Judging Sire Fertility
Transcript of Select Sires' Reproductive Moment Program
on DairyLine Radio Which Aired May 18, 2006
With Ray Nebel,
 
Senior Reproduction and Herd Management Specialist, Select Sires Inc.

Ray, this week we are talking about judging sire fertility, and that can be a bit challenging at times.
You’re right, Bill, and the big problem is binomial distribution, which means you’re either going to be pregnant or not pregnant. So it is either yes or no, and the outcome of that, even though we usually have more no’s than yes’s, the average fertility in the US dairy herd is around 35 percent, so roughly a third of the time the cow is going to get pregnant and two thirds of the time she’s not. Even in a large herd, if you bred 100 cows to one bull and 100 cows to another bull, that difference between those two, to say that they are significantly different, would have to be about 15 percentage points, so that rarely occurs that we breed enough within a herd to get a within-herd comparison of two bulls, but many producers, especially of large herds, are trying to do this and I think they are going to come up with some erroneous type of conclusions.

What may be helpful is this new summary that is coming out in May, the National Sire Summary.
That’s right. For the first time the US Department of Agriculture in Beltsville, Maryland, they run a genetics sire summary four times a year, and this coming May will be the first time they do a national fertility summary. So they have taken information from across the country from all the record processing systems, they are looking at the sire data for conception or no-conception to really get a handle on whether we can pick between bulls for fertility differences. We got a little bit of a preview, and there is not as much difference as most producers would claim and I think, again, because we see it is very hard to do this within the herd as we talked about. Hopefully it will give us some information that we can bring to the producers to show maybe the really, really high bulls and low bulls, with probably 80 to 85 percent are going to be there in the middle and have very little difference at all.

You mention this is coming out in May?
That’s right, the first one will be out this May in the May sire summary. There is a sire summary that comes out in February and the next one will come out in May, and the May sire summary with the genetics information that comes out will also have the fertility sire summary for the first time.

So Ray, what do you expect the range to be? What kind of variation do you think we are going to see in the sire fertility that we can pick from?
The range in fertility for the sires, if we take from the lowest to the highest, we are talking about 15 percentage points, but what is interesting is that about 80 to 85 percent of the bulls are going to be plus or minus three; so, three points below that to three points above average. We are only going to be able to pick up a very few really high fertility bulls and very few low fertility bulls. So what bulls to stay away from and maybe a few bulls to pick when we are really having a hard time.
Thank you, Ray. That is Ray Nebel, Select Sires Reproduction Solutions specialist.