Determination of lasalocid residues in the tissues of broiler chickens by liquid chromatography-tandem mass spectrometry

Lasalocid is a polyether ionophoric coccidiostat used for the prevention of coccidiosis in poultry at a prescribed concentration and during a certain time interval. Due to a public health concern about the presence of coccidiostat residues in poultry, the aim of the present study was to determine the levels of lasalocid residues in the edible tissues of broiler chickens (breast muscle, thigh muscle, heart, liver, gizzard, kidneys and skin/fat) fed commercially produced feed containing 100?mg?kg^?1 of lasalocid in complete feed throughout the 5-day withdrawal period (WP). The residues were investigated by liquid chromatography coupled with electrospray ionisation (ESI) tandem mass spectrometry (MS/MS) with triple quadrupole. The limit of detection (LOD) and the limit of quantification (LOQ) of the method were 0.47 and 1.44?µg?kg^?1, respectively. The average recovery based on the matrix-fortified calibrations for chicken tissues ranged between 79% and 98%. Lasalocid was found to accumulate in the liver, followed by the heart, skin/fat, kidneys, thigh muscle and gizzard. The lowest concentrations of lasalocid residues were found in the breast muscle. On day 5 of the WP, residue concentrations of lasalocid did not decline below the LOQ of the method, but were far below the maximum residue level (MRL) established for lasalocid in poultry from 20 to 100?µg kg^?1 by European Commission Regulation (EU) No. 37/2010. The results confirmed that the WP established for lasalocid is sufficient to ensure the decline of its residues in the tissues of broiler chickens to the safe residue level.     

Determination of lasalocid residues in the tissues of broiler chickens by liquid chromatography-tandem mass spectrometry

Lasalocid is a polyether ionophoric coccidiostat used for the prevention of coccidiosis in poultry at a prescribed concentration and during a certain time interval. Due to a public health concern about the presence of coccidiostat residues in poultry, the aim of the present study was to determine the levels of lasalocid residues in the edible tissues of broiler chickens (breast muscle, thigh muscle, heart, liver, gizzard, kidneys and skin/fat) fed commercially produced feed containing 100?mg?kg?1) of lasalocid in complete feed throughout the 5-day withdrawal period (WP). The residues were investigated by liquid chromatography coupled with electrospray ionisation (ESI) tandem mass spectrometry (MS/MS) with triple quadrupole. The limit of detection (LOD) and the limit of quantification (LOQ) of the method were 0.47 and 1.44?μg?kg?1, respectively. The average recovery based on the matrix-fortified calibrations for chicken tissues ranged between 79% and 98%. Lasalocid was found to accumulate in the liver, followed by the heart, skin/fat, kidneys, thigh muscle and gizzard. The lowest concentrations of lasalocid residues were found in the breast muscle. On day 5 of the WP, residue concentrations of lasalocid did not decline below the LOQ of the method, but were far below the maximum residue level (MRL) established for lasalocid in poultry from 20 to 100?μg kg?1 by European Commission Regulation (EU) No. 37/2010. The results confirmed that the WP established for lasalocid is sufficient to ensure the decline of its residues in the tissues of broiler chickens to the safe residue level.     

Detection of maduramycin residues in the tissues of chickens and pheasants by the screening test for antibiotic residues (STAR)

Maduramycin is a coccidiostat authorized as a feed additive in poultry. Council Directive 96/23/EC stipulates that monitoring of foods of animal origin for residues of coccidiostats is mandatory. The aim of the present study was to evaluate the STAR for the screening of maduramycin residues in the tissues of broiler chickens and pheasants. Both animal species were supplied feed medicated with Cygro l% premix according to recommendations for use (5 mg kg(-1) of complete feed). The residues were investigated for a period of 7 days: day 0 (the last day of the administration of maduramycin), days 1-5 (the days of the withdrawal period) and day 6 (the first day after elapse of the withdrawal period). According to STAR the positivity of the sample (the presence of residues of antibacterial substances) is indicated by a zone of inhibition exceeding 2 or 4 mm in width, depending on the test organism. Maduramycin residues were detected only on the plates seeded with the test organism Bacillus stearothermophilus var. calidolactis ATCC 10149. The results showed that there was higher potential for the presence of maduramycin residues in broiler chickens than in pheasants. All chicken tissues (muscle/thigh and breast/gizzard, liver, heart, kidneys, spleen, lungs) were positive for maduramycin (inhibition zones ≥4 mm) not only throughout the withdrawal period, but also even 5 days after elapse of the withdrawal period. In the case of pheasants the positive results were detected in the gizzard, liver, heart, kidneys, spleen and lungs. On day 5 of the withdrawal period no positive results were detected; however, on day 6 the heart and spleen were positive again.     

