Letter to the editor

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

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.

Physiological Effects of Ergot Alkaloid and Indole-Diterpene Consumption on Sheep under Hot and Thermoneutral Ambient Temperature Conditions

A controlled feeding study was undertaken to determine the physiological and production effects of consuming perennial ryegrass alkaloids (fed via seed) under extreme heat in sheep. Twenty-four Merino ewe weaners (6 months; initial BW 30.8 ± 1.0 kg) were selected and the treatment period lasted 21 days following a 14 day acclimatisation period. Two levels of two factors were used. The first factor was alkaloid, fed at a nil (NilAlk) or moderate level (Alk; 80 μg/kg LW ergovaline and 20.5 μg/kg·LW lolitrem B). The second factor was ambient temperature applied at two levels; thermoneutral (TN; constant 21-22 °C) or heat (Heat; 9:00 AM-5:00 PM at 38 °C; 5:00 PM-9:00 AM at 21-22 °C), resulting in four treatments, NilAlk TN, NilAlk Heat, Alk TN and Alk Heat. Alkaloid consumption reduced dry matter intake ( p = 0.008), and tended to reduce liveweight ( p = 0.07). Rectal temperature and respiration rate were increased by both alkaloid and heat ( p < 0.05 for all). Respiration rate increased to severe levels when alkaloid and heat were combined, indicating the short term effects which may be occurring in perennial ryegrass toxicosis (PRGT) areas during severe weather conditions, a novel finding. When alkaloid ingestion and heat were administered separately, similar physiological responses occurred, indicating alkaloid ingestion causes a similar heat stress response to 38 °C heat.

Flow-mediated K(+) secretion in horses intoxicated with lolitrem B (perennial ryegrass staggers)

AIM

To investigate the effects of lolitrem B intoxication on renal K(+) secretion in response to increased tubular flow rates.

METHODS

Results are derived from a repeated measure pilot study of seven horses fed non-perennial ryegrass feed for a week prior to exposing them to perennial ryegrass seed and hay that contained an average of 2 ppm lolitrem B. At the end of the control and treatment period frusemide (1 mg/kg I/V) was administered and serial fractional excretion of K(+)(FEK(+)) and fractional excretion of Na(+)(FENa(+)) calculated. Baseline concentration of aldosterone in plasma, serum K(+)concentration and feed K(+) concentration were also compared.

RESULTS

Key findings included a reduced change in FEK(+) from 0 to 15 minutes in response to frusemide administration (p=0.022, Wilcoxon signed-rank test) and a reduced baseline concentration of aldosterone in plasma (p=0.022, Wilcoxon signed-rank test) during the treatment period compared with the control.

CONCLUSIONS

Results suggest that lolitrem B intoxication reduced flow-mediated K(+) secretion and interfered with aldosterone production or secretion. However, further investigation is required to validate these findings and to further elucidate the underlying pathophysiology.

CLINICAL RELEVANCE

Lolitrem B intoxication in horses may cause disruption to electrolyte handling in addition to neurological deficits.

Interrelationships between Acremonium lolii, Peramine, and Lolitrem B in Perennial Ryegrass

Perennial ryegrass (Lolium perenne L.) is commonly infected with the endophytic fungus Acremonium lolii in a mutualistic relationship. The fungus produces a number of alkaloids, some of which are responsible for causing livestock disorders and/or for conferring insect resistance to the host grass. Little is known about the interrelationship between fungal growth and alkaloid production in the ryegrass plant and how this varies throughout the year. The concentrations of A. lolii and two of its alkaloid metabolites, lolitrem B and peramine, were monitored in basal (mainly leaf sheath) and upper (mainly leaf blade) parts of 17 endophyte-infected ryegrass plants on a monthly basis for 1 year. A. lolii, lolitrem B, and peramine concentrations were lowest in winter. The highest A. lolii concentrations were recorded in early summer, which coincided with the development of plant reproductive structures. Lolitrem B concentrations were highest from summer to early autumn and were consistently highest in the basal part of the plant. Peramine concentrations were generally highest in the upper part of the plant. Individual plants contained different levels of A. lolii, lolitrem B and peramine. These differences were generally maintained throughout the year. Although data for each month were variable, regression analyses showed that yearly mean concentrations of lolitrem B and peramine in individual plants were closely related to, and therefore probably largely determined by, yearly mean concentrations of A. lolii.

Molds, mycotoxins, and mycotoxicosis

Interest in mycotoxins and mycotoxicosis in humans and animals has greatly increased in recent years. Horses have long been considered very susceptible to molds. The signs, treatment, and prevention of several conditions, such as leukoencephalomalacia, aflatoxicosis, ergotism, fescue toxicity, slobbering disease, ryegrass staggers, and moldy sweet clover disease, are discussed.