Exploring the impact of heat stress on feed efficiency in tropical beef cattle using genomic reaction norm models.

Global climate change poses significant challenges to livestock production, particularly in tropical regions where cattle frequently experience heat stress (HS). HS negatively impacts feed efficiency by reducing feed intake, altering metabolic processes, and increasing energy requirements, leading to decreased animal performance. Understanding how cattle respond to environmental stressors is essential for improving efficiency by breeding programs. In this context, we investigated genotype-by-environment interaction (G × E) for dry matter intake (DMI) and residual feed intake (RFI) in Nellore cattle using bi-trait genomic reaction norm models and considering the temperature-humidity index (THI) as the environmental descriptor. Data from 22 838 animals collected between 2011 and 2023 across 21 Brazilian farms were analyzed. Meteorological data were obtained via NASA POWER, and THI values were calculated based on the average temperatures and relative humidity recorded during feed efficiency trials. Genomic data were available for 18 567 animals, and the genetic parameters were estimated using the single-step genomic best linear unbiased prediction approach. The genetic expression of feed efficiency traits was found to be influenced by climatic conditions, with heritability estimates for DMI (ranging from 0.22 to 0.39) and RFI (ranging from 0.08 to 0.28) varying across the THI gradient. Additionally, a reduction in additive genetic variance for both traits was observed under intense heat stress conditions, suggesting the important role of environmental factors on phenotypic variability of feed efficiency traits in Nellore cattle. The presence of G × E was more pronounced when THI exceeded 76, as genetic correlations for the same trait across different environmental gradients dropped below 0.80, leading to substantial sire reranking. Moreover, the genetic relationship between DMI and RFI also varied along the THI, with genetic correlations ranging from 0.64 to 0.72, highlighting alterations in the genetic expression of feed efficiency traits under different heat stress levels. These findings emphasize the need to consider genetic plasticity when selecting animals for improved feed efficiency in tropical regions. Overall, this study provides valuable insights for breeding programs aimed at improving beef cattle resilience to heat stress, ensuring sustainable production in the face of climate change.