Breeding for sustainable milk production: from nucleus herds to genomic data

The overall aim of the research reported in this thesis was to investigate ways to mitigate deterioration in functional traits and reduce the environmental impact of milk production. The more specific objectives were to obtain new information about the selection of bull dams for functional traits in an open nucleus herd, to monitor ongoing genetic trends in functional traits, and to examine a breeding program with genomic selection and contractor herds that records specific indicator traits correlated with environmental impact. A breeding scheme with expanded recording of functional traits in potential bull dams in a nucleus herd was simulated. The genetic trend in functional traits was found to be unfavourable in all scenarios. Improved recording of functional traits did not limit the unfavourable genetic response in fertility and udder health traits unless more economic weight was placed on functional traits in the breeding goal. Genetic trends in fertility and udder health traits were estimated in Swedish Red dairy cattle. The estimated genetic trend for number of inseminations in lactating cows was unfavorable. The choice of model to be used for genetic evaluation influences the estimate of genetic trend, indicating that unfavorable genetic trends may not be discovered unless the traits are evaluated in a multiple-trait model including both functional and production traits. Substantial genetic progress in breeding for environmentally friendly cows can be achieved by including environmental impact in the breeding goal, and by using phenotype records and genomic information on correlated indicator traits. The most valuable indicator traits are those with a strong genetic correlation with environmental impact that also have a high accuracy of direct genomic values. Breakeven prices for recording the indicator trait were calculated for all scenarios. They varied considerably from one scenario to another, depending on the number of phenotype records on indicator traits. Recording an indicator trait could be both genetically and economically advantageous where the genetic correlation between the trait in question and environmental impact is strong, the trait has an optimal number of phenotype records, and the reliability of direct genomic values is moderately high.