leaves 65 percent to recycle, so that now we have to detect those cows in heat and get them serviced. So, 100 percent of the time, I have not seen a herd yet where their second service rate is higher than their first service pregnancy rate.
You have conception rates, cow nutrition, semen handling and insemination procedures all kind of rolled into that.
That's right. That is why Ovsynch has become more popular, because we can easily control it. Whereas, on conception rate, as you mentioned, insemination procedures, cow comfort, nutrition and environmental effects are some of the things that go into affecting conception rate. And so much of it is out of our control, such as environmental effects, or sometimes the nutrition as far as what that cow is specifically eating. It is very hard to control conception rate. We have much more control over service rate, especially at first service.
We will continue with more next week with Ray Nebel, Extension Specialist and Professor of Reproductive Management at Virginia Tech.
(*) See an example of why this is true.
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