Occurrence of Ivermectin Residue in Cow Milk after Subcutaneous Treatment and Ticks Susceptibility to Acaricides in Nyandarua County, Kenya
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Date
2020-09
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Publisher
Kenyatta University
Abstract
Kenya's dairy farming has grown to meet the country's high milk demand. However,
parasitic infestation, more so ticks greatly hinders production in this industry. To
improve production, veterinary drugs (VDs) have been used for therapeutic and
prophylactic purposes to increase production. Frequently used VDs in dairy cows
include beta-agonists, anthelmintics, antibiotics, and steroid hormones. The primary
chemical control methods for ticks are associated with food safety, high costs, and the
emergence of resistance. There has been a great concern about the use of Ivermectin
(IVM), an antiparasitic drug that is effectively used against ecto- and endoparasites in
livestock. IVM accumulates and persists in animal tissues, hence restricted for use after
calving of animals whose milk is meant for human consumption. Despite reports of
ivermectin residues used for tick control in regions where dairy production is highly
practiced. There is limited information on the presence of ivermectin residues in cow
milk in Kenya. Therefore, it was important to conduct an analysis on cow milk in
Nyandarua County, Kenya, to evaluate the presence of IVM residues and to ascertain
whether ticks were susceptible to acaricides. One hundred and forty-nine (149) milk
samples were obtained by purposeful sampling. Twenty-four (24) samples were
collected post-treatment from days 0.5 to 57. Tick samples were also collected before
treatment. Milk samples were analyzed using quick, easy, cheap, effective, rugged, and
safe (QuEChERS), a multi-residue dispersive solid-phase extraction method coupled
with Liquid Chromatography with tandem mass spectrometry (LC-MS-MS). For
qualitative analysis, a retention time between 8.782 and 8.858 (X̅= 8.362±0.002)
minutes allowed the identification of the m/z 897.5 as the precursor ion and 3 product
ions m/z; 897.5 > 329, 897.5 > 240, and 897.5 > 183. The method performance
demonstrated a linearity of r=0.998 and 0.993 for solvent and matrix-matched
calibration curves, respectively as well as a precision of 0.081 and 10.419 on retention
time and recovery, respectively. The percentage recoveries for blank samples spiked
with 10 ng/ml ranged from 74.977 % to 101.435 % with LOD=2.5 ng/ml and LOQ=10
ng/ml, all within satisfactory limits. The IVM was detected in milk from day 0.5 to 17
with the highest mean concentration recorded on day 2 (60.90±0.98ng/ml) post treatment. Residue was detected in 55.84 % (n = 77) and 29.87 % (n=48) of samples
taken from farms and markets, respectively. Residue levels in raw, boiled, and diluted
samples indicated no significant difference in residue concentrations between raw and
boiled milk samples since fcalc (0.011) < f crit (4.196), while two-factor analysis indicated
fcal (11.510) > f crit (2.4837) because of depletion of IVM with time. Although diluting
raw samples once and twice reduced residue concentration since fcal (16.446) > fcrit
(4.196), and fcal (67.240) > fcrit (4.196) respectively, there was no significant difference
observed between single and double diluted samples since fcal (1.671) < fcrit (2.424).
Amitraz, chlorpyrifos, cypermethrin, and a mixture of (chlorpyrifos: cypermethrin)
were widely used for control of ticks in this region. R. appendiculatus recorded
resistance of between 6% and 45% to all tested acaricides, showing susceptibility. B.
decoloratus showed 45%, 85%, 50% and 64% resistance for combined treatment,
chlorpyrifos, amitraz, and cypermethrin, respectively. It was demonstrated that IVM
residues persisted for 17 days in milk, and neither boiling nor dilution degraded it, and
the two methods therefore may not be considered a safety precaution against consuming
IVM-contaminated milk. Additionally, there was evidence of emerging resistance to
cypermethrin and amitraz. Besides, the efficacy of these acaricides can be preserved
with better management, ultimately resulting in the suppression of cattle ticks.
Description
Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Master of Science (Analytical Chemistry) in the School of Pure and Applied Sciences of Kenyatta University, September 2024
Supervisors:
1. Henry Mwangi
2. Margaret Mwihaki Ng’ang’a