Increasing mercury bioaccumulation and biomagnification rates of Nile perch (Lates niloticus L.) in Winam Gulf, Lake Victoria, Kenya.

The Nile perch (Lates niloticus L.) commercial fishery for Lake Victoria in East Africa is an important source of revenue and employment. We focused on shifts in food web structure and total mercury (THg) bioaccumulation and biomagnification in Nile perch, and lower food web items collected from Winam Gulf (Kenya) sampled 24 years apart (1998 and 2022). Stable isotope carbon (δ13C) values were higher in all species from 2022 compared to 1998. Stable nitrogen isotope (δ15N) values in baseline organisms were lower in 2022 compared to 1998. In Nile perch, δ15N values were correlated with total length, but the δ15N-length regressions were steeper in 1998 compared to 2022 except for one large (158 cm) Nile perch from 1998 with an uncharacteristically low δ15N value. Total Hg concentrations were lower in lower trophic species from 2022 compared to 1998. However, the THg bioaccumulation rate (as a function of fish length) in Nile perch was greater in 2022 compared to 1998 resulting in 24.2 % to 42.4 % higher wet weight dorsal THg concentrations in 2022 Nile perch for market slot size (50 to 85 cm) fish. The contrasting observations of increased THg bioaccumulation with size in 2022 against decreases in the rate of trophic increase with size and lower THg concentrations of lower food web items imply reduced fish growth and potential bioenergetic stressors on Winam Gulf Nile perch. All samples except 1 large Nile perch (139 cm total length collected in 2022) had THg concentrations below the European Union trade limit (500 ng/g wet weight). However, for more vulnerable individuals (women, children and frequent fish eaters), we recommend a decrease in maximum monthly meal consumption for 55-75 cm Nile perch from 16 meals per month calculated for 1998 to a limit of 8 meals per month calculated for 2022.

Antibiotic Residues in Milk from Three Popular Kenyan Milk Vending Machines.

Milk vending machines (MVMs) are growing in popularity in Kenya and worldwide. Milk vending machines dispense varying quantities of locally sourced, pasteurized milk. The Kenya Dairy Board has a regulatory framework, but surveillance is weak because of several factors. Milk vending machines' milk is not routinely screened for antibiotics, thereby increasing potential for antibiotic misuse. To investigate, a total of 80 milk samples from four commercial providers (N = 25), street vendors (N = 21), and three MVMs (N = 34) were collected and screened in Eldoret, Kenya. Antibiotic residue surveillance occurred during December 2016 and January 2017 using Idexx SNAP® tests for tetracyclines, sulfamethazine, beta-lactams, and gentamicin. Overall, 24% of MVM samples and 24% of street vendor samples were presumably positive for at least one antibiotic. No commercial samples were positive. Research into cost-effective screening methods and increased monitoring by food safety agencies are needed to uphold hazard analysis and critical control point for improving antibiotic stewardship throughout the Kenyan private dairy industry.

Effect of mastitis on raw milk compositional quality.

In this study, we investigated the impact of mastitis infection on the quality of milk composition in small-scale dairy bovine herds. The purpose of this study was to find a milk quality somatic cell count (SCC) standard that could be used as an integral component of a control program. In all, 396 quarter milk samples from lactating cross-bred cows (Holstein & Zebu) were analyzed; 56% of these quarters were experiencing intramammary infection, with an overall mean SCC of 5.46 x 10(5) +/- 2.30 x 10(4)cells/ml. Infected quarters had significantly (p < 0.05) higher mean SCC levels (6.19 x 10(5) +/- 4.40 x 10(4)cells/ml) compared to healthy quarters (2.65 x 10(5) +/- 2.40 x 10(4)cells/ml). In high SCC milk and infected quarters, the concentrations of non-casein fractions, sodium, chloride, and free fatty acid were higher (p < 0.05), while the casein content, lactose, casein-to-total protein, potassium, and calcium were lower (p < 0.05) compared to normal quarters. These findings suggest a mean SCC threshold limit of 5.46 x 10(5)cells/ml for the region. It was concluded that the results could be used to propose a milk quality SCC standard that can be used as an integral component of a control program.

Evaluation of a Bacillus stearothermophilus tube test as a screening tool for anticoccidial residues in poultry.

A Bacillus stearothermophilus var. calidolactis C953 tube test was evaluated for its ability in detecting the residue of selected anticoccidial drugs in poultry, specially sulfamethazine, furazolidone, and amprolium. Various concentrations of each drug were injected into chicken liver and kidney tissues and these tissues were tested to determine the drug detection limits for each drug. The detection limit was defined as the drug concentration at which 95 % of the test results were interpreted as positive. The limits of detection in liver tissue were 0.35 microgram/ml for furazolidone, 0.70 microgram/ml for sulfamethazine and 7.80 microgram/ml for amprolium. In kidney tissues, they were 0.30 microgram/ml for furazolidone, 0.54 microgram/ml for sulfamethazine, and 7.6 microgram/ml for amprolium. It was concluded that this tube test could be used to screen for the residue of these three drugs in poultry.

Assessment of the California mastitis test usage in smallholder dairy herds and risk of violative antimicrobial residues.

This study evaluated how predictive the California Mastitis Test (CMT) is for sub-clinical mastitis under tropical smallholder dairy production conditions in Kenya. It intended to establish whether the CMT usage could be contributing to misdiagnosis and consequent mistreatment with animal drugs resulting in residue problems. Milk samples (n = 239) were aseptically collected from lactating cows in the Rift Valley of Kenya and tested using the CMT, somatic cell counts (SCC) and bacterial culture. The samples were also screened for violative drug residues using the commercial delvo test and compared to the milks mastitic status for possible association. There was a numerical but non-significant (p > 0.05) difference evident in the frequencies observed using the three different mastitis indicators. The prevalent bacterial species isolated from mammary glands with subclinical mastitis were Staphylococcus aureus (45.6%), coagulase-negative Staphylococci (13.0%), Streptococci (11.7%) and Escherichia coli 5.9%. There was an overall poor but significant (p < 0.05) correlation between the CMT and the violative antimicrobial residues in samples from all quarters, infected and non-infected respectively. The results suggest that the CMT use amongst the smallholder dairy sector as a mastitic indicator may not be a risk factor in violative antimicrobial residues problems in milk.

Factors contributing to the occurrence of antimicrobial drug residues in Kenyan milk.

The study investigated factors contributing to the occurrence of antimicrobial drug residues in milk within four major milk production districts in Kenya. The frequency of contamination was studied among small- and large-scale dairy producers to determine if there were differences between the two types of producers. Field samples (n = 1,600) were analyzed with the improved Dutch tube diffusion test, a microbial inhibitor test (Bacillus stearothermophilus). In total, 144 and 64 samples from small- and large-scale producers, respectively, were found to contain beta-lactam antibiotics at levels exceeding the established Codex maximum residue level for penicillin G (4 microg/kg). The difference in results between the two categories of producers was found to be significant (P < 0.001). To explain the higher frequency of antibiotic contamination of milk from small-scale producers, a questionnaire was constructed and used with 220 randomly selected smallholders in the selected districts. The results suggested (i) lack of understanding of risks related to antibiotic contamination of food, (ii) poor or no treatment records, and (iii) lack of a monitoring system as major risks for contamination. It was concluded that intensification of the education among small-scale dairy producers would greatly reduce the occurrence of antimicrobial residues in milk.