Friday, July 22, 2016

Fecal Egg Count Reduction

Fecal egg counts from June 23-24 ranged from 0 to 21550 epg and averaged 1207 ± 3201 epg. The large standard deviation (almost 3x the mean) indicates there was tremendous variation in the fecal egg count data among the 96 goats that started the test.

The median egg count was only 100 epg, as most of the goats had very low initial egg counts.  In fact, only 17 goats had fecal egg counts >1000 epg. 2000 epg is considered to be of "clinical significance" for the barber pole worm. It is usually the cut-off for top-performing bucks in the test.

Fecal egg counts from July 7 ranged from 0 to 8550 and averaged 776 ± 1340 epg.  While the standard deviation wasn't as large as it was on June 23-24, it was still quite large (2x the mean), indicative of a similar wide variation in egg counts. Similar to June 23-24, the median egg count was only 129 epg on July 8, with only twenty-three goats having egg counts >1000 epg.

Upon arrival, the goats were sequentially dewormed with albendazole (Valbazen®), moxidectin (Cydectin®), and levamisole (Prohibit®). The purpose of the sequential dosing was to reduce fecal egg counts to (near) zero, so that all goats started the test equally and that differences observed in the test can be attributed to genetics and not environment. In recent years, the sequential dosing has become less effective at zeroing out egg counts.

The effectiveness of an anthelmintic treatment is determined by the fecal egg count reduction (FECR) test. Pre- and post treatments are compared. FECR = [FEC1 (pre-treatment) - FEC2 (post-treatment)] ÷ FEC1 (pre-treatment) x 100.  An effective treatment should reduce fecal egg counts by 95 percent or more.  Below 80%, there is significant anthelmintic resistance.

FECR varied significantly among goats and consignments. Treatment was quite effective on some goats and in some consignments. In other goats and consignments, it was ineffective, as fecal egg counts increased substantially (in some goats) or failed to be reduced significantly after treatment (in others). The average FECR for the 96 goats in the test is not meaningful, as it is skewed by some very large increases in fecal egg count.

Treatment seemed to be most effective in goats that had high egg counts. Of the seventeen goats that had initial fecal egg counts >1000 epg, the average FECR was 86%. It increases to 91% if the least effective treatment (1% FECR) is removed from the data set.

  ID    Pre-treatment FEC     Post-treatment FEC    % FECR 
608 13550 100 99
609 3633 485 87
610 2457 400 84
612 3500 150 96
619 1875 433 77
626 5925 0 100
627 2825 0 100
629 1533 300 80
630 4525 900 80
635 1600 33 98
645 4300 267 94
655 3475 3450 1
686 4857 1533 68
691 14425 200 99
696 3475 125 96
697 21550 120 99
698 1050 0 100

FECR could not be calculated if a goat was missing a fecal sample from either June 23-24 or July 7 or if its fecal egg count on June 23-24 was 0.  A pre-treatment fecal egg count <150-200 epg is not considered very accurate for FECR. In fact, some parasitologists prefer egg counts >350 epg for FECR calculations.

 Of concern is the consignments in which egg counts increased significantly or failed to be reduced significantly by the sequential dosing. This suggests resistance to all anthelmintics on those farms.

Download Fecal Egg Count Reduction Report