Identifying the Ones That Will Stay

Prototype stayability analysis using random regression approach appears promising.

by Troy Smith, field editor

MANHATTAN, Kan. (June 16, 2016) — As tools for genetic selection, expected progeny difference (EPD) values for stayability predict the probability that a sire’s daughters will remain in the herd until 6 years of age. Age 6 is considered to be a break-even point — the threshold at which a beef female has produced enough calves (five) to recover her cost. According to Colorado State University research geneticist Scott Speidel, stayability is a significant measure of reproductive efficiency.

“Stayability is hugely important. It’s a big driver of profitability,” stated Scot Speidel, noting that cows remaining in the breeding herd after age 6 must compensate for those that fall out of production earlier.

Speidel was one of the scientists presenting research updates during the 2016 Beef Improvement Federation Annual Meeting and Symposium hosted June 14-17 in Manhattan, Kan. During the Advancements in Efficiency and Adaptability breakout session, Speidel talked about his efforts to develop a stayability analysis offering increased accuracy of prediction.

“Stayability is hugely important. It’s a big driver of profitability,” stated Speidel, noting that cows remaining in the breeding herd after age 6 must compensate for those that fall out of production earlier. “Stayability, represents 53% to 77% of the value of maternal indexes,” he added.

Speidel explained that a limitation to current stayability evaluations is the length of time that passes before observations are collected for the female progeny of a sire. The female is 6 years old, so it’s likely her sire is 8 or older, or even dead. This delay in collection of observations reduces accuracy and slows genetic progress. Consequently, Speidel is exploring a method for incorporating observations made while females are younger, with the goal of ultimately increasing the accuracy of prediction for stayability.

“We know that heritability to 6 years of age is heritable,” said Speidel. “What is the heritability when females are younger, with four, three or two calves?”

According to Speidel, analysis of American Simmental Association data suggests a heritability factor of 0.21 for stayability at 6 years of age, and heritabilities at ages 5, 4 and 3 of 0.20, 0.18 and 0.17, respectively.

Speidel says two methods utilizing observations at ages younger than 6 years of age are being studied, but a “random regression” model appears more robust, incorporating more data and allowing for prediction to any age endpoint.

“It’s predictive of genetic merit to produce a calf at a given age,” said Speidel. “I think it is promising.”

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