PSS Halothane Geno Type

[mikey]

Porcine Stress Syndrome Gene and Pork Production

 
Agdex#: 440/11
Publication Date: 06/04
Order#: 04-053
Last Reviewed: 06/04
History: 
Written by: Wayne Du - Pork Quality Assurance Program Lead/OMAFRA

 

Introduction
The porcine stress syndrome (PSS) gene is found to cause malignant hyperthermia (heat shock) when pigs are exposed to environmental stressors. This gene is commonly referred to as the halothane gene, because the PSS condition can be triggered by exposing pigs to the anesthetic, halothane gas. Researchers established the presence of the PSS condition in 1968 when they observed that physically stressed, susceptible pigs would collapse in a shock-like state and die. Pigs carrying the PSS gene are more prone to producing pale, soft and exudative (PSE) pork, which is not only unattractive to consumers because of its unappealing greyish, soft and watery appearance, but is also less suitable for further processing because of its low water-holding capacity.

Inheritance
The PSS condition is an inherited disorder in swine. Inheritance of the PSS gene is at a single locus and there are two alleles, one dominant (N) and one recessive (n). There are three possible genotypes: homozygous recessive (nn), heterozygous or carriers (Nn) and homozygous normal (NN). Swine inheriting the n allele are more sensitive to stress. Pigs that are homozygous recessive (nn) are called PSS homozygous. PSS homozygous pigs are more prone to developing PSE pork after slaughter than PSS carriers (Nn), which are more prone than normal pigs (NN).

Each parent provides one allele to his or her progeny. Possible mating combinations and resulting genotypes are listed in Table 1.

Understanding the impact of carriers (Nn pigs) in breeding is key to reducing the incidence of PSE pork. For example, if a nn boar is mated to a NN sow, 100% of the offspring will be PSS carriers. The mating of a Nn boar with a NN sow will result in 50% of the piglets being carriers. Testing of breeding pigs can assist in identifying carriers so informed breeding decisions can be made.


Table 1. Possible Mating Combinations and Resulting Porcine Stress Syndrome Genotypes
Parent A Parent B  Progeny Genotypes
NN  NN  100% NN
NN  Nn  50% NN, 50% Nn
NN  nn  100% Nn
Nn  Nn  50% Nn, 25% NN, 25% nn
Nn nn  50% Nn, 50% nn
nn  nn  100% nn

Effects of PSS Gene on Animal Well-Being, Meat Quality and Pork Production
Effects of PSS gene on animal well-being
The PSS gene causes animal suffering from the stress syndrome. Animals carrying the PSS gene lack the ability to adapt to stresses and once the PSS condition is triggered, they exhibit symptoms quickly. Table 2 summarizes some of the physical stressors that trigger the PSS condition and the symptoms that are typical in affected pigs.

Table 2. Physical Stressors Triggering Porcine Stress Syndrome and Typical Symptoms Exhibited by Affected Pigs
Physical Stressors
Rough or unfamiliar handling
Rough loading and unloading
Transportation
Mixing and fighting
Mating, estrus, parturition
Hot weather
Typical Symptoms
Rapid respiration (short and heavy breaths)
Increase in body temperature >41 C (106 F)
Marked muscle tremors
Twitching of the face
The skin becomes red and blotched
Sudden collapse or death
Effects of PSS gene on pork quality
Since the discovery of the PSS gene, much attention has been given to how it affects meat quality. To date, the impact of the gene on pork quality has been well researched and documented. The typical effect of the PSS gene on pork quality is that it causes PSE pork, which is unattractive to consumers due to its unappealing greyish, soft and watery appearance. PSE pork is also less suitable for further processing because of its low water-holding capacity.

Although any severely stressed pig can develop PSE pork, animals that carry the PSS gene are much more likely to develop PSE pork than PSS gene-free animals. The key factors causing PSE pork are the prolonged high carcass temperature after slaughter, accompanied by a rapid decline in muscle pH during the first 45 minutes post-slaughter. This rapid decline in muscle pH results from excessive muscle energy depletion and a build-up of lactic acid in the muscle. Figure 1 illustrates the relationship between post-mortem (post-slaughter) changes in muscle pH and pork quality.

