Beef cattle phenotypic plasticity and stability of dry matter intake and respiration rate across varying levels of temperature humidity index

Authors: SHAFFER, WILL - Kansas State University; HIDALGO, JORGE - University Of Georgia; Bello, Nora; NOLAND, RYLIE - Kansas State University; BORMANN, JENNIFER - Kansas State University; WEABER, ROBERT - Kansas State University; AHLBERG, CASHLEY - Kansas State University; BRUNO, KELSEY - Oklahoma State University; KREHBIEL, CLINT - Texas Tech University; CALVO-LORENZO, MICHELLE - Elanco Animal Health, Inc; RICHARDS, CHRIS - Oklahoma State University; PLACE, SARA - Colorado State University; DESILVA, UDAYA - Oklahoma State University; Kuehn, Larry; ROLF, MEGAN - Kansas State University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2025
Publication Date: 4/8/2025
Citation: Shaffer, W.R., Hidalgo, J., Bello, N.M., Noland, R., Bormann, J.M., Weaber, R.L., Ahlberg, C.M., Bruno, K., Krehbiel, C.R., Calvo-Lorenzo, M., Richards, C.J., Place, S.E., DeSilva, U., Kuehn, L.A., Rolf, M.M. 2025. Beef cattle phenotypic plasticity and stability of dry matter intake and respiration rate across varying levels of temperature humidity index. Journal of Animal Science. 103. Article skaf115. https://doi.org/10.1093/jas/skaf115.
DOI: https://doi.org/10.1093/jas/skaf115

Interpretive Summary: The objectives of this work were to evaluate how population genetic and phenotypic components for dry matter intake and respiration rate in beef cattle changed as a function of temperature humidity index, to determine whether genotype-by-environment interactions (G×E) influenced selection decisions when breeding values (BV) were sourced from disparate environments, and to evaluate model-derived accuracy of BV at specific values of the temperature humidity index. Results indicate that selection for stable performance in both traits may be possible, though at the expense of overall performance at the onset of heat stress. Furthermore, the magnitude of the additive genetic variance available for selection decreased as the temperature humidity increased, indicating that the potential for selection progress for dry matter intake is slower under extreme temperature humidity index conditions. Genetic re ranking of animals based on estimated dry matter intake BV for disparate environments was evident. This finding indicated that the optimal animal for selection may change depending on the environment. Similarly, an estimated BV may not reflect performance in different environments if G×E is not considered.

Technical Abstract: Expected changes in climate warrant research on selection for a phenotypically stable cattle population that can perform consistently across diverse environmental conditions. In this study, we utilize a heteroscedastic random regression model to: 1) characterize the additive genetic and other phenotypic components of dry matter intake (DMI) and respiration rate (RR) with respect to the temperature humidity index (THI), 2) assess the presence of genotype-by-environment interactions (G×E) by determining whether the additive genetic reaction norm changes along the observed THI range and by evaluating the additive genetic correlations between DMI or RR at different THI values, and 3) evaluate model derived accuracy of estimated breeding values (EBV) along a range of THI. Data consisted of repeated observations of DMI and RR on 788 and 569 steers, respectively, over a period of 70d. A hierarchical model with subject-specific additive genetic and permanent environment effects was fitted to each trait using Bayesian inference. Estimated population slopes, expressed as posterior median and 95% highest posterior density (HPD) interval, were -0.046 (-0.053, -0.039) kg DMI per unit increase in THI per day and 0.027 (0.026, 0.029) breaths per 30s (BP30S) RR for each unit increase in THI on the logarithmic scale, thereby suggesting environmental sensitivity for both traits. Estimated correlations between the additive genetic intercept and slope were -0.78 (-0.86, -0.69) and -0.66 (-1.0, -0.20) for DMI and RR, respectively, indicating that selection for increased DMI and decreased RR at the onset of heat stress can be expected to associate positively with mean population environmental sensitivity to THI. Heritability estimates for DMI at the onset of heat stress (i.e., THI of 70) ranged from 0.30 (0.17, 0.44) to 0.37 (0.20, 0.48) across cohorts, but decreased as THI increased. Heritability estimates for RR were low, with 95% HPD upper boundaries ranging from 0.03 to 0.08 across the range of THI evaluated. For DMI, the median additive genetic correlation between 70 and 85 THI and the Spearman correlations between estimated breeding values at 70 and 85 THI levels were 0.42 (0.26, 0.57) and 0.39 (0.26, 0.52), respectively, indicating substantial G×E. The median DMI EBV model derived accuracy at a specific THI value increased from 70 THI to 0.65 at 82 THI, at which point it stabilized. This was likely because more data points were gathered at greater THI.