Ryegrass Staggers Prevalent in Autumn after Dry Summer

New Zealand Journal of Agriculture, Volume 93, Issue 1, 16 July 1956, Page 56

Ryegrass Staggers Prevalent in Autumn after Dry Summer

By

M. C. ARMSTRONG,

Veterinarian, Department of Agriculture, Timaru

THE widespread incidence of ryegrass ■ staggers in sheep flocks in South Canterbury last autumn worried many farmers who. had had little or no experience' of this complaint previously. The disease was first reported early in February and the greatest intensity occurred during the last week of March and the first 3 weeks of April. RYEGRASS staggers is a disease . which causes a disturbance of the neuro-muscular co-ordination, resulting in spasms or convulsions of muscle tissue. This type of convulsive staggers occurs in sheep, cattle, and horses of all ages, sexes, and breeds. It occurs in most parts of New Zealand and some parts of Australia. Occurrence The incidence varies from year to year according to seasonal conditions and is' highest in years with a dry summer and autumn. Up to 75 per cent, of a sheep flock may be affected, but fortunately less than 1 per cent, die and most deaths are due to affected animals drowning in drains or creeks. Dairy cows are less often affected than sheep, beef cattle, or calves. Ryegrass-dominant pastures are responsible and both perennial and short-rotation ryegrass have caused outbreaks. The staggers is most commonly seen when the ryegrass pastures are dried up after a drought when little or no green growth is present or soon after rain when growth is coming away again. Outbreaks of staggers are not uncommon, however, on longer, green pasture such as hay aftermath, and one severe outbreak occurred in South Canterbury on 6in.-to-Bin., rank, green, spring-sown pasture fed during the following summer. Symptoms and Pathology Symptoms vary widely in severity,, from slight stiffness of the limbs when animals are driven to complete inability of animals to stand or to make any sudden movement without falling. The commonest form is that in which the animals show no abnormality until they are driven or disturbed, when they show a characteristic stiff, bounding action for a few paces and then fall. Sheep usually run with a stifflegged gait with both forelegs and hindlegs in unison and the head held high. Calves may run normally until the spasm occurs, when they usually have the legs bunched together under

the body and leap from side to side before falling. ; The milder symptoms usually, cause no loss of condition or deaths except from accident, such as drowning; even severe symptoms rarely cause death, and when they do it is probably from starvation. On falling the animals may struggle, show spasmodic convulsions, muscular tremors, and twitching and rolling of the eyeballs. Relaxation soon occurs, and after a few minutes, during, which grazing may be attempted, they rise, and if not again disturbed, resume normal walking and grazing. Symptoms may appear a few days after stock enter the pasture on which the disease develops, and may disappear in from a few days to 2 or 3 weeks whether or not the stock are given a change of feed. Symptoms rarely persist for more than 2 or 3 weeks even if the stock are left in the same paddock as that in which the symptoms developed, especially if rainfall is sufficient to produce a good growth of pasture, thus altering the

nature of the herbage being grazed. No macroscopic or microscopic lesions have been found in numerous affected animals which have been examined. No abnormality of the blood content of calcium, magnesium, ketone bodies, phosphate, or sugars has been found in affected animals. Treatment and Prevention , No satisfactory treatment is known for ryegrass staggers and it is fortunate that normal, spontaneous recovery occurs whether the feed is changed or not. Movement of the affected stock to alternate forage is the usual treatment recommended, but is often hard to arrange and in many cases apparently unnecessary. The dangerous stage in the pasture appears to be of fairly short duration in most cases, though it may last up to a fortnight in some.

When sheep or beef cattle are being moved to alternate pasture care is necessary not to drive the stock too fast, and one of the best methods is to leave the gates open, keep men and dogs away, and let the stock find their way through in their own time. Causative Agent An unidentified agent in the pasture causing ryegrass staggers has been confirmed at the Department of Agriculture Wallaceville Animal Research Station by feeding experiments with grass cut from paddocks in which severe outbreaks of the disease have occurred. Many theories have been advanced and tested regarding the causative agent of ryegrass staggers. Among these is the ergot theory. This may be disposed of by the fact that ryegrass ergot produces only ulceration of the tongue and stomachs in sheep and necrosis of the feet in cattle. Furthermore, many outbreaks of staggers have occurred in ergot-free ryegrass pastures. At present the most that can be said about the causative agent of ryegrass staggers is that it appears to be a product of a particular set of growth conditions in the plant, and future research into the pathogenesis of this disease is necessary to elucidate unknown factors. Management of Affected Flocks As mentioned previously it is advisable to shift the flock quietly to a paddock with the minimum of drains or water holes to lessen the chance of drownings. Dipping or drenching may have to be postponed in badly affected flocks. Where the incidence is light the affected animals can be shedded off after a stir-up and drive. The unaffected ones can then be drenched or dipped and the affected ones isolated and treated in 2 or 3 weeks’ time when they have recovered.