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Clinical aspects of lead poisoning in cattle

Bruce Watt, District Veterinarian, Condobolin RLPB

Introduction

Lead has been considered "perhaps the most consistently important poison in farm animals" (Jubb et al., 1992). Lead poisoning is frequently diagnosed in cattle. While lead is a multi-system toxin, the clinical signs are mainly neurological. Acute lead poisoning causes an encephalopathy, sub-acute lead poisoning can also cause gastroenteritis while chronic lead intoxication can cause peripheral nerve degeneration (Radostits et al., 2000). In cattle the disease is "probably always acute" (Jubb et al. 1992).

Cattle seem particularly susceptible to lead poisoning because they are inquisitive and "lack oral discrimination." As an example, a 4 month old calf was reported as having succumbed to acute lead poisoning after drinking 4 litres of sump oil (Slatter, 1971). There are many sources of lead which may poison cattle. These include sump oil, lead paint, old linoleum, ash heaps after lead treated timber has been burnt and environmental contamination near industrial plants or highways. In my experience however discarded batteries are by far the most likely source of lead on mixed central west farms.

CLINICAL SIGNS OF LEAD POISONING

In our farming environment, the first indication of lead poisoning in cattle is often death. It is reported that affected cattle may be frenzied, aggressive and exhibit manic behaviour. Tonic-clonic convulsions, muscle tremours, hyperaesthesia and head pressing are also reported. Apparent blindness and aimless walking are frequently observed. Affected cattle may also be dull and unresponsive. Rumen atony is also reported as is diarrhoea in sub-acute cases. (Radostits et al. 2000). A US survey found that blindness and cervical, facial and auricular muscle twitching were the most reliable and consistent diagnostic indicators of lead poisoning (Osweiler et al. 1973).

CASE PRESENTATION

Five cases of lead poisoning will be presented. These occurred within a two year period in the Condobolin Rural Lands Board. Mortality rates ranged from three cows in 70 (4%) to 9 cows in 21(43%). Overall 28 cattle died of a total of 216. In almost all cases, the first indication of lead poisoning in the herd was death. Apparently blind cattle that walked aimlessly were also reported by the owners and observed. The most common clinical observation was that affected cattle were dull and disinterested. Rumen atony and tongue flaccidity were observed on several-occasions. Two affected cattle showed neck or whole body muscle twitching. Affected cattle were often febrile. No cattle were observed either by me or the owners as being aggressive or frenzied and in no cases was diarrhoea observed or reported.

The diagnosis was confirmed by testing blood lead levels in live animals or kidney lead levels in dead animals. In eight clinical cases blood lead levels ranged from 2.6 to 7.2 umol/L (average 4.8). Blood lead levels above 1.7 umol/L are regarded as diagnostic. Kidney lead levels in two fatally intoxicated cattle were 307 and 678 umol/kg wet weight. Normal is under 10.

On one property the source of the lead was never found. On all other properties the source of the intoxication was old discarded batteries.

IMPORTANCE OF LEAD POISONING

In several surveys, lead poisoning has been the most common intoxication diagnosed in farm animals. (Osweiler et al. 1973, Sharpe, et al. 2004, Humphreys, 1979) Lead poisoning is therefore an important cause of disease and mortality in cattle and to a lesser extent other species. Lead poisoning is also an important as public health issue. The contamination of food supplies could jeopardise markets for farm produce and be a risk to human health. Finally lead poisoning is important in that in some cases the presenting signs may be vague and non-specific and the list of differential diagnoses includes the very important exotic diseases, rabies (Wyk, 1971) and BSE.

References

Jubb KVF, Kennedy PC and Palmer N (1992) Pathology of Domestic Animals, 4th edition, p 163 ff
Radostits OM, Gay CC, Bolld DC and Hinchcliff KW (2000) Veterinary Medicine, 9th edition. p 1658
Slatter DH, Sump oil a source of lead. Australian V Journal 47 9, 461 1970
Osweiler GD, Buck B and Lloyd WE, Epidemiology of lead poisoning in cattle-a five year study in Iowa. Clinical Toxicology 6:3, 367-376, 1973
Sharpe RT and Livesey CT, An overview of lead poisoning in cattle, Cattle practice, British Cattle Veterinary Association, 12:3 199-203, 2004
Wyk, JA van, Rabies in Otavi and Tsumeb, South Africa. Journal of the South African Veterinary Medical Association, 42:3, 1971
Humphreys DJ, Recent trends in animal poisoning. Trends in Veterinary Pharmacology and Toxicology. Proceedings of the First European Congress, Zeist. September, 1979