Evaluating the impact of housing on pork quality and slaughter day stress

Final report for GNE22-278

Project Type: Graduate Student
Funds awarded in 2022: $13,560.00
Projected End Date: 07/31/2023
Grant Recipient: Pennsylvania State University
Region: Northeast
State: Pennsylvania
Graduate Student:
Faculty Advisor:
Dr. Elizabeth Hines
The Pennsylvania State University
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Project Information


Pasture-based management systems are increasing in popularity due to an increase in consumer demand for more enriched environments and higher prices that can be obtained by producers targeting niche markets; however, research is limited to guide producers. This study was conducted to compare the impact of housing on pork quality, carcass characteristics, and slaughter day stress of pigs. Slaughter day stress responses were evaluated through cortisol levels which were obtained by collecting blood before transport and at exsanguination. Pork quality and carcass characteristics were evaluated through bi-weekly weight measurements, color scores, marbling scores, backfat (BF) measurements, loin eye area (LEA) measurements, and pH at 0,6,12, and 24 hours post-mortem. This study supports historical industry knowledge that housing does have an impact on pig growth, where indoor reared pigs have an improvement in performance. This study, however, did not find significant impacts to pork quality as a result of indoor or outdoor housing. Finally, lower levels of cortisol before transportation to slaughter was observed in outdoor reared pigs, however cortisol levels were similar at the time of slaughter. Further study is needed to determine if decreased cortisol occurs throughout the finishing phases. The results from this study were used to translate current available welfare and meat quality information to pasture-based operations and grow the limited pool of current research on pasture reared swine.

Project Objectives:
  1. Compare impact of housing on slaughter day stress responses.
  2. Compare impact of housing on pork quality and carcass characteristics.
  3. Develop a standardized model for pasture pork research for addressing key challenges in production.

The purpose of this project was to provide current pork quality and welfare research to producers looking to serve specialty pork markets through pasture-based operations. There is a misconception that producers and consumers desire different things when it comes to pork production; however, pork quality and animal welfare values are often shared. Pasture-based management systems provide an enriched environment for pigs and add value to pork in specialty markets. Yet, carcass characteristics and pork quality have been observed to vary when raising pigs on pasture, thus challenging producers who wish to utilize new technology and techniques in their pasture-based system.

Variations observed in previous research studies that focus on carcass development and pork quality may make it difficult for producers to develop effective management styles. Some studies have shown pigs reared outdoors having a reduction in backfat (BF) thickness when compared to indoor pigs. However, other similar studies show the outdoor pigs having an increase in BF. Growth can also be impacted by housing. Gentry et al., (2002) showed pigs reared outdoors having an increased average daily gain (ADG), while others have shown the indoor reared pigs growing at a faster rate. Inconsistency in data clouds a producer’s ability to make decisions when it comes to managing their outdoor herd. Furthermore, most of this variation appears to stem from differences in the environment, production methods, and the lack of direct comparisons to indoor reared pigs where pork quality standards have been developed.

Achieving high pork quality is the goal for all producers, and welfare plays a key role in the development of a desirable product. One of the ways we can measure the relationship between pork quality and welfare is through post-mortem pH. Muscle pH has a direct impact on the value of meat products; a lower pH results in a more acidic pork product that is less appealing to the consumer. Muscle pH is influenced by postmortem glycolysis where increased activity and stress results in glycogen build up, which converts to lactic acid in the animal post-mortem. During stressful situations, cortisol is the primary hormone released, thus when studied with pH, can be a reliable indicator of stress. The connection between stress levels of the pig and pork quality is important for the producer to understand given the influence of husbandry practices on stress level and the impact of stress on pork quality.

This research study investigated the relationship between pork quality and slaughter day stress as influenced by housing (Indoor vs. Outdoor). Pork quality and carcass characteristics of both housing groups was evaluated alongside blood cortisol levels before transportation and at exsanguination to determine pig level of stress at slaughter. We hypothesized outdoor pigs should have lower levels of slaughter day stress, as evidenced by blood parameters and carcass characteristics, due to the effect of increased in handling and external stimuli inherent to the outdoor housing environment.


