Perennial Ryegrass Alkaloids Increase Respiration Rate and Decrease Plasma Prolactin in Merino Sheep under Both Thermoneutral and Mild Heat Conditions
by
Michelle L. E. Henry 1,2, Stuart Kemp 3, Iain J. Clarke 1, 
Frank R. Dunshea 1,*
and
Brian J. Leury 1,*
Frank R. Dunshea 1,* and
Brian J. Leury 1,*
1
Faculty of Veterinary and Agricultural Sciences, University of Melbourne, Melbourne, VIC 3010, Australia
2
Gundagai Meat Processors, 2916 Gocup Rd, South Gundagai, NSW 2722, Australia
3
PastureWise Pty. Ltd., 1485 Bamganie Rd, Cargerie, VIC 3334, Australia
*
Authors to whom correspondence should be addressed.
Toxins 2019, 11(8), 479; https://doi.org/10.3390/toxins11080479
Received: 19 July 2019 / Revised: 14 August 2019 / Accepted: 16 August 2019 / Published: 19 August 2019
(This article belongs to the Special Issue Dietary Mycotoxin Exposure to Livestock and Poultry)
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.
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Keywords:
sheep; heat stress; ergovaline; lolitrem B; production; physiology; staggers
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MDPI and ACS Style
Henry, M.L.E.; Kemp, S.; Clarke, I.J.; Dunshea, F.R.; Leury, B.J. Perennial Ryegrass Alkaloids Increase Respiration Rate and Decrease Plasma Prolactin in Merino Sheep under Both Thermoneutral and Mild Heat Conditions. Toxins 2019, 11, 479.
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