50 NEBRASKA CATTLEMAN March 2026 In the absence of GxE, the performance gap between genotypes remains constant across all environments. As GxE becomes more prevalent, we can observe performance differences across environments for the two genotypes. In extreme cases, this relationship can cause reranking among animals, possibly changing the optimal selection decision from one environment to another. In addition to this variability across environments, there are cases in which genetic traits perform equally regardless of environmental stressors, which we refer to as “robustness.” When breed associations report expected progeny differences (EPDs) for animals, they assume that the genetics are purely additive. We use contemporary groups (herd, year, season) to put animals on a level playing field across herds in the genetic evaluation. In doing this, our selection tools (EPDs) assume an “average” environment when interpreting their meaning for future offspring of selection candidates. The biological causes of these GxE interactions can range widely – from heat stress to toxic fescue to elevation to supplemental feeding. Certain genetic factors predispose animals to respond differently to these environmental factors. Those different responses show up in performance. For example, a cow’s ability to appropriately control body temperature can affect milk production because energy is diverted from one process (lactation) to another (temperature control). Other animals that are genetically predisposed to utilize supplementation efficiently or have cardiovascular systems that function better at elevation will show increased performance across economically important traits. Despite the myriad ways in which environment and genetics interact, our ability to account for them in our genetic evaluations and selection decisions leaves a major gap. There are three main strategies that allow us to make genetic decisions: 1. Breed to local genetics 2. Use adaptive indicator traits 3. Integrate environment and management into selection tools Local Genetics The first of these options has been our historical approach to addressing genetics-by-environment interactions. We’ve spent centuries buying or acquiring genetics from our neighbors who raise their animals in similar conditions. This breeding scheme selects for adapted animals in the same way that natural selection does; well-adapted animals perform well, and we select higher performing animals to be parents in the next generation. As mentioned above, artificial insemination has complicated this situation. Additionally, management interventions that alter the larger environmental component of a trait are not geographically restricted. Many times, two sides of a fence between neighbors can represent entirely different environments for animals. As an approach to matching genetics and environment, this is tried and true but may fail to capture the full genetic potential through artificial insemination. It is also essential that bull purchases come from seedstock operations with similar management strategies. A low-input operation purchasing bulls from one that aggressively supplements may end up creating a genetics-environment mismatch just as much as a Florida operation bringing in a bull from North Dakota. Developing Adaptive Indicator Traits Another strategy we have for making environment-aware genetic decisions is to leverage indicator traits for adaptation. Indicator traits are easily measured phenotypes that may represent another, more economically relevant or adaptive one. The two most common traits used to indicate adaptation to environments are pulmonary arterial pressure (PAP) for high-altitude adaptation and early-season hair shedding (HS) for heat and toxic fescue adaptation. PAP is a more GENETIC TOOLS FOR BREEDING BETTER ADAPTED CATTLE CONTINUED FROM PAGE 48 CONTINUED ON PAGE 52 CONSIDER THIS
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