The overall aim of Mehtiö’s thesis was to develop new recording methods for feed efficiency traits and explore the genetic background of feed efficiency in dairy cows. In particular, the main goals were to develop simple, practical and novel methods for measuring both cow-specific diet digestibility and energy status on farms, develop models for overall and partial metabolisable energy efficiency, and assess the genetic background in all these traits. The results indicated that near-infrared reflectance spectroscopy can be used to assess cow-specific diet digestibility from faecal samples. The coefficient of genetic variation for diet digestibility was rather small but could be utilised if improving diet digestibility pays off the costs of sample collection and processing. Nonetheless, every unit improvement in diet digestibility corresponds to proportionally the same amount of savings in feed requirements and thus may become of significant interest in the future.
Two new feed efficiency traits were explored. These traits allowed more accurate modelling and may be utilised in the prediction of breeding values in the future. The results indicated that some genetic variation may exist in the efficiency of using metabolisable energy for milk production, maintenance and growth in dairy cows.
The concentration of non-esterified fatty acid (NEFA) in blood increases, when a cow is in negative energy status, and thus NEFA can be used as an indicator for energy status. In this thesis, prediction equations for blood NEFA concentration were developed. Predicted NEFA was based on the mid-infrared reflectance spectroscopy of milk samples. The results indicated that predicted NEFA and four other energy status indicator traits were moderately heritable during the first three months of lactation. Moderate genetic correlations were found between energy status indicators and the fertility trait, the interval from calving to first insemination, in the first month of lactation. This indicates an unfavourable relationship between energy status indicators and fertility. The results of this thesis provide information needed for genetic improvement of feed efficiency in dairy cows and may be utilised on farms in dairy cow nutrition and management.
MSc Terhi Mehtiö will defend her doctoral dissertation entitled "Genetics of novel feed efficiency and related traits in Nordic dairy cattle” on 30th September 2020 at 13.00 in the Faculty of Agriculture and Forestry, University of Helsinki. The public defense will take place in lecture room B2, Forest Sciences Building, Latokartanonkaari 7. Doctor Yvette de Haas from Wageningen University & Research will serve as the opponent and Professor Pekka Uimari as the custos. The dissertation is published in the series Dissertationes Schola Doctoralis Scientiae Circumiectalis, Alimentariae, Biologicae.
The public defense can also be followed remotely using the following link: https://helsinki.zoom.us/j/62326752341?pwd=bkJLSEFvbTZRSGI2Z0tiZk5vMS9mUT09 Meeting ID: 62 326 752 341, Password: 979979
Contact: Terhi Mehtiö, firstname.lastname@example.org