Genotype by environment interaction for yield and somatic cell score with alternative environmental definitions

Area of Science:

• Animal Genetics
• Dairy Science
• Environmental Interaction

Background:

• Genetic selection aims to improve traits like milk yield and health.
• Herd environments significantly influence the expression of genetic potential.
• Understanding genetic-by-environment interactions is crucial for effective breeding programs.

Purpose of the Study:

• To investigate differential genetic expression in high vs. low opportunity environments for Holstein-Friesian and Brown Swiss dairy herds.
• To compare genetic-by-environment interactions using various environmental definitions.
• To quantify potential losses in genetic gain due to contrasting herd management.

Main Methods:

• Analysis of first-lactation standardized yields (milk, fat, protein) and somatic cell score.
• Utilized bivariate and multivariate sire models to estimate genetic parameters.
• Defined environments based on herd-year standard deviation, lactation incidence, and management practices.

Main Results:

• Sire variances for yield traits were smaller in low opportunity environments for both breeds.
• Correlated yield response in less privileged environments was 0.41-0.81 of that in high opportunity environments.
• Lower correlated response for somatic cell score in environments with reduced yield-enhancing practices.

Conclusions:

• Unfavorable management interactions create unequal selection gains across contrasting environments.
• Improved nutrition, health care, and milking management are expected to enhance both genetic and phenotypic responses.
• Breeding strategies must consider environmental context to maximize genetic progress.