AR37 - Grazing Animals

Animal health and performance responses to grazing ryegrass infected with AR37 have been measured in weaned lambs and hoggets over 10 years at AgResearch Lincoln. Results from the first 6 years were published in 2005 (see paper). These results are updated to 2008 in the tables below.

Sheep growth rates over summer and autumn, when endophyte toxins are likely to be highest, have been better on AR37 than on ryegrass infected with the Standard endophyte. Growth rates on AR37 are similar to the same ryegrass without endophyte or with the AR1 endophyte (see table 1).

Epoxy-janthitrems which are produced by ryegrass infected with AR37, are tremorgenic and can cause ryegrass staggers. Ryegrass staggers is a neuro-muscular disorder which is scored on a 0-5 ascending scale, with 5 being very serious staggers (see table 2). It should noted that there is considerable variation between animals in their susceptibility to ryegrass staggers.

The incidence of ryegrass staggers on pure ryegrass, with AR37, at Lincoln, is less frequent and usually only half as severe as on ryegrass with its Standard endophyte. However AR37 can cause very serious staggers, but in the trials at Lincoln this has occurred in only one year in ten (see table 3).

In more stressful environments (hot drought-prone regions), serious outbreaks may be more frequent. The impact of ryegrass with AR37 on dairy production is currently being assessed in a three year grazing trial but the data have not yet been fully published.

Apart from ryegrass staggers, animals grazing ryegrass with AR37 show none of the adverse responses often associated with grazing ryegrass with Standard endophyte, such as increased body temperatures and respiration rates, more dags and flystrike and lower plasma prolactin concentrations.