Once the new Net Merit (NM$) formula gets implemented this August, dairy farmers from across the U.S. and around the world will have the opportunity to breed more feed-efficient cows. That will be due to the addition of feed saved, which is a combination of residual feed intake and body weight composite. Overall, feed saved is a better way to express feed efficiency and is easier to interpret than residual feed intake.
In addition to those major changes, a pair of new traits, heifer livability and early first calving, will be added to the Net Merit formula. Of the four changes, however, the headline grabbers are definitely residual feed intake and the cow body weight composite.
“The new feed saved evaluation includes the economic value of cow body weight composite (BWC) along with actual feed intake data from several thousand Holstein cows in U.S. and Canadian research herds,” wrote researchers from USDA’s Animal Genomics and Improvement Laboratory. “The trait residual feed intake (RFI) measures the difference of actual and expected feed intake,” continued the USDA scientists, working in tandem with the Council on Dairy Cattle Breeding. “Relative economic values for BWC and RFI are presented separately because BWC is available for all breeds, whereas feed saved is available only for Holsteins,” explained the scientists in their paper “Net Merit as a measure of lifetime profit 2021 edition.”
Why only Holsteins?
The reason feed saved, and thus residual feed intake are only available for Holsteins is due to the tremendous cost to obtain this data. That high cost comes from measuring every lick of feed consumed by each cow for a major portion of the lactation. Due to the power of genomic predictions, that expensive feed data can then be estimated across the entire population of Holsteins.
When looking deeper at the emphasis for the two traits, body weight composite gets more emphasis because of larger maintenance costs estimated from actual feed intake data. The emphasis at -9.4% on body weight composite and -3.8% on residual feed intake combine for a +13.2% emphasis on feed saved.
When looking deeper into the bodyweight composite, the trait was already part of the NM$ formula because maintenance costs had to be considered when estimating lifetime profitability of a cow. That original inclusion took place regardless of the feed efficiency component.
That means that the relative gain in the economic weight for the body weight composite is more associated with the review in the estimates of maintenance costs from the overall feed efficiency project. Prior to this work, we relied on National Research Council (NRC) estimates and now there is more up-to-date data showing that the costs are higher than previous estimates. In other words, even if residual feed intake was not in the formula, the body weight composite would have a higher weight.
Emphasis versus weights
Now “emphasis” is different than “actual weights” in the Net Merit formula that will be implemented in August 2021. Emphasis also factors in such matters as reliability. Overall, feed saved and residual feed intake are relatively low-reliability traits. That means when placing a weight of -12% in the August 2021 Net Merit formula, it will yield a -3.8% emphasis on feed saved. When it comes to the body weight composite, a -9% weight in the formula yields a -9.4% emphasis due to the higher reliability of conformation traits such as stature, strength, body depth, dairy form, and rump width all factored into that composite.
To read more on these two traits, click on “Two new genetic traits coming in December.”
