Abortion

 Abortion is defined relative to the stage of pregnancy when the embryo or fetus is lost. In cattle, early embryonic death refers to deaths occurring from the day of conception until about 42 days of gestation (the end of the embryonic period), which coincides with the end of differentiation. Embryos lost during this period may be either resorbed or aborted. A normal rate of early embryo resorption (0–45 days) is 9–12% and abortion or resorption after 45–60 days is usually rare (1–2%). Higher rates are attributed to disease. Bovine fetuses discharged from day 42 until approximately 260 days are generally called abortions, and from day 260 until normal term (281 ± 3 days), premature births.

 Dietary causes of embryonic death, abortion or premature birth include poisonous plants, fungi and synthetic toxicants. Plants associated with abortion or premature birth include Pinus species (P. ponderosa, P. radiata, P. taeda, P. cubensis), Juniperus communis, cypress (Cupressus macrocarpa), snakeweeds (Gutierrezia sarothrae and G. microcephala), locoweeds (Astragalus spp. and Oxytropis spp. containing swainsonine), hairy vetch (Vicia villosa), darling pea in Australia (Swainsona spp.) and leucaena (Leucaena leucocephala). Mycotoxins include ergot alkaloids from grains and grasses infected with Claviceps and Balansia spp., loline alkaloids from endophyte-infected tall fescue, trichothecenes from Fusarium spp., grains and maize silage infected with Aspergillus and Penicillium spp. and hay and straw and mouldy sweet clover (dicoumarol) contaminated with Stachybotrys spp. Xenobiotics believed to contribute to embryo or fetal loss include nitrates and nitrites, high-protein diets (excess urea), carbon monoxide, oestrogenic compounds, glucocorticoids, lead, phenothiazines, oxytocin, chlorinated pesticides (DDT, dieldrin, heptachlor) and warfarin (coumarins).