PSE pork is often characterized by a low muscle pH at 45 minutes post-slaughter, with lighter colour muscle and greater drip losses (water losses) during chilling, processing and cooking than normal pork. The light or pale colour occurs due to the denaturation (breakdown) of the pigmented protein (myoglobin) under the conditions of low pH and high temperature, as well as accumulation of water on the cut muscle surface. Results from the Ontario Pork Carcass Appraisal Project (OPCAP) conducted from 1990 to 1994 showed that the loins from the PSS carriers had a 10% lower marbling score, 6%-8% lower meat colour score, and 5% higher drip loss than loins from the normal animals. Table 3 compares muscle pH, colour and drip loss between normal pigs and PSS gene carriers.

Figure 1. The relationship between post-mortem changes in muscle pH and pork quality. (Source: Austin Murray, Lacombe Research Centre, Agriculture and Agri-Food Canada)



Text version of graphic

Pigs carrying two copies of the PSS gene (nn) tend to have a much higher chance of producing PSE pork than carriers (Nn) and normal animals (NN). It was suggested that 30%-50% of the carrier market hogs would produce carcasses with inferior pork quality. The negative effects of this gene on pork quality seem to be further increased by the trend to select for lean hogs in recent years.


Effects of PSS gene on production
During the 1980s and 90s, the use of nn sires to produce PSS carriers in market hogs was a popular practice in the hog industry. This was due to the perception that carriers would not be susceptible to stress and PSE, but would produce more desirable, lean pork with higher lean yield. However, numerous studies have shown that this belief was not actually correct. For example, the OPCAP project demonstrated that carriers had no significant effects on growth (average daily gain), back fat thickness (live animal and carcass), estimated lean yield or carcass index, although there were slight improvements in lean content, loin eye area, feed conversion (feed to gain ratio) and dressing percentage observed. Table 4 compares production performances between PSS carriers and normal pigs.


Table 3. Effect of the Porcine Stress Syndrome Gene on Loin Quality
Parameter PSS gene Carrier (Nn) Normal (NN) Significance*
Muscle pH at 45 min. post-slaughter  5.91 6.28 Yes
Muscle pH at 24 hr. post-slaughter 5.41 5.42 No
Reflectance L**  46.80 44.50  Yes
Drip loss (%) 5.02 3.06  Yes

Source: Pommier et al., 1998
* Yes means that the PSS gene had a significant effect on the measurement. No means that the PSS gene had no effect on the measurement.
** The greater the L values, the lighter the meat colour (consumers don't like meat that is too pale or too dark in colour).

Table 4. Effects of Porcine Stress Syndrome Gene on Pig Production Performance
Trait PSS gene Carrier(Nn)  Normal (NN)
Weight on test (kg)  31.4  31.6
Weight at slaughter (kg)  106.2  106.5
Days to 100 kg (days)  160.0  160.4
Average daily gain (kg/day)  0.867  0.866
Back fat at 100 kg (mm)  13.4  13.6
Feed conversion (feed:gain ratio)  2.63  2.66
Hot carcass weight (kg)  84.5  84.1

Source: Proceedings of the Ontario Pork Carcass Appraisal Project (OPCAP) Symposium (1996)


Results from the U.S. National Genetic Evaluation Program published in 1995 showed that there were no significant differences between carriers and normal pigs for growth rate, leg soundness and back fat over the tenth rib and the last lumbar vertebra. Results from all these studies showed that PSS gene carriers (Nn) had no significant production-performance benefits.

Effect of the PSS gene on economic returns
The presence of the PSS gene in pigs tends to cause development of PSE pork, higher mortalities and loss of meat yield, which directly translate into economic losses for the entire pork production chain. The PSS gene is one of the major swine genes that cost the pork industry profits. In 1994, U.S. researchers reported that the total loss from colour and PSE-related problems was $1.05 per hog in the U.S. They also estimated that of this amount, losses of $0.79 per pig were directly controllable by hog producers and pre-slaughter handling. It was also reported in 2001 that on average, a total of $0.34 lost on every hog marketed in the U.S. was due to PSE, which was mainly because of the yield losses from shrinkage. As well, death losses due to PSS cost an additional $0.06-$0.07 per hog marketed. Based on these estimations, PSE-related direct costs could reach approximately $2.5 million per year for a pork industry with an annual production of 5-6 million hogs such as Ontario. Furthermore, loss of market share in the world exports causes additional economic losses.

