Beef cattle

Residual Genomic Breeding Values as Indicators of Heat Resilience in a Beef on Dairy Population

---

Abstract

Heat stress limits cattle productivity, particularly in beef × dairy crossbred systems managed under limited environmental control and high thermal load. This study characterized the genomic response to heat load in a Beef-on-Dairy (BxD) Angus × Holstein and Angus x Jersey population and proposed a residual genomic breeding value (rGEBV) as an independent indicator of heat resilience. Daily phenotypic records from automated feed-bunk systems included dry-matter intake (DMI), eating rate (ER), and bunk-visit frequency (BV). Ruminal temperature (RT), measured via intraruminal bolus sensors every 15 minutes, was summarized as daily means for analysis. Reaction-norm genomic models were fitted for each trait using a derived environmental gradient-Heat Load (HL)-instead of the raw temperature-humidity index (THI). HL was defined as the difference between the daily THI and an estimated threshold, with values below the threshold set to zero. This approach focused on the portion of the environment that effectively represents heat stress, improving interpretability of genomic slope parameters. The THI thresholds marking the onset of heat load were 72.1 (DMI), 79.5 (ER), 61.7 (BV), and 72.5 (RT). Animals were genotyped with SNP panels imputed to 150K density, and analyses were conducted using the BLUPF90 suite integrated with R. The genomic relationship matrix (GRM) accounted for ancestry differences to represent breed composition in this multibreed population. The genomic intercept described performance under thermoneutral conditions, while the slope captured each animal's sensitivity to increasing THI. The THI midpoint-defined as the median of all positive HL values-was used to calculate the heat-load GEBV (hlGEBV), representing expected performance under moderate heat load. Midpoint THI values were 75.6 (DMI), 81.7 (ER), 70.0 (BV), and 77.4 (RT). To isolate resilience from productivity, a residual GEBV (rGEBV) was obtained as the residual from the regression hlGEBV ~ Intercept, capturing deviations in heat-load performance after adjusting for baseline productivity. This residual represents heat resilience-the ability to maintain or recover performance beyond thermoneutral potential. Correlations among genomic parameters revealed consistent biological patterns. For DMI, ER, and BV, intercept and slope GEBVs were moderately to strongly and negatively correlated (r = −0.94, −0.73, and −0.81; p < 0.001, respectively), indicating that animals with higher baseline performance tended to be more heat-sensitive. Residual GEBVs showed moderate to high correlations with heat-load GEBVs (r = 0.50 for DMI, 0.96 for ER, 0.77 for BV, and 0.99 for RT; p < 0.001). In contrast, residual and intercept GEBVs were uncorrelated (r ≈ 0), suggesting that residual genetic variation is largely independent of baseline performance. Reliability of selection-candidate bulls increased with the number of progenies in the training population. Overall, rGEBV provides a robust genomic indicator to identify animals capable of sustaining productivity under heat load, supporting selection for resilience in climate-challenged systems.

Keywords: 2026

How to Cite:

Deeb, N., Gouveia, G., Johnson, J., Ribeiro, V., Ross, P., Utsunomiya, A., Utsunomiya, Y. & Vieira, M., (2026) “Residual Genomic Breeding Values as Indicators of Heat Resilience in a Beef on Dairy Population”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286424. doi: https://doi.org/10.31274/wcgalp.23999

Rights: 1