Lecture 10: Reproductive Toxicants and Induced Abortion

What are some nitrate accumulating plants?

• johnson grass, sudan grass, oats, wheat, corn

• exposed to fertilizers and especially seen in drought periods

What effects can nitrate accumulating plants have?

• late gestation abortions

• fetal hypoxia and death

• methemoglobinemia

How is nitrate exposure diagnosed?

test ocular fluid of abortus

What effect dos ponderosa pine ingestion have?

• Isocupressic acid

• Vasoconstriction at caruncles

• Hemorrhagic placentitis

• Up to 50% abortion rate in cattle grazing pine needles

How is ponderosa pine ingestion diagnosed?

• hx of ingestion and circumstantial evidence

What toxin is found in these astragalus and oxytropis spp. commonly found in the central U.S. that causes more economic losses than any other plant?

swainsonine → neurologic signs, abortion, fetal abnormalities (hydrops/arthrogryposis)

cattle get “hooked” and can’t quit

What is this plant found in the south central U.S. during the spring that can cause abortion and RFM if ingested?

guiterrezia spp. (mono and di-terpenes)

What are the effects of fescue infected with neotyphodium coenophialum ingestion?

• toxic alkaloids → ergovaline → causes peripheral vasoconstriction “fescue foot”

• summer slump in cattle: decreased repro efficiency/infertility, embryos fertilized with semen from bulls grazing on infected fescue lack ability to develop, decreased milk

• fat necrosis throughout the body

How is fescue toxicity avoided?

• Rotate off of fescue in summer

• Re-plant pastures

• Avoid seedhead grazing - Mow or heavy graze

Besides infectious organisms and toxins, what else can cause bovine abortion?

• heat stress

• trauma

• malnutrition

Why might you induce abortion?

• Accidental breeding of young heifers: Bull running with herd year round, Increased risk of dystocia

• Pregnancy in feedlot heifer: Decreased rate of gain

• Fetal maceration

• Fetal mummification: May also surgically remove

• Hydrops conditions

Why might abortion be induced in these cows?

hydrops conditions - fluid buildup in at least two areas of unborn fetus

What are the progesterone sources in cattle? Why is this important to know for induced abortions?

• Corpus Luteum ovulation to term

• Placenta is an additional source 150-250 days gestation

• Corpus Luteum final month of gestation (Placental progesterone declines during this time)

• The goal is to target the source of progesterone that is appropriate for the stage of gestation at time of induction of abortion

What drugs are used to induce abortion in cattle?

• Prostaglandin F2a: Dinoprost (Lutalyse), Cloprostenol (Estrumate)

• Corticosteroids: Dexamethasone

How do PGF2a drugs cause abortion?

• PGF2a causes luteolysis

• The CL does not respond to PGF2a before day 5-6 post ovulation.

• Has no effect on placental progesterone production

How do corticosteroids cause abortion?

• Corticosteroids reduce placental progesterone production.

• They have no effect on the CL

What are the abortion strategies that can be used between day 5-150 of gestation?

• Single injection of PGF2a

• Abortion in 5-7 days

• Fertile estrus 3-5 days later

What are the abortion strategies that can be used between day 30-120 of gestation?

• The pregnancy can be manually disrupted

• May take 3-4 weeks for abortion to occur

• This is difficult sometimes

What are the abortion strategies that can be used between day 150-240 of gestation?

• Must remove ovarian and placental progesterone

• Combination of corticosteroids and PGF2a required: 25mg dexamethasone and 25mg Lutalyse

• 95% efficacious with abortion in 5 days

• Treatment of choice in the “unknowns”

strategy will work between 5-283 days of gestation

What are the possible side effects of induced abortion?

• Abortion after 120 days of gestation leads to RFM in 80% of cows treated: Membranes are usually lost within 7 days, Usually not a problem, but warn client

• 4% of heifers treated in feedlot will develop fetal mummification

• Acute toxic metritis is very rare following abortion induction