Presumptive polioencephalomalacia in beef cattle: A deceptive etiology
Felipe Reggeti, Van Mitchell
Animal Health Laboratory, University of Guelph, Guelph, ON (Reggeti); Metzger Veterinary Services, Linwood, ON (Mitchell).
AHL Newsletter 2024;28(3):8.
Steers from a feedlot facility in Ontario were examined for neurological signs consisting of ataxia, blindness, head pressing and recumbency. A new case was reported every 2-3 days for a total of 12 animals affected over a period of 3 weeks. The animals weighed approximately 500 kg, and the dry matter intake (DMI) was estimated to be around 13 kg. They received a total mixed ration (TMR) consisting of haylage, wheatlage, oat hulls, high moisture corn, corn silage and dry distillers grain. Some of the feed was “spoiled” and the wheatlage was 2 years old and sour smelling. The first 2 affected animals died before a veterinarian was involved in the case, and postmortem examinations were not performed. However, since the clinical signs were compatible with polioencephalomalacia (PEM), 6 g of 99% thiamine/head/day was added in the feed. Since cases continued to occur, parenteral injections of thiamine were initiated.
Excessive sulfur intake is an important risk factor for the development of PEM; therefore, water and feed samples were submitted for analysis. The feed contained 0.35% sulfur on a dry matter basis. A water sample collected from a water trough contained 5,109 ppm sulphate (equivalent to 1,703 ppm sulfur), and the sulfur content on a DMI basis was estimated to be 0.65%. With this information, the total sulfur concentration (TSC) relative to DMI (0.35% feed + 0.65% water) was 1%. Since the recommended maximal tolerable level of total sulfur in the diet for cattle is 0.3-0.5% dry matter (depending on amount of forage fed), a presumptive diagnosis of PEM due to excessive sulfur intake was suggested.
To confirm whether the water was the source of excessive sulfur (as there was no sulfur smell to the water), another sample was collected directly from the tap. This sample was submitted to a different laboratory, and the result was 37.9 ppm sulfate (~12.6 ppm sulfur). The significant discrepancy of the results between the 2 water samples raised concerns for laboratory error or contamination. The troughs were routinely washed on a weekly basis, and contamination with a sulfur-containing substance appeared to be unlikely. It was then discovered that the first water sample was collected in a clear sterile container used to test for the presence of coliform bacteria in drinking water, and some of these containers have sodium thiosulfate added to save laboratory preparation time and expense. Interestingly, the other element reported to be somewhat elevated in the first water sample was sodium (425 ppm), consistent with presumptive addition of sodium (thio)sulfate.
After adjusting the TMR containing 4 different fermented ingredients (some of poor quality), no additional cases occurred. Out of the 12 affected animals, only the two that were not treated with thiamine died, while the remaining 10 animals fully recovered. This case illustrates the importance of identifying the specific etiology in cases of PEM. Based on the initial analyses, a diagnosis of sulfur-related PEM could have been made; however, the sulfur content in the water was in fact acceptable and the root of the problem was not excessive sulfur consumption. It was speculated that the inadequate diet might have stimulated over-growth of thiaminase-producing bacteria, or caused impaired thiamin absorption/utilization. This was supported by response to thiamin administration, and correction of the problem after adjusting the TMR. AHL
Reference
1. National Research Council. Chapter 28: Sulfur. In: Mineral Tolerance of Animals, 2nd edition. The National Academies Press. 2005:378-379.