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Materials and methods:

Materials and methods:

Prior to the initiation of these experiments, all animal use, handling, and sampling techniques were approved by the Institutional Animal Care and Use Committee.

Animal housing:

Fifty pigs (White Walker [Top Cut Genetics, LLC, IN] by Yorkshire-Cross sow [Penn State Herd]) were divided across two housing treatments: Indoor (n = 25), and Outdoor (n = 25). At eighty-one days of age, pigs were split into ten separate groups by sex and weight to create five pens for the Indoor group (29.28kg) and five pens for the Outdoor group (30.64kg; P = 0.27). The five Indoor groups were housed in five separate pens (7.06m2 each) on solid concrete flooring with no bedding in a fully enclosed barn with proper ventilation at the Penn State swine facility. The five Outdoor groups were housed on perennial cool season grass pasture that included species such as white clover, red clover, orchard grass, and tall fescue. The pigs were contained in welded wired panels that formed individual pens (23.78m2 each) at the same research facility. Shade was provided for Outdoor pigs using an 80% shade cloth (QC Supply: Clinton, NC) to ensure that one third of the pen space was covered. Pens were rotated to fresh pasture every two weeks. Both groups were fed a standardized grow-finish ration via a Smidley® flap top feeder (Smidley, Britt, IA) ad libitum and given free access to clean water via an Edstrom nipple drinker system (Avidity Science, Waterford, WI).

Pig Growth:

Individual pig weights were collected on an electronic Waypig scale (Farmer Boy Ag, Myerstown, PA) with a Digi-Star scale head (Fort Atkinson, WS) every two weeks, resulting in ten weigh periods. Slaughter weights were collected the day before pigs were loaded onto the trailer approximately 24h before slaughter. All pigs were harvested at a commercial abattoir on the same day, and hot carcass weights (HCW) were collected immediately after slaughter.

Cortisol Evaluations:

Blood was collected on individual pigs at two time periods: 24 hours before transporting for slaughter, and at exsanguination. Pigs were loaded onto a bilevel livestock trailer where treatment pens were combined. However, separation was still maintained for both treatment groups. Transportation took between 3.5-4 hours, and pigs were immediately put into lairage upon arrival. Pigs were kept in their respective treatment groups during lairage (14hr). All pigs were stunned using a CO2 chamber comprised of a mixture of gases (Carbonyl Sulfide: ≤ 0.5 ppm; Hydrogen Sulfide: ≤ 0.5ppm; Nitric Oxide: ≤ 2.5 ppm; Nitrogen Dioxide: ≤ 2.5 ppm; Non-volatile Hydrocarbons: ≤ 10 mg/kg; Sulfur Dioxide: ≤ 5 ppm; Volatile Hydrocarbons: ≤ 0.005% by volume; Lornic INC; Holland, MI), and subsequently exsanguinated. The entire slaughter process for both treatment groups was completed within 30 minutes. Exsanguination blood samples were placed into 6ml EDTA tubes (VWR International; Radnor, PA) and transported on ice for 30 minutes to be centrifuged at 4℃ and 3,400 RPM for 15 minutes. Plasma samples were ultimately stored at -80℃ until further analysis. Twenty-four hours prior to plasma analysis, samples were moved to a refrigerator at 3℃, and then allowed to reach room temperature (20℃) 30 minutes prior to performing the cortisol test. An ELISA cortisol kit for swine was used to obtain the cortisol concentrations (ID: KA2338, Abnova; Taipei, TW). Samples were initially incubated at 37℃ for one hour, and then terminated with wash solution. After a TMB color reagent was added to each sample well that oxidizes as it comes in contact with an HRP conjugate (horseradish peroxidase), they were incubated at room temperature (20℃) for an additional 20 minutes. Once the stop solution was applied and allowed to mix for 2-5 minutes, the absorbency was read at 450nm. Cortisol absorbances were obtained using a Spectrostar Nano plate reader (BMG Labtech; Cary, NC).

