Production and physiological effects of perennial ryegrass alkaloids under thermoneutral conditions in Merinos

Abstract

A confined feeding study was conducted to compare the production and physiological effects of feeding three doses of wild-type perennial ryegrass alkaloids via whole seed to Merino sheep housed under thermoneutral conditions (21°C, 50% relative humidity). Eighteen Merino ewe weaners (16 months; initial bodyweight 47 ± 1.94 kg) were offered Nil, Low (50 µg/kg liveweight ergovaline, 22 µg/kg liveweight lolitrem B) or High (100 µg/kg liveweight ergovaline, 44 µg/kg liveweight lolitrem B) doses of alkaloids for 21 days. Dry matter intake tended (P = 0.072) to decrease in a linear manner with increasing dietary alkaloid concentration. Rectal temperature and respiration rate increased (P = 0.002 for both) in a linear manner with increasing dietary alkaloid concentration. Oxygen consumption increased linearly (P = 0.064) and quadratically (P = 0.015) with increasing alkaloid concentration, being highest in the Low dose and intermediate in the High dose group. Plasma prolactin decreased linearly (P = 0.002) with increasing dietary alkaloids. These data clearly show that animal production and efficiency are compromised when sheep consume perennial ryegrass alkaloids, even over a short period of time. This study indicates that a pyrogenic response can occur when alkaloids are consumed, even under thermoneutral conditions.

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

“…A key finding from the present study was that DMI was decreased by 22% in response to consumption of rye grass seed that contained moderate levels of endophyte alkaloids. A reduction in DMI due to alkaloid consumption has been reported in previous studies by the same authors when thermoneutral and moderate heat conditions were used for the same period of time [ 14 , 16 ]. Furthermore, this finding is consistent with a previous study which found feed intake decreased in cattle fed endophyte infected tall fescue (containing ergovaline) under 32 °C ambient temperature conditions [ 3 ].…”

“…A previous study using goats found only a small percentage (1.6%) of whole perennial ryegrass seed passes through to the faeces [ 15 ] so seed was fed whole. Additionally, previous studies by the authors have found feeding seed whole produces consistent PRGT effects [ 14 , 16 ]. Lolitrem B levels are higher than ergovaline in plant tissue [ 17 ], in the current study seed was fed which contained lower levels of lolitrem B compared to ergovaline.…”

“…Liveweight gain was not significantly affected in this study and this is likely due to the short time period used. Liveweight has been found to decrease in a number of grazing based PRGT studies [ 19 , 20 , 21 , 22 ], and with controlled alkaloid intake under thermoneutral and moderate heat conditions [ 14 , 16 ]. A recent review has highlighted the clear production effects of ergot alkaloid consumption [ 8 ], reporting the clear link between decreased DMI and liveweight.…”

“…Alkaloid dosing levels were based on ergovaline and lolitrem B concentrations used in previous studies [ 14 , 16 ], when moderately high concentrations of alkaloids were fed, resulting in compromised animal production and a heat stress response. However, in these studies sheep did not consume all alkaloid offered, possibly because of feed aversion.…”

“…A previous study undertaken by the authors [ 14 ] investigated the interaction between alkaloid consumption and moderate heat stress (maximum ambient temperature 33 °C) and demonstrated a strong interaction between alkaloid consumption and moderate heat conditions. However, southern Australia experiences summer conditions which can reach and exceed 40 °C, far in excess of that studied previously.…”