The effect of endophyte infection of perennial ryegrass on liveweight gain, feed intake and some physiological measurements in grazing lambs

Abstract

Twenty 8 month old Coopworth wether lambs were continuously grazed for four weeks on perennial ryegrass (Lolium perenne ) infected at two levels with Acremonium lolii endophyte. Lambs were allocated (n=10) to one of high (>95% of plants infected) or low (<5% plants infected) endophyte treatments. Both treatments contained Grasslands cv. Nui perennial ryegrass. Individual feed intake over an 18 day period was determined using the alkane technique. The lambs were also regularly weighed and scored for dags. At the end of the grazing trial serum prolactin, rectal temperature and respiration rate were measured. Ergovaline concentrations in the pasture were also measured. There was no significant difference in liveweight change of lambs from different treatments, with mean liveweight gain for both groups over 24 days +260 g dry matter/head/day. Mean dry matter feed intake was 2.4 kg DM/hd/day, this was high but did not significantly differ between groups. Respiration rate (133 vs 107 breaths/min) and rectal temperature (40.9 vs 40.4 °C) were higher in lambs grazing the high endophyte treatment which had higher ergovaline concentration (790 vs 0 ug/kg DM), these same lambs had depressed serum prolactin concentration (7.1 vs 23.9 ng/ml) compared to lambs grazing the low endophyte treatment. These results indicate that ergovaline may have a role in inducing heat stress and depressing serum prolactin levels in lambs grazing high endophyte ryegrass. There was no significant difference between lambs from high and low endophyte treatments for faecal moisture content (77.5 vs 78.5%) or dag scores [1-5] (1.3 vs 1.4).