Lecture 10- Reproductive Toxicants and Induced Abortion in Cattle

Toxic causes of abortion

Nitrates; Ponderosa pine; Locoweed; Broomweed

Toxic causes of infertility

Locoweed; Fescue

Toxic teratogens

Poison hemlock; Lupines; Tree tobacco; Skunk cabbage

Nitrate‑accumulating plants

Johnson grass; Sudan grass; oats; wheat; corn; fertilizer exposure; drought periods increase risk

Nitrate pathophysiology

Methemoglobinemia → fetal hypoxia → late‑gestation abortion (lecture: “Methemoglobinemia; fetal hypoxia and death”)

Nitrate abortion diagnosis

Test ocular fluid of abortus

Nitrate prevention

Test hay; >1% nitrate = toxic

Ponderosa pine toxicant

Isocupressic acid

Ponderosa pine pathophysiology

Vasoconstriction at caruncles → hemorrhagic placentitis → abortion (up to 50% of cattle grazing needles)

Ponderosa pine diagnosis

History of ingestion + circumstantial evidence

Locoweed species

Astragalus and Oxytropis spp.

Locoweed toxicant

Swainsonine

Locoweed clinical effects

Neurologic signs; abortion; fetal abnormalities (hydrops, arthrogryposis); up to 40% abortion rate; cattle become “hooked” and cannot quit grazing

Locoweed diagnosis

Circumstantial evidence; major economic losses

Broomweed/Snakeweed species

Gutierrezia spp.

Broomweed toxicants

Mono‑ and diterpenes

Broomweed clinical effects

Abortion + retained fetal membranes; typically in spring

Fescue species

Festuca arundinacea infected with Neotyphodium coenophialum

Fescue toxicant

Ergovaline (toxic alkaloid)

Fescue pathophysiology

Peripheral vasoconstriction (“fescue foot”); summer slump; decreased reproductive efficiency; infertility; decreased milk; fat necrosis; embryos fertilized with semen from bulls grazing infected fescue fail to develop

Fescue management

Rotate off fescue in summer; re‑plant pastures; avoid seedheads; mow or heavy graze

Other causes of abortion

Heat stress; trauma; malnutrition

Reasons to induce abortion

Accidental breeding of young heifers; bull with herd year‑round; dystocia risk; feedlot heifer pregnancy (↓ gain); fetal maceration; fetal mummification; hydrops; surgical removal possible

Progesterone sources by gestation

CL from ovulation to term; placenta contributes days 150–250; CL again dominant in final month as placental progesterone declines

Abortive drugs

PGF2α (dinoprost/Lutalyse; cloprostenol/Estrumate); corticosteroids (dexamethasone)

PGF2α mechanism

Luteolysis; CL unresponsive before day 5–6 post‑ovulation; no effect on placental progesterone

Corticosteroid mechanism

Reduces placental progesterone; no effect on CL

Induction strategy 5–150 days

Single PGF2α injection; abortion in 5–7 days; fertile estrus 3–5 days later

Induction strategy 30–120 days

Manual disruption of pregnancy; abortion in 3–4 weeks; difficult procedure

Induction strategy 150–240 days

Must remove CL + placental progesterone; use 25 mg dexamethasone + 25 mg Lutalyse; 95% effective; abortion in 5 days

Induction strategy for unknown gestation

Use combination PGF2α + corticosteroid; effective 5–283 days

Side effects of induced abortion

Abortion >120 days → RFM in 80% of cows; membranes usually expelled within 7 days; warn clients; 4% feedlot heifers develop mummification; acute toxic metritis rare