Reproductive Management Genetic Tools to Help
Transcript of Select Sires' Reproductive Moment Program
on DairyLine Radio Which Aired July 22, 2004
With Dr. Nate Zwald
University of Wisconsin, Madison
This week’s Reproductive Moment is with Dr. Nate Zwald, who just recently completed his Ph.D. in dairy cattle genetics from the University of Wisconsin, Madison. He is here today to discuss how we can breed healthier cows. Dr. Zwald, we now have new genetic tools to help, what specifically are those tools?
There are five different traits that are now genetically evaluated to directly measure health and fitness in dairy cattle. Productive life is the measure of how long a cow lives; somatic cell score is a measure of mastitis resistance; and then calving-ease. These traits have all been available for over 10 years. But, two new fitness traits have recently been started to be evaluated by Animal Improvement Programs Laboratory, a section of USDA.
The first one is called maternal calving-ease. This trait evaluates how easily daughters of a particular sire calve. The second, and perhaps most interesting one, is daughter pregnancy rates, which is a measure of how quickly daughters of a particular sire get bred back after calving.
How do they go about selection? Do they just choose one trait?
Certainly not just one. When you think about it, all of these traits are actually quite related to each other. First of all, if a cow has a difficult calving, she also often is more difficult to get bred back. Furthermore, if she doesn’t get bred back quickly or in a timely manner, she is more likely to leave the herd early. Of course, incidence of mastitis negatively affects reproduction and longevity, so really we have a group of traits that can all be selected for to improve the reproduction and longevity of cows. The way to incorporate these into your breeding program is through an index like net merit, which includes each of the five traits that we discussed.
Doesn’t the low heritability of these traits make progress slow?
The low heritability of these traits does make genetic progress slower than other traditional traits, but that doesn’t mean we cannot make progress. If we look at some popular sires from the late 1980’s and early 1990’s, we find examples of some sires that wouldn’t have been nearly as popular if all of our current traits for selection were evaluated back then. Sires like MASCOT, LUKE and MICHAEL would not have been used to as large a degree if we had all of these things available. There are also certain sires from that era that only get more popular over time like RUDOLPH, DUSTER and LEADER. These sires are often referred to as customer satisfaction sires. Well, it is no wonder customers are satisfied with these sires, because their daughters are all healthy, long-lasting, profitable cows. The traits we have available now would have identified these sires earlier.
What if they want to put more weight on one of these traits than what is offered?
That is a good point, Bill, because currently the net merit formula has about 31 percent of its weight on these traits. Even when including confirmation as an indirect indicator of longevity, we still only account for about 45 percent of the index. At least 55 percent of the weight is on production, and even though production is still the main driver for profit, many producers are recognizing that it is more difficult to keep cows healthy than it is to get the healthy cows to milk. Therefore, if you want to put more emphasis on health and longevity, and the current indexes allow you to do so, you should work with your A.I. representative to create an index that works for your herd.
That was Dr. Nate Zwald, who just recently completed his Ph.D. in Dairy Cattle Genetics from the University of Wisconsin, Madison.
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