Selection for Lifetime Net Merit
Improves Health Traits
By: Jenny Hanson, Communications Manager, CRI
Mar-Bec Dairy in western Wisconsin is a prime example of what can happen when good genetics are combined with exemplary herd management. For many years now dairy producer Marty Hallock has believed in the power of genetics. Therefore, he uses high Lifetime Net Merit (LNM) sires and it shows in the performance of his herd. "LNM is all about total profit," explains Hallock, "We use it to select for a long-term, profitable cow rather than one that milks a lot but only lasts a few months or one that lasts but never produces."
LNM is an index which includes production, conformation and health traits. Over time, health traits have earned more emphasis. Now, they account for 41 percent of the index. The individual health traits included in LNM are Productive Life, Daughter Pregnancy Rate (DPR), Somatic Cell Score (SCS), calving ease and stillbirths. This article will clearly show how selecting for high LNM sires can improve a herd's daughter fertility and somatic cell counts.
Creating Fertile Cows
DPR accounts for nine percent of the LNM index. This trait ranks sires on the ability of their daughters to become pregnant in a timely fashion. The trait holds high economic value as reproduction is arguably the most important factor in dairy herd management.
Although DPR is reported in a percent of pregnancy rate, the easiest way to analyze the economic impact is to convert it to days open. Each positive point of DPR is equal to four fewer days open. Each negative point of DPR is equal to four more days open, relative to the herd.
+1.0 DPR = 4 fewer days open
The impact of choosing high LNM sires, thus more high DPR sires, in Hallock's herd is eye opening. The table below includes breeding information from first lactation cows. The cows are grouped according to their sire's DPR.
Table 1. Comparison of first lactation cows by sire's DPR.
Sire's DPR | Conception Rate | Services Per Conception |
< 0 | 33% | 3.1 |
0.0 to 1.0 | 38% | 2.7 |
1.1 to 2.0 | 43% | 2.3 |
As the table indicates, daughters of high DPR sires average higher conception rates and fewer services per conception. Since the table shows daughters of high DPR sires get bred sooner, the information supports the fact positive DPR equals fewer days open.
The DPR advantage can also be seen through the herd's ResultsTM report. The Genex Results report shows the difference between daughters of high and low ranking DPR sires.
The report above shows there is a 4.36-point difference in DPR between the top and bottom quartiles of sires. Using the equation from above, you would expect daughters of the top quartile of sires for DPR to have 17 fewer days open than the daughters of the bottom quartile of sires (4.36 DPR x 4 = 17). However, this report shows the animals from high DPR sires actually average 22 fewer days open. Within this herd, good herd management procedures make the improved performance from high DPR sires even more evident.
As stated previously, DPR is one of the traits included within the LNM index. Therefore, sires with a high LNM generally also have a positive DPR and produce daughters with fewer days open. An analysis from Mar-Bec Dairy's Dairy Comp 305, below, shows the relationship between high LNM sires and average days open. Daughters of bulls over +$400 LNM have significantly fewer days open than daughters of bulls less than +$250 LNM.
Table 2. Comparison of first lactation cows by sire's LNM.
Sire's LNM | Days Open |
+$1 to +$250 | 150 |
+$251 to +$400 | 133 |
> +$400 | 97 |
Breeding for Healthy Production
Like DPR, SCS accounts for nine percent of the LNM index. SCS is used to improve resistance to mastitis. Bulls with a low SCS (less than 3.00) are expected to have daughters with lower levels of mastitis than bulls with a higher SCS.
Analyzing the impact of lower SCS sires on the Mar-Bec herd can be completed through a Results report (below). When ranked according to their SCS, the top 25 percent of sires used in the herd averaged +2.79 SCS. The bottom 25 percent of sires averaged +3.23. The difference in SCS between those sires is very similar to the difference in log Somatic Cell Counts between their daughters.
Examining the farm's Dairy Comp 305 information shows the strong relationship between high LNM sires and the Log SCC of their daughters. Daughters of bulls over +$400 LNM have significantly lower Somatic Cell Counts.
Table 3. Comparison of first lactation cows by sire's LNM.
Sire's LNM | Log SCC |
+$1 to +$250 | 2.8 |
+$251 to +$400 | 2.3 |
> +$400 | 1.7 |
Doing What They're Bred to Do
Cows do what they are bred to do. Therefore, cows mated with high LNM sires will produce offspring that live longer and healthier lives, breed back, have good udders, correct feet and legs, and make milk efficiently.
Mar-Bec Dairy utilizes Genex daily technician service for heat detection and breeding. The team of Dave Franck, Jason Woodard, Tim Nemitz and Adam Zwiefelhofer provides daily service. Zwiefelhofer and Becky Brain provide MAPTM mating and Reproductive Profit ManagerTM consulting services.
