SHEEP
FECRTs and Larval Count
Calculating the results
Helpful Hints & Tips
F AECAL EGG COUNTS FECs do not differentiate between different parasite species apart from Nematodirus . Eggs are allowed to hatch in the laboratory into larvae and identified to parasite species under a microscope. The FECRT may show that some parasites survived the drench but the larval culture is necessary to show which parasite species these are. • Sum the individual FECs from each group at Day 10-14 and divide by the number of lambs in the group to get a mean FEC for each group. • Use the formula below to calculate the % FEC reduction for each group.
• Weaning time is a good time to do a FECRT as commonly lambs have not been previously drenched. As it is early in the season, it is a good idea to do a couple of FECs before weaning to check that there are enough eggs in the lambs’ faeces to start the FECRT. Ideally you’d have an average of 500-700 epg with all lambs positive, but at least 300 epg is necessary (otherwise it’s unlikely to get good numbers of all worm species). • If the FECRT is done when the worm challenge is high and a control group is an animal welfare concern then this group should be removed from the test. The control group is a good source of information for the laboratory parasitologist when interpreting the results but it is not absolutely necessary. You can use the Day 0 results instead of the control at Day 10 in the calculations. • Make a call about courier reliability when planning the test. Doing Day 14 is easier so that samples can be sent in the week. Going a few days over day 14 is fine, you just may find some eggs in the levamisole group due to this drug not commonly killing immature worms. • The pasture that these lambs have previously grazed on is what is assessed. Don’t make assumptions about different parts of the property that lambs do not regularly graze and were not grazing on before Day 0. In other words, manage the group to sample the area of the farm you are interested in – lambing paddocks are a good representation usually. Keep them away from the quarantine paddock by the yards! • Day 0 can be made more efficient (and therefore the test more cost-effective) by the farmer pre-weighing and organizing the groups before the vet arrives. The same applies to Day 10-14. BUT they can’t yard the animals too early or it becomes harder to get faecal samples.
= Drench Group Mean FEC Day 10-14 Control Group Mean FEC Day 10-14
% FEC Reduction
x 100
PARASITE SPECIES LARVAL COUNTS A total larval count for each group is given with the % contribution of each parasite species to this total number.
• To get a parasite species larval count at day 10-14 for each group follow the calculation below.
Parasite Species % Composition
x Group Total Larval Count
100
• Then use the formula below to calculate the % larval count reduction for each parasite species in each group.
% Parasite Species Larval Count Reduction
= Drench Group Larval Count Day 10-14 Control Group Larval Count Day 10-14
x 100
Drench Check
A drench check is a quick way of looking at whether a certain drench is killing adequate numbers of parasites on a property. Follow all the instructions as per the FECRT but with only one group. A control group can be added for a more robust test. Check all drenching equipment is working well if not using a syringe to drench i.e. calibrate drench guns at the beginning and end of drenching at the least. If no control group is included substitute the Day 0 results for the Day 10-14 control into the calculations. Ensure drenches used for drench checks are relatively fresh, and well shaken. The quality of information out of a drench check depends on how well it is done!
Boehringer Ingelheim Animal Health New Zealand Ltd Product Guide 2022 13
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