Birth Defects Reported
Due to Specific Worm Products
Benzimidazole worm products should not be given in the first month of pregnancy to avoid abortions and birth defects. The benzimidazole wormers include Albendazole and oxfendazole. Research done by M. Navarro using a benzimidazole wormer call netobimin which converts to Albendazole in the gut caused abortions and various birth defects. In sheep the period of susceptibility to birth defects is days 14 to 24, with day 17 being the most sensitive. In this study 14 ewes pregnant 17 days were given retobimin and 6 ewes were left as controls (not given the benzimidazole). Eight lambs all normal were born to the six control ewes. Of 25 lambs delivered to the 14 treated ewes, 4 were aborted during the first trimester, and 5 were aborted in the last trimester. One of the aborted lambs and six others delivered at term had birth defects. These birth defects affected the spine, jaw bone, spinal column, rectum, legs, head and kidney.
We have long known that we should avoid the use of benzimidazole in early pregnancy, and we have recommended against their use in any pregnant ewe. In pregnant ewes it is safe to use lvomec or Tramisol wormers. There is no wormer that is effective against tapeworms that is safe in early stages of pregnancy.
A great time to worm ewes is in the lambing jugs after they lamb. The hormone change in the ewes body causes the worm larvae to come out of their dormant stage and become more susceptible to a worm treatment. This would be a good time to use a benzimidazole wormer and follow up again prior to the ewes going to pasture.
Benzimidazole wormers should not be given in early pregnancy to avoid abortions and birth defects.
J.D. Bobb, D.V.M.
International SheepLetter
Vol. 18 No.7, December 1998
Article from M. Navarro Veterinary
Record 142:86-90 1998
(The AASRP Newsletter)
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