Effects of physical enrichment and social housing on calves' growth, behaviour, affective state and cognitive ability

Dairy calves are commonly reared in artificial environments in the dairy industry. It is essential to understand and satisfy their motivations so as to improve their welfare, promote their behavioural and cognitive development and increase their growth and adaptability to environmental changes. The first aim of this dissertation was to study effective ways to complicate calves' housing environments and understand how the environment complexity impacts behaviour and improves calves' welfare. We investigated the effectiveness of physical enrichment protocols and determined calves' preferences for and ways of interacting with various physical enrichment items. A fixed multi-item enrichment presentation schedule was considered an effective protocol. Nets filled with scented hay seemed to be the most attractive item tested, which stimulated calves to show five types of interaction behaviours towards them. We then determined how the provision of the physical enrichment items in the effective protocol identified, pair housing, and the combination of both components in calves' pre-weaning period affect pre- and post-weaning weight gain, pre- and post-weaning behaviours, fear responses to novelty and memory ability. We found that adding complexity to pre-weaning calves' housing environments using the three methods appeared likely to improve their welfare by providing outlets for natural behaviours, mitigating undesirable behaviours, promoting growth, increasing behavioural flexibility or improving memory ability. In addition, since calves' fear responses in repeated fear tests are inconsistent, this dissertation also aimed to investigate the potential mechanisms resulting in this uncertain reliability. We investigated whether calves have visual lateralization in 8 processing fear in novel object tests and if initial monocular presentation of novel objects affects calves' fear responses. The results suggested that the poor test-retest reliability in repeated novel object tests could not be explained by visual lateralization in processing fear, and eye laterality might not be considered a useful measure of fear at this age.