Doxycycline and sulfadimethoxine transfer from cross-contaminated feed to chicken tissues

During feed preparation at feed mills or during feed mixing in bins at farms, the accidental contamination of feed at trace levels by veterinary drug residues, commonly known as carry-over, can accidentally but frequently occur. To evaluate the concentrations of residual antimicrobials in poultry edible tissues, due to contaminated feed, sulfadimethoxine and doxycycline were administered for 10 days to chickens in poultry feed incurred at the contamination levels frequently found during national feed monitoring programmes (1–5?mg?kg^?1). Sulfadimethoxine and doxycycline residual concentrations detected in muscle (<LOD and 31?µg?kg^?1, respectively), liver (13 and 56?µg?kg^?1, respectively) and kidney (56 and 115?µg?kg^?1, respectively) were compared with their maximum residue limits (MRLs) fixed by EC 470/2009 and EU 37/2010 Regulations for a preliminary risk evaluation.     

Distribution of semduramicin in hen eggs and tissues after administration of cross-contaminated feed

Semduramicin is an ionophore coccidiostat used in the poultry industry as a feed additive. Cross-contamination of feeds for non-target animals with semduramicin is unavoidable. However, it is not known whether undesirable residues of semduramicin may occur in food after cross-contaminated feed is administered to animals. The aim of the work was to determine the levels of semduramicin in hen eggs (yolks and albumen) and tissues (liver, muscle, spleen, gizzard, ovarian yolks and ovaries) after administration of feed contaminated with 0.27 mg kg^?1 of this coccidiostat. The residues were determined using LC-MS/MS. The distribution pattern confirmed the high lipophilicity of semduramicin. Residues were found mainly in egg yolks (28.8 µg kg^?1), ovarian yolks (19.5 µg kg^?1) and liver (2.57 µg kg^?1), while hens’ muscle was free from semduramicin (LOD = 0.1 µg kg^?1). Among edible tissues, the maximum level (2 µg kg^?1) was exceeded only in the liver.     

Determination of halosulfuron-methyl residues and dissipation in wheat by QuEChERS and LC-MS/MS

A sensitive and rapid analytical method based on QuEChERS (quick, easy, cheap, effective, rugged and safe) sample preparation and LC-MS/MS detection was developed for the analysis of halosulfuron-methyl residues in wheat. The recoveries of halosulfuron-methyl in both the wheat plant and grain ranged from 87% to 119% and from 75% to 97%, respectively, with relative standard deviations (RSDs) of 3–9%. The limit of quantification (LOQ) was 0.005 mg kg^?1 for wheat plant and 0.001 mg kg^?1 for wheat grain. The half-life of halosulfuron-methyl in the wheat plant was 0.9–9.5 days. The terminal residue levels of halosulfuron-methyl in wheat grain were below 0.01 mg kg^?1 at harvest.     

