Has the optimum time for faecal nematode egg count reduction testing in sheep in New Zealand changed?

Aim: To determine what, if any, changes have taken place in the optimum time, for undertaking faecal egg count reduction tests (FECRT) in sheep in New Zealand.

Methods: A comparison was made between the numbers and types of nematode genera adequately represented for testing purposes (faecal nematode egg count (FEC) of ≥50 epg) in initial FECRT case submissions to a veterinary laboratory in New Zealand, during two 4-year periods, in 1992-1995 and 2006-2009.

Results: Although there were some minor differences between them, the seasonal patterns of occurrence remained basically the same for all parasite genera in both datasets, with their individual peak periods of representation occurring during February to May in all instances. Not surprisingly, this period of maximum seasonal occurrence for each parasite genus also coincided with those months of the year when the greatest numbers of worm genera were adequately represented for faecal nematode egg count reduction (FECR) testing.

Conclusions: The results of this study indicate that the optimum time for conducting FECRT in sheep in New Zealand continues to be during the late summer-autumn months of February to May. However, they also reaffirmed that even during this optimal period there are still likely to be many occasions when relatively few nematode genera may be sufficiently well represented for satisfactory FECR testing. Accordingly, veterinary practitioners ought to be aware that, in order to obtain a complete picture of the resistance status of all worm genera on a particular property, such testing may need to be carried out on more than one occasion.