Interpretive Summary: Ergot alkaloids induce vasoconstriction of bovine uterine and ovarian blood vessels
By: Jackie Walling
Accounting for about one billion dollars’ worth of economic losses in species, fescue toxicosis is associated with impairing growth and reproduction function in cattle. A recent article published in the November 2018 Issue of the Journal of Animal Science investigates chronic exposure of ergot alkaloids on systemic blood flow to reproductive organs in cattle and the resulting consequences of reproductive function. Ergot alkaloids are metabolites produced from endophytic fungus infecting Kentucky-31 Tall Fescue commonly found in the southeastern United States. Fescue toxicosis, caused by ergot alkaloids, is characterized by reductions in feed intake and weight gain, elevated respiration (RR) and body temperature, vasoconstriction to extremities, and possible negative reproductive performance.
Thirty-six Angus heifers unexposed to ergot alkaloids were divided into two groups for a 63-day study based on consumption of fescue seed: endophyte-infected seed (E+) and non-infected seed (E-). E+ seed consisted of 500 µg/kg ergovaline and ergotamine causing toxicosis equivalent to moderate environmental exposure. Controlled diets ensured full consumption of ration and weekly measurements assessed feed intake and general performance. Heifers’ cycles were synchronized to evaluate vasoconstriction and reproductive performance.
Feed intake did not differ, but average daily gain was greater in E- heifers. E- had higher BW and positive changes according to the Body Condition Score chart while E+ was lower and negatively changed. RR, rectal, and skin temperatures remained similar between groups showing elevations related to increasing barn temperatures and heat stress. Hair coat scores were higher in E+ indicating a more retained and rougher coat contributing to heat stress and elevated measures brought on by ergot alkaloids. Heart rate and blood pressure differed from previous studies by remaining similar instead of dropping in E+ heifers.
Vasoconstriction of the caudal artery was seen in E+ heifers. On d10 and 17 of estrous, the uterine artery and vein along with the ovarian artery were constricted more in E+ than E-. The ovarian vein in E+ was smaller on d0 and 17 of estrous. Reductions occurred at the lowest levels of progesterone concentration when estrogen levels were rising. This diminishes estrogen circulation and inhibits proper cycling.
Reproductive performance showed no differences between groups regarding progesterone concentration or luteal area. Serum prolactin changed with environmental factors, but no differences resulted between groups. Because several toxicosis symptoms were present in E+, steady prolactin was unexpected as a reduction in prolactin is normally characteristic for toxicosis. Examination of ovaries showed no difference in the largest size of follicles present, but a reduction in the number of 6 to 9 mm follicles existed in E+ heifers.
Overall, prominent vasoconstriction of several vessels suggests ergot alkaloids effect systemic blood flow to reproductive organs. Restriction in flow reduces circulation of hormone concentrations and efficiency of feedback loops going from those organs to the brain. This interrupts normal signaling and disrupts normal cycling making pregnancy harder to attain as suggested by the reduced number of follicles present on ovaries. Not all symptoms for toxicosis were present in E+ heifers, but the discrepancies could be a result of the controlled level of toxicity induced. Understanding how ergot alkaloids effect the reproductive system could initiate treatments to combat its effects.
For the complete article, visit the Journal of Animal Science.