Pithomyces chartarum spore counts in rumen contents and faeces of sheep exposed to autumn pasture at three different grazing pressures

Three groups, each of 18 lambs were grazed during autumn in paddocks which had been divided longitudinally by temporary fencing to give twofold differences in grazing intensity between the groups. During the period when spore numbers were elevated the high grazing pressure (HGP) group lost some body weight (−34 g/day). The low grazing pressure (LGP) group gained +90 g/day and the intermediate grazing pressure (IGP) group gained weight slightly (+14 g/day). There were two spore rises during the experimental grazing period, a minor and a major rise. Peak pasture spore counts were 88 000, 130 000 and 282 000 spores/g grass for the LGP, IGP and HGP groups respectively. These were reflected in the peak rumen content counts which were 6640, 17 050 and 24 470 spores/g and the faecal peak counts which were 141 400, 330 800 and 568 200 spores/g for the LGP, IGP and HGP groups respectively. Liver injury scores were 0.9, 2.6 and 1.7 and peak mean serum GGT levels were 139, 312 and 220 U/I for the LGP, IGP and HGP groups respectively. The greater liver injury in the IGP groups was considered due to the greater total consumption of spores caused by the combination of pasture spore concentration and dry matter intake.