J. Anim. Sci. 2005. 83:1397-1402
© 2005 American Society of Animal Science
Use of a crush-reducing device to decrease crushing of suckling piglets by sows
J. H. Jeon*,
D. J. Kim*,
J. H. Han*,
S. C. Yeon
,
S. H. Bahng
,
B. S. Myeong and
H. H. Chang*,1
* Division of Applied Life Science, College of Agriculture, Gyeongsang National University, Jinju 660-701, Republic of Korea;
and
Department of Surgery, College of Veterinary Medicine, Gyeongsang National University, Jinju 660-701, Republic of Korea; and
and
Division of Mechanical Engineering, Sangju National University, Sangju 742–711, Republic of Korea
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Abstract
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Weanling pigs tend to avoid wind, and suckling piglets are thought to be more sensitive to wind than weanlings, owing to their thinner s.c. fat layer. We developed a crush-reducing device based on the anticipated behavior of suckling piglets toward wind and evaluated the performance of the device through field testing. The crush-reducing device consisted of six photo sensors, a controller, six solenoid valves, and an air compressor. In this study, 206 sows and their suckling piglets (Landrace xYorkshire) were investigated to ascertain the individual effects of several factors. Some of the newborn piglets were cross-fostered before the crush-reducing device was implemented. Litter weights were measured on d 0 and 4 to determine the influence of the crush-reducing device on the weights of suckling piglets. The crushing of suckling piglets by sows was affected by season (P < 0.01) and litter size (P < 0.05), but not by the parity of the sows; however, the number of crushed piglets per litter was less (P < 0.01) in the crush-reducing device group (0.05 ± 0.02 crushed piglets/litter) than in the control group (0.23 ± 0.04 crushed piglets/litter), regardless of litter size or season. The BW gain of suckling piglets did not differ between the control and the crush-reducing device groups. Based on these results, the crush-reducing device is expected to decrease the number of crushed piglets per litter without influencing the BW gain of suckling piglets, thereby greatly contributing to the productivity of pig breeders.
Key Words: Air Ejection • Crushing • Preweaning Mortality • Suckling Piglets
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Introduction
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Suckling piglets die for various reasons, and more than 50% of piglet deaths occur within 4 d of birth (English and Morrison, 1984
; Svendsen et al., 1986). The most commonly reported causes of death among live-born pigs are starvation, diarrhea, and crushing by the sow (Friendship et al., 1986). Death by crushing comprises a large percentage of the total number of suckling piglet deaths, and pig breeders experience great economic losses as a result. According to Bøe (1994), 14.4% of suckling piglets die within 3 wk after birth, and Kunz and Ernst (1987) reported that 47.4% of suckling piglet deaths are caused by crushing. Crushing is closely related to sow behavior, and 54% of crushing deaths occur when sows lie down from a standing position (Weary et al., 1998). Many pig breeders make every effort to decrease the crush rate (e.g., by equipping farrowing crates with support bars to prevent sows from suddenly rolling or lying down; Weary et al., 1998). Nevertheless, many suckling piglets still die from being crushed. The death of suckling piglets adversely affects the productivity of farms; therefore, implementing an effective management regime until 3 d after birth could decrease the occurrence of piglet deaths (Holyoake et al., 1995). Weanling pigs become more sensitive to cold as wind velocity increases (Riskowski et al., 1990), and the lower critical temperature of weanling pigs differs according to wind velocity (Boon, 1982). As wind velocity increases, weanlings tend to lie on top of each other for warmth. Given the behavior of weanling piglets in relation to wind velocity, we assumed that suckling piglets also are sensitive to wind because they have a thinner s.c. fat layer than weanlings. Thus, the present research was performed to develop a crush-reducing device based on the sensitivity of suckling piglets to wind velocity.
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Materials and Methods
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Animals, Housing, and Experimental Period
Two hundred six sows and their suckling piglets (Landrace x Yorkshire) were held in pens in a windowless farrowing house (Table 1). Some newborn piglets were cross-fostered immediately after parturition. Data for these individuals were collected, and the crush-reducing device was operated after cross-fostering.
The pen floors were slatted and the sows were housed in farrowing crates (210 cm x 60 cm) located in the pens (240 cm x 160 cm). Ventilation was automatically controlled by fans. An infrared lamp (250 W), which was installed above the creep area, was turned on by a farmer when the farrowing room temperature was below about 29°C.
