CASE NOTES

Lessons from a lead toxicity case when the lead source is unknown

Katelyn Braine, District Veterinarian, Murray Local Land Services, Deniliquin NSW

Introduction

The most common source of lead toxicity in livestock is lead acid batteries but other sources can include lead-based paint, sump oil or any other lead-based material. Sometimes the source of lead goes unnoticed by producers until the diagnosis of lead toxicity is made. This report describes the lessons learnt from a lead toxicity case in cattle in the Murray Local Land Services region when the lead source could not be determined.

CASE SUMMARY

Lead toxicity was diagnosed in a mob of 30 beef cows with six-month-old calves at foot. Three of the calves developed vague neurological signs including dullness, reluctance to move, absence of menace response and apparent blindness prior to death. No clinical signs or death were observed in the cows.

A diagnosis of lead toxicity was made on a high lead kidney level of 230 µmol/kg wet weight after post-mortem of the third calf that had died.

The mob was grazing a bare paddock and fed cereal hay daily along the ground.

The source of the lead exposure was not determined.

Blood testing results

EDTA blood samples were collected from the 27 calves, 1 bull and 30 cows two days after they were removed from the paddock and any potential lead source.

Three calves returned blood lead levels (range 0.8 to 1.16 µmol/L) above the maximum residue limit (MRL) for lead (≥0.24 µmol/L).

A further five calves and five cows had detectable blood lead levels (range 0.1 to 0.22 µmol/L) but under the MRL for lead (≥0.24 µmol/L).

Although the calves were unweaned, it was decided to treat the calves as individual units because they were showing clinical signs of lead toxicity, irrespective of the cows. As all the dams returned blood lead levels below MRL, movement restrictions were only placed on the three calves with blood lead levels above MRL, rather than placing movement restrictions on all calves until they were weaned.

Finding the lead source

A brief paddock inspection was completed at the time of post-mortem and no lead source was identified.

Following the diagnosis of lead toxicity, a second visit was conducted to try a find the lead source. Areas where the mob of cattle had access to were inspected for any potential lead source. These areas included the paddock, cattle yards and laneway from the yards to the paddock.

The trailer used to feed out the hay was also inspected for lead paint or another lead source, but it did not appear to have any lead and was assessed as unlikely.

Access to sump oil was also discussed but deemed unlikely.

When searching the cattle yard, a battery was found leaning up against the outside of the fence of the yards. The cattle could have had access to the battery by putting their head through the railing. However, the battery appeared intact and therefore it was unlikely to have been the lead source.

When rechecking the paddock, areas where feed had built up, including along boundary fence lines and tree lines, were inspected to check for a lead battery. This inspection was conducted because built-up feed could have hidden a battery while most of the paddock was bare. Areas where electric fences were or had been were also inspected for a lead battery. No lead battery was found in the paddock. However, a wire cable was found partly buried that contained lead attachments on the cable (Figure 1). A painted gate found in the paddock was also inspected for lead paint but was assessed as low risk. In the absence of any other lead source found at that point in time, the lead on the cable was the only suspected lead source identified.

Image of thick wire cable partially buried in soil

Figure 1. Wire cable containing lead attachments

The mob of cattle were removed from the paddock that day and from any potential lead source.

Following the blood lead test results of the mob, the number of cattle with detectable lead in their blood did not match the suspected lead source. Another inspection of the paddock was completed, this time by the producer’s wife, and a lead battery was found cut up in pieces in the hay fed on the ground (Figure 2).

Image of hay spread on ground with part of broken battery

Figure 2. Battery pieces baled and fed out in hay. Image source: producer

When the battery pieces were found in the hay, the producer remembered there was a battery in the corner of another paddock that was baled for hay the year before. The producer went and checked this corner and found that the battery was no longer present and some chopped up battery remnants were found in the paddock. Around 2/3 of the battery pieces found were found chopped in the hay and 1/3 were found in the original paddock.

A risk assessment was then conducted on the risk of battery pieces in other bales of hay that was fed out to other mobs of cattle. Based on the number of bales of hay produced from the paddock and the fact that the producer was feeding out 6-8 bales of hay per day, it was calculated that it was likely that all bales of hay from the original paddock had been fed out by that point of time. Due to this assessment and because no other mobs of cattle on the property that were being fed hay were showing clinical signs of lead toxicity, the risk of other mobs of cattle being exposed to lead through the hay was assessed as low.

Lessons learnt

Always test for lead, even if there is no known risk of exposure to lead and/or lead toxicity is low on your differential diagnosis list—lead toxicity was initially low on the differential diagnosis list due to the initial clinical picture with clinical signs only in the calves and not in the cows. It was also initially thought that because the paddock was bare any potential lead source would be easily seen. Despite the fact that the likelihood of lead toxicity was deemed low at the beginning of the investigation, it was still tested for to rule in/out a notifiable disease and returned a positive result.
Keep looking for the lead source—as discussed above lead sources can show up in many different materials and sizes. When the lead source is small, a smaller proportion of animals affected is expected. On the other hand, if the lead source is large, a larger proportion of animals is more commonly affected. The initial suspect lead source found in this case was a small source of lead and the total number of cattle with detectable lead in their blood was not consistent with the initial suspect source. When this type of discrepancy occurs, it is important to keep searching for a lead source that fits with the findings from the clinical investigation. Additionally, when searching for a lead battery don't assume the battery will be intact, it could be chopped up in the hay or otherwise damaged. Identifying the source of lead was important in the end to prevent further issues of exposure to lead in the paddocks where the pieces of battery were found.
Utilise the people around you—a fresh mind and another set of eyes can always be helpful to think outside the box and find the answers to questions from a case. In this instance a fresh set of eyes was able to identify the chopped up battery. If it wasn't for this detection, the lead source would not have been identified. Finding the source of lead was important to prevent further issues of exposure to lead in the paddocks where the battery pieces were found.

Acknowledgements

I would like to acknowledge the laboratory staff for their assistance in diagnostic testing and the NSW DPI Residues Coordinator, Liz Bolin, for her assistance in this case.