Determining the cause of a growing number of cases involving sudden deaths in finishing pigs can be a daunting task because the pigs commonly show no outward signs of disease. Investigation into these sudden deaths requires four steps:
Step #1: Very careful observation of the pigs, looking for subtle symptoms or clinical signs that are not readily apparent. This process may call for visiting the barn, sometimes at odd hours, or simply sitting on a bucket for an hour watching and listening to pigs. Don’t underestimate the value of objective observation.
Step #2: Perform necropsies of affected pigs to assess whether there are specific lesions which might identify a likely cause for pigs to suddenly die. Often a complete set of tissues or blood work is submitted to a diagnostic lab. But the gross lesions observed on necropsy of a dead pig can be misleading and confusing, depending on how long it has been dead. For instance, congested lungs that don’t collapse, reddened intestines, or pale muscles are commonly observed in any dead pig.
Step #3: Collection of complete and accurate information to support observations (listed below) is an important step. Focus on information that appears relevant to the problem. Keep an open mind as to which information could be biased or misleading.
Step #4: Develop an objective analysis to formulate a plan of intervention. Don’t rely on assumptions that may derail an investigation. Instead, take the time to perform a systematic investigation.
A case in point
Recently, during a one-week span, a producer found a dead pig per day in an 800-head finisher containing 230-lb. pigs. Observations revealed that two pigs in the barn had skin lesions, so the entire barn population was treated with an injectable antibiotic to treat an apparent erysipelas outbreak. For two days, no dead pigs were found, but then pigs started dying again.
Upon necropsy of the new deaths, no gross lesions were observed. However, in the meantime, another 800-head barn of 160-lb. pigs on the same site was also affected. All pigs in both barns were injected with antibiotics and an erysipelas bacterin. Tissues sent to a diagnostic lab found no evidence of infection. Pig mortality rose to 8-12 per day in both barns. The feed supplier reported no problems from other producers feeding the same ration.
The producer and veterinarian observed that some of the affected pigs apparently had seizures and appeared weak. Three more dead pigs were submitted to the diagnostic lab but the only major finding was the presence of ribs that bent rather than snapped. Serum calcium rates in acutely affected pigs were only one-half of the expected value.
In this case, the cause of sudden deaths was the result of a non-apparent metabolic bone disease exacerbated by a feed mixing error that was confirmed by additional testing.
When investigating sudden pig deaths, gathering a complete history of mortality requires farm observations and answers to numerous questions, including:
• Determine the number of sick or affected pigs, number of dead during a timeframe, total dead, and whether sporadic pigs or groups are affected.
• Assess the role of genotype, size and weight of pigs affected, whether they are healthy or gaunt in appearance.
• Plot the number affected, treated or dead on a daily timeline.
• Determine location of deaths, in one flow or multiple flows, one building or multiple buildings, one end or one side of barns, specific pens and the area within the pen dead pigs were found.
• Review barn environment and condition of fans, heaters, curtains and waterers.
• Look for changes in feed, water, facilities, vaccinations, medications, weather and people traffic.
• Observe with care the robustness and behavior of pigs.
• Collect complete samples of feed, water, blood and tissues from affected pigs.
• Be sure to conduct a complete necropsy of dead or affected pigs and record suspected abnormalities from gross observation of tissues at the diagnostic lab.
Frequent causes of sudden deaths
The Iowa State University Veterinary Diagnostic Laboratory has identified 10 frequent causes of pig deaths:
1. Toxemia from bacterial intestinal infections (E. coli, gut edema disease, salmonellosis);
2. Bacterial systemic infections or toxemia (erysipelas, actinobacillus, streptococcus, salmonella, hemophilus, endotoxins);
3. Mulberry heart disease;
4. Trauma (savaging, inadvertent commingling);
5. Intermittent events (electrical shock, hypothermia, asphyxiation) from facility flaws;
6. Metabolic diseases including bone diseases, porcine stress syndrome or lactic acidosis;
7. Intestinal accidents (twisted guts), gastric ulcers, hemorrhagic bowl syndrome;
8. Feed-related imbalances and mixing errors;
9. Toxicities from plants, minerals, chemicals and gases.
10. Neurological disorders from water deprivation, brain infections and toxins.
Kent Schwartz, DVM; Darin Madson, DVM
Iowa State University Veterinary Diagnostic Laboratory