CASE NOTES
Planning and logistics for bleeding a large number of cattle
Linda Searle, District Veterinarian, Murray Local Land Services, Deniliquin
Posted Flock and Herd November 2024
Introduction
Livestock ingesting lead can cause a food safety issue. Whenever an animal is diagnosed with lead toxicity the group of animals that have had access to the lead source must be blood tested. Cattle testing above the maximum residue level (MRL for lead is less than 0.24 µmol/l) are prevented from entering the food chain. This article focuses on the planning and logistics of bleeding large numbers of cattle to locate any animals with blood lead levels above the MRL.
CASE REPORT/SERIES
Lead toxicity was diagnosed in a cow after a blood test revealed a blood lead level of 3.44 µmol/L. Upon death, the cow was post-mortemed revealing a kidney lead level of 139 µmol/kg wet weight.
The cow had been part of a large mob and it was one of three cattle that had shown neurological symptoms and then subsequently died. There remained 1,167 cattle that needed to be bled to see if any had blood lead residue levels above the MRL.
To meet the guidelines of the procedure described in 'Biosecurity - Lead affected food producing animals in New South Wales' blood testing must be performed within 42 days of removal from the lead source so that animals that are below this level can have no lead status. Any animal with levels of or above 0.24 µmol/L are marked with a PB1 status on their RFID tag. Animals with a PB1 status may not enter the food chain. These animals can be retested again 12 months after removal from the lead source. Once the blood lead level falls below 0.24 µmol/L the animal has the PB1 status removed.
The owner of the cattle is responsible for paying for the blood testing of at-risk cattle.
Planning for this bleeding event was conducted as for an emergency response using an incident action plan template.
The main concerns for this event were workplace health and safety (WHS) of all involved, as well as ensuring accurate collection, labelling and recording of the blood samples.
The cattle in this mob were individually identified with RFID tags but they did not have individually numbered management tags. The livestock manager and the district vet agreed that identifying the cattle with an individually numbered management tag would aid in the management of this mob.
Two full days of bleeding were planned to allow time for the animals to be bled and because the facilities used could not contain all of the animals at once.
Figure 1: Cattle in yards for bleeding
Prior to the event long grass around the site was slashed and gates, head bail and all other parts of the facility were inspected, greased, and made sure to be in good working order.
To ensure that all animals were bled and correctly identified information was verified using several techniques.
As a new management tag was being applied it was numbered sequentially. This process meant that the number on the management tag matched the number on the blood tube, which was also the number of animals which had been bled at that point. The numbers on the management tags had been pre-written. The blood tubes were also numbered prior to blood collection. This step was taken because it was easier to label the tubes before they got contaminated with blood or faeces and also to helped ensure that no mistake was made in the numbering of the tubes.
As each job was done by a different person it was essential to have one person whose job it was to ensure that all of the numbers match up. This person was dubbed the 'recorder'. The recorder had a printed paper sheet in front of them. This sheet had 3 columns and was pre-numbered in order. Each page contained 150 pre-filled sample numbers. A blank row was listed next to the sample numbers. In this row the last 3 digits of the RFID number was recorded.
The scanner was linked via Bluetooth to either an iPhone or iPad (devices would run out of charge and needed to be rotated). The live scanning function was utilised so that as a tag was scanned it was visible both on the wand and on the device in front of the recorder. While we started off trying a to use the Allflex app to record data we ended up using the tag manager mobile app as it would allow the recording of information from all different tag brands (the Allflex app used would only record Allflex tags), as well as allowing a note to be entered next to each RFID. In this case the management tag number was recorded next to the RFID in the app.
Each person would call out the number so that everyone present could hear and ensure that everyone was at the same number. The person putting the management tag number in the ear would call out the number on the tag. The person scanning the cattle would then read out how many animals had been scanned. The bleeder would call out the number on the tube when they had finished bleeding and put the blood tube into an individually held compartment in a cardboard box (we used the old bruco boxes).
If at any stage one of the numbers did not match the other numbers, the recorder would call a stop to proceedings until the discrepancy was sorted out. Once a blood sample had been collected and put into the box it would be marked on the paper sheet with a small dash.
On the second day with 103 cattle to go a spare NLIS tag sitting on the table was accidentally scanned when the scanner was changed to being paired to the iPhone due to the battery being low on the iPad. This error meant that the process had to change slightly. A new session was started on the scanner. To ensure consistency of the data the person scanning cattle still shouted out the number of cattle scanned and then came up to the recorder and told them quietly the number of animals scanned on the new session. This information was then recorded on the paper key list.
