




































In ternationa l
Scholars
Journa ls

 

African Journal of Pig Farming ISSN 2375-0731 Vol. 6 (1), pp. 001-005, January, 2018. Available online at 
www.internationalscholarsjournals.org © International Scholars Journals 

 

Author(s) retain the copyright of this article. 

 

Review 
 

Effect of stocking density on pig production 

 
Jin Ho Cho and In Ho Kim* 

 
Department of Animal Resource and Science, Dankook University, No. 29 Anseodong, Cheonan, Choognam, 

330-714, Korea. 
 

Accepted 11 September, 2017 
 
Numerous stressors such as environmental, nutritional, pathological or equipment related ones are operative 
in swine facilities. Among many factors, socking density increases social stress and influences pig 
performance. Many studies have reported that reducing space allowance could induce decreases in growth 
performance of pigs. In addition, high stocking density induces a behavioral problem and influences 
physiological stress during transport. Thus, the optimum stocking density has to be defined for improving pig 
production. 

 
Key words: Performance, pigs, stocking density, stress. 

 
INTRODUCTION 

 
Under commercial conditions, because marginal profit 
increases with the size of pig operations (Martin and Kruja, 
2000), the pork industry is shifting toward larger production 
units. Housing pigs in large numbers and groups is a means 
of reducing housing costs and simplifying some aspects of 
management challenges. The provision of an adequate 
space allowance gives pigs sufficient space for drinking, lying 
and feeding. The main requirement for a pig during feeding is 
to be able to get to, and remain at the feed trough without 
feeling that their feeding space is threatened (Baxter, 1985a). 
Also, pigs will choose a resting area based on the security of 
that area (Baxter, 1985b). From 25 kg to heavier body 
weights, pigs lie together most of the day. As they grow up, 
pigs begin to prefer recumbent lying postures (Ekkel et al., 
2003). Space allowances should facilitate these behaviors 
(Table 1).  

High stocking density may cause a behavioral problem 
for pigs. At higher stocking densities, the likelihood of 
heightened aggression, competition and disease 
outbreak rapidly rises, and when this happens, the 
negative relationship between space and growth 
becomes even worse (Lebret et al., 2006). Curtis (1996) 
reported that the reduction in feed intake found in large 
groups may be caused by an increase in social pressure 
in larger as compared to smaller groups.  
 
 
 
*Corresponding  author.  E-mail:  inhokim@dankook.ac.kr.  Tel: 
+82-41-550-3652. Fax: +82-41-553-1618. 

 
 
 
 
 

 
Stressors existing in swine production systems would 

include cold/hot environmental temperatures (Stahly and 

Cromwell, 1979), microbial infections (Webel et al., 1997), 

insufficient space allowances (Brumm and Miller, 1996; 

Wolter et al., 2000), social mixing (Barnett et al., 1993; 

Marchant et al., 1995) and nutritional deficiencies or 

imbalances (NRC, 1998). These stressors cause growth 

retardation, changes in hormone release, increases in 

disease susceptibility, and/or behavioral changes. Also, 

physiological response to stressors (such as heat and 

spacial restriction) results in activation of the sympathetic 

nervous system and release of catecholamines and 

glucocorticoids reduce body weight (Breinekova et al., 

2006). Pig performance being subjected to stressors is 

common in commercial swine production. Stress may cause 

oxidative changes due to an increase in reactive oxygen 

species (ROS) or a decrease in the antioxidant status 

(Lykkesfeldt and Svendsen, 2007).  
The primary goal of this review is to describe an optimum 

stocking density and its effects on growth performance and 
stress in pigs. 

 
SPACE ALLOWANCE 

 
Space allowance is an important factor in the 
establishment of social rank (Baxter, 1985a). When pigs 
are housed in space restricted environments, the domi-
nance hierarchy becomes less stable (Jensen, 1982). 
Decreased stability most often results from the inability of 
a subordinate pig to retreat from a threat or act of 



  
 
 

 
Table 1. Categories of space requirements of pigs.  

 
Group Space requirement   
Body-occupation 
space 

 

Body-activity space 
 

 
Social space 

 

 
System space 

  
A pig lying down occupies more space than one standing up, a supine pig 
occupies more space than one in the semi-sternum position. 

 
The space required for body posture changes, like getting up or down, 
lying supine, turning round/grooming itself. 

 
The space required for socialization with other pigs or access by 
stockpersons. 

 
The space required by different management systems, e.g. straw vs. 
slats, gestation stalls, group in yard, wet feeding vs. dry hoppers, etc. 
 

 
Dead space The space required for partitions, passages, corners and pen furniture   
Gadd (2003). 

 

 

aggression on behalf of the dominant pig. Therefore, the 
dominant pig does not recognize submission, and a fight 
may continue unnecessarily or resume later (Baxter, 
1985a; Turner et al., 2003).  

