Milksolids production from cows grazing perennial ryegrass containing AR1 or wild endophyte

Abstract

A 3-year farmlet experiment was carried out at Dexcel, Hamilton to evalua te the effects of AR1 (no lolitrem B or ergovaline production) and wild (standard or natural) endophyte-infected ryegrass on milksolids production and cow health. Two farmlets (7 ha each) were managed as self-contained systems with cows rotationally grazing treatment paddocks from September 2000 to May 2003. In the 2000/2001 milking season, cows grazing AR1 endophyteinfected ryegrass produced 10% more milksolids than those grazing wild endophyte-infected ryegrass (247 versus 224 kg/cow, SED = 8.4, P<0.01). Treatment differences were smaller and not statistically significant in the second and third milking seasons. A combined analysis of the 3 milking seasons data, showed a significant milksolids production advantage to cows grazing AR1 endophyte-infected ryegrass pastures (318 versus 292 kg/cow, SED=9.2, P<0.01). Milk composition was similar in all seasons. Milksolids production averaged over 3 milking seasons was significantl y higher in cows grazing AR1 endophyte-infected ryegrass in summer (110 versus 103 kg/cow, SED=2.9, P<0.01) and autumn (50 versus 44 kg/cow, SED=2.1, P<0.01), and showed a similar effect in spring (157 ver sus 147 kg/cow, SED=5.5, P<0.1). Ryegrass staggers occurred in cows grazing wild endophyte-infected pastures in January 2001, coinciding with the highest concentrations of lolitrem B over the 3 seasons (>3.5 mg/kg). Cow temperatures, respiration rates and plasma prolactin concentrations were seldom affected by endophyte treatment. Annual pasture production was similar across AR1 and wild endophyte-infected ryegrass farmlets from September 2000 to September 2001 (14.7 versus 14.4 t DM/ha, SED = 1.11, NS) and from September 2001 to September 2002 (14.1 versus 12.9 t DM/ha, SED = 0.73, NS). AR1 endophyte-inf ected ryegrass pastures remained free of contamination from wild endophyte-infected ryegrass for at least 3 years after establishment, as indicated by low concentrations of lolitrem B detected in pasture samples. Keywords: dairying, heat str ess, Lolium perenne, Neotyphodium lolii, novel endophytes, pasture production, prolactin, ryegrass staggers