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Group Size and Alley Width Affect the Movement of Market Pigs

by 5m Editor
14 September 2010, at 12:00am

When handling near-market weight hogs, group sizes of four or eight pigs are preferable for minimising stress based on handling and behavioural measures, according to L. Kavanagh, S. Goumon and H.W. Gonyou in the Prairie Swine Centre Annual Report 2009.


Harold Gonyou

Summary

The objective of this study was to examine the interaction between group size and alley width on the ease and speed of movement of near-market pigs. Pigs were moved in different group sizes through a three-sided simulated handling course, in which alley width could be changed. Data were collected on heart rate, duration, handling and behavioural measures.

Moving a group of four or eight animals is preferred for minimising stress and alley width of 0.9 metres appears to be most conducive to easy handling.

Introduction

Current recommendations advise that pigs should be moved on farm in small groups of five or six. However, packing plants routinely move groups of 25 to 50 pigs with ease from lairage pens to the squeeze tub. One difference is in facility design. On farms, the alley is generally limited to the width of two pigs (approximately 0.6 metres), whereas in plants the alleys may be tow to three metres wide. Therefore, handling challenges and stress related to larger group sizes on farms may be due, in part, to crowding resulting from space limitations. As farms increase the number of pigs handled and loaded each week, specialised handling and loading facilities may be warranted in order to minimise stress, speed the process and reduce labour costs. In this perspective, the Prairie Swine Research Centre group examined the interaction between the group size and the alley width on the ease and speed of movement of near-market pigs.

Experimental Procedure

This study was undertaken at the Prairie Swine Centre. Forty-four finishing pigs within three weeks of market, weighing between 100 to 115kg, were used each day during this trial. A randomised block design was used with treatments in a 4×4 factorial arrangement: 1) alley width (0.6, 0.9, 1.2 or 2.4 metres), and 2) group size (four, eight, 12 or 20 pigs). Alley width sizes were based on the shoulder widths of pigs (approximately 30cm) and included two, three, four and eight body widths (0.60, 0.9, 1.2 and 2.4 metres). Five replicates of each alley width, group size combination was undertaken.

Pigs were moved through a three-sided simulated handling course (Figure 1). One handler was used, moving the pigs with paddle and board only. Once the animals were moved from the holding pen to the starting pen, they were left for five minutes to rest and to acclimatise to the pen and unfamiliar pigs. After the run of the course, pigs were held in the end pen for five minutes before being returned to their respective holding pens.


Figure 1. Handling Course

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“When handling near-market weight hogs, group sizes of four or eight pigs is preferred for minimising stress based on handling and behavioural measures"

Heart rate data were collected from five minutes prior to running the course, while pigs where in the starting pen, and until five minutes after the end of the run while pigs waited in the end pen. Each run of the course included two pigs wearing a heart monitor. Pigs were also scored for vocalisations (squeals), turn-backs, piling, slipping and falling events. The time to complete the course was measured. The number of touches and slaps given by the handler to move pigs through the course were recorded. At the end of each run, the handler also provided a subjective rating of handling ease or difficulty using a visual analogue scale where ‘minimal difficulty’ was labelled at one end, ‘average difficulty’ in the centre of the scale, and ‘maximum difficulty’ at the end of the scale.

Results and Discussion

Pigs moved in groups of 12 or 20 emitted more squeals than those moved in groups of four or eight (figure 2). They took significantly more time to complete the course (figure 3) than smaller groups (four or eight animals).

In addition a significantly higher number of turn-backs were also recorded when pigs were moved in groups of 12 or 20 (compared to four or eight), and in group size eight compared to four (figure 4).

This highlights the challenge of moving animals in larger group sizes, which results in a stressful situation. The handling measures (figure 5) showed that handling became more challenging as group size increased. This matches the results found for the behavioural measures in that group size of four was rated as easier to manage by the handler than larger group sizes and group sizes of four and eight required less handler intervention than group sizes 12 and 20.


Figure 2. Number of vocalizations for each alley width

Figure 3. Time to complete the handling course for each group size

Figure 4. Interaction between group size and alley width

Figure 5. Interaction between group size and alley width effects on the number of touches or slaps given by the handler

Overall, the results from the behavioural and handling measures indicate that group size of four is preferred, based on the number of turn-backs and the subjective handling scored, or that group sizes of four and eight are equally superior to the larger group sizes, based on measures of vocalizations and handling (touches and slaps).

The number of touches and slaps administered by the handler (figure 5) suggest that the middle alley widths of 0.9 metres and 1.2 metres are most conducive to easy handling.

However, an interaction between group size and alley width for the handling intervention measure of touches and slaps was found and suggests the alley width of 0.9 metres is preferable as there was no significant difference found between group sizes on this measure. In addition, the number of touches and slaps given were relatively low compared to those given in group size 20 in the wider widths of 1.2 metres and 2.4 metres. The higher number of squeals emitted by pigs when moved in alley width of 0.6 metres (figure 2) compared to the wider widths was a reflection of the tight space causing pigs to bump into other pigs and/or bunch up.

The increased difficulty in managing pigs in a wide alley width was the reason for more turn-backs in the 2.4 metres alley width compared to the smaller widths. Moving pigs in groups of 12 and 20 resulted in many more turn-backs (figure 4) in the alley width size 2.4 metres compared to 0.9 metres, for example, where the number of turn backs is uniformly low in group sizes of four, eight 12.

An interaction between group size and alley width was found for turn-backs and confirms this as the difference in the number of turn backs between group sizes increased dramatically when the alley width was set at 2.4 metres.

A higher average heart rate was measured in group size 20 compared to group sizes of four and eight animals during the pre- and post-periods (table 1). This difference was likely a result of stress from mixing with unfamiliar pigs. Pigs sometimes fought during these periods. Thus, when released from the start pen to run the course, heart rates may have lessened for the pigs experiencing higher stress as a result of mixing as they were given the opportunity to escape a conflict situation.

Furthermore, although the researchers found higher maximum record heart rates in group size 20 compared to groups of four or eight pigs during the run, the physical activity of the run may have confounded the accuracy of heart rate measures.

Implications

Maximising the ease with which animals are moved and handled requires taking into account a variety of factors. The results support the current recommendations and suggest that moving pigs in group sizes that are appropriate for the alley width used can reduce handling time and contribute to improved welfare.

This study could be extended in order to assess the effect of ramp widths on pig’s movement during loading and unloading.

Acknowledgement

Strategic programme funding provided by Alberta Livestock Meat Agency. Project funding provided by Sask Pork, Alberta Pork, Manitoba Pork Council & Saskatchewan Agriculture Development Fund.

Further Reading

- You can view other papers from the Prairie Swine Research Centre Annual Report 2009 by clicking here.


September 2010
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