PSS Gene Test
In the 1980's, researchers developed the halothane gas-screening test to detect mutant genotype pigs. However, this testing method was unable to distinguish between normal pigs (NN) and PSS carriers (Nn). In the 1990s, researchers in Canada developed a quick, simple and accurate DNA test for PSS gene detection, which makes it possible to identify all three PSS genotypes and to evaluate the effect of the PSS gene on production performance and meat quality traits. The University of Toronto's Innovation Foundation patented the DNA test. The accuracy of the test is approaching 100%. The DNA test provides the pork industry with a powerful tool to detect the PSS gene in live pigs and eradicate it from the entire pig population. Table 5 lists several labs in Ontario and Quebec that currently provide this genetic testing service to the pork industry.


Table 5. Laboratories Providing the DNA Test for Porcine Stress Syndrome Gene in Ontario and Quebec
Lab Service Division
University of Guelph P.O. Box 3650
95 Stone Road West,
Guelph, Ontario, N1H 8J7 (519) 823-1268
Contact: Dr. Chen
schen@lsd.uoguelph.ca

Vita-Tech Laboratories
1345 Denison Street
Markham, Ontario,
L3R 5V2 (416) 798-4988
(800) 667-3411
Contact: info@vita-tech.com

CDPQ
2795, boul. Laurier bureau 340
Sainte-Foy Québec G1V 4M7 (418) 650-2440
Contact: Pierre Falardeau
cdpq@cdpqinc.qc.ca

Table 6. Porcine Stress Syndrome Genotypes across Breeds Tested in Ontario (1990-1994)
Breed Total of Number of Pigs Tested Homozygous Normal (NN) Heterozygotes
(Nn)  Homozygous PSS (nn)
Duroc  533  489  43 1
Hampshire  279  262  17 0
Landrace 745  628 115 2
Yorkshire  1320  1180 136 4

Total  2877  2559 311 7

Source: Proceedings of the Ontario Pork Carcass Appraisal Project (OPCAP) Symposium (1996)

PSS Gene Frequency in the Ontario Swine Population
The frequency of the PSS gene in pig populations varies according to genetic breeds and country of origin. Results from the same OPCAP study referred to earlier show that this stress gene exists with variable frequencies in all of the major breeds tested in Ontario. Table 6 summarizes PSS gene incidence in four Ontario breeds tested in the OPCAP study.

The general belief within the Ontario pork industry is that the PSS gene is not commonly found in Ontario pigs and may have been completely eradicated from the Ontario swine population since the OPCAP study was completed in 1994. However, results from recent (2002-2003) routine tests carried out at the University of Guelph indicate that the PSS gene still exists with a higher than expected frequency, indicating that more work is needed to eliminate the gene from Ontario pigs.

Recommendations
Numerous studies support the conclusion that the PSS gene, even in the carrier state, contributes to poor meat quality. The positive effects brought by the PSS gene in terms of body composition do not offset its adverse effects on meat quality and financial returns. Therefore, it should be eradicated from the entire Ontario commercial pig population. This can be achieved by taking the following measures:

All market hog producers should adopt a PSS gene-free policy.
When purchasing new breeding materials (animals, semen and embryos), producers should require that all purchases be certified PSS gene-free.
On-farm selected breeding stock replacements should be tested for the PSS gene if their PSS gene status is not clear.
Genetics suppliers must ensure that no PSS gene exists in herds that are marketed as PSS gene-free.
The eradication of the PSS gene from the Ontario commercial pig population requires commitments and coordinated efforts from all parties involved in the pork chain. With such clear evidence of the detrimental effect of the PSS gene on pork quality and industry profitability, this is the time for the Ontario pork industry to completely remove the PSS gene from Ontario pigs and breeding stocks.