Carcass and pork quality:

A digital handheld meat pH meter (HI99163; Hanna Instruments, Woonsocket, RI) was used to collect loin pH measurements at four sample times post slaughter (0h, 6h ,12h, and 24h). Loin eye area was calculated in square inches using a standard pork loin eye area grid (Iowa State University Extension, Ames, IA). Subjective color scores and marbling scores were individually obtained (Pork Quality Standards chart; Pork Checkoff, Des Moines, IA). Colorimeter values were obtained using a CR – 300 Minolta colorimeter in the CIE color space (L*, a*, b*) (Konica Minolta, Wayne, NJ).

Statistical analyses:

All statistical analyses were performed using SAS 9.1 (Cary, NC) statistical software and analyzed using the PROC MIXED method, with pen as the experimental unit and the fixed effect being housing type (Indoor vs. Outdoor). All pork quality and growth measurements were evaluated as related to housing type. All analyses were considered statistically significant at P ≤ 0.05.

Research results and discussion:

Pig Growth:

Starting weight averages for both treatments were similar at 29.28kg for the Indoor groups and 30.64kg for the Outdoor (P = 0.27). Total ADG was also evaluated through the collection of individual pig weights every two weeks with the Indoor groups having a higher weight gain throughout the sixteen weeks of the finishing period (P ≤ 0.001). Final pig weights were taken the day before slaughter and were shown to be different between treatments with the Indoor group finishing at an average weight of 126.52kg and the Outdoor group at an average weight of 112.72kg (P ≤ 0.001).

Carcass characteristics and pork quality:

HCW for the Indoor group was different than those seen from the Outdoor group at 96.63kg and 84.39kg respectively (P ≤ 0.001). Subjective color scores (P = 0.17) and marbling scores (P = 0.53) showed no significant difference between treatments. Additionally, objective color score was not significantly impacted by housing with L* (P = 0.77), a* (P =0.95), and b* (P = 0.40) colorimetry values showing no significant differences. Loin eye area (LEA) was also not significantly impacted by housing (P = 0.07). Loin pH measurements did show variation between the treatment groups with the Indoor group having a higher pH value at 0h and 24h post-slaughter. The Indoor group’s average pH value was 6.33 at 0h, while the Outdoor group’s average pH was at 6.20 (P = 0.03). At 24h, the Indoor group dropped to a pH of 5.62 and the Outdoor group dropped to 5.46 (P ≤ 0.001). However, the Outdoor group had a higher 6h post-slaughter pH measurement at 6.00 with the Indoor group having a pH measurement of 5.87 (P = 0.01). Additionally, no significant difference was seen at 12h post-slaughter (P = 0.81).

Cortisol levels associated with slaughter day stress:

Cortisol levels measured from blood samples taken 24 hours before transportation to the slaughter facility showed significant differences between the two housing groups with the Indoor group at 0.81 AU and the Outdoor group at 0.64 AU (P = 0.01). However, exsanguination cortisol levels were similar between both housing groups at 1.00 AU and 1.01 AU for the Indoor group and Outdoor group respectively (P = 0.93).


Research conclusions:

Overall, pigs reared on pasture showed decreased growth performance, but housing’s impact on pork quality is minimal. Additionally, outdoor-reared pigs show lower levels of cortisol before transportation to the slaughter facility, but no differences are observed at exsanguination. The benefits that come from increased consumer interest and potential increases in welfare need to be weighed with the decreased growth performance of hogs reared on pasture. Although pork quality is not significantly impact by housing, the potential increase in cost necessary to get outdoor-reared hogs to market weight could potentially cancel out the premiums paid for pasture-reared pork product.


Participation Summary

Education & Outreach Activities and Participation Summary

25 Consultations
1 Published press articles, newsletters
4 Webinars / talks / presentations

Participation Summary:

15 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:


Insufficient research on pork quality is available to producers who are interested in pasture-based management systems. Since a large majority of pork quality and animal welfare stems from management practices, and stressors that occur before slaughter, it is important that scientific findings support pork production while pigs are still on farm. This project generated data for research and extension publications. Furthermore, results of this project have been disseminated through Extension programs where we can discuss results and application directly with producers. This included events such as the annual PASA conference and Extension workshops.

