Lifetime Net Merit (NM$) has driven genetic progress since 1994 by promoting a balanced selection of all available, economically-important traits to maximize profitability of dairy cows.
August 2021 will bring one of the most exciting updates with important enhancements to Net Merit. Three new traits are being added: Feed Saved, Early First Calving and Heifer Livability. Although strengthening the emphasis on health and growth of calves is a great advancement, the incorporation of feed efficiency has received more attention. The reason is simple: feed costs are one of the most important drivers of herd profitability.
The same research that allowed genomic selection for Feed Saved also showed that maintenance costs were previously underestimated. The new NM$ better reflects the differences in production costs between cows.
In this conversation with top scientists, we learn more about the changes and benefits of the August NM$ update. Our panel is composed of these four experts.
Kristen Parker Gaddis, PhD, Geneticist at Council on Dairy Cattle Breeding
Paul VanRaden, PhD, Senior Research Geneticist, USDA Animal Genomics and Improvement Laboratory
Rob Templeman, PhD, Professor, Michigan State University
Tom Lawlor, PhD, Geneticist, Holstein Association USA
This update to Net Merit, the 2021 version, is quite significant. What is the main takeaway?
Kristen Parker Gaddis:
Net Merit has always been based on the best available research to provide unbiased estimates of expected lifetime profit. The 2021 update incorporates newer traits of significant economic importance and revises previous assumptions. Using a comprehensive index like Net Merit – which accounts for all traits appropriately and without bias – is the best way to maximize profitability through genetic improvement in all evaluated traits.
New traits provide more useful information about the genetic qualities of each animal, and they increase the need to combine the many Predicted Transmitting Abilities (PTAs) using a selection index. Instead of trying to decide what traits you want most, NM$ calculates what traits will return most profit to most herds. This efficient and elegant approach was recommended by Hazel in 1943 and referred to as “net merit” in the first sentence of that classic paper. Since then, improving cows and bulls has required accurate PTAs for traits that contribute to profit and accurate math to estimate the profit. Computers do the math, based on robust research, so producers do not need to examine every single animal for every single trait.
When profit margins are tight and feed costs (typically half of variable costs) seem to be drifting higher, we need to provide dairy producers the best genetic selection tools to continue to be profitable. Selecting for feed efficiency also makes sense for environmental stewardship. NM$ 2021 represents an important step forward for economic and environmental sustainability of dairy production.
One of our strengths in U.S. dairy is our ability to quickly move new research findings into the hands of the farmers. This is what has been done with Net Merit $ 2021. Utilizing this information will help producers control costs and improve profits.
Kristen Parker Gaddis
What are the major changes in the revision?
Three traits will be added in Net Merit in August – Early First Calving, Heifer Livability and Feed Saved. These additions will accelerate progress for improved health and growth of calves and improved feed efficiency in cows using direct information for these traits. There are also changes in the emphasis given to traits. More emphasis is being given to longer Productive life and smaller Body Weight Composite, based on the best research available.
How many traits are now in Net Merit?
There are over 40 traits in Net Merit. These are represented as individual traits, such as milk yield, livability, and somatic cell score, as well as composites like calving ability, health dollars and type (udder composite, feet and leg composite, body weight composite). Each trait is included based on its economic value, considering both income and expenses using the recent research and projections. New for 2021 is the reporting of the relative emphasis of each trait. The relative emphasis describes the trait’s economic importance and reflects the amount of data available and prediction reliability.
How do we expect the revision to impact specific groups of animals?
There will be an increase in the variation of Net Merit, reflected by an increased range of Net Merit PTAs for all animals – both male and female. The average Net Merit PTA for A.I. bulls is expected to increase from $460 to $554. A slight decrease in reliability is expected due to the inclusion of Feed Saved, which has limited available data. Even with a reduction in reliability, the updated Net Merit is a valuable index because it more comprehensively describes income and expenses. An additional 2.2% progress is expected to be achieved using NM$ 2021, compared to the previous formula. The correlation between NM$ 2018 and the new 2021 version is high at 98.1%.
What are we selecting for when we use NM$ 2021?
The goal of NM$ since 1994 is to select for all traits that affect profit and estimate how much lifetime profit each animal will transmit to its progeny. Yield traits and Productive Life have highest value in the index by generating more income per lactation and more lactations. Many other traits measure costs that are not as heritable or valuable as extra yield, but those costs from many other traits all add up. As more traits are evaluated, the accuracy of estimating profit increases because previously hidden costs or incomes are now directly included.
Kristen mentions “relative emphasis.” Previously in the NM formula, we talked about economic values of traits. What’s the difference?
Before 2021 we used the terms relative value, relative emphasis and relative weight interchangeably, and each term measured percentage of selection using absolute values that sum to 100% across traits. In August, the terms now differ by which standard deviation (SD) is used in the calculation. Genetic SD are used in relative value and PTA SD in relative emphasis. The PTA SD were estimated from young bulls born in 2019 that have less reliability for some of the new traits. Relative value measures the potential importance of the traits, whereas relative emphasis better reflects a trait’s actual impact when selecting younger animals with less reliability.
