Effects of locoweed (Oxytropis sericea) on reproduction in cows with a history of locoweed consumption

Locoweed (Oxytropis sericea) was fed to 4 open cycling cows that had repeat edly consumed locoweed in previous grazing trails. They received locoweed a t 20% of their diet for 30 d (0.68-0.76 mg swainsonine/kg/d). Locoweed indu ced an immediate rise in serum swainsonine (the locoweed toxin) and a conco mitant drop in serum alpha-mannosidase activity in all cows accompanied by abnormal estrus behavior, increased estrous cycle lengths and failure to co nceive. Serum progesterone (P4) profiles demonstrated that estrous cycles l engthened from an average of 19 d before locoweed feeding to an average of 34 d (range 24-43 d) while on locoweed. After locoweed feeding ceased, norm al estrous cycles-returned within an average of 14 d (range 7-25 d) Two of the 4 cows conceived on their first post-locoweed estrus at 7 and 25 d. The third cow bred twice at 13 and 31 d after lowoweed feeding stopped, and th e fourth cow bred 3 times at 11, 31 and 52 d before conception occurred. Pr egnancies in all 4 cows progressed normally to 7 mo gestation when locoweed was again fed at 20% of the diet for 40 d (gestation days 213 and 253) to 2/4 cows, of which aborted 10 d after lowoweed feeding stopped (263 days ge station). The other cow fed lowoweed calved normally as did the 2 pregnancy control cows. Serum P4 and estradiol (E2) profiles during pregnancy appear ed normal before, during and after locoweed feeding except in the cow that aborted, whose P4 declined and E2 increased prematurely. The general trend of serum prolactin was similar in locoweed-fed and control cows.