The social and feeding behaviour of growing pigs in deep-litter, large group housing systems

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Abstract

Two studies compared the social and feeding behaviour of Large White×Landrace entire male (non-castrated) growing pigs housed in deep-litter, large group and conventional housing systems. In Study 1, an ethogram of behaviour was developed. The pigs were housed at 1 m2 per pig (200 pigs per pen) and 8.3 pigs per feeding space in the deep-litter system and 0.70 m2 per pig (45 pigs per pen) and 8.5 pigs per feeding space in the conventional system. In Study 2, the social and feeding behaviour of entire male growing pigs were compared. Eight hundred and eighty crossbred entire male pigs were used. There were 200 pigs per pen (1 m2 per pig; 8.3 pigs per feeding space) in the deep-litter system and 20 pigs per pen (0.49 m2 per pig; 10 pigs per feeding space) in the conventional system. When the average pig live weight was 60 kg, five non-focal pigs were removed from each pen resulting in 0.65 m2 per pig (7.5 pigs per feeding space). In both studies, ad libitum feed was provided in double-spaced, wet–dry feeders. In each study there were four replicates, with 10 focal animals per treatment per replicate randomly selected for behaviour observations. All observations were conducted during day light. In Study 1, behaviour was observed when pigs were 21–22 weeks of age and in Study 2 social behaviour observations were conducted from 19 to 22 weeks of age, while feeding behaviour was observed from 20 to 22 weeks of age.

Pigs housed in the deep-litter system spent more (P<0.01) time standing and less (P<0.05) time sitting and lying, and spent more (P<0.001) time in locomotion compared to conventionally housed pigs. There was an increase (P<0.05) in physical pen interactions and a higher (P<0.001) incidence of social tactile interactions and agonistic (P<0.001) and sexual behaviours (P<0.01) in the deep-litter treatment. Such differences in social behaviour may be responsible for differences in growth performance commonly observed in deep-litter systems.

Pigs in the deep-litter treatment spent less time (P<0.05) within 1 m of the feeder, had fewer (P<0.05) feeding events, had a longer (P<0.05) duration of feeding and a lower (P<0.05) frequency of social interactions around the feeder compared to pigs in the conventional treatment. The difficulties in gaining and maintaining access to the feeder in the conventional pens may be responsible for the shorter but more frequent feeding bouts observed. It is possible that the relatively unrestricted feeding that occurred in the deep-litter treatment may have resulted in increased fat deposition and poorer feed conversion efficiency, as observed in the industry setting, because of changes in feeding patterns that affect feed utilisation.

Introduction

Deep-litter, large group housing systems for growing pigs have been developed as an alternative housing system. Large groups of pigs in such alternative housing systems are usually kept on deep-litter between 2 and 8 weeks of age (∼5–20 kg live weight) till slaughter (∼22 weeks of age, live weight ∼110 kg). Conventionally however, growing pigs are housed in a more confined system indoors and with automated ventilation, fully or partially slatted floors and liquid manure handling systems. The number of pigs per pen tends to be in the range of 5–50 pigs with a floor space allowance of a maximum of about 0.7 m2 per pig. In contrast, deep-litter systems are naturally ventilated, have a floor base of deep-litter consisting of rice hulls or straw, accommodate larger group sizes (ranging from 150 to 2000 pigs per pen) and the pigs have a greater space allowance of approximately 1 m2 per pig.

Deep-litter systems are cheaper to establish and are perceived as being more “welfare-friendly” for pigs and more environmentally sustainable, as the need for effluent ponds is eliminated and the deep-litter substrate is used as a natural fertiliser. However, recent industry records indicate that pigs grown from 2 weeks of age to slaughter at 22 weeks in deep-litter large group systems show a number of growth performance problems compared to conventionally housed pigs (Connor, 1995, Payne, 1997, Brumm, 1999, Honeyman et al., 1999, Payne et al., 2000). For instance, pigs in the former systems are 10% less efficient in converting feed provided to live weight gain (feed:gain) and may be 1–2 mm greater backfat.

