SERUM SWAINSONINE CONCENTRATION AND ALPHA-MANNOSIDASE ACTIVITY IN CATTLE AND SHEEP INGESTING OXYTROPIS-SERICEA AND ASTRAGALUS-LENTIGINOSUS (LOCOWEEDS)

Serum alpha-mannosidase activity and swainsonine concentration were de termined in 4 cattle and 15 sheep (3 groups of 5 each) that were admin istered ground locoweed (Oxytropis sericea or Astragalus lentiginosus) containing swainsonine at dosages of approximately 0.8 mg/kg of body weight/d (cows, 30 days each) and 0, 1.0, and 1.5 mg/kg/d (sheep, 11 d ays each). The cattle developed mild clinical signs of locoism, includ ing signs of depression, lethargy, and slight intention tremors. Clini cal signs of toxicosis were not observed in the sheep. Within 24 hours of initial treatment, serum alpha-mannosidase activity in cows and sh eep, measured by the release of 4-methylumbelliferone from an artifici al substrate, was markedly decreased to 28 and 40 mu mol of 4-methylum belliferone/L, respectively. Mean serum alpha-mannosidase activity of control cows and sheep was 400 +/- 94 and 422 +/- 42 (mean +/- SD), re spectively. In the treated animals, decreased serum alpha-mannosidase activities returned to normal or higher activities within 6 days after treatment was discontinued. Using a jack bean alpha-mannosidase assay , increased swainsonine activity (153, 209, and 381 ng/ml, respectivel y) was detected in the serum of cattle and of sheep in the high- and l ow-dose groups within 24 hours after treatment with locoweed. Swainson ine concentration remained high, with mean concentrations of 204, 435 and 395 ng/ml (cows and 2 sheep groups, respectively) during the treat ment period. After treatment, swainsonine was rapidly cleared, with es timated serum half-life of 16.4, 17.6, and 20.3 hours (cows, and high- and low-dose sheep groups, respectively). Significant differences in either alpha-mannosidase activity or swainsonine concentration were no t detected between the 2 groups of treated sheep. These results sugges t that serum alpha-mannosidase and swainsonine values are sensitive in dicators of locoweed intoxication in cattle and sheep. Furthermore, it suggests that swainsonine is rapidly absorbed, resulting in rapid inh ibition of senun alpha-mannosidase activity, leading to high serum swa insonine concentration. After exposure is eliminated, swainsonine is r apidly cleared from the serum, with serum alpha-mannosidase activity r eturning to normal values shortly thereafter.