The effects of group size and floor space allowance on productivity, health and welfare were tested on 1728 grow-finish pigs (barrows) of PIC genetics. Group sizes were 18 (small) and 108 (large) pigs per pen, and space allowances were 0.52 m2/pig (crowded) and 0.78 m2/pig (uncrowded), creating four experimental treatments: small crowded, small uncrowded, large crowded, and large uncrowded.
Pigs housed in crowded groups had poorer performance than uncrowded pigs. Overall, average daily gain (ADG) was 4.2 % lower for crowded pigs than uncrowded pigs. During the final week of the trial, when the pigs were most crowded, the difference was 9.8 %. Final body weights differed by 2.1 %. Although crowded pigs spent less time at the feeder, had fewer meals, and had longer latencies between their meals than uncrowded pigs, average daily feed intake (ADFI) values did not differ. Overall feed efficiency was reduced by 6.6 % in the crowded treatment pigs.
Measurement of cortisol concentrations in the saliva, which are indicative of the level of stress a pig is experiencing, indicated that neither the group sizes nor space allowances used in the current study affected the stress level of the pigs. Postural behavior, carcass measurements, injuries, morbidity and mortality were unaffected by space allowance as well.
Pigs housed in large groups had poorer performance than pigs housed in small groups. Overall, the ADG of large group pigs was 3.5 % less than that of small group pigs and final body weights differed by 3.0 %. ADG differences were most evident during the first two weeks of the trial, at which time the difference was 5.4 %. The 3.3 % difference in initial body weights indicated that setbacks may have been occurring at group formation. FE also differed, with pigs in large groups being 6.0 % less efficient than pigs in small groups.
Although large group pigs experienced more lameness and leg sores throughout the trial, the number of animals requiring treatment with antibiotics or requiring removal from the trial did not differ between the group sizes. Stress levels and carcass measurements did not differ.
Large group housing for grow-finish pigs is not as detrimental to pig performance and vitality as once presumed. Pigs in large groups do not seem to suffer reduced welfare as long as regular and thorough health checks are performed. Deleterious effects of large groups were generally confined to the initial adaptation period. Marginal losses occurring at that time are most likely to be recovered through reduced input and labor costs associated with large group housing.
Under restricted space allowances, the gains of pigs in large groups were negatively affected much earlier on than for pigs in small groups. However, the effect of space restriction on gains of pigs in large groups is much more gradual over time, and the net effect of crowding at the end of the trial was similar among pigs in large and small groups. There was limited evidence, and none related to productivity, that pigs in large groups were able to use space more efficiently under crowded conditions than were pigs in small groups.