Sudden death in sows: AHL pathology results, 2010-2021

Josepha DeLay

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2021;25(4):14.

Diagnostic investigation of sudden (unexpected) death cases in sows and gilts can be challenging, mainly due to the logistics of performing a necropsy on these large animals.  Transportation to a diagnostic laboratory can be difficult to accommodate, and on-farm necropsies are awkward due to sow size.  Tissue autolysis and decomposition are often rapid due to the combined effects of the relatively high environmental (indoor) temperature, and the animal’s size and fat content, maintaining a high carcass temperature following death.

To summarize and better understand the causes of sudden death in Ontario sows and bred gilts, sow mortality cases submitted to the Animal Health Laboratory were reviewed.  The AHL laboratory information management system (LIMS) database was searched for relevant cases involving sows or gilts that were received between January 2010 and November 2021.  Only those cases with a pathology component (necropsy and / or histopathology) and for which the clinical history was compatible with sudden (unexpected) death were included in the review.   

A total of 43 sow or gilt sudden death cases were submitted to the AHL over this 12-year period (range 0-10 cases / year, average 4 cases / year).  The submissions included 2 necropsies carried out at the AHL and 41 on-farm necropsies, with histopathology and various other diagnostic tests subsequently conducted at the AHL.

The causes of death in all submitted sows and gilts, based on histopathology findings and results of ancillary tests, are listed in (Table 1).  No definitive cause of death was identified in 10/43 animals (23%).  Among the remaining cases, the cause of death was attributed to systemic disease or to respiratory, gastrointestinal, cardiovascular, or musculoskeletal disease.  Systemic disease was diagnosed most frequently [18/43 (42%) cases] and included septicemia, polyserositis, and suspected heat stroke.  Definitive etiologies for septicemia were identified in 6 cases, including Streptococcus suis (5 cases) and Streptococcus dysgalactiae ssp. equisimilis (1 case).  For other cases, a diagnosis of systemic disease was based on histopathology findings.

Table 1. Causes of sudden death in sows and gilts submitted to the AHL, 2010-2021.

Cause of death/body system affected Number of cases Comments
Unknown cause of death 10  
Systemic 18

Septicemia: 13 cases

Polyserositis: 3 cases

Suspected heat stroke: 2 cases

Respiratory 9 Bacterial pneumonia +/- influenza: 8 cases
Gastrointestinal 4 Porcine proliferative enteritis / Lawsonia: 4 cases
Cardiovascular 1 Acute myocardial degeneration, r/o ionophore toxicity, vitamin E / selenium deficiency, sepsis

The level of detail about herd mortality rates and duration that was provided in clinical histories was highly variable.  From cases with on-farm necropsies, a description of gross findings was included for only 15/43 (35%) of cases.  This information is valuable to pathologists when interpreting histologic findings in light of the clinical context.  Not including necropsy findings with a diagnostic submission is a missed opportunity for communication with diagnosticians about important features of the disease condition in the herd.

For most cases necropsied on-farm, organs sampled for histopathology included lung and a good range of filtering organs such as liver, spleen and kidney.  Despite the clinical history of sudden death, vital organs such as heart, brain, and skeletal muscle were collected and submitted from relatively few cases: brain - 2/43 (5%) cases; skeletal muscle - 6/43(14%) cases; heart - 19/43 (44%) cases. 

This case series describes the cause of death in sows dying unexpectedly, and for which relatively subtle or no gross lesions were evident during postmortem examination.  Those sows with an obvious cause of death, such as splenic torsion or gastric ulceration and hemorrhage, would not typically have further diagnostic testing performed and would not be included in the database searched for this review.  As a result, this data is not representative of the overall causes of sudden death in sows and gilts.  Among the animals examined, a cause of death was not identified in a disappointing, but expectedly high number of cases (23%).  Thorough gross examination and collection of a wide range of tissues for histopathology could improve the diagnostic success rate for sudden death cases involving all ages of swine, including sows and gilts.  Brain is especially difficult to sample on-farm in mature swine, however a lateral approach for brain removal is helpful in these animals (see AHL Labnote 33:  AHL