Animal Sciences Research and Reviews

Special Circular 156

Pen Space and Pen Density Effects on the Feed Intake and Performance of Pigs Fed to Heavy Weights

K.M. Irvin and P. Dimsoski
Department of Animal Sciences

Summary

The objective of this experiment was to determine the space requirements of pigs fed from 165 to 300 pounds. Data were collected from 208 barrows and gilts assigned to one of three pen densities, 12, 16, or 24 pigs per pen (1.30, 0.98 and 0.65 m² per pig; 14, 10.5 and 7 square feet per pig). The average daily gains were very similar for the three pen densities when comparing gains week by week. As the pigs approached 300 pounds, the pens with 24 pigs grew slower. Feed intake per pig per week was similar early in the experiment. By mid-trial, the pigs in the pens with 24 pigs ate less (P < 0.05) than the pigs in the other two pen densities. For the total trial, feed intake per pig per week was less (P < 0.01) for the 24 pigs per pen group. Feed conversion and backfat means by ultrasound were similar for the pigs in the three pen densities. Average daily gain and feed intake were higher for the pigs at lower density, but feed conversion and backfat were not different. Heavy-weight pigs required more space per pig to maintain the higher performance in average daily gain and feed intake.

Introduction

Pig performance can be affected by many factors, including space allowance, group size, and pig weight. These effects also are related to economics of production. The question becomes, "at what pen density has one affected performance to the extent of lower economic returns?" Also, the shift to higher slaughter weights in the United States suggested the study of effects on pig performance of feeding pigs to heavier weights. The objective of this experiment was to determine the space requirements of pigs fed from 165 to 300 pounds.

Methods and Materials

The experiment was conducted at the Western Branch of the Ohio Agricultural Research and Development Center, South Charleston, Ohio. Data were collected from 208 barrows and gilts assigned to one of three pen densities, 12, 16, or 24 pigs per pen (14, 10.5, and 7 square feetper pig). Pigs were housed in a finish facility with a curtain on one side and at 1:4 ratio of slatted to concrete floor. During the trial duration, average outside air temperature was approximately 20 C^o during May through August. Pigs were fed ad libitum a pelleted corn-soybean meal diet (13.3% CP, 0.62% lysine, 0.61% calcium, and 0.51% phosphorus).

Equal numbers of barrows and gilts of the same age, weight, and breed composition were randomly assigned to one of three pen densities (12, 16, and 24 per pen). Pen size was held constant. There were four replications per pen density for a total of 12 pens. Data collection began when the pigs in the pen averaged 165 pounds and ended when the pigs in the pen averaged 300 pounds. Weights for each pig and pen feed disappearance were measured weekly. At the end of the test, backfat was measured for each pig by ultrasound.

Results and Discussion

Results for average daily gain, feed intake, and feed conversion are presented in Tables 1 to 3, respectively. Table 1 contains average daily gain by week and by groups of weeks. There was some variability in gain, but during most weeks gains were similar. Overall average daily gains were the greatest for the pigs in pens of 12, second greatest for pigs with 16 per pen, and were slowest for the pigs with 24 pigs per pen. The difference is statistically significant at the P < 0.01 level for overall gain. The pigs that were the most crowded gained the least, while the pigs in the least crowded pens gained more. A very marked difference in gain occurred during the last week of the trial when the most crowded pigs were reaching an average of 300 pounds.

Table 1. Least square means for average daily gain (pounds) by period, for differing pen densities.
	Number of pigs per pen			Probability F test P value
Period	12	16	24
Week 1	1.04a	0.86a	0.84a	0.336
Week 2	0.89a	1.03a	0.94a	0.314
Week 3	0.91a	0.84a	0.58b	0.070
Week 4	0.90a	0.97a	0.97a	0.820
Week 5	0.64a	0.87a	0.89a	0.789
Week 6	1.37a	0.81a	0.70b	0.052
Week 7	0.69a	0.78a	0.74a	0.810
Week 8	0.72a	0.71a	0.56b	0.073
From 165 to 230 pounds	0.95a	0.94a	0.83c	0.004
From 230 to 300 pounds	0.72a	0.80a	0.69a	0.246
From 165 to 300 pounds	0.88a	0.86a	0.76c	0.0003
abc Means with different superscripts are different. If superscripts are different by one letter (P < 0.05). If superscripts are different by two letters (P < 0.01).