Deposition and depletion of maduramicin residues in eggs after oral administration to laying hens determined by LC-MS

The coccidiostat maduramicin has been approved as a feed additive for chickens and turkeys, although it is prohibited for use in laying hens. In the present study, laying hens were divided into three groups and fed for 14 days with medicated feed containing maduramicin, at three different concentrations: 50, 100 and 500 µg kg^?1. Eggs were collected during treatment and for 26 days after the end of feeding with medicated feed. Maduramicin residues were found exclusively in egg yolk, with the highest concentration in egg yolk of 459 µg kg^?1 for the highest dose. The maximum concentration of maduramicin in whole egg was 16.6 µg kg^?1 for the group receiving feed containing the maximum permitted level of maduramicin in feed (50 µg kg^?1). The half-life of elimination of maduramicin, calculated for post-treatment days 1–10, was 6.5 days. Twelve days after drug administration, the concentration of the maduramicin in egg yolk for Group 3 (fed with 500 µg kg^?1 maduramicin) still exceeded 20 µg kg^?1, while the concentrations for Groups 1 and 2 were 1.2 and 2.7 µg kg^?1, respectively.     

Bioaccumulation of cyanuric acid in edible tissues of shrimp following experimental feeding

Due to concerns that cyanuric acid (CYA)-contaminated feed had been used in aquaculture and could enter the human food chain, a method to quantify CYA residues in the edible tissues of fish and shrimp was previously developed and validated. This paper provides further data on the deliberate feeding of CYA to shrimp to determine the extent of residue accumulation in edible tissue. Liquid chromatography–tandem mass spectrometry (LC–MS/MS) was employed for the analysis of CYA in shrimp tissue. Edible tissue of shrimp fed 1666 or 3333?mg?kg^?1 CYA in their diet (approximately 55 and 124?mg?kg^?1 body weight) contained 0.767 and 0.406?mg?kg^?1 CYA, respectively. The residue levels are below the World Health Organization (WHO) tolerable daily intake level for CYA and are generally considered unlikely to pose a human health risk.     

Assessing the depletion of lincomycin in feathers from treated broiler chickens: a comparison with the concentration of its residues in edible tissues

ABSTRACT

Lincomycin is the first antimicrobial agent described for the lincosamide class and it is commonly used for the treatment of infectious enteric and respiratory diseases in poultry. Maximum residue limits (MRLs) in edible tissues have been established for this antimicrobial, however, no regulation has been proposed yet for by-products that are not intended for direct human consumption. Feathers are a by-product from poultry farming that might be used as an ingredient for diets fed to other farm animal species. The presence of antimicrobial residues in them is not monitored in spite of the fact that several studies have proved that they can persist in feathers. Currently though, no evidence has been presented regarding the behaviour of lincomycin in this matrix. Hence, this work intended to assess the depletion of lincomycin residues in feathers of birds treated with therapeutic doses and compare them with those detected in muscle and liver samples. Samples were collected for several days after ceasing treatment from a group of broiler chickens treated with a 25% lincomycin formulation. Methanol and Florisil® columns were used to extract and retain the analyte, and samples were analysed using a triple quadrupole mass spectrometer (API 5500, AB SCIEX?). On day 1 after ceasing treatment, average concentrations of lincomycin detected in feather samples reached up to 8582 μg kg^?1 and by day 16, these had only declined by 63%, to an average of 3138 μg kg^?1. Lincomycin residues were detected in feathers at every sampling point, even after they were not detectable in edible tissues. Depletion time was 98 days for feathers, considering the LOQ established for the methodology as cut-off value for the calculations. Data showed that lincomycin is highly persistent in feathers, which may result in this matrix becoming a re-entry route for its residues into the food chain.     

The decrease of lasalocid residue in the edible tissues by silymarin supplementation of chicken diet

Widespread use of coccidiostats, in spite of beneficial control of protozoan infections in poultry, implies a risk of residues in edible tissues, and there is increasing interest in the development of strategies for prevention of veterinary drugs residue in food-producing animals. The aim of this study is assigned to clarify the impact of silymarin addendum in the diet on lasalocid concentration in the liver and breast muscles from the broiler. Four groups of chickens received a feed with lasalocid at levels between 75 and 200 mg kg^?1. Other four groups received a feed with lasalocid (75–200 mg kg^?1) plus silymarin. Significant differences of lasalocid concentrations between the liver and breast muscles were observed. Moreover, the chickens from the groups supplemented with silymarin shown significant decreases of lasalocid concentrations in the analysed tissues. The herbal substance did not counteract the ionophore in the treatment of coccidiosis and did not change biochemical parameters of blood. These findings suggest that silymarin might be used in chicken feeding in order to reduce the risk from lasalocid contamination of the broiler edible tissues.     