References
Gibson, J. P., R. O. Ball, B. E. Uttario and P. J. O'Brien. 1996. The Effects of PSS Genotype on Growth and Carcass Characteristics. Proceedings of the Ontario Pork Carcass Appraisal Project Symposium. P. 35-38.
Goodwin, G. G. 1994. Genetic Parameters of Pork Quality Traits. Ph.D. Thesis. Iowa State University, Ames, U.S.
Pommier, S. Al, C. Pomar and D. Godbout. 1998. Effect of the Halothane Genotype and Stress on Animal Performance, Carcass Composition and Meat Quality of Crossbred Pigs. Can. J. Anim. Sci. 78:257-264.
Related Links
Lab Service Division, University of Guelph
Vita-Tech Laboratories
CDPQ

 

[mikey]

Hog Contracts Signal Producers To Improve Quality
Steve Martinez

 

Barry Runk/Grant Heilman Photography
 
Nearly 70 percent of hogs in the U.S. are sold to pork slaughter companies (packers) under pre-arranged marketing contracts, up from 11 percent in 1993. Marketing contracts between packers and hog producers typically specify the quantity of hogs to be purchased on specified dates and places, and provide hog producers a secure outlet and specific pricing terms. Many of these contracts awarded price premiums for carcass leanness and weight, providing strong incentives for producers to raise lean hogs needed for the lower fat meats demanded by consumers. From 1992 to 2002, the percentage of lean muscle of a typical pork carcass rose from 49.5 to 55.5 percent.

But this leanness came at a cost. The genetic lines that produced leaner hogs were often carriers of the “stress” gene, which was linked to a condition referred to as “pale, soft, and exudative” (PSE). PSE pork—which is disliked by packers, retailers, and consumers—has a very light color, soft texture, and is subject to fluid loss. Controlling the PSE condition proved to be difficult because packers must be able to measure and reward producers for reducing PSE-related attributes. However, indicators of the PSE condition could not be readily measured at high-speed processing lines that slaughter 1,000 hogs per hour. In addition, by the time PSE problems become apparent (20-24 hours postmortem), the identity of the producer may have been lost.

Packers turned to marketing contracts to maintain incentives for producing leaner hogs and, at the same time, control PSE-related attributes. These marketing contracts strove to limit PSE problems by specifying and monitoring input requirements—most importantly genetic lines. How hogs are handled also influences PSE. For example, minimal force while moving hogs, nonslip loading ramps, and less crowding of hogs while on the way to the packing plant all make for less stressed hogs.

While considerable progress has been made in breeding out the stress gene, two pork quality audits revealed that the PSE condition actually worsened—rising from 10.2 percent of slaughter hogs in 1992 to 15.5 percent in 2002. This suggests hog-handling problems may have become an important contributor to PSE-related problems. Some large pork companies stipulate in their marketing contracts that producers raise hogs in a humane manner or in a way that optimizes pork quality.

 
Wonder how many hogs in the Philippines are PSE positive?I would think the native hog is PSE negative.

[mikey]

Allen D. Leman Swine Conference
Volume 21 1994, pages 206-209
College of Veterinary Medicine,
University of Minnesota.


Published by: Veterinary Outreach Programs, UNIVERSITY OF MINNESOTA.



Observations by the author at slaughter plants and farms all over the United States, Canada, Europe, and Australia indicate that producers are responsible for about 50% of the pale, soft, and exudative (PSE) pork on the market, and packers are responsible for the other 50%. Surveys conducted in slaughter plants in two different countries indicated that PSE levels varied over 100% between different producers.

Genetics is probably the single most important factor contributing to the prevalence of PSE pork today. Some pork-grading systems motivate producers to breed pigs that carry the stress gene. These animals have maximum lean and weight gain (Aalhus et al .,1991). Unfortunately, they also have high levels of PSE. Some of the highest levels of PSE were recorded in hybrid pigs, which had been selected for leanness and rapid growth. The breeding companies have recognized the problem and have taken steps to produce lines that will have lower levels of PSE. DNA testing methods will enable the PSS (porcine stress syndrome) gene to be eliminated (Sellers, 1993).

