SERUM ALPHA-MANNOSIDASE ACTIVITY AND THE CLINICOPATHOLOGICAL ALTERATIONS OF LOCOWEED (ASTRAGALUS-MOLLISSIMUS) INTOXICATION IN RANGE CATTLE

Subclinical intoxication of livestock with Astragalus and Oxytropis sp ecies (locoweeds) results in decreased animal feed conversion, reduced weight gains, and reproductive failure. Sensitive diagnostic methods to definitively diagnose and monitor intoxication are needed to minimi ze these losses and better manage locoweed-infested pastures and range lands. Sera from cattle grazing locoweed were evaluated for alpha-mann osidase activity, serum biochemical values, electrolytes, and thyroid hormone concentrations. As the cows began to ingest locoweed, the mean serum alpha-mannosidase activities dropped significantly (400.0 muM t o 72.5 muM). Changes in other serum chemistry values were less specifi c; however, individual animals (generally those ingesting more locowee d) had elevated levels of alkaline phosphatase (ALP), aspartate aminot ransferase, and lactate dehydrogenase, with decreased serum total prot ein (5.8 +/- 0.8 g/dl) and albumin (2.3 +/- 0.3 g/dl). Mean serum thyr oid concentrations (both T4 and T3) were lower in animals that were in gesting locoweed. The calculated swainsonine dose correlated statistic ally with serum alpha-mannosidase activity, ALP, albumin, Cl, CO2, and thyroid hormone T3. This correlation suggests that serum alpha-mannos idase activity along with potential changes in ALP, albumin, and thyro id hormone concentrations is a sensitive indicator of locoweed exposur e and intoxication. These parameters may also be useful for monitoring intoxication and allowing subclinically affected cattle to be removed from infested areas before irreversible damage occurs.