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This article was published in 1986
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Untoward Reactions Subsequent to Avermectin Treatment in Cattle
C.H.R. DENT, Veterinary Inspector, Carcoar and Jane EAGLESON, M.S.D. Sydney
PART 1: CASE HISTORY — C.H.R DENT
INTRODUCTION
In November and December, 1985, a competent and experienced cattle raiser from Mandurama (Carcoar P.P. District) had several Murray Grey yearling heifers and steers become ill and/or die after being given 'Avomec' (M.S.D.'s avermectin B1 injectable anti-parasiticide) at correct dose-rates. 3 heifers and 5 steers were involved, out of 220 such cattle given this product in four drenching groups on four days, the product having been purchased locally and three 'lots' being used: the weather was fine and dry at the time.
PROPERTY HISTORY
2,000 acres, owned by the same family since 1859, (now 4th generation). Country is undulating and basaltic, and has 28 cattle paddocks of Phalaris, Ryegrass, Sub. and White Clovers and natural pastures, used in rotational grazings by 14 mobs of cattle. 28 farm dams, 3kms. of creek frontage.
Murray Greys first used here about 20 years ago, with purchase of first bull: no females have been purchased for 17 years, but (MG) bulls have come in from four studs ( 1 at Carcoar, 1 at Orange 1 at Bathurst, 1 at Sutton Forest): currently, 370 MG breeders, 175 x 2½ y.o. heifers, 75x 15 m.o. heifers, 220 x 12-30 m.o. steers and 440 x 3.m.o. calves: 440 ewes for fat-lamb.
Pre-1980 drought, had 500 MG breeders but sold off 250 during drought, and is now 'building-up' again.
Calving percentages about 99% in past 2 years.
Supered half-property each year from 1940 to 1983: last put 1cwt/acre on half property and selected paddocks.
Hay - all home grown and stored; normally 300 tonnes (average) in store. In drought, fed out 480 tonnes (non bought-in): in 1985 stored 380 tonnes.
DRENCHING, VACCINATION PROGRAMME:
(a) Drenching Normal programme is --
February-March: heifers and weaner steers
April: fat steers drenched
October: fat steers drenched.
Other cattle drenched on 'clinical signs'.
(b) Vaccination style="margin-left: 35px;"No Clostridial vaccine used on property, (despite repeated advice). Claims no losses from E.T., but reports 6-8 lost from Bloat and 2-3 from Hypomag. over last decade.
CASE HISTORY
(The cattle had not been drenched before).
At 3pm 29 October, 50 or so heifers were given 'Avomec': within 24 hours, 3 had died, one overnight and the other two by 4pm on [blank gap]. A local practitioner conducted p.m. examinations and diagnosed Enterotoxaemia.
At 3pm on 18 November, 55 yearling steers were given 'Avomec'. On 20 November, I was eventually contacted and requested to examine 2 'sick' (see 'Signs' below) steers. This done, M.S.D. Sydney was contracted and arrangements made for owner to deliver sick animals to the R.V.L., Orange by truck some 40 road kilometres away. The first was delivered there by noon 21 November, the second by 4.30pm on 21 November and the third by 22 November, (see later).
| DRENCHED | FIRST SIGNS | DELIVERY TO R.V.L. | Video | |
|---|---|---|---|---|
| No. 1: M.G. Steer 350kgm | 3pm, 18/11 | 8am, 20/11 | 12pm, 21/11 | Yes |
| No.2: M.G. Steer 400kgm | 3.00pm, 19/11 | 8.00am, 21/11 | 4.30pm, 21/11 | Yes |
| No.3: M.G. Steer 300kgm | 3.00pm, 19/11 | 8.00am, 21/11 | 1.00pm, 22/11 | No |
SIGNS
When 'No.1' was seen by me, it was initially seen resting in tree shade away from its herd-mates in a paddock of long Phalaris. As it was approached in a Suzuki-jeep, it rose unsteadily to its feet and wandered off, but seemed drowsy and ataxic, with about 5cms of its tongue tip protruding and its ears drooped: its 'rest site' showed evidence of regurgitated ruminal contents and slobbered saliva.
A cattle dog approached the steer quietly, but was induced into a flight reaction by the steer suddenly charging it, although the steer soon desisted because of disorientation. Even so, it was apparent that the steer was blind because it sauntered into the jeep's side. When left alone, it soon wandered off apparently aimlessly, still ataxic and drowsy.
My field diagnosis was of either C.N.S. abnormality (? a typical polioencephalo-malacia,), an allergic reaction (? oedema of throat causing dyspnea,etc.,) or an ascending (? Clostridial) toxaemia from the injection site (high, on the side of the neck) causing encephalomyelitis.
'No.2' was seen by me at the same time as ('No.1'), but was not so advanced in its clinical signs: it was with its herd mates, was mildly ataxic, and had slight tongue protrusion, and bulging eyes; it also charged the dog, but also soon desisted.
'No.3' was from the same steer group, but was not noticed 'sick' until 22 November, (not on video): when seen by Dr. Eagleson, it could only arise with assistance, walking on its knees, slobbering, but tongue not protruding apparently blind, ears droopy, and with some muscle twitching.
LABORATORY REPORTS
On Arrival
'No.1' - almost dead, 'flat', euthanased
'No.2' - was able to walk but swayed, was uncoordinated, balanced poorly : knuckled its fetlocks, and showing generalised muscle twitching, multiple skin injuries/abrasions from its truck ride, tongue-protrusion, drooling of saliva, and apparent blindness. Euthanased.
'No.3' - not changed much since first seen. Euthanased.
Pathology (GROSS): (No.1-3)
No reaction at injection site.
No significant gross pathology, except emphysema and aspiration pneumonia in 'No.1'.
Spleen (severely congested) - Barbiturate euthanasia.
Histopathology: (No.1-3)
Mild diffuse degenerative changes in liver kidneys and lungs (+ aspiration pneumonia in No.1 + patchy consolidation along lines of possible allergic response in both No.2 and No.3).
Lymphoid hyperplasia in lymph nodes. No significant findings in heart, cervical spinal cord.
Brain - 'a few scattered arterioles show swelling and proliferation of endothelial cells (significance uncertain)'.
'In summary, it appears some neurological toxin is responsible for the clinical syndrome, with changes at the biochemical level not reflected microscopically.
'Avomec' injection would appear to be the precipitating cause'.
No.4
M.G. Steer, delivered to R.V.L. by owner on 10/12/85. Not seen by me at all. Had been treated with AVOMEC on 20/11/85, and was not able to be found by owner until 9/12/85: long paddock grass cover,etc., was to blame. On arrival at R.V.L.: poor condition, weak, also had 'pink eye'. On standing, its hind limbs were placed well forward (under the abdomen), and its forelegs were placed slightly backward (under the thorax).
The head was carried low, with jaw only inches from the ground and ears dropped: there was a generalised muscle tremor.
When forced to move, steer dragged tips of hooves of forefeet: slight ataxia, particularly noticeable when it turned because forelegs crossed.
Laboratory Reports: (Barbiturate euthanasia).
Pathology and histopathology: 'Similar to previous animals from this property', despite 3 weeks illness, except bilateral corneal ulceration and opacity, plus hypopyon in right eye'.
Further cases will be presented by Dr. Eagleson, who was appointed to conduct a field 'double blind' trial using 1 X NID 'Avomec' and vehicle Propylene glycol.