In-house validation of an ELISA method for screening of semicarbazide in eggs

An enzyme-linked immunosorbent assay (ELISA) method is described for the semi-quantitative determination of semicarbazide (SEM), the marker residue for the banned nitrofuran drug, nitrofurazone, in chicken eggs. The sample homogenate is subjected to acid hydrolysis and derivatisation with o-nitrobenzaldehyde, followed by ethyl acetate/hexane extraction and detection by ELISA. The ELISA procedure has been validated using 0.3, 1.0 and 3 µg kg^?1 of SEM in fortified samples. Detection capability (CC_ß) was based on the acceptance of 5% false compliant results for a given concentration level according to Commission Decision 2002/657/EC and was determined to be 0.3 µg kg^?1 with a respective limit of detection of 0.13 µg kg^?1. A validated LC–MS/MS method was used for the analysis of incurred egg samples and the results compared with ELISA. A good correlation between the results obtained from ELISA and LC–MS/MS within the concentration range 0.12–20.3 µg kg^?1 was observed in samples collected from chickens fed with a medicated ration of nitrofurazone (r?=?0.992, n?=?14). Validated ELISA enabled reliable monitoring of SEM levels in eggs collected from incurred chickens over a 90-day period.     

Fungal and bacterial metabolites in commercial poultry feed from Nigeria

Metabolites of toxigenic fungi and bacteria occur as natural contaminants (e.g. mycotoxins) in feedstuffs making them unsafe to animals. The multi-toxin profiles in 58 commercial poultry feed samples collected from 19 districts in 17 states of Nigeria were determined by LC/ESI–MS/MS with a single extraction step and no clean-up. Sixty-three (56 fungal and seven bacterial) metabolites were detected with concentrations ranging up to 10,200?µg?kg^-1 in the case of aurofusarin. Fusarium toxins were the most prevalent group of fungal metabolites, whereas valinomycin occurred in more than 50% of the samples. Twelve non-regulatory fungal and seven bacterial metabolites detected and quantified in this study have never been reported previously in naturally contaminated stored grains or finished feed. Among the regulatory toxins in poultry feed, aflatoxin concentrations in 62% of samples were above 20?µg?kg^?1, demonstrating high prevalence of unsafe levels of aflatoxins in Nigeria. Deoxynivalenol concentrations exceeded 1000?µg?kg^?1 in 10.3% of samples. Actions are required to reduce the consequences from regulatory mycotoxins and understand the risks of the single or co-occurrence of non-regulatory metabolites for the benefit of the poultry industry.     

Evaluation of three different microbial inhibition tests for the detection of sulphamethazine residues in the edible tissues of rabbit