McGlone and Newby (1994) attempted to determine the 
optimal amount of space required by a pig to achieve 
maximum performance. Authors evaluated group sizes of 
10, 20 and 40 pigs per pen during the grow-finish period 
(23 to 95 kg of BW) and found no difference in growth 
performance. However, in a group of growing pigs, those 

with a restricted space allowance (0.25 m
2
/pig), grew 

more slowly than pigs with a greater space allowance 

(0.56 m
2
/pig) (Hyun et al., 1998) for each week of the four 

weeks study. Pigs with the restricted space allowance 
showed reduction in feed intake at the 4th week. Pigs with 
restricted floor space showed an increase uncharacte-
ristically in the behaviours and amounts of aggression 
(Hyun et al., 1998). As pigs become more aggressive, 
they use more energy and growth rates decline (Hyun et 
al., 1998). Increased aggression may also lead to 
increased injury levels and disease, and thus, increased 
stress. With an increase in stress, it is possible to reduce 
the gains potential, which in turn reduces appetite and 
average daily feed intake (Chapple, 1993). Furthermore, 
increased stress can increase the occurrence of 
stereotypic behaviors and vices, such as tail biting 
(Baxter, 1985b).  

Space allowance has traditionally been expressed 
empirically by categorizing pigs into a series of weight 
ranges and by designating space on a per animal basis 
(Brumm and NCR-89 Committee on Management of 
Swine, 1996).  

Recommendations on space allowance for optimum 
feed intake have been set by the National Research 

Council (1988) with 0.6 m
2
/pig at 25 to 60 kg live weight 

and 1.0 m
2
/ pig at 60 kg live weight. In Korea, there is 

legislation on pig stocking density. Also, in the EU, mini-
mum stocking rates, listed in Table 2, are the minimum 

 
 
 
 

 

space requirements mandated by EU law.However, in the 
US, there is no legislation on pig stocking density. The 
National Pork Board does, however, made recom-
mendations in its Swine Care Handbook (Table 2). These 
recommendations are based on the minimum space 
required to achieve maximum performance. 
 

 

EFFECT OF STOCKING DENSITY ON GROWTH 
PERFORMANCE 
 
Stocking density has a significant impact on growth 
performance. Stocking rate can have a major effect on 
feed intake as shown by Brumm and Gonyou (2001) who 
found that a major response to space restrictions was a 
decrease in feed intake. Stocking density allowances 
were seen excessively in pigs which have been shown to 
be necessary for maximum performance (Edwards et al., 
1988).  

When growing-finishing pigs are given less than optimal 
space per pig, feed intake always decreases (Brumm et 
al., 2001), often resulting in a reduction in average daily 
gain (ADG), with variable effects on the gain : feed ratio 
(G:F). Social interaction with another pig reduces growth 
performance and feed intake regardless of stocking 
density. Certain studies have demonstrated a reduction in 
growth performance with increasing stocking density 
(Petherick et al., 1989; Gonyou et al., 1992). Swine 
producers try to maximize profits by minimizing both 
performance retardation and underutilized space. Crow-
ding stress deleteriously affect the growth performance of 
pigs. Pigs, housed on deep-straw for six weeks in groups 

of 20 or 80, were provided with a low (50 kg/m
2
) or high 

(32 kg/m
2
) space allowance in Turner et al. (2003) study.  

They reported that groups of 80 pigs had a lower ADG 
than groups of 20 (0.684 vs. 0.732 kg). Wolter et al. 

(2002) demonstrated that double stocking (0.64 m
2
/pig 

vs. 0.32 m
2
/pig) reduced growth rate to ten weeks after 



 
 
 

 
Table 2. Minimum recommended stocking densities for growing-finishing 
pigs in Korea, EU and US.  

 

Country Live weight (kg) Space allowance (m
2
) 

 10-30  0.30 

Korea
1
 30-85  0.60 

 85-110  0.90 

 <10  0.15 

 10-20  0.20 

 20-30  0.30 

Europe
2
 30-50  0.40 

 50-85  0.55 

 85-110  0.65 

 >110  1.00 

 5.4-13.6 (12-30 lb) 0.15-0.23 (1.7-2.5 ft
2
) 

 13.6-27.2 (30-60 lb) 0.27-0.37 (3-4 ft
2
) 

U.S.A
3
 27.2-45.6 (60-100 lb) 0.46 (5 ft

2)
 

 45.6-68.0 (100-150 lb) 0.55 (5 ft
2)

 

 68.0-market (150 lb -market) 0.74 (8 ft
2)

 
 

1
 http://english.mifaff.go.kr; 

2
httpp://www.dardni.gov.uk; 

3
http://www.pork.org.

