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This article was published in 1981
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Panicum laevifolium - a Cause of Photosensitisation in Sheep
F.L. Clark, B.V.Sc., Veterinary Inspector, Armidale
P. laevifolium is an introduced grass species from South Africa. It was first recorded in N.S.W. as naturalised at Guyra in 1932. Since then the grass has been reported from many areas on the coast, tablelands and western slopes of N.S.W.
Over the last 30 years many cases of photosensitisation in sheep due to ingestion of P. laevifolium have been reported from the northern tablelands.
As the grass is a free seeding, summer growing, annual species and is frost susceptible, it must re-establish itself from seed every year. Since the grass cannot compete with healthy pasture, infestations, except in drought years, are usually confined to old cultivation paddocks, along roads or tracks and around stock yards, i.e. places where the pasture cover has been disturbed.
The usual history of outbreaks in normal seasons on the Northern Tablelands, is that sheep have been placed in fallow cultivation paddocks especially paddocks where potatoes were sown the previous season. P. laevifolium readily becomes established in these paddocks following summer rain.
During severe droughts, such as occurred in 1965-66 and 1979-81, widespread damage occurred to sown pastures with many introduced grasses and clovers drying out, leaving bare earth areas in paddocks. Summer storms promoted a heavy germination of P. laevifolium in the drought damaged pastures.
P. laevifolium appears to be very palatable to stock, particularly sheep which graze it, in preference to other pasture species. Lambs are particularly susceptible to poisoning with P. laevifolium and when depastured with their mothers will show symptoms and die whilst the ewes still remain apparently unaffected. Adult sheep however, can become affected and losses can occur if they are allowed access to P. laevifolium for a longer period.
There are a few reports of symptoms in cattle, however, cattle generally appear to be fairly resistant and have been fattened on lush stands of the grass which would have been lethal to sheep.
All stages of growth of P. laevifolium appear to be toxic to sheep, however, the majority of outbreaks in the summer of 1980-81 occurred on short new shoot. This was probably because practically the only feed available on many properties during January - February, 1981 was short growth of the grass which was grazed at the first opportunity. However, enough cases occurred on fully grown stands to determine that mature plants were also palatable and toxic.
P. laevifolium causes photosensitisation in sheep. Outbreaks occur usually between December and April with the majority of cases in January and February.
The symptoms of photosensitisation may occur in lambs within 3 - 10 days after they have been placed in infested paddocks. Often there is a high incidence of affected lambs in a flock. The first signs noted is thickening and drooping of the ears. This is followed by inflammation of the eyelids, discharge from the eyes and hardening of the skin of the face with itching and rubbing. Affected sheep tend to seek shade. Unfortunately on many northern tableland paddocks and especially if previously used for crops, there is little shade available.
Jaundice is common in badly affected sheep indicating that the photosensitisation is of hepatotoxic origin.
Severely affected cases usually die, however, recovery can occur in less severe cases if sheep are removed from contact with P. laevifolium and placed in a shady place, usually in a shed or in a temporary enclosure erected in a dense clump of trees. They should be hand fed and have adequate water.
Outbreaks during the summer of 1980-81 were by far the most numerous ever recorded on the Northern Tablelands and thousands of sheep, mainly lambs, died. Losses were confined to sown pastures in the higher rainfall zone. Native grass pastures were not affected as generally these survived drought conditions better and still had good ground cover whilst sown pastures on many properties had practically died out due to the drought.
The worst affected area, was the Guyra district where basalt soils predominate. On many properties it was impossible to find paddocks not infested with P. laevifolium.
A survey of losses on a small group of adjoining properties in the Guyra area is given below and this will indicate the extent of losses experienced.
| Property A | 180 lambs died out of 350 |
| Property B | 150/300 lambs |
| Property C | 200/2000 lambs |
| 6/200 rams and 100/400 ewes | |
| Property D | 210/632 crossbred lambs |
| 82/424 Merino lambs | |
| 160/950 2 tooth Merino ewes | |
| 23/222 18 month old Merino rams | |
| Property E | 160/300 Merino lambs |
| 119/128 crossbred lambs |