Effect of subacute swainsonine (locoweed; Oxytropis sericea) consumption on immunocompetence and serum constituents of sheep in a nutrient-restricted state
Taylor, J.B.; Strickland, J.; May, T.; Hawkins, D.E.
Veterinary and Human Toxicology 42(4): 199-204
2000
ISSN/ISBN: 0145-6296 PMID: 10928681 Document Number: 520025
The subacute dose-response effects of swainsonine (SW) consumption on immunocompetence and serum constituents of sheep in a nutrient-restricted state were investigated. Sheep (23 wethers, 5 ewes) were assigned to 1 of 5 SW treatments (0, 0.2, 0.4, 0.8, or 1.6 mg swainsonine/kg bodyweight/day). Swainsonine was delivered by feeding locoweed (Oxytropis sericea) with grama grass and alfalfa hays for a 28-day treatment period followed by a 21-day recovery period without locoweed. Body weights were measured weekly and behavioural changes were monitored for clinical signs of SW toxicity. Venous blood was collected weekly for lymphoblastogenesis and serum constituent analyses. Clinical signs (sluggishness, decreased responsiveness) of swainsonine toxicity were observed from day 14 to 35 in the 0.8 and 1.6 mg treatments. Subacute oral exposure did not appear to affect lymphoblastogenic analyses. Acute and subacute alterations in various serum constituents did indicate subclinical effects of SW ingestion. Linear, quadratic and cubic dose-response relationships were detected for some serum constituents (e.g., alkaline phosphatase, aspartate aminotransferase). Subacute SW consumption at the levels investigated does not seem to affect the immunocompetence of nutrient restricted sheep. The lack of change in serum alkaline phosphatase at the 0.2 mg SW/kg bodyweight per day dose indicates the potential for a no adverse effect level of SW consumption in nutrient restricted sheep. In combination with measurable SW in serum, increases in serum alkaline phosphatase and aspartate aminotransferase activities, and declines in serum Fe and cholesterol during subacute exposure to SW establish these markers as potential indicators of subclinical SW toxicosis.