Abstract

The cow’s ability to reproduce is essential for milk production. Traditionally genetic evaluations for fertility have been based on measures on insemination- and calving dates, which in general are highly influenced by on-farm decisions. Unfortunately, the low heritability of classical fertility traits makes the genetic improvement slow. This thesis aims to provide information useful for a genetic evaluation utilising progesterone (P4) based fertility traits having higher heritability, and by using genomic information to try to identify genetic markers associated with fertility. The aim was also to investigate the characteristics of oestrous expression, pregnancy losses and their phenotypic relationships to P4 profiles as future potential traits included in breeding evaluation. Progesterone data from two data sets were used in the analyses: in Papers I and II from Swedish Red (SR) and Swedish Holstein (SH) dairy cows, and in Papers III and IV from Holstein-Friesian cows from four different countries. Swedish Red cows had higher conception rate, more intensive oestruses and longer oestrus durations compared to SH cows, irrespectively housing systems. Conception rate was found to increase with stronger oestrus intensity (OI), from 24% for with weaker and more uncertain oestrous symptoms, e.g. red and swollen vulva, to 54% for primary oestrous symptoms, e.g. standing. A total pregnancy loss of 65% was found for Swedish dairy cows, with an early embryonic loss of 29%. Swedish Red cows had significantly lower total pregnancy loss compared to SH cows (62 vs 68%). Early embryonic loss and total pregnancy loss had a tendency to decrease, while OI increased, with increasing cycle number. Cows with pregnancy losses had somewhat higher P4 levels at the day of insemination and lower P4 levels at some time points during gestation compared to pregnant cows. Heritability estimates were moderate for delayed cyclicity and commencement of luteal activity (CLA; 0.24 and 0.18 respectively) as well as the genetic correlation with milk yield in early lactation (rg=0.57 and 0.45). This may imply deterioration in these traits if not considered in the breeding evaluation. A genome-wide association study identified 44 genetic markers associated with the seven endocrine fertility traits. Three chromosomes were further fine-mapped for delayed cyclicity, cessation of cyclicity, CLA and oestrous cycle length using imputed sequences. Five regions with several possible candidate genes related to reproductive functions were identified. However, due to the high linkage disequilibrium it was not possibly to pinpoint a specific causal mutation. In the future, emphasis should be put on how automated P4 registration and oestrus detection could be used to improve and increase the number of registrations for e.g. OI and CLA and how we beneficially can include these in the genomic breeding evaluation.

Keywords

dairy cattle, fertility, oestrus, pregnancy, progesterone, embryonic loss, GWAS, imputation

Published in

Acta Universitatis Agriculturae Sueciae
2018, number: 2018:28
ISBN: 978-91-7760-196-8, eISBN: 978-91-7760-197-5
Publisher: Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences

SLU Authors

• Nyman, Sofia

  • Department of Animal Biosciences, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Animal and Dairy Science
Genetics and Breeding


Permanent link to this page (URI)

https://res.slu.se/id/publ/104191