Table 2 contains feed intake data by week and by groups of weeks. Feed intakes were similar for most weeks of the trial, with some variation week by week. When groups of weeks were compared, the pens with 12 and 16 pigs per pen had similar feed consumption, while the pens with 24 pigs per pen consumed less (P < 0.01) feed.

The most crowded pigs responded with lower feed consumption.

Table 2. Least square means for feed intake per day (pounds), by period for differing pen densities.
	Number of pigs per pen			Probability F test P value
Period	12	16	24
Week 1	21.31a	20.59a	19.95a	0.275
Week 2	21.94a	23.05a	19.30b	0.103
Week 3	25.24a	22.90a	20.31a	0.156
Week 4	23.03a	23.14a	18.97b	0.062
Week 5	22.26a	21.98a	20.01a	0.111
Week 6	23.40a	22.14a	21.35a	0.296
Week 7	22.96a	21.58ab	19.87b	0.051
Week 8	23.70a	22.57a	17.86c	0.005
From 165 to 230 pounds	22.81a	22.44ab	19.90c	0.011
From 230 to 360 pounds	22.88a	22.25ab	19.53c	0.009
From 165 to 300 pounds	22.87a	22.32a	19.69b	0.004
abc Means with different superscripts are different. If superscripts are different by one letter (P < 0.05). If superscripts are different by two letters (P < 0.01).

Table 3 contains feed conversion data by week and by groups of weeks. Feed conversion was similar for each week and for the total trial.

Table 3. Least square means for feed conversion by period for differing pen densities.
	Number of pigs per pen			Probability F test P value
Period	12	16	24
Week 1	2.99	3.59	3.57	0.312
Week 2	3.50	3.12	3.03	0.282
Week 3	3.86	3.91	4.22	0.638
Week 4	3.49	3.51	3.24	0.297
Week 5	3.67	3.90	3.78	0.845
Week 6	3.92	4.44	4.45	0.342
Week 7	3.62	4.06	4.12	0.497
Week 8	4.88	4.08	4.39	0.6552
From 165 to 230 pounds	3.45a	3.51	3.63b	0.226
From 230 to 360 pounds	4.25	4.16	4.28	0.826
From 165 to 300 pounds	3.87	3.86	3.94	0.775
ab Means with different superscripts are different (P < 0.10).

Backfat was measured for each pig by ultrasound when the pigs in a pen averaged 300 pounds live weight. Backfat averages were 32.27, 33.57, and 31.23 mm for 12, 16, and 24 pigs per pen (P > 0.10), respectively. Even though the backfat measures were not statistically different, a trend could be observed regarding backfat. The pigs that grew slowest and ate less also were the pigs with the smallest backfat.

Average daily gain and feed intake were higher for pigs that were raised at a lower pen density, but feed conversion and backfat were similar for all three pen densities. Heavy weight pigs required more space per pig to maintain a higher average daily gain and feed intake. A generally accepted space per pig during finishing is 8 square feet. However, 300-pound pigs are heavier than normally fed. A corresponding increase in space could be required to maintain optimum performance. With the performance levels indicated in this study, the number of pigs per year that could move through a finishing facility can be calculated to evaluate the impact on economics. Pigs at heaviest weights in pen density of 24 had comparatively less feed intake and less daily gain; however, their feed efficiency remained the same. Therefore, on an economic basis, the cost of feed per unit of gain remains the same. This indicated that the volume of gain per year produced by a finisher could be increased by raising pigs in the higher pen density level.