As pre-arranged with the laboratory, a digital key list was required due to the large number of samples. The easiest way to generate this list was to download the data from the scanner. Due to the error of scanning a tag that was not in an animal the two sessions used had to be combined omitting the tag that should not have been there, which was the last tag in the first session. To ensure no transcription errors had occurred when placing the two lists together every 10th animal was checked via all the recorded means, that is the paper sheet and the data recorded on the app. As all entries matched up it was certain that the dataset was accurate.
Laboratory specimens collected at Deniliquin are usually sent via courier to EMAI at Menangle and then sent via a second courier to the regional vet lab in Benalla. However, due to the large number of samples and the concern about samples being lost it was arranged with the laboratory that the samples would be driven straight to Benalla by LLS staff as this laboratory is only a two-hour drive from Deniliquin. Completion of this task was coordinated by the lab at EMAI to ensure that everything was processed correctly.
Needle stick injury was suggested as a risk during this process so new sharps disposal containers with needle-removing lids were purchased for this job. Bleeders were instructed that caps should not be put in their mouths, there should be no recapping of needles and sharps should go straight into the sharps disposal containers using the needle-removing lids once blood collection was complete. No needle stick injuries occurred during this event.
Blood samples were tested in pools of two to decrease the cost to the producer. Samples from positive pools then need to be tested individually.
After the completion of blood testing, four animals with blood lead levels above the MRL were found with levels ranging from 0.34 µmol/L to 1.7 µmol/L.
Discussion
Planning for a large-scale bleeding operation of cattle is vital to ensure success. By approaching the event as an emergency exercise, it allowed thought to be put into the planning and logistics required to complete the task.
The number of staff needed for the job, the skills that staff members needed, and WHS requirements were identified prior to the start of the job. It was decided that only staff vaccinated for Q fever would handle cattle.
A learning from the day was that it would have been better to have a separate staff member in charge of the site who was not doing one of the other jobs. It was very difficult to manage the needs of staff such as knowing when bleeders needed to be rotated to a different job to have a bit of a break while also performing a role.
In general, more people to ensure the smooth flow of events would have made things easier. There were 10 people on the first day and 14 people for day two. Not everyone was there all day but day two flowed better even though some of the bleeders were a bit fatigued after day one. We also rotated the bleeding job more frequently on day two.
While induction of staff members to the site, the jobs and WHS requirements was managed well on the first day, it could have been improved on the second day when some staff members who had not been present on the first day arrived.
It had originally been assumed that staff could be trained to bleed cattle during the event but due to the hectic pace of events this training was not possible. Experienced bleeders did most of the bleeding. We had two bleeders going at a time, rotating for every second cow to help keep the pace. We trialled having three bleeders in the rotation but it didn't work so we went back to two. Staff who had some previous experience but had not bled for a while did some bleeding.
Some staff members were better suited to some jobs then others. Working out the couple of roles each staff member was well suited to and rotating them around those jobs meant things went more smoothly and improved the experience of the staff.
It worked well to have staff members that were about to take over a job watch the person before them do the job and have the person they were relieving explain what they needed to do in that job before they switched over.
Another learning was that a battery pack to charge one device would have made using the app easier rather than rotating devices. The charger in our emergency trailer we were using was not sufficient for the job.
The app would have been more useful in the situation where there were already uniquely numbered management tags. A digital key list could have been prepared from the csv file emailed from the app with the RFID and management tags listed with a paper copy serving as a backup. If you are using this app for data management, ensure that the function of emailing files is working prior to use.
The battery on the scanner held well and did not need to be charged.
I would also ensure spare NLIS tags were not in a location where they could be accidentally scanned.
Acknowledgements
The author would like to acknowledge the assistance of all the Murray Local Land Services staff who assisted with bleeding the cattle and Team Lead Mark Corrigan for his assistance in planning the event. I would also like to thank the manger of the cattle and their team for their assistance with bleeding the cattle. DPI residue coordinator Liz Bolin and Emily Stearman (at the time acting business partner for Animal Biosecurity & Welfare) were invaluable for their advice and experience in planning this event. I would also like to thank the laboratory staff who helped coordinate and do the lead testing.