Outreach for the pilot study completed in 2021 has been presented at several conferences and seminars. At the 2022 PASA Conference, we presented our findings at the “A Pilot Study to Benchmark Pastured Pig Performance” session. Producers in attendance (15) expressed a desire for more research in pasture management systems. In April of this year, we presented a poster on “Pilot Study to Benchmark Pastured Pig Performance” at the 2022 Penn State Extension Conference, where we discussed results from our study with extension educators across all 67 counties of Pennsylvania, expanding reach of our research to a broader producer audience.

Feb 10 - Chelsea Becker - Impacts of Housing on Pork Quality

The pilot data has also generated an extension article that has been featured in Lancaster Farming (reach 60,000+) to support producers who have pasture-based pig operations. 

Lancaster Farming Article: https://www.lancasterfarming.com/farming-news/4-types-of-pasture-management-systems-for-swine/article_f13aceb4-f4bb-50fc-9983-a272ee38ff38.html

The research gathered from the current study in 2022 has been presented at PASA through two seminars entitled “Effects of Pigs on Pasture” and “Impacts of Housing on Pork Quality”. The attendees for each seminar (20) were actively interested in the current research to help guide them on production practices and many producers were able to provide feedback for future projects. Individual consultations with producers are on-going as word-of-mouth on research is shared. 

Journal articles and educational publications are in development based on this work. We expect to publish two peer-reviewed articles and several extension publications.  

Project Outcomes

1 Grant applied for that built upon this project
4 New working collaborations
Project outcomes:

Th results from this research project have been able to serve as a foundation for farmers looking to raise their pigs on pasture. Minimal research is available to producers looking to manage their hogs and pastures in a way that maximizes pork quality and profits. The information gathered from this study has been able to help producers make best management decisions to ensure profitability and overall sustainability

Knowledge Gained:

The pigs were placed on project in May 2022 and slaughtered in September 2022. Since that time, we have been processing meat samples and data collected from pig growth, pork quality, and pasture management. Serum cortisol and lactic analysis is scheduled to be conducted in the spring of 2023. 

A large amount of information regarding raising hogs on pasture has been obtained since beginning this study. The Indoor group consistently showed a higher average daily gain (P ≤ 0.02). Subsequently, we observed a difference in hot carcass weights with the Indoor group having a higher average weight (P<0.001). We saw no differences in pork color scores (P=0.18), marbling scores (P=0.53), loin eye area (P=0.07), or colorimeter values: L (P=0.78), A (P =0.96), B (P=0.41). Additionally, pH measurements were obtained at four time points post slaughter: 0 hours (P=0.03), 6 hours (P=0.01), 12 hours (P=0.8), and 24 hours (P<0.001). At two time points (0,24) the Indoor group had a larger pH average, while the Outdoor group showed a larger average at the 6 hour time point. However, it is important to note that these averages did not show variation that exceeded 0.20. 

Ultimately, conclusions of the study support that pastured pork is an option for livestock producers, however careful consideration for expectation on pig growth performance, nutritional requirements, and impact on land should be carefully considered, as pork quality is not impacted by pasture rearing and may not garner expected premiums to recoup cost of production. 

Assessment of Project Approach and Areas of Further Study:

The approach of this research project was carefully evaluated, and feedback from the pilot study was used to develop the current protocols. Valuable information was obtained regarding pigs reared on pasture to help guide producers on effective management practices for their herd. Although there may be many variables associated with any pasture-based livestock operation, this project has served as a starting point for further research trials that may be able to evaluate additional obstacles for the producer.

 Directions for further research projects include the addition of heritage swine breeds to mimic what is typically seen among small scale producers that grow their hogs on pastured or wooded lots. Additionally, the incorporation of consumer preference testing through sensory analysis on pasture-raised cooked pork products would be beneficial to producers. Knowledge of consumer pork preference would help guide producers on best management practices that could ultimately impact the overall quality of their pork products.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.