May 29, 2019

Interpretive Summary: Ergot alkaloid exposure in pregnant ewes

Interpretive Summary: Ergot alkaloid exposure during gestation alters. I. Maternal characteristics and placental development of pregnant ewes.

By: Dr. Caitlin Vonderohe

Tall fescue is a drought-tolerant, disease resistant, hardy grass that is used as the primary cool-season forage in the southeastern U.S. An edophyte found in tall fescue is responsible for the hardiness of the plant, but ingestion of the ergot alkaloids produced by this endophyte causes reproductive problems, and reduces weight gain. This occurs because ergot alkaloids are similar to serotonin and dopamine, and can similarly cause reductions in prolactin and vasoconstriction. Ergovaline, one of the primary ergot alkaloids, is a vasoconstrictor that may adversely affect placental and fetal development. A recent study published in the Journal of Animal Science, by Britt et al., “Ergot alkaloid exposure during gestation alters I. Maternal characteristics and placental development of pregnant ewes” assessed how feeding tall fescue during mid-late gestation alters maternal characteristics and placental development.

Fifty-seven Suffolk ewes, naïve to endophytes, were blocked by body condition score and divided into groups for estrous synchronization and exposure to a Suffolk ram. Ewes were checked daily to estimate breeding date and confirmed pregnant by ultrasonography. Pregnant ewes were assigned to one of four diets, consisting of a negative control, a positive control (with endophyte-infected fescue fed throughout gestation), and two diets with endophyte-infected fescue fed at the beginning or the end of gestation. Blood was collected on days 29, 50, 85 and 133 and later tested for glucose. Some of these samples were used to assess T4, T3, and cortisol on a subset of the ewes. Ewes were placed under general anesthesia on day 133 of pregnancy, and blood and amniotic fluid were sampled prior to the fetuses being removed from the uterus. Placentomes were evaluated and sub-sampled. Ewes were subsequently euthanized.

Ewes that were switched to a endophyte-infected forage late in pregnancy had lower feed intake than other treatments. Similarly, these had lower prolactin concentration compared to ewes fed endophyte-infected fescue throughout gestation, and ewes fed endophtye-free fescue. This indicates that feeding endophyte-infected fescue during late gestation reduces prolaction production which may significantly affect mammary development. Uterine and placental weights were lower in ewes fed endophyte infected-fescue throughout gestation and in late gestation. Assessment of placentomes also indicated abnormal vascular development in placentomes collected from ewes fed endophyte-infected fescue throughout pregnancy. Similarly, ewes fed endophyte infected fescue in late gestation had increased fetal weight compared to caruncle weight – which may have negatively affected placental efficiency.

Overall, feeding endophyte-infected fescue seed during mid and late gestation causes suppression in prolactin. Exposing ewes to ergot alkaloids during late gestation has the most significant impact on placental development by reducing placental and uterine weights and affect vascular development of the placentome. It is important to further explore this phenomenon to better assess the phenomenon of ergot alkaloid toxicosis during late gestation.