Benchmarks for Evaluating Reproductive Performance
Part 2
Transcript of Select Sires' Reproductive Moment Program
on DairyLine Radio, Which Aired May 13, 2004
with Ray Nebel
extension specialist and professor of reproductive management,
Virginia Tech
On this week’s Reproductive Moment we continue our discussion from last week: Benchmarks for Evaluating Reproductive Performance. We are with Ray Nebel, extension specialist and professor of reproductive management at Virginia Tech.
Ray, what benchmarks should producers be using on a herd level to monitor reproductive performance?
When we evaluate reproductive performance, there are different areas at which we could normally look. Days-open is from the time that the cow calves to the time she conceives. Our goal, in general, is 140 days-open, hence a thirteen and a half month calving interval. There is also an intervention level, where we need to do something, and that number has been set at 175. That directly relates to calving intervals. Calving interval takes that 140 days-open and adds the gestation number, or how long she is going to be pregnant. In cattle, the gestation number is 280 days. So, 140 days-open plus 280 days gestation gives us our total days from when she calves to when she calves again, 420 days, and that is the calving interval. Now, most of us think of months. Therefore, we divide the total number of days by 30.4, which is the average days in a month. Using our 420 day example, that comes out to roughly 13.5 months. So, 140 days open equals a 13.5 month calving interval:
140 days-open + 280 days gestation = 420 days gestational interval / 30.4 avg. days in a month = ~13.5 months
What are the other parameters that constitute days-open?
- When do we start days to first-service?
- How well do we get the cow pregnant: conception rates?
- Heat detection.
These three combined go in to factor in days-open. Days-open is a general goal and the three that determine that are when do we start? The goal there would be 75 days. We don’t want any cow to be bred past 100 days. We want them all bred prior to 100.
The goal for conception rate would be about 45 percent, so if we breed 100 cows we want 45 of them pregnant. We definitely want to be above 30.
Heat-detection is probably one of our most critical areas today, and the goal I have is to catch six out of ten. If you are catching less that four out of ten, then you need to beef up the program.
Ray, if you could pick one category, and only one, which one would it be?
Historically, it has been days-open. But, days-open doesn’t really tell you what you need to prove. So, in the last five years the category that has really gained a lot of popularity, which we really didn’t touch on, is called pregnancy rate, because it combines the two most important factors, conception-rate and heat-detection. Pregnancy rate is the conception rate times the heat-detection. It really tells you how fast cows are getting pregnant.
So, if we had a 45 percent conception rate and 60 percent heat-detection, it says every 21 days, the length of the average estrus interval, we are getting roughly 27 percent of the cows pregnant. It asks: How many cows are eligible to be caught in heat? And, of the cows caught in heat, how many get pregnant? So, it defines the speed of getting cows pregnant.
That is really the most important figure because it changes every 21 days. When we change something on the farm, we can monitor it almost immediately. Days-open and calving intervals take so long to see a change because they are yearly averages. So, when we make a change, we almost forget what we did by the time we can find out if it improved anything.
There is a decline in reproductive performance in today’s dairy herds because of the demands we are putting on them as far as milk production. But, the biggest factor is good management: knowing our cows, doing a good job and looking at the details. It is interesting that the highest-producing herds also do the best jobs toward reproduction. So, that negative effect of production and reproduction is somewhat contradictory. But, what it says is that good managers that get more milk are also good managers who do a better job at reproduction.
Ray Nebel, extension specialist and professor of reproductive management at Virginia Tech.
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