At one plant, a certain line of commercially available hybrid pigs constituted 10% of the pigs received each day. Ninety percent of the pigs that were dead on arrival or died in the yards came from these hybrids. Genetics has a large effect on death losses (Murray et al., 1998). Genetics is not the sole explanation for differences between producers. A survey conducted at a vertically integrated operation indicated that PSE levels varied 5-10 percentage points among producers who raised identical pigs in identical buildings. Handling, management, and transport also had an effect. Several surveys have shown that pigs transported a short distance will have more PSE compared to pigs transported a longer distance. Observations by the author have indicated that pigs hauled very short distances for under 30 minutes are often more stubborn and difficult to drive at the plant compared to pigs hauled longer distances (Grandin, 1993a). Pigs hauled long distances are more likely to have DFD (dark firm dry) meat because glycogen stores become depleted.

PSE can be reduced by fasting pigs 12 to 24 hours prior to slaughter (Warris and Bevis, 1987; Eikelenboom et al.,1990). Pigs should have access to water at all times. To reduce the possibility of carcass weight loss, a shorter fasting period of 12 hours prior to stunning and slaughter is recommended (Grandin, 1993).

Excitable pigs

There are problems with excitable pigs. The leanest animals with large muscles often have the worst excitability problems. Shea-Moore (1998) found that high lean pigs were more fearful. These pigs often have the worst meat quality problems. Pork from stress gene pigs which are grown to heavy weights is tougher and drier than pork from pigs which are stress gene free (Monin et al., 1999). Excitable pigs are very difficult to handle at the slaughter plant. This creates both meat quality and welfare problems. Handling excitable pigs at 1000 per hour in a single file race is difficult to do quietly. Some plants have installed two stunners to improve handling. Fortunately some of the vertically integrated companies have removed the stress gene from their herds. This has resulted in calmer pigs which are easier to handle. They are now breeding pigs for quality instead of quantity.

Handling of pigs can also be improved by installing a system which eliminates the single file races. The Danes have developed a CO2 stunning system where pigs are stunned in groups. Cattle move very easily through a single file race because their natural behavior while walking from pasture to pasture is to move in single file. Pigs do not have the instinct to walk in single file. When pig excitability increased, problems with single file races increased. When pig excitability is reduced single file races will have fewer problems.

Many excitable pigs are animals that have been raised in confinement (Grandin, 1993). Genetics is a major factor. Observations by the author in identical pig confinement buildings and in the same slaughter plant indicated that changing genetics improved handling. Pigs with a calmer temperament were easier to handle and PSE was reduced. There is a definite need for breeding companies to select pigs for temperament. This is especially important for pigs raised in confinement.

In confinement buildings, producers must provide pigs with more environmental stimulation. Providing confinement pigs with additional environmental enrichment, such as toys and people entering the pens, produced calmer pigs that were easier to drive (Grandin,1989; Pederen,1993). Producers need to eliminate practices such as keeping pigs in darkened rooms. Playing a radio in the building can help get pigs accustomed to sounds. Pigs that have been finished in a pen with a radio playing at a reasonable volume are less likely to be startled by sudden noises.

Producers should walk in the finishing pens every day to get the pigs accustomed to handling. The person should quielty walk through each pen in a different random direction each day to teach the pigs to quietly flow around them. The person should not stand in the pen and allow pigs to chew on their clothes. This trains the pigs to approach and chew instead of driving. Geverink et al (1998) reported that confinement pigs which have been driven in the aisle during finishing were easier to handle. Moving pigs out of their finishing pen one month prior to slaughter improved their willingness to move (Abbott et al., 1997)

Observations by the author have also indicated that raising finishing pigs on plastic or metal floors produces animals that are hard to drive because they do not know how to walk on concrete. Plastic or metal floors work well for young pigs, but during the final finishing phase, confinement pigs should be raised on a concrete surface. Producers must also avoid producing pigs with a high incidence of either hernias or spraddle legs. Both of these conditions have a strong genetic component.

