by Tom Brink, RAAA CEO

Definition: Stayability predicts differences in the ability of an animal’s retained daughters to remain productive in the herd, calving every year, through six years of age. Units are in percentage terms; higher is better.

STAY is an IGS-calculated EPD, with millions of cow records behind it. RAAA’s total herd reporting policy, which has been in place for more than 25 years, also adds considerable data quality and quantity to the estimation of our STAY EPD.

The main difficulty with STAY is that it is a lowly-heritable trait (10-15 percent genetically influenced). Thus, 85-90 percent of observed outcomes in the pasture are the result of environmental influences, not genetics. This situation makes STAY a difficult trait to see in an individual herd. Most of what producers notice in terms of cows staying in, or falling out of over time, is caused by non-genetic/environmental factors.

RAAA has done two detailed validation analyses using Red Angus phenotypic data to test the efficacy of its STAY EPD. Both showed a favorable result and indicated that the Red Angus STAY EPD is working and does have predictive power, albeit within the broader context of a trait that has large environmental influences, as discussed above.

Validation #1: Red Angus sires were split into quartiles using their STAY EPD ranking from high to low. Daughter parity data was analyzed and compiled across the sire quartiles. Daughters of sires in the top quartile for STAY EPD, on average, produced 1.4 more calves per lifetime compared to daughters of sires in the bottom quartile for STAY EPD.

Validation #2: Red Angus females that produced seven or more successive calves in their lifetimes were analyzed as a group. The objective was to determine whether our STAY EPD analysis was finding these females from within the greater Red Angus cow population and rewarding them with higher-than-average STAY EPDs. The analysis revealed that these long-lasting females did, on average, have higher STAY EPDs compared to breed average.

Final thought: The primary challenge we face with STAY is that it is a lowly-heritable trait. The correlation between a given animal’s STAY EPD and good or bad outcomes in the pasture is, therefore, low. However, when we study the bigger picture across the entire Red Angus database, we find that our STAY EPD is effectively doing its job to identify genetic differences in
female longevity.

Questions on this topic that concern specific animals should be directed to Lindsay Upperman, Ph.D., at the RAAA office.