Development of a model for investigation of perennial ryegrass toxicosis in sheep

Chronic elevation of plasma cortisol causes differential expression of predominating glucocorticoid in plasma, saliva, fecal, and wool matrices in sheep

There is increasing interest in using nonblood measures of glucocorticoids to assess the physiological response to chronic stress conditions. In sheep, cortisol has been measured in various matrices including saliva, feces, and wool, but comprehensive studies of the relationship between plasma concentrations of cortisol and concentrations in these nonblood matrices are lacking. Therefore, we tested the hypothesis that administration of cortisol to sheep would result in elevated concentrations of cortisol in blood, saliva, feces, and wool. Merino ewes were administered with saline or 2 mg/kg BW/d hydrocortisone acetate (HCA) by intramuscular (i.m.) injection for 28 d. This treatment was imposed to mimic circulating cortisol concentrations experienced during periods of chronic stress. Cortisol and cortisone were directly measured in plasma, saliva, and wool before, during, and after treatment with saline or HCA. A 14-d pre-treatment and a 14-d post-treatment period were used to measure time taken for glucocorticoid concentrations in each of the matrices to return to baseline levels. Cortisol was also measured in feces before, during, and after treatment. Wool growth was also measured. Before treatment, there was no difference in the concentration of cortisol or cortisone in plasma, saliva, feces, or wool in animals treated with saline or HCA. In contrast, treatment with HCA increased (P < 0.05) concentrations of both cortisol and cortisone in plasma, saliva, and wool and of cortisol in feces. In plasma, cortisol concentrations were higher than cortisone (P < 0.05), whereas saliva cortisol and cortisone concentrations did not differ significantly. In wool, the concentration of cortisone was about 19-fold higher than that of cortisol during treatment and post-treatment periods. Treatment with HCA inhibited wool growth. These results demonstrate that an increase in glucocorticoids in the blood of sheep is reflected in increases in saliva (after 7 d of treatment), feces (21 d), and wool (14 d). Therefore, measures of glucocorticoids in these matrices may provide a measure of activation of the adrenal glands over time in sheep, thereby providing a retrospective indicator of chronic stress. With respect to wool, it appears that cortisol is predominantly metabolized to cortisone in the skin or wool follicle and is stored as cortisone. Therefore wool cortisone may also provide an important measure in quantifiying chronic stress in sheep.

Timed environmental exposure indicates sample stability for reliable noninvasive measurement of fecal cortisol metabolite concentrations in sheep

The use of noninvasive techniques to evaluate stress responses in animals has become an increasingly popular method of animal welfare assessment in both production animals and wildlife. In particular, using fecal samples to measure fecal cortisol metabolites (FCMs) as a quantitative measure has proven ideal as samples can be collected remote to the animal after defecation without the need for invasive procedures. Colorimetric enzyme immunoassays (EIAs) have been shown to have a high level of selectivity and sensitivity for FCM concentration analysis, equivalent to the traditionally used radioimmunoassay. Regardless of the assay system used, species- and sample-specific validation must be undertaken to ensure the reliability of results, particularly where sampling is undertaken in a novel species or where environmental conditions might impact FCM stability in the fecal sample. To determine the limit of environmental exposure acceptable for analysis of FCM concentrations in ovine scat samples collected from a paddock under conditions of stable heat and humidity, this study quantified FCMs in ovine feces shortly after defecation (2-7 h) and after timed environmental exposure (1-9 d). Samples were determined to show stable FCM concentrations for up to 5 d by this analysis. Understanding the impacts of environmental exposure, and therefore the viability of remote fecal collection methods for quantitative analysis of FCM by EIA, is important to assess the utility of noninvasive measures of endocrine status in animals where the exact timing of defecation may not be known.

