The occurrence of ryegrass staggers and heat stress in sheep grazing ryegrass-endophyte associations with diverse alkaloid profiles

Abstract

AIMS: To compare ryegrass pastures infected with endophytes producing diverse alkaloids for their ability to cause ryegrass staggers in grazing lambs; to compare respiration rates and rectal temperatures of these lambs after exposure to heat stress, and to compare liveweight gains during the study period.METHODS: Ryegrass pastures of cultivar Trojan infected with NEA endophytes, branded NEA2 (T-NEA2), endophyte-free Trojan (T-NIL), Samson infected with standard endophyte (S-STD), Samson infected with AR37 endophyte (S-AR37) and endophyte-free Samson (S-NIL), were grazed by lambs (n=30 per cultivar) for up to 48 days in February and March of 2012 and 2013. Pasture samples were analysed for alkaloid concentrations and lambs were scored for ryegrass staggers at intervals during the study period. Liveweight was recorded at the start (Day 0) and end of the study, and rectal temperatures and respiratory rates were measured in lambs exposed to heat stress on Days 23 and 26, in 2012 and 2013, respectively. RESULTS: Concentrations of alkaloids were lower in 2012 than 2013, associated with warmer and drier conditions in 2013, and the prevalence of ryegrass staggers was low in 2012. In 2013, concentrations of ergovaline were similar in T-NEA2 and S-STD, but concentrations of lolitrem B were lower in T-NEA2 than S-STD. S-AR37 produced epoxy-janthitrems but no lolitrem B or ergovaline. In 2013, by Day 20, 9/30 (30%) sheep grazing S-STD had severe staggers (score ≥4), and by Day 47 all sheep had been removed from this cultivar due to severe staggers. By Day 47, 18/30 (60%), 4/30 (13%) and 0/ 30 (0%) sheep grazing S-AR37, T-NEA2 and T-NIL pastures, respectively, had severe staggers. There were no differences in mean daily weight gain of lambs between cultivars in either year. In both years, mean rectal temperature and respiration rate following exposure to heat stress were highest in sheep grazing S-STD and T-NEA2, and lowest in sheep grazing T-NIL. CONCLUSIONS: In lambs grazing different ryegrass pastures infected with endophytes, ryegrass staggers was most severe on S-STD, less severe on S-AR37 and least on T-NEA2. When under heat stress, lambs grazing ergovaline-producing S-STD and T-NEA2 pastures had increased respiration rates and rectal temperatures compared with lambs grazing T-NIL.CLINICAL RELEVANCE: If ambient temperatures are suitable, NEA2-branded endophytes have the potential to express concentrations of ergovaline sufficient to induce heat stress in grazing sheep.

Identification and Structure Elucidation of Epoxyjanthitrems from Lolium perenne Infected with the Endophytic Fungus Epichloë festucae var. lolii and Determination of the Tremorgenic and Anti-Insect Activity of Epoxyjanthitrem I

“…This is well within the concentrations that are typically observed in the field although concentrations of endophyte-expressed alkaloids is weather dependant. It has been reported that in New Zealand under moist, cool conditions in 2012, the total epoxyjanthitrem concentrations ranged between 18.5 and 26.0 ppm in the January to March period, and in 2013 when it was warmer and drier, they ranged from 27.0 to 50.5 in February and March [32].…”

Ergot alkaloids in New Zealand pastures and their impact

“…Other characterised strains which express ergovaline, such as NEA2, have been commercialised (Stewart et al 2014). While this endophyte brand is a mix of NEA2 and NEA6 it is promoted as expressing only low levels of lolitrem B and ergovaline they have the potential to produce toxic concentrations under adverse environmental conditions and have reached 0.9 μg/g DM of ergovaline in autumn Fletcher et al 2017).…”

“…Some of these characterised Epichloë endophyte strains associated with ryegrass, such as AR5, AR6 and some NEA brand endophytes, that either have been or are commercially available, can produce ergovaline concentrations similar to those found in ryegrass with its standard endophyte and depending on host genetics can reach 1.1 μg/g DM (van Zijll de Jong et al 2008;Logan et al 2015). This can result in heat stress responses similar to that of the standard endophyte (Fletcher et al 2017).…”

“…In a later report, Fletcher et al (2017) considered that many farmers do not appreciate the potential for ergovaline to induce animal production problems especially since it is only relatively recently that endophytes which express ergovaline have been marketed. Some of these commercially-available endophytes that express ergovaline can result in increased body temperature and respiration rates similar to that which would occur in animals grazing standard endophyte-infected pastures when exposed to heat stress.…”

Examining the Impacts of CO2 Concentration and Genetic Compatibility on Perennial Ryegrass—Epichloë festucae var lolii Interactions

“…NEA2 produces all three alkaloids but at more moderate levels than the E+ strain. AR1 produces only peramine, while AR37 does not produce any of the three alkaloids found in the E+ strain but rather produces a different set called epoxy-janthitrems (see [52] and references therein). These so-called "novel" strains induce other metabolic changes in the host plants beyond the differences in alkaloid production [53][54][55].…”