Date of Award


Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy


Biological Sciences

First Advisor

Dr Craig Murphy

Second Advisor

Prof Roy Sleator

Third Advisor

Prof Donagh Berry


Improving dairy cow production efficiency is highly desirable because of its well-documented impact on profitability and sustainability. Long-term gains in dairy cow production efficiency have already been delivered through genetic selection. Nonetheless, achieving further improvements in production efficiency could cement the economic and environmental efficiency of the dairy industry, globally. To date, several components contributing to production efficiency have been overlooked, with many studies focusing on dairy cow production efficiency over short periods rather than lifetime efficiency. Therefore, the objectives of this thesis were to quantify the genetic variance components of complementary dairy cow efficiency metrics; including dry matter intake, lactation length, lactation yields, and survival, and to quantify the usefulness of linear type traits in predicting the genetic merit for difficult to measure efficiency-related traits during different stages of lactation and across different parities. Results indicate that considerable genetic variation existed for the range of production efficiency-related traits investigated, with heritability estimates ranging from 0.02 for survival from first to second parity to 0.66 for first parity milk protein percentage. This exploitable genetic variation indicates that potential exists to breed for improved lifetime production efficiency by lengthening lactations and increasing the number of the lactations achieved while not necessarily reducing milk yield or increasing somatic cell count as cows get older. Additionally, the usefulness of some linear type traits as predictors of the genetic merit for survival, particularly in older cows, has been demonstrated and it has been determined that linear type traits have limited use as predictors of the genetic merit for dry matter intake in grazing Holstein-Friesian dairy cows.

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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