A Survey of Farm of Origin and Slaughter Plant Effects on Pork Quality

INTRODUCTION

The issue of meat quality has grown to be of major concern in the swine industry. Cannon et al. (1995) reported that the condition referred to as pale, soft, and exudative (PSE) pork caused U.S. packers significant losses. It is well known that animal handling practices, pre-slaughter management, and genetic factors affect meat quality. However, there is little information available on the impacts of farm of origin and slaughter plant on pork quality. Thus, the objective of this experiment was to evaluate the influence of farm of origin and slaughter plant on pork quality while controlling genetic line, a major source of variation.

MATERIALS AND METHODS

Experimental Design and Treatments.

This study investigated the effects of farm of origin and slaughter plant on pork quality. The study was carried out as a 4 × 2 factorial arrangement with the following treatments: 1) Farm of origin (A vs B vs C vs D) and 2) Slaughter plant (1 vs 2). Pigs were harvested on four days (summer, fall, winter, and spring) and a summary of environmental conditions on each harvest day at each farm and slaughter plant are presented in Table 2.

Animals

Thirty-two trailer loads of pigs carrying a total of 4500 animals from four commercial farms were transported to two commercial slaughter plants. All pigs were the progeny of line 337 sires mated to C22 dams (PIC USA, Franklin, KY). Transportation time to each plant ranged from 3.5 to 10.5 h (Table 1). On each slaughter day, one truckload of pigs from each farm was dispatched to each plant. Pre-slaughter handling was standardized with pigs being mixed and loaded onto a livestock trailer on the afternoon prior to slaughter and transported directly to the slaughter facility. Pigs were electrically stunned and harvested using standard commercial procedures following an overnight rest period. A sub-sample of 800 pigs (25 pigs/farm/plant/slaughter day) was randomly selected for meat quality evaluation.

Slaughter and Meat Quality Evaluation

At 45 min, 3 h and 24 h postmortem, longissimus pH was measured at the level of the 10^th rib using a PH-STAR^TM. At 24 h postmortem, carcasses were fabricated and the boneless loin from the left side of each carcass was removed, vacuum packaged, and transported to the University of Illinois Meat Science Laboratory for meat quality assessment. At 48 h postmortem, loins were removed from the package, weighed, and purge loss was calculated. Objective color (L*, a*, and b* values) was measured on the cut surface of the loin at the 10^th rib using a Minolta Chromameter CR-300. A chop (1.3 cm) was cut, weighed, placed in a Whirl-pak bag, suspended in a 4^oC cooler for 48 h, reweighed, and drip loss was recorded. Another chop (2.5 cm) was placed in a Whirl-pak bag and frozen (-20^oC) for proximate analysis. Two loin chops (2.5 cm) were cut from the longissimus posterior to the 10^th rib and were vacuum packaged and then frozen (-20^oC) for a period of 14 d, and were thawed prior to being cooked for Warner-Bratzler shear force and sensory evaluation.

Shear Force, Cooking Loss and Sensory Evaluation

Chops were thawed for 24 h at 4^oC, and cooked to an internal temperature of 70^oC. The chops were weighed before and after cooking to determine cooking loss. Chops were placed in a cooler (4^oC) and removed upon reaching an internal temperature of 25^oC. Four 1.3 cm diameter cores were taken parallel to the muscle fibers from each chop and the shear force values for the four cores were averaged for each sample. Chops for sensory evaluation were prepared and cooked using the same procedures as for shear force. Six panelists were trained according to the procedures for sensory evaluation described by the American Meat Science Association (1978). Panelists evaluated juiciness, tenderness, and off-flavor intensity using a 15 cm structured line scale (0 = extremely dry, tough, and intense off-flavor to 15 = extremely moist, tender and no off-flavor). Cooked chops were cut into 1 cm cubes and served warm to the taste panel. Panelists were seated in individual booths under red lighting and water was provided to cleanse the palate.

Statistical Analysis

The GLM procedure of SAS (SAS Inst. Inc., Cary, NC) was used to analyze the data. The model used included the fixed effects of farm of origin, slaughter plant, slaughter date and the two- and three-way interactions. Means were evaluated using the PDIFF and STDERR options of SAS.

RESULTS AND DISCUSSION

The main effect treatments of farm of origin and slaughter plant were significant (P < 0.05) for all the variables evaluated. However, there were significant (P < 0.05) farm of origin × slaughter plant interactions for most of the important fresh pork quality traits and, therefore, only the interaction means are presented (Table 2).

There were no farm of origin × slaughter plant interactions (P > 0.05) for Minolta a* values. Pigs harvested at Plant 1 had greater (P < 0.001) longissimus Minolta a* values, indicating pork with more reddish color, when compared to pigs from Plant 2. Hambrecht et al. (2002) evaluated three processing plants and showed that they also produced pork with different Minolta a* values, with Farm D having the highest values, Farm C the lowest, and the other two farms being intermediate.

Farm of Origin and Slaughter Plant Interactions

Farm of origin × slaughter plant interactions (P < 0.05) were observed for 45-min pH, 3-h pH, ultimate pH, Minolta L*, Minolta b*, purge loss, drip loss, cooking loss, shear force, and taste panel juiciness and tenderness. Pigs from farm D differed from farms A, B, and C as they produced similar (P > 0.05) 45-min pH, ultimate pH, L*, purge loss, cooking loss, and shear force values at Plants 1 and 2, and even produced greater (P < 0.05) 3-h pH and b* values at plant 2 compared to plant 1. The interaction differed for drip loss and tenderness as pigs from farm C produced similar (P > 0.05) values at both slaughter plants, while farms A, B, and D all produced more desirable (P < 0.05) drip loss and purge loss values at slaughter plant 1 than plant 2.
Overall, Plant 2 produced poorer quality pork than plant 1 for three of the four farms evaluated. It is difficult to understand why pork quality traits were not always superior in one particular plant, but sometimes were similar or reversed depending on the farm and variable evaluated. Especially, as every effort was maintained to standardize pre-slaughter handling, genetic line, and day of transport. There has been very little or no published research reporting on the effects of slaughter plant, farm of origin, or their interaction on pork quality. One possible explanation for some of the differences evaluated in this study could be location of the farms relative to the slaughter plants. For example, farm D had the furthest average distance from both slaughter plants, while the other farms average transport times were relatively similar (Table 1).

Implications

1. Farm of origin and processing plant were significant sources of variation for most fresh pork quality traits.
2. There were significant interactions between farm of origin and slaughter plant for most of the important meat quality traits. – These results suggest that the slaughter plant which generated the most desirable meat quality differed among the four farms
3. Finally, these data also highlight the importance of simultaneously optimizing conditions at the farm, during handling and transport, and at the slaughter plant for achieving desirable pork quality.
4. Follow up studies are in progress to understand the reasons for this variation and to establish programs to consistently produce high quality pork.

REFERENCES

American Meat Science Association. 1978. Guidelines for cookery and sensory evaluation of meat. American Meat Science Association – National Livestock and Meat Board, Chicago, IL.

Cannon, J. E., J. B. Morgan, F. K. McKeith, G. C. Smith, S. Sonka, J. Heavner, and D. L. Meeker. 1995. Pork chain quality audit packer survey: Quantification of pork quality characteristics. J. Muscle Foods: 6:369.