Perennial Ryegrass Alkaloids Increase Respiration Rate and Decrease Plasma Prolactin in Merino Sheep under Both Thermoneutral and Mild Heat Conditions.

Michelle L E Henry,Brian J Leury,Frank R Dunshea,Iain J Clarke,Stuart Kemp

doi:10.3390/toxins11080479

Abstract

A study was undertaken to determine the effects of feeding two levels of perennial ryegrass alkaloids (nil vs. moderate) under two climatic conditions. Alkaloids were fed via endophyte-infected perennial ryegrass seed and hay. Twenty-four Merino ewe weaners (six months, initial BW 32 ± 1.7 kg) were used in a study that lasted for 21 days after 14 days of adaptation. Sheep were fed either a control or alkaloid (Alk, 110 μg/kg LW ergovaline and 75 μg/kg LW lolitrem B) supplemented diet. Sheep were exposed to either constant thermoneutral (TN, 21–22 °C, 49% RH) or mildly heated (HS, 33 °C 1000–1500 h, 28% relative humidity) conditions. Dietary Alk and HS reduced dry matter intake (DMI) (p < 0.001, p = 0.02, respectively) with the combination of both reducing DMI by 42%. Reductions in DMI resulted in a lower daily gain in the Alk treatment (p < 0.001). Feed digestibility was reduced in the combined treatment (p = 0.03). Rectal temperature, respiration rate, and skin temperature increased in the Alk treatment. Plasma prolactin concentrations were decreased by Alk and increased by mild HS. The data indicate that production is compromised in the presence of Alk and mild HS, with this effect being exacerbated by a combination of both.

Highlights

Perennial ryegrass (Lolium perenne) is a persistent and productive pasture grass found in the cool temperate, winter-spring rainfall region of Australia [1]
The data indicate that production is compromised in the presence of Alk and mild heat stress (HS), with this effect being exacerbated by a combination of both
Key Contribution: This study demonstrated that there are physiological and production effects of perennial ryegrass endophyte alkaloids at dietary concentrations below those that cause clinical symptoms, such as tremors

Summary

Introduction

Perennial ryegrass (Lolium perenne) is a persistent and productive pasture grass found in the cool temperate, winter-spring rainfall region of Australia [1]. Lolitrem B is an indole-diterpenoid, is neurotoxic and has been shown to adversely impact many biological systems, including gut motility and gastrointestinal function [2]. It is the main alkaloid responsible for the development of tremors and staggering in sheep [3], and this has been well documented in New Zealand [3,4] and Australia [1]. Ergovaline ingestion is associated with elevated rectal temperature [4,5,6,7,8], reduced prolactin secretion in sheep [5] and may reduce animal production [1,4]

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