Vasoconstriction in horses caused by endophyte-infected tall fescue seed is detected with Doppler ultrasonography.

The study is about the vasoconstriction effects of endophyte-infected tall fescue seed on horses, investigated through Doppler ultrasonography.

Research Purpose and Hypotheses

• The study aimed to test the hypotheses that tall fescue (TF) seed infected with Neotyphodium coenophialum endophyte induces vasoconstriction in horses and that ground seeds cause more pronounced vasoconstriction compared to whole seeds.

Research Methodology

• The investigation used ten horses which were subjected to one of three treatment types: endophyte-free ground seed (E-G; applied to four horses), endophyte-positive whole seed (E+W; applied to three horses), and endophyte-positive ground seed (E+G; used on three horses).
• The study was divided into two periods of 14 days each (P1 and P2). During P1, the horses were adapted to a concentrate and alfalfa cubes which were given routinely.
• In P2, fescue seed was mixed into the concentrate part of the diet while alfalfa cubes were freely provided. The quantity of the fescue seed given was gradually increased.
• Using Doppler ultrasonography, the distal palmar artery of each horse’s left foreleg was examined over 4 days during each period, with each day involving five replicate scans.
• Scans measured different variables such as artery luminal diameter, peak systolic velocity, end diastolic velocity, and blood flow variables. Other factors such as the horse’s temperature, heart rate, respiration rate, and environmental conditions were also recorded.
• Blood samples were taken to measure inflammatory cytokine mRNA abundances, and on specific days during P2, to measure prolactin concentrations.

Findings

• Results indicated that the consumption of E+G TF seed led to a decrease in artery lumen diameter, circumference, and area in comparison to E-G seed. E+W seed showed an intermediate response.
• Blood flow volume was found to be reduced in horses receiving E+G seed compared to those receiving E-G seed during P2.
• Other ultrasonography variables, cytokine mRNA and prolactin concentrations, along with factors such as the animal’s temperature, heart rate, respiration rate or ambient temperature and humidity were not significantly different across the treatment groups.

Conclusion

• The data supports the hypothesis that the consumption of E+G fescue seed does cause vasoconstriction in horses and that this effect can be effectively detected using Doppler ultrasonography.
• Doppler ultrasonography emerges as a potential and convenient biomarker for monitoring the diameter of the palmar artery of horses that graze on endophyte-infected fescue pastures, therefore, indicating early signs of fescue toxicosis.