Genomic regulation of oestrous behaviour in dairy cows

Concurrent to the impressive improvement achieved over the last few decades for the trait of milk production in dairy cows was a steady decline in several fertility traits including oestrous behaviour (OB). An understanding of the genomic regulation of OB, which is currently lacking in dairy cows, will present new opportunities for managing this trait to help improve fertility. The research described in this thesis therefore aimed to achieve this understanding by studying gene expression in the bovine anterior pituitary (AP) and four brain areas (amygdala, hippocampus, dorsal hypothalamus and ventral hypothalamus) that are involved in regulating OB. A series of different analyses were performed that included model based association of gene expression with OB scores, gene co-expression and differential expression. In the association analyses, the identified genes included those previously not known to be related to OB associated processes as well as several genes expressed in mid-cycle that may have a function in the proper expression of OB at the next oestrus.Expected genesknown to be involved in OB associated processes like socio-sexual behaviour (e.g. OXT, AVP, GABRA6, HTR2A, DRD2), anxiety, stress and feeding motivation (e.g. POMC, MCHR1, TTR) were found along with genes associated with nervous system related processes (e.g.CHRM1, CHRM3, CHRNA5, CTLA4, IL1RL1, MARCO), suggesting a link between neuronal plasticity and OB. In the co-expression analyses, biological terms found common to several OB correlated consensus modules included general cellular processes like oxidative phosphorylation, ribosome and biosynthetic processes, indicating increased transcription and protein synthesis. These processes are primary events in the activation of neuronal cells and pathways involved in female reproductive behaviour and they precede the oestrogen driven expansion of dendrites and synapses. Hub genes within the OB correlated modules (e.g. NEFL, NDRG2, GAP43, THY1, TCF7L2 etc.) are strong candidates among genes regulating OB expression. Further, we showed the phenomenon of chromosomal regional regulation of transcription to exist in the bovine genome. To conclude, this study has revealed important new aspects of the genomic regulation of OB in dairy cows with the key findings presented within the framework of the GAPPS modules. The new knowledge could be used to optimize fertility of dairy cows by aiding to improve existing or to devise novel reproductive management tools like diagnostic tools to determine the reproductive health, energy and fertility status of the cow, oestrus detection tools and so on.