The experiment was performed from September 2001 to February 2004, covering four seasons: spring (March to May), summer (June to August), fall (September to November), and winter (December to February). Temperatures in the farrowing room ranged from 22.0 to 26.0°C in spring, 23.1 to 29.5°C in summer, 21.1 to 25.3°C in fall, and 19.4 to 24.3°C in winter.
According to English and Morrison (1984) and Svendsen et al. (1986), suckling piglets are most vulnerable up until the fourth day after birth, and more than 50% of deaths occur during this period. For this reason, the crush-reducing device was operated from birth until d 4 to minimize the stress on sows and suckling piglets caused by the air ejections. Only crushing that occurred during this period was analyzed in this study.
Experimental Device
Crushing occurs most frequently when sows lie down from a standing position (Weary et al., 1998); therefore, the crush-reducing device was developed to obstruct the access of suckling piglets to the sows. This was done by ejecting compressed air beneath the sows’ bellies when the sows were standing or sitting.
Figure 1 shows how the crush-reducing device works. The photo sensor, which is fixed to the upper shoulder of the sow, detects behavior such as standing and sitting that may crush piglets, and sends a signal to the controller. The controller then turns on the solenoid valve, and air from the compressor is released through the air-ejection hose. The air prevents suckling piglets, which are sensitive to wind velocity, from remaining underneath the sow’s belly and prevents sows from breeching, thereby decreasing the incidence of crushing.
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Figure 1. Overall schematic of the crush-reducing device. The 1) photo sensor, which is fixed to the shoulder of the sow, detects behavior that may crush piglets (such as standing and sitting) and sends a signal to the 2) controller. The controller then turns on the 3) solenoid valve, and air from the 4) compressor is released through the 5) air-ejection hose in back-and-forth and right-to-left directions.
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Suckling piglets dislike wind at velocities as low as 0.25 to 0.36 m/s at a temperature of 21.0°C (Sainsbury and Sainsbury, 1967), but continuous air ejection may be fatal owing to the thin s.c. fat layer of suckling piglets. Therefore, intermittent air ejection was applied to minimize the stress on both the sows and the suckling piglets. To ensure intermittent air ejection, compressed air was released for 5 s at 5-s intervals. This was accomplished with a dip-switch mechanism on the controller.
Suckling piglets sense cold at wind velocities exceeding 0.25 m/s at 21.0°C (Sainsbury and Sainsbury, 1967). The device was therefore designed to eject compressed air at a velocity greater than 0.25 m/s, based on the results reported by Sainsbury and Sainsbury (1967) and the reported optimal temperature of 12.7 to 23.8°C for a farrowing room (England et al., 2001). The actual ejection velocity of the compressed air was measured at 0.41 to 2.50 m/s.
Figure 2 shows the crush-reducing device installed in a farrowing crate. The photo sensor, which is installed 60 cm from the front end of the farrowing crate and 120 cm above the floor, detects the position of the sow. The air is then ejected through the ejection hose in back-and-forth and right-to-left directions when the sow stands or sits, thereby obstructing access to the sow by the suckling piglets.
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Figure 2. Photograph of the crush-reducing device installed in a farrowing crate. The 1) photo sensor, which is installed 60 cm from the front end of the farrowing crate and 120 cm above the floor, detects when a sow stands up. Air is then ejected through the 2) ejection hose in back-and-forth and right-to-left directions.
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A 3-hp air compressor was used in the crush-reducing device to ensure adequate air ejection given the air-ejecting time and the number of farrowing crates. A direct-reflex photo sensor was used to detect sow behavior. Designed with six channels, one controller could control six farrowing crates simultaneously. Table 2 shows the specifications for each component of the crush-reducing device.
Statistical Analyses
The deaths of piglets by crushing and disease were monitored by a veterinarian through daily inspections of the control and crush-reducing device groups. The weights of suckling piglets were measured on d 0 and 4. The number of crushed piglets per litter was determined, and litter weights were compared on d 0 and 4 for both the control and the crush-reducing device groups to identify the influence of the crush-reducing device on the weight gain by suckling piglets. Small piglets have a greater risk of poor survival and lower weight gain compared with heavier littermates (Weary et al., 1996; Milligan et al., 2002). Wechsler and Hegglin (1997) excluded suckling piglets that weighed <800 g on d 0 from their crush-rate analysis. For this reason, to accurately determine the influence of the crush-reducing device, suckling piglets weighing <800 g on d 0 and those that were diseased or malformed also were excluded from all data analyses in our study.