Deep-litter systems are disparate in the type and amount of bedding provided, the number of pigs per group, floor space allowance per pig, method of providing feed and water and the construction materials used to build the deep-litter, large group system. Few rigorous comparisons have been conducted between the various modifications of deep-litter systems or between deep-litter, large group and conventional housing systems. Nevertheless, while many key factors in addition to the basic features of the system will vary, such as climate, disease status and location, it is possible that the apparent growth performance differences between deep-litter, large group and conventional housing systems are largely behavioural and possibly stress related.

The scientific literature on comparative effects of deep-litter and large group sizes on social and feeding behaviour and stress physiology of growing pigs is very limited. There is a plethora of information on the effects of environmental enrichment on the social behaviour and growth performance of growing pigs (Wood-Gush and Vestergaard, 1989a, Wood-Gush and Vestergaard, 1989b, Beattie et al., 1995, Beattie et al., 1996, Beattie et al., 2000a, Beattie et al., 2000b; Peterson et al., 1995, O’Connell and Beattie, 1999), however the majority of research has been conducted in conventional systems with smaller groups of pigs. Furthermore, little is known of the social behaviour of pigs in large groups in deep-litter systems. Aggressive behaviours may be higher in larger groups of pigs, as individual animal recognition may not be functional (Spoolder et al., 1999). On the other hand, aggression may be reduced on deep-litter pigs with the attention of the pigs redirected from pen mates to the litter. Furthermore, the greater availability of resources in these large groups may reduce the need for aggression (Hemsworth and Barnett, 2001), or the pigs may be socially tolerant in these large groups (Hughes et al., 1997). Factors that may affect the feeding and social behaviour and performance of pigs in deep-litter systems, such as the provision of litter, increased group sizes and space allowance, require attention.

To compare the behaviour of growing pigs in deep-litter, large group systems to that of pigs in conventional systems, it is necessary to conduct controlled studies in which inputs unrelated to the system, such as locality, feed, feeder type and genetics are similar. Therefore, the aim of the present studies was to examine the social and feeding behaviour of entire male growing pigs in deep-litter, large group housing systems compared to pigs in conventional housing systems. An ethogram of the behaviour of growing pigs in deep-litter and conventional housing systems was developed in Study 1, to enable a comparative study of social and feeding behaviour in Study 2, while controlling for locality, feed, feeder type and genotype.

Section snippets

Animals and housing treatments

The care and experimental use of pigs in these experiments conformed to the requirements of the Australian Prevention of Cruelty to Animals Act 1986 and the NHMRC “Australian code of practice for the care and use of animals for scientific purposes”. These studies were conducted in a deep-litter, large group housing system and a conventional housing system at a large commercial piggery in Corowa, NSW, Australia (36°S latitude, 146.5°E longitude). The two housing treatments were located

Study 1

The following ethogram was defined for entire male growing pigs in the deep-litter, large group system and the conventional system.

Discussion

The behaviours described in the ethogram from Study 1 were identified as relevant behaviours to study differences in the social and feeding behaviour of entire male growing pigs in deep-litter, large group systems and conventional systems in Study 2. The behaviours defined in the ethogram are similar to behaviours observed by Kelley et al. (1980), McGlone (1985) and Stolba and Wood-Gush (1989) in growing pigs and by Jensen, 1980, Jensen, 1982 in group-housed dry sows.

Social tactile interactions

Conclusions

In conclusion, Study 1 defined the behavioural repertoire of entire male growing pigs in deep-litter, large group housing and conventional group housing systems. It is these behaviours that need to be observed in order to quantify the effects of social and feeding behaviour on the growth performance of entire male growing pigs in deep-litter, large group housing systems. Furthermore, the results from Study 2 showed that there were differences in the social and feeding behaviour of entire male

Acknowledgements

We wish to acknowledge financial support from the National Pork Industry Development Program and QAF Meat Industries Ltd. The technical support from J. Boyce, E. Leeson, D. Harrison and other members of the Research and Development Unit at QAF Meat Industries and the Victorian Institute of Animal Science, Department of Primary Industries, Animal Welfare Centre is also gratefully acknowledged.

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