 

 

 

weaning. Wolter et al. (2003) investigated the subsequent 
effects of eight weeks space restriction in weanling pigs. For 
eight weeks, space restricted pigs showed growth 
retardation when compared with pigs provided with 
adequate space (27.4 vs. 29.3 kg of BW). Smith et al. (2004) 
reported that nursery pigs with the greatest space allowance 

(0.35 m
2
/pig) were 5.6% heavier than pigs with the least 

amount of space (0.23 m
2
/pig). Kerr et al. (2005) 

demonstrated that growing pigs maintained at low stocking 
density had a higher weight gain (8.23 kg) than their high 
stocking density counterparts (7.42 kg) for five weeks at the 
same room temperature. White et al. (2008) reported that 

reducing stocking density from 0.93 to 0.66 m
2
/pig resulted 

in 4.0% less body weight, 17.0% less ADG, 10.7% less 
average daily feed intake (ADFI) and a 7.8% less G : F ratio. 
Recently, Cho et al. (2010) reported that for the six-week 
nursery period, the crowding reduced ADG of gilts (577: 0.50 

m
2
/pig, 536: 0.25 m

2
/pig, and 558 g/d: 0.25 m

2
/pig) and 

barrows (578, 539 and 527 g/d).  
Numerous previous studies evaluated the effects of space 

restrictions while using similar nutrient densities for all 

treatments (Moser et al., 1985; NCR-89, 1993). In these 

studies, ADFI reduced as a result of space restriction. 

However, Kornegay et al. (1993) did not observe a space × 

lysine interaction in nursery pigs. Further studies revealed no 

improvement in performance when finishing pigs were fed 

higher levels of energy and lysine with reduced space (NRC-

89, 1993) or amino acids (Hahn et al., 1995). A study by 

Brumm and Miller (1996) indicated that added energy and 

lysine in growing-finishing pig diets did not overcompensate 

for the reduction in performance from a reduced space 

allowance. 

 
 

 

Edmonds et al. (1998) suggested that pigs with lower feed 

intakes as a result of space restriction did not have higher 

CP requirements than those with more space. Krohn et al. 

(2000) distributed pigs in nine groups with six pigs in each at 

three different stocking densities (0.27, 0.44 and 0.52 

m
2
/pig). They reported that no significant differences within 

any of the different behavioral categories could be observed 

between the three housing densities. Brumm et al. (2001) 

reported no residual effects of nursery crowding on grow-

finish performance. Pigs that were crowded during the 

nursery period and uncrowded during the grow-finishing 

period had similar, although numerically rather lower, daily 

gains (849 vs. 867 g/d, during the grow-finishing period) than 

pigs that were uncrowded during both the nursery and grow-

finishing period. 
 

 

EFFECT OF DIFFERENT SUPPLEMENTATION FOR 
REDUCING CROWDING STRESS 

 

Marco-Ramell et al. (2011) demonstrated that plasma 
proteins in animals stressed by increased stocking 

density (0.50 m
2
/pig vs. 0.25 m

2
/pig) were more oxidized 

and an increase in oxidative stress markers was detected 
in the high density animals.High stocking density is an 
agriculture-related situation which causes crowding stress 
in pigs and potentially affects their immune systems. 
Protection against disease can be induced through 
immune system, enhancing defense mechanisms. Stress 
has been generally shown to affect the immune function 
of animals (Kelly, 1985), while vitamin C supplementation 
has been associated with enhanced immune system 



 
 
 

 

competence. Vitamins E (150 vs. 120 mg/kg) and C (300 
vs. 100 mg/kg) have been shown to depress the stress 
responses of pigs (25.1 ± 4.4 kg) undergoing vibration 
stimulation during transportation (Peeters et al., 2005). 
Also, essential oils have demonstrated ability to reduce 
stress, stimulate sluggish circulation, boost the immune 
system and induce uplifting or relaxing effects. Wenk 
(2003) reported that the beneficial effects of essential oils 
on farm animals may arise from activation of feed intake 
and secretion of digestive juices, immune system 
stimulation and anti-bacterial, coccidiostatic, antiviral and 
antioxidant properties. 
 
 
EFFECT OF STOCKING DENSITY ON 
REPRODUCTIVE PERFORMANCE 
 
Rutledge (1980) reported that there was gilts allowance in 
small groups (six pigs) with an average of 11 piglets 
given birth to whereas gilts reared in a larger group (ten 
pigs) had an average of ten pigs given birth to. Kuhlers et 
al. (1985) selected gilts at about 30 kg and reared them in 
pens of eight or 16 pigs. Gilts reared in the smaller groups 
were more than the total pigs given birth to with 1.0. When 
comparing gilts raised in litters of either five or ten pigs, 
Kirkpatrick and Rutledge (1988) found that gilts in small 
litters had 1.1 more embryos at day 30 post-mating. Stewart 
and Diekman (1989) reported that gilts raised in litters of 6 

had 0.3 more pigs in first parity than gilts raised in litters of 
12. However, the impact of stress post-weaning has not 
been adequately studied to determine if group size or 
space allowance has a negative impact on reproduction. 

 

CONCLUSION 

 
Now, swine industry is changing on a large scale. High 
stocking density reduces the welfare of pigs. Numerous 
results of researches show that the negative effects on 
performance was associated with large groups and the 
reduced floor-space allowance. According to this review, 
nursery, growing and finishing pigs require space 

allowances of >0.30, 0.60 and 0.90 m
2
/pig, respectively. 

Future researches are needed to evaluate environmental 
configuration designs that may enhance growth and 
reproductive performance of pigs. 
 

 
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