Select Sires

Benchmarks for Evaluating Reproductive Performance
Transcript of Select Sires' Reproductive Moment Program
on DairyLine Radio, Which Aired May 6, 2004
with Ray Nebel
extension specialist and professor of reproductive management,
Virginia Tech

This week’s Reproductive Moment is with Ray Nebel, extension specialist and professor of reproductive management at Virginia Tech. This week we are talking about benchmarks for evaluating reproductive performance. Ray, I have been hearing that reproductive efficiency of today’s dairy herds isn’t what it used to be.

Bill, that is an interesting comment, because, in the popular press most dairymen would tell you it is harder to get cows pregnant today than they remember 10 to 20 years ago. A big part of that is our production level today. Twenty years ago the average cow probably averaged 15,000 pounds per lactation and now it is 20,000 pounds per lactation. Along with that, production doesn’t come without an expense. Part of that expense has been that it is a little bit harder to get those cows pregnant.

So, as production goes up, it takes away from reproduction?

What happens hormonally, now that we know a little bit more about the physiology, is that she partitions nutrients for that increased milk production, but that partitioning of nutrients takes away from the building-blocks that we need for reproduction. One of the most critical hormones, that most dairymen probably have not heard of, is insulin growth factor one. It is very similar to growth hormone, and that is one of the building-blocks that we need to increase the folliculigenisis, which is going to supply the eggs, or ovum, that is going to be fertilized when we breed artificially.

What about the direct effect with recumbent BST?

Good question. RBST, or POSILAC™, has got a negative connotation as far as its effects of reproduction. But, it is interesting that herds that use POSILAC increase milk production, and along with that increased milk production we can see a decline in reproduction. It is not a direct effect, in that what is happening is that, again, when we have a higher demand for nutrients, we need a higher dry-matter intake. In herds that can meet that higher demand for nutrients in dry-matter intake, we see no detrimental effect. In reverse, there have been some studies, and we have conducted one here at Virginia Tech, that show if we give supplemental BST at time of breeding, we can actually increase conception rates. That is because it gives an initial shot, or increase, in the circulating levels of insulin growth factor. So, the negative is on a herd basis: can we increase the dry-matter intake to meet her demands? But, a positive is: we are increasing, or supplementing, her own natural hormone levels to increase conception. It is actually a two edged sword.

What is your advice for producers to keep track of all this?

I have a saying, "You don’t know where you are going until you look where you’ve been." We really need to look at past performance and what changes we are going to make. I would make a recommendation that where we need to be at 135 days open really depends upon where we are today. If I go to a herd that is 200 days open, we are not going to change to 135 overnight. But, if I go to a herd that is 150 days, then we can make that recommendation. We need to know where we are today, and set some guideposts of where we want to be. It is critical that we have the records, so we can use them to set goals for where we are going.

Ray Nebel, extension specialist and professor of reproductive management at Virginia Tech.

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