Minimising endophyte contamination from ryegrass seed in cow dung

Abstract

Perennial ryegrass pastures in New Zealand are usually established from seed naturally infected with the wildtype endophyte. New pastures can now be sown with perennial ryegrass that has no endophyte or has been infected with a new endophyte. Cows can contaminate pastures by consuming ryegrass seed infected with the wild-type endophyte on old pastures, and transferring the seed in their dung onto new pastures. A quarantine period before grazing new pastures may allow cows to eliminate wild-type endophyte-infected perennial ryegrass seed from their digestive tract, preventing contamination from this source. A trial was run at Dexcel, Hamilton, to define an appropriate quarantine period. Cows grazed wild-type (high endophyte) ryegrass pastures containing seedheads for 4 days before grazing Lotus corniculatus (quarantine pasture) for a further 4 days. This procedure was repeated five times from November 2000 to April 2001. Dung samples were collected daily after shifting cows off high endophyte ryegrass. Pastures contained viable ryegrass seed on seedheads from December to April, and ryegrass seedlings germinated in dung samples collected from January to April. Viable endophyte-infected perennial ryegrass seed was present in dung for 2 days after removal from the seed source, with 0.8% of the seed eaten remaining viable. Ryegrass seed endophyte viability was reduced from 100% to 40% after passage through the digestive tract of the cows. It is recommended that cows do not graze endophyte-free pastures or those sown with ryegrass containing a new endophyte for at least 2 days after grazing high endophyte ryegrass pastures containing ryegrass seedheads. Keywords: dairy cows, dung, perennial ryegrass, ryegrass endophyte, seedheads, seed transfer