Conception Rates vs. Pregnancy Rates
(Part One)
Transcript of Select Sires' Reproductive Moment Program
on DairyLine Radio Which Aired June 22, 2006
With Ray Nebel,
 Select Sires’ reproductive solutions specialist
Ray, this week we are talking about Conception Rates versus Pregnancy Rates. What is the difference between the two?
Good question, Bill. I know a lot of dairy producers are getting confused. Conception rate is a term that we have used for the last 50 years. It relates to how many breedings produce how many pregnancies. So if we breed the cow three times, and we produce one pregnancy, it is about a 33 percent conception rate, or 3.3 breedings per conception. But, there is no time element involved, so over what period? Pregnancy rate actually multiplies the conception rate times the heat detection. Pregnancy rate tells us how fast cows are getting pregnant. If we want to start breeding at 60 days, the first heat period should be about 81 days. What percent of the herd has gotten pregnant? We might have a 50 percent conception rate during that time, but if we only catch half the cows that means we only have a 25 percent pregnancy rate. It is a little bit confusing. Conception rate has no time interval, whereas pregnancy rate has a time interval and the actual efficiency of getting the cow pregnant.
Let’s talk about conception rate list, starting with the lactation group.
When we look at the conception rate, there are a lot of things that could influence our efficiency of getting cows pregnant. When we look at the records, the first thing we look at is lactation group, or parity. First-lactation cows, when they were heifers, came into the herd, and it depends on whether they are grouped separately or grouped with older cows. The second-lactation group is usually a unique group because those animals in first lactation were probably still growing. They were adapting to the milking facility, so you had compensatory growth, plus lactation. A lot of times we call it sophomore slump. The second-lactation group a lot of times shows up to be the lowest-conception-rate group. Then we usually lump the older cows, or three-plus lactations, together. So, in a lactation group we look at first, second, third and greater to see if there are any differences. If there are, we then can pinpoint where in management we need to make changes.
How about the service number?
Usually our first service -- our first chance of putting semen in the cow -- is where we get our highest conception rate. If we take 100 cows, we have, let’s say, 80 normal cows and 20 "problem" cows. Say we get half of those normal cows pregnant. Now we have 40 normal cows and 20 problem cows. The problem cows have become a lot higher percent of the total [breeding population]. Usually, on second service, conception rate goes down from first service. Now, on some farms today we see a lower first-service conception, and to me that says the cows were not ready to breed when we started our first service at the beginning of our breeding program. Looking at service numbers can tell us if we are on target of when we want to start, and it gives us an idea of how well we are doing. If we have a lot of cows that go beyond four services it can identify “do we have a group of real problem breeders?”. So service number also tells us something about what is going on: Are we starting too early, how many problem cows do we have, and is there a group that we really need to work on?
Ray Nebel, senior reproduction and herd-management specialist at Select Sires.