Too Many Hogs in a Pen Depresses Growth

By Dr Morgan Morrow, NCSU Swine Extension - In the 1990s we saw an explosion in the number of finishing floors in North Carolina. Most of those floors were built and budgeted to provide about 7.5 square feet of finishing space per pig. Over time, and as the pressure to produce more pork from available resources has increased, we have seen more pigs placed in those buildings on some farms. Consequently, the space available for the individual pig has decreased. The question is, have profit and performance suffered?
calendar icon 10 May 2002
clock icon 5 minute read

Dr Morgan Morrow
Swine Veterinary Specialist
While there is little to no data on the profitability of these space-stressed groups of pigs, two recent studies confirm that pig performance is compromised.

Drs. Harold Gonyou and Ray Stricklin of the Prairie Swine Centre, Inc., in Saskatoon, Saskatchewan, Canada, concluded that their results confirmed "previous studies reporting a negative effect of increasing group size on productivity." They also said, "Our study suggests that gain and intake reach a plateau at less space allowance than previously reported."

Their abstract says:

"Six group sizes and three levels of floor area allowance were studied in a 6 X 3 factorial arrangement. Group sizes were 3, 5, 6, 7, 10, and 15 pigs per pen. Floor area allowances were 0.030, 0.039, and 0.048 m2 X BW(.)667. All pens were square and equipped with a single space feeder and nipple drinker near one corner. Pigs were fed a pelleted diet. Initial eights averaged 25.0 kg, and pigs remained on test for 12 weeks. Pigs were weighed, feed intake was determined, and the size of the pens was increased at 2-week intervals. Pen size was adjusted to provide the space required for the midpoint of each weigh period."

"Two replicates of the study were conducted. The average daily gain (ADG) was reduced with increasing group size (899, 851, 868, 872, 857, and 821 g, SEM = 16.4, for 3, 5, 6, 7, 10, and 15 pigs, respectively; P < 0.05), but the CV for gain (mean = 0.185) did not differ among group sizes."

"The ADFI also decreased with increasing group size (2.49, 2.34, 2.32, 2.28, 2.28, and 2.21 kg, SEM = 0.036, for 3, 5, 6, 7, 10, and 15 pigs, respectively; P < 0.05). Feed efficiency (gain/intake) was highest for group sizes of 7 and 10 pigs (0.381) and lowest for pens of three and five pigs (0.363; P < 0.05). The ADG and ADFI (832 g and 2.25 kg, respectively) for the most crowded space allowance were reduced, compared to more spacious allowances (ADG and ADFI of 875 and 877 g, and 2.35 and 2.36 kg, for 0.039 and 0.048 m2 x BW(.)667, respectively; P < 0.05). Efficiency did not differ among space allowances."

Another study by Dr. Young Hyun and others confirms the depression of growth rate of pigs subjected to restricted space allowance. In addition, they showed that pigs subjected to restricted space allowance, high cycling temperature, and regrouping simultaneously exhibited ADG depressed by 31 percent.

The Hyun abstract says:

"The effects of many single stressors have been reported, but how pigs perform when subjected to more than one or two stressors at a time, as is common in commercial swine production, has not. To study this, 256 Yorkshire x Hampshire or purebred Duroc pigs (34.7 +/- 0.5 kg) were subjected to one of the eight treatment combinations (2 x 2 x 2 factorial) of ambient temperature (constant thermoneutral [24 degrees C] or high cycling temperature [28 to 34 degrees C]), stocking density (0.56 or 0.25 m2/pig), and social group (static group or regrouped at the start of weeks 1 and 3) during a 4-week experiment. The temperature regimens were imposed in two adjacent, mechanically ventilated rooms, and each tempera-ture was imposed in each room across two trials."

"Four barrows and four gilts were assigned to each of the eight pens in the two rooms, and they always had free access to water and a corn-soybean-meal-based diet. Treatments were imposed after a 7-day acclimation period at 24 degrees C and 0.56 m2/pig. Weight gain and feed intake were measured weekly."

"The main effects of each of the stressors for 4-week ADG and ADFI were significant (P < 0.05). The stress of high temperature, high stocking density, and regrouping depressed 4-week ADG by 12 percent, 16 percent, and 10 percent and ADFI by 7 percent, 6 percent, and 5 percent, respectively. Of the possible 60 stressor interactions for ADG, ADFI, and gain:feed (G:F), there were no significant three-way interactions and only 6 two-way interactions, suggesting that the effects of the individual stressors were additive."

"Accordingly, the growth rate of pigs subjected to the single stressor of high cycling temperature, restricted space allowance, or regrouping was depressed 10 percent, 16 percent, and 11 percent, respectively, and ADG of pigs subjected to all three stressors simultaneously was depressed by 31 percent. Stressor additivity was further corroborated by examining the effect of stressor order, or the number of stressors imposed simultaneously. As the number of stressors increased from 0 to 3, ADG, ADFI, and G:F decreased linearly."

"These data suggest that multiple concurrent stressors affect growth performance of pigs in a predictable fashion (i.e., additively) and indicate that avoidance or removal of a given stressor is advantageous, even when other uncontrollable stressors persist."

1. Gonyou, Harold and Ray Stricklin. 1998. Effects of floor area allowance and group size on the productivity of growing/finishing pigs. J. Anim. Sci. 76(5):1326-1330.
2. Hyun, Young, et al. 1998. Growth performance of pigs subjected to multiple concurrent environmental stressors. J. Anim. Sci. 76(3):721-727.

Reproduced Courtsey

Source: North Carolina State University Swine Extension - April 2002
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