ABSTRACT
Objective
Our objective was to determine whether parasite resistance to extended-release eprinomectin
was present in an operation after 3 yr of eprinomectin use.
Materials and Methods
Fall-born Angus × Simmental heifers (224 ± 22 d of age; 171 ± 17.8 kg initial BW)
were stratified by d −2 fecal egg count (FEC) and BW and assigned to 1 of 9 groups
(7 heifers per group). Groups were then assigned to 1 of 3 treatments: extended-release
eprinomectin (ERE; n = 3), extended-release eprinomectin and oxfendazole (ERE+O; n
= 3), or saline control (CON; n = 3). Throughout the experiment, FEC and packed cell
volume were evaluated 6 times, and a fecal egg reduction test was conducted on d 28.
Results and Discussion
There was a treatment × time interaction (P < 0.01) for FEC as FEC was not different on d −2 and 28. However, CON had greater
FEC than ERE and ERE+O on d 55 and 83. Additionally, at d 55 ERE had greater FEC than
ERE+O. On d 112 and 167, FEC was similar among all treatments. Fecal egg reduction
for ERE and ERE+O were above the 90% threshold (91 and 98% reduction, respectively).
There was no treatment × time interaction or treatment effect (P ≥ 0.14) for packed cell volume.
Implications and Applications
Based on the fecal egg reduction test (>90%), parasite resistance was not present
in an operation after 3 yr of use of extended-release eprinomectin.
Key words
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Article info
Publication history
Accepted:
May 8,
2020
Received:
February 27,
2020
Footnotes
Boehringer Ingelheim provided funding for this research. The authors declare no conflicts of interest.
Identification
Copyright
© 2020 American Registry of Professional Animal Scientists. Published by Elsevier Inc. All rights reserved.
