CASE NOTES
Grass seed infestation of the ear of lambs with penetration through the auditory meatus
Dan Salmon, Riverina Livestock Health and Pest Authority
Posted Flock & Herd June 2011
Introduction
Grass seed penetration is a significant problem of domestic animals in Australia.
During years of prolific growth, the barbed awns of many native and introduced grass species penetrate the ears and feet of dogs and the eyes and skin of sheep.
History
Three hundred 6-month-old merino x South African Meat merino (SAMM) lambs were shorn 4 weeks earlier, dipped 2 weeks later (post shearing) then placed in a paddock with a Brassica spp forage crop and access to large round bales of grass hay.
Several died with others unthrifty and reluctant to move.
Clinical findings
Twenty lambs died with another 30 affected.
Affected lambs were in poorer condition than their cohorts (fat score 2 compared to fat score 4).
They had lesions at the base of their ears approximately 2-4cm diameter which the continually kicked with their hind legs. They had lesions on their rumps approximately 3-15cm diameter which they continually chewed.
Both sets of lesions had the appearance of skin abrasions with crusted blood.
Body temperatures of two of the most severely affected lambs were >40.5°C. They had no eye preservation reflex but apparently normal pupillary reflex. When helped to stand they had a stumbling gait but fell after a few metres.
Fig 1. Ear lesion
Fig 2. Rump lesion
Post-mortem findings
There were slight changes in the viscera: several small patches of consolidation in the lungs, about 20cc of clear pericardial fluid with no fibrin clots, pale liver and pale and slightly swollen kidneys.
4-6 grass seed awns with the appearance of barley grass (Hordeum leporinum) were observed in each ear canal causing a suppuratives otitis media with the inflammation extending through the auditory meatus to a suppurative inflammation of the caudal cerebellar peduncles.
Fig 3. post-mortem appearance
Fig 4 Necrosuppurative lesions of caudal cerebellar peduncles
Treatment
The ears of the affected lambs were flushed with warm saline using a 20cc hypodermic syringe and treated with long-acting oxytetracycline injection.
Several more died but the majority recovered and could not be distinguished from the rest of the mob 6 weeks later.
Discussion
The incident described here of penetration of the ears of lambs is unusual in the author's experience.
The source of the grass seeds apears to have been the hay that the lambs were eating. It was in large (500kg) round bales and the owner observed that they were foraging deep into the bales, even so it would have been expected to produce eye lesions as well as ear lesions.
The ear lesions would seem to be caused by the lambs kicking at the irritated ears, but the cause of the rump lesions is less obvious.
There were no indications of any skin infestation or infection wich might have caused irritation of the rump.
It may be that the lambs were trying to reach the ears with their teeth, but this appears unlikely. A possible explanation is referred irritation of the rump resulting from the CNS lesions.