The benefits of individual housing is evidenced in many studies as lowering the risk of diseases, however, group housing may improve welfare by facilitating socialization, play behavior and greater ability to move and exercise as well as choose a preferred area. In a few studies, it was shown that smaller groups of about 2-6 calves allows for more calf interactions and acts as a form of enrichment by adding stimuli. Proper management may also reduce risk of infection in a group housing system. For example, stocking density in a group setting is important in managing diarrhea or scours. In one study it was found that calves had a 74% greater risk of getting diarrhea if space allowance per calf was less than 3.28 sf2. In another study, it was concluded that at least 14.44 sf are needed between cattle to reduce transmitting infectious bovine rhinotracheitis (IBR).
Larger groups are more difficult to keep clean and control nutrition and disease and calves are typically exposed to more pathogens in larger groups which make them more at risk for contracting diseases. Epidemiological research has shown that it is the larger groups that increase calf morbidity and mortality, rather than any group housing. A disadvantage of housing solely with peers without any contact with the mother is the cross-suckling behavior that occurs. However, incorporating some type of suckling system that will satisfy the calves innate sucking behavior may reduce this incidence.
Here is a video of calves thriving in group housing with an automatic milk teat feeder. As you can see, they have space to run around, socialize and play unlike in individual hutches.