Evaluating the Presence and Depletion of Residual Ivermectin in Milk Following Subcutaneous Injections on Lactating Cows

Abstract

Dairy farming industry in Kenya has experienced significant growth due to the rising consumption of milk and dairy products. Consequently, to improve output,
veterinary drugs were administered prophylactically and/or therapeutically to dairy cattle. Commonly used drugs included beta-agonists, anthelmintics, antibiotics, and steroid hormones. Parasitic diseases more so tick infestations hindered production. Chemical methods were primarily used in tick management however, the technique proved expensive and developed resistance. Conversely, ivermectin effectively controlled ecto- and endoparasites in livestock, hence gaining popularity in tick management. Nonetheless, its residues accumulated in animal tissues, rendering it unacceptable on animals that produced milk for human use. Apparently, farmers in tick-infested areas in Nyandarua County, Kenya used ivermectin, but there lacked adequate evidence to show that it occurred in milk. Thus, this study examined the performance of Liquid Chromatography tandem mass spectrometry (LC-MS-MS) in order to analyse the presence and depletion pattern of ivermectin residues after it excreted in cow milk following subcutaneous treatment of dairy cows. Between day 0.5 and day 57 following treatment, 24 milk samples were purposefully collected and stored at -20°C.. The samples were prepared using QuEChERS, a solid-phase extraction technique.
Further, positive Electrospray ionization (+ESI) LC-MSMS qualitative analysis identified a precursor ion with the mass number of m/z 897.5 and corresponding product ions—m/z 897.5 > 329, m/z 897.5 > 240, and m/z 897.5 > 183—within a retention time of 8.782-8.858 (mean = 8.362±0.002) minutes. The solvent and matrixmatched calibration curves displayed satisfactory linearity with r=0.998 and 0.993 as their respective correlation coefficients. Additionally, the limit of detection was 2.5 ng/ml and limit of quantification reached 10 ng/ml. The analyte recovery ranged from 74.977% to 101.435%, within satisfactory limits. Hence, ivermectin residues were quantified in milk samples from the 0.5th to 17th day. The highest concentration (60.90±0.98 ng/ml) was observed on 2nd day. No traces of the residue were detected beyond day 18 and as a result, the study recommends a withdrawal period of 18days after subcutaneous ivermectin treatment. It is therefore important to perform further research on other dairy and animal products that people consume.