This summer has had its fair share of hot days and, equally important, hot nights. Pigs need cool nights to dissipate heat during periods of hot weather.
Anecdotes suggest that heat-stressed, grow-finish pigs are more likely to develop disease. But reliable data to support this perception is usually not available. Still, when grow-finish pigs develop disease, it is costly and worthy of investigation.
In finisher pigs, enteric diseases seem especially troublesome in the summer months. Both infectious and non-infectious insults contribute to diarrhea in grow-finish pigs. Non-infectious insults include gastric ulcers, intestinal volvulus (twisted bowel), hemorrhagic bowel syndrome (HBS) and variations in feed ingredients or formulations. Inconsistency in feed consumption and the effect of heat on feed quality are likely risk factors for non-infectious conditions.
Data from diagnostic laboratories suggest that the most common infectious agents of diarrhea are Lawsonia intracellularis (ileitis) and salmonella, with Brachyspira, hemolytic Escherichia coli, whipworms and Transmissible gastroenteritis (TGE) also contributing at much lower frequencies.
It is widely accepted that the prevalence of gastric ulcers rises in hot summer months. Data from the Iowa State University Veterinary Diagnostic Laboratory (ISU-VDL) suggest that frequency of diagnosis of ileitis increases in the July-September period (Figure 1).
Another disease that appears to have some seasonal tendency that favors the warm months is enteric salmonellosis, particularly as it occurs in grow-finish age groups (Figure 1). Most of the cases of enteric salmonellosis are caused by Salmonella typhimurium. Figure 2 tracks the number of cases from ISU-VDL for salmonellosis in pigs greater than 8 weeks of age (2003-2011).
Erysipelas is another disease that seems to be worse in the summer months, although data from ISU-VDL suggests that this disease is diagnosed year-round with fewest cases during the summer months (Figure 3). However, observations are that outbreaks of acute erysipelas may be more severe in summer months because the fever is compounded with summer heat, particularly in heavy hogs.
The accurate diagnosis of the cause of disease is increasingly important in modern swine production. Lawsonia intracellularis, also known as porcine proliferative enteropathy (PPE) or ileitis, salmonella, and erysipelas are very common infections in U.S. swine herds. But they need to be differentiated from other causes of diarrhea (e.g. Brachyspira) or septicemia (e.g. Actinobacillus suis) for successful treatment and prevention.
There are effective vaccines for ileitis, salmonella and erysipelas; the adage, “an ounce of prevention is worth a pound of cure,” often applies to these agents.
Click to view graphs.
Kent Schwartz, DVM
Iowa State University Veterinary Diagnostic Laboratory