Production Management Featured Articles
The Effects of Raising Pigs in Large Groups
By Dr. Tim Safranski and Dr. Joe Zulovich, University of Missouri - Production technologies and practices often change over time. Sometimes they change gradually, and sometimes more abruptly. Occasionally, especially with abrupt changes, they leave us wondering why we didn’t think of that sooner. This article looks at the latest thinking on large groups.
As long as pigs have been raised indoors we have wondered what should be the optimal number of pigs per pen. Certainly housing finishing pigs as individuals is cost prohibitive. Research has suggested that pigs housed in large groups have a greater level of aggression. Most production systems have settled on group sizes of about 25 pigs.
Historically, research data has shown that young pigs in large groups show a reduced feed intake. The same phenomenon was not seen with bigger pigs, and investigators concluded that was because they adapt behaviorally to maintain feed intake, while the younger pigs do not change their feeding behavior.
In the May 2001 issue of the Journal of Animal Science researchers from the University of Illinois and United Feeds (Wolter et al., 2001) reported the results of their most recent study on group size. The project compared the effects of various group sizes on growth, feed efficiency and carcass characteristics. Fourteen-hundred pigs were weaned between 15-19 days of age averaging 13 pounds. They were moved to a wean-finish facility and housed in eight pens each of 25, 50 or 100 head. Regardless of group size, all pigs were provided 7.3 square feet. Two nipples and three feeder holes were provided per 25 head, and a 10 diet phase feeding program was used for the mixed sex pigs.
These scientists had observed reduced performance in large groups through eight weeks post-weaning in earlier studies, and some of that was repeated in this trial. Specifically, at the end of the first eight weeks, pigs in pens of 25 averaged 76.7 pounds, while pigs in pens of 50 and 100 averaged 74.7 pounds. In this particular trial they did not observe differences in feed intake, but the poorer daily gain was because of poorer feed conversion. Interestingly, by the time the pigs were slaughtered, there were no longer differences in weights, feed intakes or feed conversions. They also measured the carcass composition and found no differences among treatment groups. Liveweight at slaughter averaged about 278 pounds , with a 209 pound average carcass weight. The lean percentage for the three groups ranged from 53.4 to 53.8%, and was not statistically different among groups.
The conclusion of the authors was that pigs could be successfully housed in groups from 25 to 100 pigs per pen without detrimental effects. The effective or usable space per pig is slightly higher in large groups because of how the large group pens are arranged. Large group pens often have the feeder and water access located in the center, and this arrangement enables more pigs to rest and sleep around the perimeter of the pen and not be disturbed when a few pigs want to eat or drink.
The percentage of pigs removed from the pens of 25 for health reasons was higher than in the larger group sizes, but the authors suggested that was due to chance. Overall mortality was not different, and ranged from 1-3%. The level of care during this project probably helped to assure success. To make large groups work effectively, the caretaker must be diligent at observing each pig daily for signs of illness in order to stop problems early. For example, if I need to observe 200 animals, it is easier for me to observe 20 pens of ten pigs than one pen of 200 pigs.
The concept of larger group sizes is compelling, and may help to reduce facility costs in some situations. Housing pigs in large groups will necessitate very good husbandry skills, and can make the treatment or sorting of individual animals more challenging.
Wolter, Ellis, Curtis, Augspurger, Hamilton, Parr and Webel. 2001. Effect of group size on pig performance in a wean-to-finish production system. Journal of Animal Science, 79: 1067-1073.
Source: University of Missouri Outreach and Extension - September 2001
