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Housing unweaned calves individually in barren environments negatively affects their growth, cognitive ability, and adaptability to environmental changes in later life. Social housing has been shown to improve those aspects, whereas physical environmental enrichment has rarely been studied in calves. Little is known about whether the combination of both components offers further benefits. Furthermore, curiosity has been considered an intrinsic factor underpinning cognitive performance, which has yet to be determined in calves. The first objective was to compare the effects of providing physical enrichment items and pair housing calves before weaning, and their combination on the weight gain, behaviour and cognitive ability of calves once regrouped after weaning. The second objective was to investigate if calves' exploratory behaviour in a novel environment can predict their cognitive ability. Forty-eight Holstein calves were allocated to eight groups 2 days after birth. Within each group, two calves were assigned to individual pens and four to two pair pens. One individual pen and one pair pen within each group were provided with brushes, chains, teats, and nets filled with strawberry-scented hay as physical enrichment items. Remaining pens received no additional enrichment items. All calves from a group were introduced to one post-weaning pen when the youngest calf was 9 weeks of age. Calves were weighed on days 1 and 7 in post-weaning pens. They were video-recorded on days 1, 3 and 11 and behavioural data were collected. Spontaneous object recognition tests were conducted within one week after behavioural data collection to assess cognitive ability in terms of how long after exposure calves recognised objects, indicated by differential expression of exploratory behaviour. Physical enrichment items and pair housing had interactions on average daily gain (F 1,33 = 5.460, p = 0.026), with calves in physically enriched pair pens showing higher average daily gain than those in non-enriched pair pens and tending to show higher average daily gains than those in physically enriched individual pens. Physically enriched calves expressed more exploratory behaviour and social sniffing than non-enriched calves (F 1,111 = 20.691, p < 0.001; F 1,111 = 14.433, p < 0.001). Pair housed calves spent more time cross-sucking than individually housed calves (F 1,111 = 8.848, p = 0.008). Compared with non-enriched calves, physically enriched calves were more inclined to explore the novel object than the object already presented 15-min ago (χ2 = 3.282, df = 1, p = 0.070). There was no association between exploratory behaviour upon initial introduction to post-weaning pens and performance in object recognition tests. In conclusion, the combination of physical enrichment and pair housing improves calves' average daily gain after weaning when compared with either component alone. Physical enrichment seemed to improve calves' memory and adaptability to change, whilst pair housing did not. Calves' exploratory behaviour in novel environments may not contribute to their cognitive performance. • The combination of enrichment items and pair housing improved calves' later growth. • Enrichment items improved adaptability to environmental changes whereas pair housing did not. • Enrichment items tended to improve recognition memory whereas pair housing did not. • There was no association between exploratory behaviour and object recognition memory. [ABSTRACT FROM AUTHOR]

• Access to physical items (e.g. brush, teat) improved growth; pair housing did not. • Physical items reduced undesirable behaviours (e.g. non-nutritive sucking). • Social housing promoted positive behaviours (e.g. locomotor play and sniffing). • The combination of physical items and social housing showed no further improvement. • The treatments had no effect on calf fear in novel environment and object tests. The objective of this study was to determine the effects of social housing, the provision of physical enrichment, and the interaction between the two on calf growth, behaviour and fearfulness. Forty-eight calves were randomly allocated to either individual (IP, sixteen calves) or pair (PP, thirty-two calves) pens from 2 days to 8 weeks of age. Half of the calves in each housing treatment were provided with physical enrichment items (stationary brushes, plastic chains, rubber teats and haynets filled with strawberry-scented hay; PE). The remaining calves received no physical enrichment items (NPE). Concentrate consumption within each pen was measured daily and calves were weighed at birth and weekly thereafter. Concentrate feeding efficiency was then calculated by the ratio between average daily gain within each pen and daily concentrate consumption within each pen. When calves were 2–5 weeks of age, they were recorded by a camera between 06:00 h and 20:00 h twice weekly, and behavioural data were collected using instantaneous scan sampling at 5-min intervals. Their behavioural responses to a novel environment and a novel object were then assessed once each at 5 or 6 weeks of age. PE calves tended to have greater average daily gains than NPE calves (mean ± IQR; 610.6 ± 151.8 g/d vs. 568.8 ± 77.1 g/d; p = 0.095). PE calves spent more time consuming hay than NPE calves. Among calves in IP pens, PE calves consumed less concentrate but had better concentrate feeding efficiency than NPE calves. For home pen behaviours, PE calves showed less frequent non-nutritive sucking than NPE calves (0.802 ± 0.451 % vs. 1.897 ± 0.401 % of scans) and less frequent cross-sucking. Furthermore, PP increased or tended to increase the time spent on locomotor play, fixture sniffing, social sniffing, allogrooming and cross-sucking, but tended to decrease non-nutritive sucking compared to IP. No treatment effects were found on behaviour in the novelty tests. In conclusion, physical enrichment may improve calf growth more effectively than social housing does. Physical enrichment and social housing may satisfy diverse natural behaviours and reduce undesirable behaviour in different ways. However, these treatments had no effect on calf fear responses in novel environment and object tests. The combination of physical enrichment and social housing showed no further improvement in calf welfare. [ABSTRACT FROM AUTHOR]