Isolation vs. group rearing in monozygous twin heifer calves

Seven pairs of monozygous (MZ) twin heifer calves were assigned at birth to either isolation or group rearing. The isolation effects on feed intake, social development, survival activity, and learning ability were studied. There were no differences found in the average daily gain between the isolates and the group reared calves. Large variations in feed intake were randomly distributed across the treatments. There were no correlations between dominance rank at 15–17 months of age and body weight or age. An intraclass correlation of 0.93 between twin pairs indicated a strong genetic base for dominance. The group calves spent significantly longer eating than isolates. It was found that time recumbent did not differ, nor did laterality, between rearing regimes. The isolates achieved their goal in T-maze tests in significantly less time than group calves in the first 2 days of a 3-day trial. In comparing isolation rearing with weaning, there appeared to be no measurable detrimental effect on the calves and it may have enhanced their human-animal bond.