Slaughter plant factors

After pigs arrive at the plant, handling and chilling practices will have a large effect on the incidence of PSE. I estimate that handling practices account for 10%-15% of the variation in PSE, and chilling practices account 20%-40%.

Improvements in handling practices have enabled several plants to ship 10% more pork to Japan. These handling procedures will reduce PSE:

Schedule trucks to prevent delays during unloading. Heat builds up rapidly in a stationary truck. Do not overload trucks.

Rest pigs for 2-4 hours prior to slaughter (Malmfors, 1982; Milligan et al., 1996). Trucks must be scheduled to allow adequate resting time.

Shower with cool water during hot weather (Smulders et al.,1983).

Handle gently in the stunning chute. Rough handling during the last 5 minutes prior to slaughter increases PSE, because pigs become overheated. Handlers must be taught behavioral principles of pig handling. Over-exertion and excitement shortly prior to stunning increases PSE in stress-resistant pigs that do not have the stress gene (Sayre, 1963; Barton-Gade, 1985).

Reduce or eliminate electric prods in the stunning area. Stressful handling shortly before slaughter will damage meat quality (Warriss et al., 1990; D'Souza et al., 1998; Van der Wal, 1997).

Reduced squealing in the stunning area will help reduce both PSE and bloodsplash. Squealing is associated with increased stress and lower meat quality (Warriss et al, 1994). The last five to ten minutes prior to stunning is most critical for reducing PSE.

Fill the crowd (forcing) pen which leads up to the single file race only half full. Move small groups fo pigs. In group stunning systems the staging areas that leads into the stunning areas should be filled half full. Pigs need room to turn.

Replace electric prods with other driving aids such as flags, panels, or paddles.

Eliminate distractions which make pigs balk and refuse to move such as air drafts blowing in their faces, sparkling reflections on the floor, shadows or small moving objects such as chains. If pigs constantly back up, the distraction that is scaring them must be removed (Grandin, 2000, 1996). See the behavior section of this webpage.
Lower temperature

Gentle handling, rest, and showering helps lower body temperature. Pigs that are overheated are more likely to have PSE or DFD meat (Gariepy, 1989). Heat damages the meat, both in live pigs and shortly after slaughter, making proper chilling important. Sometimes carcasses are jammed together or there is insufficient refrigeration. Some managers make the mistake of maximizing pig numbers by overloading the cooler. They are saving a few pennies on numbers and throwing dollar bills away in carcass shrink losses. It is easier to quantify pigs per hour and person hours than shrink loss and customer dissatisfaction. The industry needs to change its mind set and eliminate the "ram and jam" mentality. To succeed in the marketplace of tomorrow, quality must come first and quantity second.

Segmented market

A segmented market causes losses to be passed from the producer to the next person in the marketing chain. A producer who sells pigs live-weight has no motivation to improve quality. Live-weight selling or a carcass marketing system that fails to reward quality are the major causes of quality problems. The producer gets the wrong economic incentives. Some grading systems reward lean, highly muscled pigs with high levels of PSE. The electronic probes currently being used by the packing plants measure fat thickness and the size of the loin, but there is no PSE measurement. This motivates the producer to select breeding stock for rapid gain, leanness, and muscle growth. These selection pressures have resulted in high levels of PSE because pigs carrying the stress gene are kept as breeding stock. The swine industry needs to use an accurate method for measuring PSE so that a PSE measurement can be added to the fat and loin eye size measurements. The producer must be financially rewarded for producing lean pigs with low levels of PSE. Changing the carcass measurement and payment system to include PSE measurement will motivate producers to reduce the incidence of the stress gene in their herds. The bottom line is that the producer has to be financially rewarded for producing quality pork instead of maximum tonnage.

Bloodsplash

Bloodsplash is damage to the meat caused by either small pinpoint haemorrhages or large blood clots in the meat. It is a severe cosmetic defect that affects the appearance of the meat. Haemorrhage problems are mainly caused by problems inside the plant, but nutritional factors such as low levels of selenium and vitamin E may possibly contribute to it by weakening capillary walls. Lean pigs often have more problems with bloodsplash.