How are the economic weights calculated?
The economic value is that trait’s contribution to profit, holding all other PTAs in the index constant. For example, higher milk PTA adds little extra value (just extra water!) if the daughters do not give extra pounds of protein or fat. Revisions of NM$ begin by updating price estimates for income and cost items such as milk components, feed, cull value, replacement cost, and somatic cell premiums. Traits get credit for their direct incomes and expenses – plus possible correlated effects on other traits not in the index. Before 2018, Somatic Cell Score (SCS) got indirect credit for mastitis costs, but after Mastitis was directly included in 2018, SCS gets credit only for the premiums generated in the milk check.
What is the expected genetic progress through use of NM2021?
The average genetic progress for NM$ across all herds in DHI has been about $60 in recent years. The new NM$ 2021 formula estimates more progress than the 2018 version – mainly due to lower marginal feed consumed for yield and higher value for extra lactations. Both of those will increase the range of NM$ values. Correlations of each trait with NM$ will change minimally – except for residual feed intake where some progress is now expected and for type composites with a trend toward smaller cows and less upward trend for UDC and FLC. Most of the progress still comes from the trend for higher-producing cows that can stay longer in the herd.
What is the difference between Feed Saved and Residual Feed Intake?
Residual Feed Intake (RFI) is the difference between actual and expected feed intake based on her milk production and maintenance requirements for her body weight. In other words, RFI is a measure of a cow’s metabolic efficiency. The lower and more negative RFI indicates the efficiency of that cow in using her feed intake to produce milk, adjusting for her body weight (BWC). To select for feed-efficient cows, Feed Saved (FS) might be more useful as FS combines RFI and the feed intake required for maintenance. Selecting for higher FS will help producers save on feed costs due to greater metabolic efficiency (RFI) or smaller body weights or, most likely, both!
How is Feed Saved factored into NM?
That’s a great question! After all, why create PTAs on a new trait when it does not seem to be listed as a trait within NM? But Feed Saved is in NM$ 2021…indirectly. FS is a combination of RFI and BWC, and both RFI and BWC are in NM$ 2021 with the proper economic weights and genetic weightings. We’ve used RFI and BWC (instead of FS) in NM$ 2021 because BWC has historically been part of the NM index. The economic weight on BWC also needs to reflect its association with cull values, housing costs and heifer raising costs.
What has recently been discovered about maintenance costs?
Cow maintenance costs previously were based on older research studies, like the last revision of Nutrient Requirements of Dairy Cattle published by the National Research Council in 2001. About 10 years ago, the USDA began funding a large research consortium that initiated collection of feed intake information on over 5,000 cows at several leading dairy science universities in the U.S. This data led to much of the feed intake data used to measure and develop RFI and Feed Saved. That data also resulted in a reassessment of cow maintenance costs, which were determined to be substantially greater than previously reported. Even if FS or RFI were not included in NM$ 2021, the emphasis on BWC would need to be modified to reflect these new findings on cow maintenance costs.
Why does Body Weight Composite (BWC) receive such a high weight in the new Net Merit?
Significant improvements were made to the formula relative to feed utilization, including feed intake data on cows, improved estimates of maintenance costs, and the added feed costs to produce an extra pound of milk, fat, and protein. The new research indicates a lower marginal feed cost for producing more milk and a higher maintenance cost. The higher maintenance costs resulted in more of a negative weight on BWC.
UDC and FLC receive less emphasis in NM 2021. Why is that, and what is the expected result?
A selection index reflects our current population and how we want to change it. We have made tremendous improvement in the conformation of our cows, and future improvements can be made more slowly. Comparing the predicted genetic merit of the cows from using NM$ 2021 with NM$ 2018, we see improvements for UDC of +1.6 versus +1.8; +0.6 versus +0.8; and a decrease in BWC of -1.5 versus -1.0. The change in BWC represents a decrease of 52 pounds of mature body weight versus 35 pounds.
You’ve analyzed this revision closely with producers, fellow geneticists and A.I. industry. After this robust review, how do you describe this revision?
The 2021 update to the NM$ formula had a longer review process, with more comments and eyes looking at it than any other revision. It has been a great collaborative effort and one that will be repeated in the years ahead. As we change our cows, new discussions will be necessary – about the optimum gestation length, age at first calving, somatic cell score and body weight, to name just a few traits. A larger research study, or more expansive knowledge, or a change in prices will necessitate a future NM$ revision. Dairy producers should feel very confident in using NM$ as a fundamental tool in their genetic program – aimed at creating the best herd of cows 10 years down the road.
*United States Department of Agriculture, Agricultural Research Service
JOÃO DÜRR, CEO COUNCIL FOR DAIRY CATTLE BREEDING