Performance of Coopworth ewe lambs exposed to low levels of ryegrass endophyte (Neotyphodium lolii) alkaloids and allowed access to a mycotoxin deactivator

Abstract

During February–April, Coopworth ewe lambs grazing a pasture dominated by naturalised perennial ryegrass (PRG) exhibited slight signs of ill-thrift and heat stress. PRG represented 85% of the herbage; 90% of the PRG population was infected with Neotyphodium endophyte. Concentrations of ergovaline and lolitrem B in perennial ryegrass were each within the range 0.5–1.0 mg/kg DM during this period. Two groups of 30 lambs rotated weekly between two paddocks that offered 6 t DM/ha of mature, low-quality pasture. They received an allowance of crushed barley and peas (80 : 20) at 100 g/head per day. One group was treated with a mycotoxin deactivator, Mycofix® Plus, mixed into their mash during processing (5 g/100 g). No sign of ‘staggers’ was observed in the lambs at any time. Lambs with access to Mycofix Plus made great use of shade; their occupancy of shade increased steeply with ambient temperature over the range 18−38°C (P < 0.001). For the control group, occupancy of shade was low (P < 0.001) and independent of temperature (P < 0.001). Instead of using shade on hot days, the control lambs whose respiration rate was higher than treated ewes (P < 0.001) commonly stood by the wire fence, huddled in the open. Over the first 56 days of treatment, while pasture remained dry, weight change in control and treated lambs was –13 and +16 g/day, respectively (P < 0.010). The need for greater investigation of the effects of endophyte alkaloids on livestock is discussed.

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

“…Respiration rate was similar in the NilAlk Heat and Alk TN treatment, suggesting that alkaloid ingestion increased heat load similarly to 38 °C heat. Grazing studies have found increases in rectal temperature and respiration rate over summer and autumn [ 4 , 12 ]. However, the amount of PRG alkaloid consumed by individual sheep was not measured due to the grazing nature of the studies.…”

“…Body temperatures were observed to rise above 41 °C and respiration rates increased, causing heat stress in sheep [ 1 ]. Previous work undertaken under grazing conditions in Australia have shown heat stress (increased respiration rate) when grazing Coopworth ewes on Victorian perennial ryegrass and subterranean clover mix [ 12 ]. The cost of PRGT in Australia has been estimated to be $100 million per annum [ 13 ].…”

Evidence of dehydration and electrolyte disturbances in cases of perennial ryegrass toxicosis in Australian sheep

“…Past studies have accessed postmortem reports from government laboratories [12][13][14] or used in-field trials in which very few or no animals were allowed to reach the severity of clinical signs associated with non-recovery; therefore; postmortem sampling has been difficult to achieve. 9,[15][16][17] A specific diagnosis of PRGT has historically been considered to be one of exclusion. Histopathological findings are difficult to interpret in isolation, as the diagnostic value of the classical PRGT lesion, namely, proximal axonal bodies of Purkinjie cells in the cerebellum, 18 is questionable.…”

FORAGES AND PASTURES SYMPOSIUM: Fungal endophytes of tall fescue and perennial ryegrass: Pasture friend or foe?12

“…The heritability of resistancesusceptibility to the subclinical effects of endophyte is unknown. Feed additives (Reed et al, 2011a) and immunization (Prestidge, 1993) are possible ways to counteract toxicoses, although the costs and diffi culty in administering these treatments may limit their adoption by farmers.…”