Identification and Distribution of Novel Metabolites of Lolitrem B in Mice by High-Resolution Mass Spectrometry

Lolitrem B is the most potent indole-diterpene mycotoxin produced by Epichloë festucae var. lolii (termed LpTG-1), with severe intoxication cases reported in livestock. To date, there are no in vivo metabolism studies conducted for the mycotoxin. A mouse model assay established for assessing toxicity of indole-diterpenes was used to investigate metabolic products of lolitrem B. Mice were administered lolitrem B at 0.5 and 2.0 mg/kg body weight (b.wt) intraperitoneally before body and brain tissues were collected at 6 h and 24 h post-treatment. Samples were cryoground and subjected to a biphasic or monophasic extraction. The aqueous and lipophilic phases were analysed using liquid chromatography high-resolution mass spectrometry (LC–HRMS); data analysis was performed with Compound Discoverer™ software. A total of 10 novel phase I metabolic products were identified in the lipophilic phase and their distribution in the liver, kidney and various brain regions are described. The biotransformation products of lolitrem B were found to be present in low levels in the brain. Based on structure–activity postulations, six of these may contribute towards the protracted tremors exhibited by lolitrem B-exposed animals.

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.

Treatment with potassium bromide mitigates ataxia and reduces tremor in lambs with perennial ryegrass toxicosis

Aims: To assess the use of potassium bromide (KBr) as a therapeutic intervention for perennial ryegrass toxicosis (PRGT) in lambs fed ryegrass seed containing lolitrem B. Methods: Male lambs aged 10-12 months (n = 43) were assigned to receive ryegrass seed containing lolitrem B, at a dose of 0.16 mg/kg/day (Groups 2, 3 and 4), or lucerne chaff and molasses (Groups 1 and 5). Lambs in Groups 2 and 3 were observed for clinical signs and gait changes until defined signs of PGRT were observed, when they were transferred, with lambs in Group 1, to the Testing phase of the trial. Lambs in Group 3 were then treated with a single oral dose of 300 mg/kg bromide. Lambs in Groups 4 and 5 received KBr daily from the start of the trial (540 mg/kg bromide over 3 days then 20 mg/kg daily) and were transferred to the Testing phase after 18 days. Clinical examination and gait assessment, and surface electromyography of the triceps muscle, measuring root-mean-square (RMS) voltages, were carried out on Days 0, 1 and 2 of the Testing phase followed by necropsy, histopathology, measurement of concentrations of bromide in serum and CSF and faecal cortisol metabolites (FCM). Results: In Group 3 lambs, mean composite gait scores decreased between Testing phase Day 0 and Days 1 and 2 (p < 0.001), but increased in lambs in Group 2 between Day 0 and Day 2 (p = 0.015). Scores for lambs in Group 3 on Day 2 were lower than for lambs in Group 2 (p < 0.001). Mean RMS voltages on Day 2 were higher in lambs in Group 2 than Group 3 (p = 0.045). Mean concentrations of bromide in serum were >800 µg/mL in lambs in Groups 3 and 4 on Day 2. Concentrations of FCM were higher in lambs from Group 2 than in Groups 1 or 5, but were similar in Groups 2, 3 and 4. Histopathological findings in the cerebellum of lambs from Groups 2, 3 and 4 were similar, showing pyknosis of neurons within the granular layer of the cerebellum and Purkinje neuron proximal axonal spheroid formation. Conclusions and clinical relevance: A single oral dose of 300 mg/kg bromide in lambs with neurological signs of PRGT resulted in reduced composite gait scores and reduced RMS voltages, indicating a significant improvement in clinical signs of ataxia, movement disorder and muscle tremor associated with the neurotoxic effects of lolitrem B.

Tremorgenic effects and functional metabolomics analysis of lolitrem B and its biosynthetic intermediates

The neuroactive mycotoxin lolitrem B causes a neurological syndrome in grazing livestock resulting in hyperexcitability, muscle tremors, ataxia and, in severe cases, clonic seizures and death. To define the effects of the major toxin lolitrem B in the brain, a functional metabolomic study was undertaken in which motor coordination and tremor were quantified and metabolomic profiling undertaken to determine relative abundance of both toxin and key neurotransmitters in various brain regions in male mice. Marked differences were observed in the duration of tremor and coordination between lolitrem B pathway members, with some showing protracted effects and others none at all. Lolitrem B was identified in liver, kidney, cerebral cortex and thalamus but not in brainstem or cerebellum which were hypothesised previously to be the primary site of action. Metabolomic profiling showed significant variation in specific neurotransmitter and amino acid profiles over time. This study demonstrates accumulation of lolitrem B in the brain, with non-detectable levels of toxin in the brainstem and cerebellum, inducing alterations in metabolites such as tyrosine, suggesting a dynamic catecholaminergic response over time. Temporal characterisation of key pathways in the pathophysiological response of lolitrem B in the brain were also identified.