In the statistical analyses, the dependent variable was the number of deaths per litter by crushing. To decrease the effect of a few litters that had high losses, the 206 litters were classified as having 0, 1, or 
2 crushing deaths. The parity of sows was grouped into categories of 1 or 2, 3 or 4, and 5 or 6. Litter sizes were grouped according to the number of piglets per litter, where small was <9 piglets per litter, medium was 9 to 10 piglets per litter, and large was 11 piglets per litter. All data were analyzed statistically using SAS (SAS Inst., Inc., Cary, NC). A 
2 analysis was used to test the effects of treatment, parity, litter size, and season on the crushing of suckling piglets by sows.
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Results and Discussion
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A high incidence of crushing was associated with higher parity, larger litter sizes, and warmer seasons (Table 3); these results were comparable to those of Weary et al. (1998).
Breeding environment and the management regimen can affect the number of piglets crushed per litter. In this study, however, the control and the crush-reducing device groups were subjected to the same breeding environment and management regimen. The crush per litter was lower (P < 0.01) in the crush-reducing device group (0.05 crushed piglets/litter) than in the control group (0.23 crushed piglets/litter; Table 4), and the rates for both groups were considerably lower than the typical crush rate (approximately 0.7 piglets/litter) estimated from the results of previous studies (English and Morrison, 1984; Svendsen et al., 1986; Kunz and Ernst, 1987; Bøe, 1994).
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Table 4. Mean ± SE of the number of crushed piglets per litter and the significance between the treatments according to treatment, parity, litter size, and season from birth to d 4
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Among the controls, the crush per litter of the low (1 to 2) parity group was less than (P < 0.05) that of the higher parity groups (Table 4
). This was similar to data reported by Weary et al. (1998), in which sows with a higher parity showed a higher crush per litter. Among the crush-reducing device groups, however, piglets were crushed only in the 3 to 4 parity group (Table 4).
We found no difference in the crush per litter between the control and the crush-reducing device groups in the small and medium litter size groups (P = 0.12), but there was a difference in the large litter size group (P < 0.01; Table 4). This result is consistent with the higher incidence of crushing among larger litter sizes reported by Weary et al. (1998). In terms of season, there was no difference in the results between the control and the crush-reducing device group for fall and winter (P = 0.13), although we found differences in spring and summer (P < 0.05). The crush per litter was higher in summer than in the other seasons (Table 4), which was accounted for by the greater heat stress experienced by the sows. In the crush-reducing device group, crushing occurred only in the fall. According to Weary et al. (1998) and Herskin et al. (1998), piglets can be crushed when the sow rolls over. The crush-reducing device does not operate when a sow rolls; therefore, it is likely that some piglets in the crush-reducing device group were crushed when the sow rolled over.
The average litter weight on d 4 was similar in the crush-reducing device group and the control group. As the suckling piglets weighing < 800 g on d 0 were excluded in this experiment, there was no weight decrease in litters owing to nascent suckling piglets (Figure 3). Weanling pigs showed relatively high BW increments under conditions of low wind velocity (Sällvik and Walberg, 1984). Therefore, because there was no difference in the BW increment between the control and the crush-reducing device groups, we conclude that the wind of the crush-reducing device contributed very little or had no influence on the BW increment of suckling piglets. Moreover, we observed no incidence of diarrhea among piglets that was attributable to the air jets of the crush-reducing device group.
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Figure 3. Mean litter weight on d 0 and 4. Mean litter weight did not differ between the control group (CG) and the crush-reducing device group (CRDG) on d 0 and 4. Values are means plus positive halves of SE.
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1 Correspondence—phone: +82-55-7515510; fax: +82-55-7516113; e-mail: hhchang{at}nongae.gsnu.ac.kr.
Received for publication March 6, 2004.
Accepted for publication March 4, 2005.
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Literature Cited
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Bøe, K. 1994. Variation in maternal behaviour and production of sows in integrated loose housing systems in Norway. Appl. Anim. Behav. Sci. 41:53–62.
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Abstract
Introduction
