Effects of perennial ryegrass infected with either AR1 or wild endophyte on dairy production in the Waikato

Abstract

A 3‐year farmlet experiment was carried out at Dexcel, Hamilton to compare the effects of ryegrass infected with either AR1 (no lolitrem B or ergovaline production) or wild endophyte on milksolids production and cow health. Two farmlets (7 ha each) were managed as self‐contained systems with cows grazing rotationally from September 2000 to May 2003, with 2.6 cows ha–1 in 2000/01 and 3.0 cows ha–1 in 2001/02 and 2002/03. AR1‐infected ryegrass pastures remained free of contamination from volunteer wild‐endophyte‐infected ryegrass plants for at least 3 years after sowing. Mean annual pasture production and ryegrass tiller density were similar for both AR1‐ and wild‐endophyte‐infected ryegrass farmlets in 3 years, with low numbers of black beetle. A combined analysis of the three lactations data showed that cows grazing AR1‐infected ryegrass pastures produced 8.9% more total milk‐solids than cows grazing wild‐endophyte‐infected pastures (318 versus 292 kg cow–1, SED = 9.2, P = 0.006). The difference between treatments averaged across lactations was 0.1 kg milksolids cow–1 day–1, but the magnitude of the difference varied from week to week. This highlighted the benefits of evaluating the effects of endophyte strain over the entire lactation and for consecutive years, in order to include effects of seasonal variations in alkaloid concentration. Milk composition was similar for both treatments in all lactations. Ryegrass staggers occurred in cows grazing wild‐endophyte‐infected pastures in January 2001, coinciding with the highest concentrations of lolitrem B over the three lactations (>3.5 mg kg–1 DM). Cow body temperatures, respiration rates and plasma prolactin concentrations measured during periods of heat stress were only occasionally affected by endophyte treatment. Results from this 3‐year farmlet evaluation demonstrate that renovating pastures with AR1‐infected perennial ryegrass can offer significant improvements in milksolids production and elimination of ryegrass staggers.