Determining the Optimum Stocking Density in Nursery Pigs

Posted in: Pork Insight Articles, Prairie Swine Centre, Production by admin on October 26, 2015

Producers must balance the potential negative consequences of high stocking densities and the economic incentive to maximize production when determining the number of pigs placed per pen or building unit. The minimum space requirement in the Canadian Code of Practice for the Care and Handling of Pigs (k= 0.0335) is based on extensive research on grower-finisher pigs. However, comparatively little research has been done on nursery pigs, and there is speculation that these requirements over-estimate the space needs of nursery pigs. The aim of this research project is to determine the optimal density for nursery pigs that considers both production goals and animal welfare. The three year project will be completed in two phases, with phase 1 studies taking place at Prairie Swine Centre and phase 2 taking place in two commercial production barns (one in SK and one in MB). Both phases will compare the effects of six different density treatments in nursery pigs.

INTRODUCTION

Floor space allowance is a complex issue in swine production, and one that is critical for both economic and welfare reasons. There is currently a significant body of research on the effects of space allowances in grow-finish pigs (Edwards et al., 1988, Ekkel et al., 2003, McGlone and Newby, 1994, Pastorelli et al., 2006). The values established have been used as the basis for space allowance requirements for nursery pigs (NFACC, 2014). Relatively little is known regarding the effects of stocking density on nursery pigs (EFSA, 2005, Gonyou et al., 2006). Because nursery pigs are commonly observed to overlie one-another when resting, the k value which is appropriate for finishing pigs may in fact overestimate the space requirements of nursery pigs.

Although individual pig growth declines at higher densities, overall farm productivity can increase as higher numbers of pigs are produced per unit of building space (Kornegay and Knotter, 1984). Thus, the economic optimum for space may be lower than that for achieving maximum growth rate. However, stocking at higher densities can also negatively affect the welfare of the pig, with risk of immune suppression and increased disease susceptibility (Turner et al., 2000) or restriction of pigs’ ability to express normal behaviour.

It has been recommended that evaluations of space requirements for pigs should include changes in the behaviour of pigs, and establish the welfare relevance of such changes, to support calculation of space allowances based on what space an animal needs rather than solely on the basis of production performance (Ekkel et al., 2003). Group size and seasonal differences should also be evaluated or controlled for as these factors may also influence growth and behavior (Hyunh et al., 2005, Spoolder et al., 2012),. It has been suggested that larger groups of pigs may require less space, due to the sharing of free space (McGlone and Newby, 1994). However, this has also been disputed (Street and Gonyou, 2008).

 

This study will examine measures of productivity and welfare in nursery pigs, and will include an economic analysis comparing space allowance treatments above and below the Code requirement of k= 0.0335.

MATERIALS AND METHODS

Phase 1

Animals: Density studies at PSCI were conducted using 1,200 newly-weaned pigs that were housed in the nursery for 5 weeks. Piglets were housed at one of six different densities (k= 0.023, 0.0265, 0.0300, 0.0335, 0.0370, and 0.0390) in pens of either 10 or 40 pigs/group. For four replicate trials were completed over a one year period, with one replicate per season.  Pigs were weighed weekly and pen size was adjusted weekly to the prescribed density based on the predicted average body weight. Two temperature and humidity monitors (iButtons) were placed in each pen, suspended approximately 15cm above pig height to monitor conditions at pig level. An additional iButton was suspended in the center of the room to monitor room temperature and humidity throughout the trial.

Data collection: Video cameras were placed above each pen to record pig behaviour for a 24 period once per week. An infra-red setting was used during the hours of darkness. Scan sampling at 15 minute intervals was used to identify laying postures and overlying behavior.  The time budgets of four focal piglets, including the amount of time spent feeding, drinking, standing, lying and socializing were also evaluated for each week. Standard nursery diets were provided ad libitum, and feed weigh backs were recorded weekly. Total feed consumption and animal weights were recorded on a weekly basis.

Lesion scores were assessed weekly as pigs were weighed, and used as an estimate of aggression (Table 1). Saliva samples were collected weekly from four focal pigs for determination of cortisol as an indicator of stress. The immune response was tested in six pigs per pen, with  pigs receiving vaccines for Mycoplasma hyopneumonie. Serum samples were collected at three time points to determine M.hyo specific IgG as a measure of immune competence.

Phase 2

Animals: Two commercial operations with good health status and levels of productivity were identified through industry contacts and provincial pork agencies. One site was selected in Manitoba and the second in Saskatchewan. The same six density treatments used in phase I will be tested. Unlike phase I, pens in phase 2 will kept at a constant size, and the number of pigs per pen will be adjusted based on the expected weight at nursery exit (approximately 25 kg). Animals are fed and cared for following the standard management practices on each farm and information on temperature and humidity within the rooms will be collected using iButton data loggers, similar to the methods used in phase I.

Data collection: Pigs on trial will be weighed to determine average daily gain. At the same time skin lesions, ear tip necrosis, tail biting and general health will be assessed by a trained observer. Morbidity, mortality and any treatments will be recorded throughout the trial. At three time points, time lapse videos will collected over 7 hours. Postures and lying behaviours of the pigs will be assessed using scan sampling, as described for phase I.

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