Ergot alkaloids induce vasoconstriction of bovine uterine and ovarian blood vessels

Abstract

Fescue toxicosis is a syndrome that impairs growth and reproduction in cattle grazing endophyte-infected tall fescue [Lolium arundinaceum [(Schreb.].) Darbysh)] in the United States, resulting in approximately $1 billion in annual economic loss in species that utilize this forage resource. Approximately 90% of tall fescue contains an endophytic fungus (Epichloë coenophiala) that produces ergot alkaloids. Ergot alkaloids cause vasoconstriction and reduced blood flow to the extremities; however, it remains unknown how blood flow to the reproductive organs is affected in cattle. Therefore, the objective of this study was to determine if ergot alkaloids from endophyte-infected tall fescue reduce blood flow to the reproductive organs, thus hindering reproductive function. Angus heifers (n = 36) naïve to ergot alkaloids were placed in Calan gates and randomly assigned to receive either endophyte-infected fescue seed (E+) or noninfected fescue seed (E-; control) in a total mixed ration for 63 d. Weekly measurements were taken to monitor heifer growth and response to ergot alkaloid exposure. Reproductive measurements, including ovarian structures, uterine and ovarian vessel diameter, and hormone concentrations were determined after heifers were synchronized using the standard CO-Synch + 7 d CIDR protocol to ensure all measurements were collected at the same stages of the estrous cycle (0, 4, 10, and 17 d). Data were analyzed using repeated measures in PROC MIXED of SAS. Average daily gain was decreased for the E+ group (0.8 kg/d) compared to control heifers (1.0 kg/d). Body condition scores tended to be greater in control heifers compared to the E+ group (P = 0.053). Additionally, hair coat and hair shedding scores were greater in E+ heifers compared to controls (P < 0.05). Heart rate, rectal temperature, respiration rate, and blood pressure did not differ between treatments (P > 0.05). Vasoconstriction was observed in the caudal artery, but not the caudal vein, in heifers consuming the E+ fescue seed (P < 0.05). No differences were observed in antral follicle counts, corpus luteum area or circulating progesterone concentrations in E+ heifers compared to controls (P > 0.05). There was a significant decrease in the diameter of arteries and veins servicing the ovary and uterus on day 10 and 17 of the estrous cycle. Reduction in blood flow to the reproductive organs during critical times in the estrous cycle may contribute to the reduced ovarian function and pregnancy rates associated with fescue toxicosis.

Figure 1.

Experimental time line for (A) animal and feed and (B) reproductive measurements used for beef heifers consuming endophyte-infected (E+) and noninfected fescue (E−) seed. (A) Samples of TMR were collected biweekly and tested for nutrient content and ergot alkaloid analysis. Weekly animal measurements (*) included blood sampling, animal weights, body condition scores, respiration and heart rates, hair coat and shedding scores, blood pressure, and rectal temperatures. (B) Reproductive measurements (^‡) via Doppler ultrasound consisted of ovarian mapping and characterization of the uterine and ovarian vessel characterization.

Figure 2.

Change in body weight (kg) of beef heifers consuming endophyte-infected (E+) and noninfected fescue (E−) seed throughout the treatment period. *Effect of treatment (P < 0.0001); treatment × day interaction (P < 0.0001).

Figure 3.

Changes in hair coat score (HCS, black lines) and hair shedding score (HSS, gray lines) in beef heifers chronically exposed to either endophyte-infected (E+) or noninfected fescue (E−) seed. As expected, HCS and HSS decreased throughout the treatment period. *Effect of treatment (P = 0.002); treatment × day interaction (P = 0.0004) for HCS. ^‡Effect of treatment (P = 0.0069); treatment × day interaction (P < 0.0001) for HSS.

Figure 4.

Changes in uterine (A) and ovarian (B) artery (black lines) and vein (gray lines) area (mm²) in beef heifers chronically exposed to either endophyte-infected (E+) and noninfected fescue (E−). Vessel measurements were taken at critical times (day 0, 4, 10, and 17) based on ovarian activity within the estrous cycle. (A) *Effect of treatment (P < 0.01); treatment × day interaction (P < 0.01). (B) *Effect of treatment (P < 0.01); treatment × day interaction (P < 0.05) for ovarian artery. ^‡Effect of treatment (P < 0.01); treatment × day interaction (P < 0.01) for ovarian vein.