Genotype × region and genotype × production level interactions in Holstein cows

Area of Science:

• Animal Genetics
• Dairy Science
• Agricultural Science

Background:

• Genotype by environment (GxE) interactions are crucial for Holstein cattle breeding programs.
• Understanding GxE effects optimizes genetic evaluations and breeding strategies in diverse regions.
• Chilean Holstein cattle present unique environmental conditions influencing GxE.

Purpose of the Study:

• To quantify genotype by environment interaction effects in Chilean Holstein dairy cattle.
• To analyze GxE for key production and reproduction traits.
• To inform regional genetic evaluation program design.

Main Methods:

• Analysis of calving records from 1998-2015.
• Classification of herds into central (Mediterranean, confined) and southern (temperate, grazing) regions.
• Further categorization by high/low production environments (fat + protein yield).
• Application of four-trait mixed animal models including fixed and random effects.
• Estimation of genetic correlations (rg) between environmental categories for traits like milk yield (MY), fat yield (FY), protein yield (PY), fat content (FC), protein content (PC), age at first calving (AFC), and calving interval (CI).

Main Results:

• Genetic correlations (rg) decreased with increasing environmental differences for MY, FY, FC, PC, and CI.
• A statistically significant rg < 0.60 was found for AFC between extreme environments (0.26).
• rg values < 0.80 were observed for AFC, CI, MY, FY, and PY between some environmental categories.
• GxE effects were moderate between Mediterranean/confinement and Temperate Oceanic/grazing systems, and within production levels.

Conclusions:

• Separate genetic evaluations based on rg < 0.60 may have limited impact on overall breeding objective improvement unless extreme environments are considered.
• Moderate decreases in selection response and re-ranking of candidates are anticipated for AFC, CI, and yield traits across different environments.
• GxE interactions in Chilean Holstein cattle are present but generally moderate, influencing selection decisions.