Investigating genotype by environment interaction for beef cattle fertility traits in commercial herds in northern Australia with multi-trait analysis

Authors: COPLEY, JAMES - University Of Queensland; HAYES, BENJAMIN - University Of Queensland; ROSS, ELIZABETH - University Of Queensland; SPEIGHT, SHANNON - University Of Queensland; FORDYCE, GEOFFRY - University Of Queensland; WOOD, BENJAMIN - University Of Queensland; Engle, Bailey

Submitted to: Genetic Selection Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2024
Publication Date: 10/31/2024
Citation: Copley, J.P., Hayes, B.J., Ross, E.M., Speight, S., Fordyce, G., Wood, B.J., Engle, B.N. 2024. Investigating genotype by environment interaction for beef cattle fertility traits in commercial herds in northern Australia with multi-trait analysis. Genetic Selection Evolution. 56. Article 70. https://doi.org/10.1186/s12711-024-00936-0.
DOI: https://doi.org/10.1186/s12711-024-00936-0

Interpretive Summary: Genotype by environment interactions (GxE) affect a range of production traits in beef cattle but quantifying the effect of GxE in commercial, multi-breed herds is challenging. The primary aim of this study was to use multi-trait models to investigate GxE for three heifer fertility traits in a large, tropical beef multibreed dataset (n = 21,037). Environmental levels ranged from desirable to harsh, and were defined by two different descriptors, heat stress and nutritional availability. In order to establish if low genetic correlations between environments were due to GxE differences or poor genetic linkage between animals in each environmental, new phenotypes were simulated that had no GxE influence to use as a comparison to the real phenotypes. Only one case of statistically significant GxE for any fertility trait was detected. Other early indications of GxE that were observed from the real phenotypes did not prove significant when compared to the simulated phenotypes. The lack of compelling evidence of GxE indicates that direct selection for fertility traits can accurately be made, regardless of environment.

Technical Abstract: Background: Genotype by environment interactions (GxE) affect a range of production traits in beef cattle. Quantifying the effect of GxE in commercial and multi-breed herds is challenging due to unknown genetic linkage between animals across environment levels. The primary aim of this study was to use multi-trait models to investigate GxE for three heifer fertility traits, corpus luteum (CL) presence, first pregnancy and second pregnancy, in a large tropical beef multibreed dataset (n = 21,037). Environmental levels were defined by two different descriptors, burden of heat load (temperature humidity index, THI) and nutritional availability (based on mean average daily gain for the herd, ADWG). To separate the effects of genetic linkage and real GxE across the environments, 1000 replicates of a simulated phenotype were generated by simulating QTL effects with no GxE onto real marker genotypes from the population, to determine the genetic correlations that could be expected across environments due to the existing genetic linkage only. Correlations from the real phenotypes were then compared to the empirical distribution under the null hypothesis from the simulated data. By adopting this approach, this study attempted to establish if low genetic correlations between environmental levels were due to GxE or insufficient genetic linkage between animals in each environmental level. Results: The correlations (being less than <0.8) for the real phenotypes were indicative of GxE for CL presence between ADWG environmental levels and in pregnancy traits. However, none of the correlations for CL presence or first pregnancy between ADWG levels were below the 5th percentile value for the empirical distribution under the null hypothesis from the simulated data. Only one statistically significant (P < 0.05) indication of GxE for first pregnancy was found between THI environmental levels, where rg = 0.28 and 5th percentile value = 0.29, and this result was marginal. Conclusions: Only one case of statistically significant GxE for fertility traits was detected for first pregnancy between THI environmental levels 2 and 3. Other initial indications of GxE that were observed from the real phenotypes did not prove significant when compared to an empirical null distribution from simulated phenotypes. The lack of compelling evidence of GxE indicates that direct selection for fertility traits can be made accurately, using a single evaluation, regardless of environment.