A single exposure to the tremorgenic mycotoxin lolitrem B inhibits voluntary motor activity and spatial orientation but not spatial learning or memory in mice

The indole diterpenoid toxin lolitrem B is a tremorgenic agent found in the common grass species, perennial ryegrass (Lolium perenne). The toxin is produced by a symbiotic fungus Epichloë festucae (var. lolii) and ingestion of infested grass with sufficient toxin levels causes a movement disorder in grazing herbivores known as 'ryegrass staggers'. Beside ataxia, lolitrem B intoxicated animals frequently show indicators of cognitive dysfunction or exhibition of erratic and unpredictable behaviours during handling. Evidence from field cases in livestock and controlled feeding studies in horses have indicated that intoxication with lolitrem B may affect higher cortical or subcortical functioning. In order to define the role of lolitrem B in voluntary motor control, spatial learning and memory under controlled conditions, mice were exposed to a known dose of purified lolitrem B toxin and tremor, coordination, voluntary motor activity and spatial learning and memory assessed. Motor activity, coordination and spatial memory were compared to tremor intensity using a novel quantitative piezo-electronic tremor analysis. Peak tremor was observed as frequencies between 15 and 25Hz compared to normal movement at approximately 1.4-10Hz. A single exposure to a known tremorgenic dose of lolitrem B (2 mg/kg IP) induced measureable tremor for up to 72 h in some animals. Initially, intoxication with lolitrem B significantly decreased voluntary movement. By 25 h post exposure a return to normal voluntary movement was observed in this group, despite continuing evidence of tremor. This effect was not observed in animals exposed to the short-acting tremorgenic toxin paxilline. Lolitrem B intoxicated mice demonstrated a random search pattern and delayed latency to escape a 3 h post intoxication, however by 27 h post exposure latency to escape matched controls and mice had returned to normal searching behavior indicating normal spatial learning and memory. Together these data indicate that the tremor exhibited by lolitrem B intoxicated mice does not directly impair spatial learning and memory but that exposure does reduce voluntary motor activity in intoxicated animals. Management of acutely affected livestock suffering toxicosis should be considered in the context of their ability to spatially orientate with severe toxicity.

Measuring wool cortisol and progesterone levels in breeding maiden Australian merino sheep (Ovis aries)

Hormonal assessment tools are important for determining the reproductive success of production animals. This study used non-invasive wool assessment to quantify changes in progesterone and cortisol levels in reproducing female merino sheep. Wool samples were collected from a group of n = 46 maiden merino ewes (22-25 months old), naturally joined under natural light conditions in southern New South Wales (NSW), Australia. Three shearing opportunities were conducted as part of standard on-farm management practices. The wool samples were collected at three different dates during 2017, January (prior to rams being put out with the mob and to provide a baseline level since previous shearing in May 2016), September (during very late stages of gestation-approximately 2 weeks prior to parturition) and December (ewes had given birth and ~2-month-old lambs were at foot). Analysis of cortisol and progesterone was conducted concurrently from the same sample of wool. The hormones in wool samples quantified using commercially available cortisol and progesterone enzyme-immunoassay kits. Wool cortisol concentrations increased significantly (p = 3.04E-14) from pre-joining in January (1.33±0.12 ng/g) to late gestation in September (3.59±0.12 ng/g). Concentration of wool cortisol post-lambing in December (3.27±0.14 ng/g) did not decline significantly (p = 0.124) after gestation however remained significantly higher (p = 3.82E-10) than pre-joining levels. Wool progesterone (PG) concentrations increased significantly (p = 1.83E-33) from pre-joining (0.04±0.005 ng/g) in January to late gestation in September (5.53±0.13 ng/g) with a significant (p = 5.44E-59) decline observed in December (0.05±0.003 ng/g) to post- pregnancy concentrations. No significant difference was shown between pre-joining and post lambing PG concentrations (p = 0.057). Our results showed that non-invasive assessment of hormones in Merino sheep wool reflected significant increase in both cortisol and progesterone guided by pregnancy.