Personality is individual differences in behaviour consistent over time and/or across contexts, which means that an individual displaying personality has a tendency to behave in a certain way and is less able to instantaneously modify behaviour adaptively to current circumstances. One possible explanation for this is that consistency in behaviour represent limitations in plasticity. Plasticity is assumed to be costly or constrained, and behaviours might then be linked, due to selection pressure as well as genetic correlations, to traits that are less plastic. One such trait is growth rate, which has been found to correlate to a set of behaviour traits including boldness, activity and aggressiveness. 

I suggest in this thesis that variation in milk production might be another life-history trait that is in a complex relationship with personality. One reason to assume variation in milk production to be correlated to personality is that behaviour is suggested to be associated with current and future reproduction expectations. In mammals, milk yield and milk quality can be regarded as a female’s investment in her offspring, and therefore, correlations between behaviours and investment in residual reproduction value (future fitness) are predicted. Individuals that expect higher future (compared to current) reproductive success, are expected to behave more carefully and be slower and shyer, compared to individuals with higher current reproductive expectations. Linked to expectations based on variation in growth rates, individuals with higher current reproductive expectations are likely to be individuals that also are fast growing and therefore may die earlier.

It has been suggested that the understanding of personality in cows may be valuable for basic dairy research as well as for improving management routines. Cows in dairy production are handled several times per day and it is of great importance in terms of time, economy and welfare that the management is efficient. Personality traits are likely to contribute to levels in productivity and investigation of the relationship between personality gradients and life-history traits may therefore be valuable to improve our understanding of how personality origin and evolve.

For these reasons, I aimed to
1) determine consistent behavioural traits among individuals in a population of loose housed dairy cows, and
2) investigate the relationship between cow personality and individual production level.