Infectious lameness in growing pigs is an emerging problem in the United States. Lameness is an animal welfare concern and increases production costs. Mycoplasma hyosynoviae is considered to be the most common cause of infectious lameness. It is a dynamic organism in that its colonization of the joint can be transient and only a fraction of colonized pigs develop disease. Conventional polymerase chain reaction (PCR) testing for the pathogen is done post mortem and can be difficult to interpret without additional information about the pig, joint and joint fluid. Antemortem tests that are applicable to a broad range of lameness agents would significantly improve diagnostic testing for infectious lameness. Antemortem tests would also allow producers to monitor treatment success in affected pigs. In human and canine literature, clinical pathology of joint fluid is a core ante mortem diagnostic test for multiple type of arthritis. Clinical pathology is an analysis of the protein, pH and cell types within the joint fluid. Combined with PCR and culture, clinical pathology could be a key diagnostic tool for swine. However, a technique for the ante mortem collection of joint fluid in the field and reference ranges for normal animals for clinical pathology must be developed before these tools can be applied to commercial swine operations.
The objectives of this study were:
1. To create standard case definition of Mycoplasma hyosynoviae (MHS) arthritis in growing swine
2. To do a retrospective case review of lameness cases at the Iowa State University Diagnostic Lab to understand the common causes of lameness at the diagnostic lab
3. To create reference range values for clinical pathology parameters for swine synovial fluid from clinically normal pigs
4. To apply and evaluate antemortem joint fluid collection techniques and clinical pathology to non-lame and lame pigs under field conditions
Materials and Methods:
For objective one, a literature review using PubMed, Agricola and the AASV swine information library was conducted to develop a clinical case definition for MHS arthritis in swine. To perform the retrospective lameness case review, all cases related to lameness in swine were pulled from 2010 to 2015. Cases that did not meet the age, weight, project type, billing and diagnostic testing criteria were removed. Cases were then reviewed manually to verify relevance to lameness in growing hogs. The cases were then assigned a main and other diagnosis using specific diagnostic criteria from Disease of Swine. Frequency counts of the cases in each diagnostic category were tabulated.
In objective 2 four biopsy instruments were assessed in their ability to successfully collect a joint tissue sample in cadaver pig legs. These tools were tested repeatedly using 12 rear and four front legs from euthanized finisher pigs. Usability of each instrument was recorded on a scoring rubric. Elbow, stifle, and hock joints were biopsied then opened for gross examination to assess the impact of the technique and instrument on the native tissue. Samples from each biopsy instrument were pooled in formalin and submitted to a state veterinary diagnostic laboratory to evaluate tissue type and specimen quality.
In objective 3, the main objective was to collect joint fluid samples from clinical normal finisher pigs to create clinical pathology reference intervals for collected volume, total nucleated cell count (TNCC), total protein, pH, red blood cell count (RBCC), percentage of neutrophils, percentage of lymphocytes, and percentage of large mononuclear cells for each joint. To accomplish this, 54 healthy finisher pigs were anesthetized and antemortem joint fluid was performed. On pigs in which an antemortem sample could not be attained, a post-mortem sample was collected. The joint fluid was submitted for clinical pathology analysis (for reference interval creation) and for bacterial culture, Mycoplasma hyosynoviae (MHS) PCR, Mycoplasma hyorhinis (MHR) PCR. Twelve joints on each pig were also opened and assessed for cartilage and joint tissue abnormalities.
This objective also investigated the utility of several anesthetic protocols for this procedure, including combinations of telazol, ketamine, acepromazine and lidocaine.
In objective 4, seven clinically lame commercial finishing pigs in a production flow with a history of infectious lameness received an intramuscular (IM) injection of Telazol (4.4mg/kg), Ketamine (2.2mg/kg) and Xylazine (4.4mg/kg) (TKX). Once under anesthetic, two joint samples were collected per pig, one carpus and one hock. Joint samples were submitted for bacterial culture, Mycoplasma hyosynoviae (MHS) PCR, Mycoplasma hyorhinis (MHR) PCR and clinical pathology. The clinical pathology parameters on the lame pigs were compared to the reference ranges generated in objective three.
Literature review has been completed and used to formulate a case definition for the diagnosis of M. hyosynoviae (MHS) in growing swine. A case was deemed positive for MHS if specimens submitted from an affected group of animals demonstrating clinical lameness, had at least one positive MHS PCR on joint fluid or joint tissue and histopathological lesions consistent with MHS. From the diagnostic lab lameness case review, Mycoplasma hyosynoviae and infectious arthritis caused by other bacteria cases represented about 40% of the 464 lameness cases examined.
For the creation of the reference ranges, there were 37 hock samples and 46 carpus samples that were eligible for inclusion into the reference range dataset as some samples were removed for insufficient volume, blood contamination, culture contamination or synovial tissue abnormalities.
Telazol, ketamine and xylazine was the only protocol that was suitable for collection of joint fluid from market sized animals. The depth of anesthesia produced by the other protocols was insufficient. The recovery time for these procedures is several hours.
Lastly, in the clinical lameness field case, antemortem joint samples were successfully collected in 7/7 pigs. Sampled pigs recovered well and did not have adverse effects from the procedure. Diagnostic testing and clinical pathology results indicate that there did not appear to be an infectious cause of lameness in these pigs.
Industry Impact
The creation of a reference range dataset for synovial fluid from non-lame healthy finisher pigs provides a novel diagnostic tool to practitioners and production companies. In human, equine and canine medicine, clinical pathology is a core diagnostic test for lameness and arthritis. Coupled with culture, molecular testing for mycoplasma species and histology on the joint tissue, clinical pathology completes the diagnostic picture for a joint. Due to the transient nature of many infectious arthritis agents, multiple pieces of evidence indicative of infectious agents are critical for accurate diagnosis. This complete diagnostic picture allows the veterinarians to more confidently and accurately determine a diagnostic and treatment plan to the diagnostic case. Improved diagnosis and treatment plans are a direct benefit to pigs and caretakers alike.
The implications of improving our ability to collect necessary diagnostic samples and to develop useful diagnostic assays for infectious lameness are directly and immediately relevant to swine producers. Economic losses due to lameness are far reaching, including reduced average daily gain, culls, euthanasia, cost of labor and treatment and loss of high value genetic stock. For the pig, infectious lameness is painful and reduces the pig’s ability to access vital resources including feed and water. As there is increased public attention to swine production, particularly with respect to welfare and the judicious use of antibiotics, it is essential that the swine industry drives the development of tools to better identify and diagnose lameness. The resources and deliverables generated by this project are critical to informing treatment options and ensuring the judicious use of antibiotics.
Contact information:
Dr. Locke Karriker:
Dr. Paisley Canning: