The most natural ways of selecting herd fertility come to us through our eyes and looking at an animal’s production history, but are we changing our operations and our animals by not looking beyond? phenotype and examining the data that contains the answers to the precision of selection for a given operation?
Jared Decker, associate professor and extension specialist in beef cattle genetics at the University of Missouri, explained fertility genetics during an Oklahoma State University webinar and offered his advice to producers who want make more informed decisions about fertility.
“Whenever we make a selection decision based on animal performance or appearance, it doesn’t take into account these environmental and management differences,” Decker said. “What that ultimately means is that when we try to make a selection on the appearance of an animal – its phenotype – it will just be a less precise form of selection. is that when we do phenotypic selection, there is a hard cap on the accuracy of our breeding decisions, and mathematically that cap is the square root of the heritability of that trait.
Decker used the example of a trait like birth weight, where heritability is quite high. He said 46% of the variation is attributed to additive genetics, so the cap on that phenotypic selection accuracy is 0.68.
“With marbling, heritability is also quite high, but if we slaughter an animal, look at its carcass and measure the marbling, that animal can no longer be a bull,” he explained. “Phenotypic selection for certain traits just doesn’t work. For other traits such as fertility, heritability is low enough that the ceiling of our selection precision is very low. Heritability for many fertility traits will be between 5% and 15%. “
Much of the variation in these traits, Decker says, is due to the animal’s circumstances and factors other than additive genetics.
EPDs should be a benchmark for fertility
When asking producers how they make selection decisions regarding fertility and reproduction, a common response is the practice of culling open cows.
“That’s good, but in terms of genetic progress, it leaves a lot to be desired,” he said. “We leave a lot of value and information on the table when we focus on phenotypic selection for low hereditary traits and actually all traits for which an expected difference in progeny is available. There is no cap on the accuracy of EPD and we can achieve 100% accuracy if we put enough data and information into the process. When we select on genetics, we are no longer limited by the heritability of the trait.
Decker said there are various EPD tools that pave the way for producers to genetically improve fertility, but another important breeding decision that can help a herd’s fertility is crossbreeding.
“A crossbreed cow will be 25% more productive over its lifetime and a big part of that improvement will be higher fertility,” he said. “If you decide to breed directly, it becomes even more important to select more fertile females. If you are going to give up the fertility gains of the cross, then you had better select it using EPDs to identify those more fertile lines to bring into your herd.