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

Progress 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 will be conducted to compare the impact of housing on pork quality and carcass characteristics of pigs as well as comparing slaughter day stress responses. Slaughter day stress responses will be evaluated through cortisol and lactate levels which will be obtained by collecting blood before transport and at exsanguination. Pork quality and carcass characteristics will be evaluated through bi-weekly weight measurements, color and marbling scores, backfat (BF) measurements, loin eye area (LEA) measurements, and pH at 0,6,12, and 24 hours post-mortem. The results from this study will be 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 is to provide current pork quality and welfare research to producers looking to serve specialty pork markets. There is a misconception that producers and consumers want different things when it comes to pork production; however, pork quality and animal welfare values are often shared (3). 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, challenging producers who wish to utilize new technology and techniques in their pasture-based system.

Pigs reared outdoors have been observed to have a reduced backfat (BF) thickness when compared to indoor pigs (8,10). However, other similar studies show the outdoor pigs having an increase in BF (7). Growth can also be impacted by housing. Gentry et al., (2002) showed pigs reared outdoors had an increased average daily gain (ADG), while others have shown the indoor reared pigs growing at a faster rate (9,12). 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 production methods and 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 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 (2). Muscle pH is influenced by postmortem glycolysis where activity and stress results in glycogen build up, which converts to lactic acid in the animal post-mortem (2). During stressful situations, cortisol is the primary hormone released, thus when studied with pH, can be a reliable indicator of stress (14). 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.

Our proposed study will investigate the relationship between pork and slaughter day stress as influenced by housing (Indoor vs. Outdoor). Pork quality and carcass characteristics of both housing groups will be evaluated alongside blood cortisol and lactate levels at exsanguination to determine pig level of stress at slaughter. We hypothesize outdoor pigs will 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 housing environment. Data collected during this study will influence animal welfare and pork quality in pasture-based management systems.


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 rearing and growth

Fifty crossbred Yorkshire pigs of similar breeding will be divided across two housing treatments, Indoor (n = 25), and Outdoor (n = 25). Each group of 25 will be housed in pens of 5 pigs. The Outdoor group will be housed fully on pasture at Penn State’s swine facilities, with shade provided and rotated to fresh ground every two weeks. The Indoor group will be housed in a typical finishing barn with concrete flooring (no bedding) within the swine barn at Penn State. Both the Indoor and Outdoor groups will be provided free access to a standardized grow-finish ration and clean water provided via a nipple drinker system. All pigs will be weighed on a digital scale every two weeks throughout the trial. Live animal weights will be collected on a digital scale at the farm on the day before slaughter and used as the marketing weight. Slaughter and hot carcass weights will be collected at the harvest facility.

Stress Evaluations

Blood will be collected from each pig at exsanguination using a sterile 100ml cup following carbon dioxide stunning. The blood will be divided into two processing tubes for storage with a portion stored for later analysis of blood cortisol and blood lactate at slaughter. Blood will be evaluated for cortisol concentration utilizing radio-immunoassay technique, while lactate concentration will be evaluated utilizing a lactate analyzer.

Carcass and meat quality measurements

Hot carcass weights (HCW) will be collected at the slaughter facility. Once the carcass is split, meat quality will be evaluated on one side of the carcass, consistent across all pigs. All meat quality measurements will be collected on the longissimus Dorsi (LD) or loin. Color and marbling scores will be assigned subjectively using the Pork Checkoff, Pork Quality Standards chart, and objectively using a Minolta colorimeter that assigns L*A*B* values associated with color and light scores in the CIE color space. Backfat measurements are obtained in centimeters using a pork backfat ruler. The loin eye area will be calculated based off cross-sectional measurements. The pH measurements will be collected within the loin eye at 0,6,12, and 24 hours post exsanguination using a digital pH meter.  

Statistical analyses

All statistical values will be obtained using SAS 9.1 (Cary, NC) statistical software. Pen will be the experimental unit and housing (Indoor vs. Outdoor) will be the fixed effect. All pork quality and stress measurements will be evaluated as related to housing.

Participation Summary

Education & Outreach Activities and Participation Summary

4 Webinars / talks / presentations

Participation Summary:

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 will generate data for research and extension publications. Furthermore, results of this project will be disseminated through Extension programs where we can discuss results and application directly with producers. This will include events, such as the annual PASA conference and Extension workshops.

We have already begun outreach for this project by using the data we gathered from our pilot study. 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. 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.  

Project Outcomes

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

We are still in the processing stages of this project, but we believe our research can 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. We hope to use the information gathered from this study 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 conducting 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. 



Assessment of Project Approach and Areas of Further Study:

Further study is needed to understand what potential aspects of pasture most
influenced pig growth or if there are other methods of husbandry for pigs on
pasture that will influence pork quality or welfare.

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.