These procedures have effectively reduced bloodsplash in many plants which use electric stunning:

For electric stunning, use an amperage power supply where the amperage remains constant and voltage varies with pig resistance. Old fashioned voltage-regulated stunners allow amperage spikes that damage the meat. Some plants have built their own electronic constant amperage power supplies. These units can lower bloodsplash over 100%. To ensure good animal welfare, a minimum of 1.25 amps must be used to reliably induce a grand mal seizure and produce instantaneous unconsciousness (Hoenderken, 1983). For large market pigs, a minimum of 300 volts should be used and slightly lower voltages can be used for lighter market pigs (Hoenderken, 1983; Gregory, 1988). Some plants have attempted to reduce bloodsplash by reducing amperage to 0.5 amps. This must never be permitted because scientific research has shown that low amperages or frequencies over 800 Hz fail to induce instantaneous unconsciousness.

Bleeding a pig within 10 seconds after stunning will reduce bloodsplash. Prone sticking systems accomplish this, but older, hanging sticking systems sometimes have intervals of over 30 seconds. Quick bleeding also improves animal welfare because it reduces the possibility of an animal reviving (Hoenderken, 1983; Blackmore and Newhook, 1981).

The operator must be careful to avoid double stunning and causing the pig to contract more than once (Grandin, 1985/86). Double stunning can be caused by allowing the stunning applicator to slide during the stun or turning on the electricity before the applicator is pressed firmly against the pig. The pig should not squeal when the stunner is applied.

Worn cords and switches should be replaced. Slight disruptions in electrical continuity will cause bloodsplash. Wet cords can also cause problems.

Reduce electric prod usage. In a research trial, elimination of electric prods reduced bloodsplash (Calkins et al.,1980).

CO2 stunning will reduce bloodsplash (Velarde et al., 1999). The disadvantage is that it is expensive to operate and it requires well trained maintenance technicians.
Other Factors

Both PSE and bloodsplash will fluctuate with weather changes. Observations by the author indicate that PSE levels may double during the first 4 hot days of spring. Bloodsplash tends to worsen when temperatures fluctuate. It is very important to take weather into account when new methods for reducing PSE or bloodsplash are being tested. In one study, the amount of bloodsplash reduction benefit provided by new handling and stunning procedures greatly fluctuated, depending on the weather (Grandin, 1988). On some days, it provided great reductions in bloodsplash and on other days, almost no reduction. The procedures must be tested over a period of weeks to eliminate confounding effects of weather.

Bloodsplash can be reduced by the use of CO2 stunning (Velarde et al., 1999). Recent observations in a plant equipped with both state-of-the-art CO2 and constant amperage electrical stunning equipment indicated that PSE and bloodsplash levels were almost identical. CO2 definitely reduces bloodsplash compared to old-fashioned voltage regulated electrical stunning equipment. New CO2 stunning systems could provide handling advantages by eliminating the need to line pigs up in single-file chutes. However, there have been concerns about humaneness (Hoenderken, 1983). Some genetic lines of pigs react very well to CO2 and others may possibly be stressed. The Yorkshire breed reacts very well (Forslid, 1987), but stress-susceptible pigs may possibly be conscious during the initial excitation phase (Troeger and Waltersdorf, 1991). Therefore, CO2 may be an excellent method in a vertically integrated system where pig genetics could be controlled, but animal welfare may be poor for certain genetic types of pigs.

Conclusions

The biggest problem facing some segments of the industry is the emphasis on quantity rather than quality. Producers need to be provided with a marketing system that provides economic incentives to improve pork quality rather than just grow heavier pigs. In the 90's the "mind set" of a large segment of the United States pork industry was commodity based. The entire mind set of the industry needs to change from commodity-based to consumer-based. When this occurs, new procedures will be developed quickly. Fortunately, the industry has become more quality oriented and this has resulted in improvements in pig handling and changes in genetics.

Until this happens, nobody will be motivated to invest the time or the money to change systems.