The aim of the present study was to evaluate three microbial inhibition tests (MIT) based on inhibition of growth of the test organisms: (a) four plate test (FPT) containing Bacillus subtilis BGA, (b) screening test for antibiotic residues (STAR) containing Bacillus stearothermophilus var. calidolactis_ATCC 10149 and (c) the Premi®Test containing Bacillus stearothermophilus var. calidolactis. The tests were used to determine sulphamethazine (SMZ) residues in edible tissues of rabbit after oral administration up to day 15 of the withdrawal period (WP). A solvent extraction procedure was used to enhance the capability of the tests to detect SMZ residues at or below the maximum residue limit (MRL). Para-aminobenzoic acid (PABA) was employed to previously identify SMZ residues in the first stage of the residue screening. The presence of SMZ residues in the samples was confirmed and quantified by a validated HPLC method. The Premi®Test detected SMZ residues in the muscle and heart tissue up to day 9 of the WP, and in the liver, lungs and kidneys up to day 10 of the WP. The STAR detected SMZ residues in the edible organs of rabbits up to day 8 of the WP. The kidneys were positive up to day 5 of the WP, the liver until day 4 of the WP and the lungs until day 3 of the WP. No SMZ residues were detected in the muscle and heart. By using the solvent extraction procedure, SMZ residues were detected in the muscle extract up to day 10 of the WP and the muscle was positive until day 6 of the WP. No detection sensitivity was observed using the FPT. After solvent extraction, SMZ residues were detected in the muscle extract until day 8 of the WP and the muscle was positive until day 3 of the WP. No positive results were detected after the addition of PABA into/onto the agar medium. PABA at a concentration of 10 µg ml^?1 completely reversed the inhibitory activity of SMZ and enabled reliable identification of SMZ in the examined samples. Using HPLC, SMZ was detected in the muscle samples until day 10 of WP (0.02 mg kg^?1) and in the liver until day 12 of the WP (0.09 mg kg^?1). The results obtained by the HPLC method and the limit of detection (LOD) of screening tests for SMZ (FPT 0.4 µg ml^?1, STAR 0.2 µg ml^?1, Premi® Test 0.05 µg ml^?1) allowed us to state that the most suitable screening tests for the detection of SMZ residues in the edible tissues of rabbits at level corresponding to the MRL of 0.1 mg kg^?1, established for sulphonamides, are the Premi®Test and STAR in conjunction with the solvent-extraction procedure.     

Development and validation of multi-residue method for determination of 412 pesticide residues in cotton fiber using GC-MS/MS and LC-MS/MS

The new global concept is to care about textiles and clothes safety to improve the protection of the human health and the environment from the harmful pesticide residues. Very few articles have been published for determination of several pesticide classes in cotton fibers in one multi-residue method. A simple, efficient, sensitive, accurate, and reliable multi-residue method was developed for the determination of 412 residual pesticides in cotton fibers using modified QuEChERS method with Liquid and Gas Chromatography coupled to Triple Quadrupole Mass Spectrometer (LC-MS/MS &; GC-MS/MS) for qualitative and quantitative analysis according to the international standards concepts. The developed method covered several pesticide classes, including 43 carbamates, 16 pyrethroids, 27 organochlorines (OCs), 54 organophosphorus (Ops), 31 urea derivatives, 7 Polychlorinated biphenyl (PCBs), 6 Neonicotinoid, and 228 other pesticides. Most of the target pesticides were listed in Oeko-Tex Standards, the EU Ecolabel for textile products, and the Egyptian recommendations of the Agricultural Pesticide Committee (APC-Egypt). The method optimization and validation were carried out according to the EU guidelines. The results were shown to be reliable where the corresponding average recoveries within the acceptable range of 70–120%; the relative standard deviations were less than 20%. The limit of quantitation (LOQ) of this method is 0.01 mg kg^?1 all pesticides except for 3 GC-compounds and 19 LC-compounds which have LOQ of 0.05 mg kg^?1.     

Pilot survey of hen eggs consumed in the metropolitan area of Rio de Janeiro,Brazil, for polyether ionophores,macrolides and lincosamides residues

A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method, which has recently been developed and validated, was used for the identification and quantification of polyether ionophore, macrolide and lincosamide residues in commercial eggs sold in the metropolitan area of Rio de Janeiro, Brazil. The method was applied to 100 samples and the results showed a high incidence of polyether ionophore residues (25%). Salinomycin was detected in 21% of samples, but only two non-compliant results (5.3 and 53 µg?kg^?1) were found if maximum limits (tolerances) established by European Union were adopted in Brazil and if a method decision limit (CCα) of 3.4?µg?kg^?1 was considered. In 8% of analyzed samples, more than one studied coccidiostat was found. The lincosamide, lincomycin, and the macrolide, tylosin, were detected at trace levels in 4 and 1% of the samples, respectively. Lasalocid, clarithromycin and erythromycin were not found.     

Analysing organochlorine pesticides in strawberry jams using GC-ECD,GC-MS/MS and QuEChERS sample preparation

This paper describes a comparison of adaptations of the QuEChERS (quick, easy, cheap, effective, rugged and safe) approach for the determination of 14 organochlorine pesticide (OCP) residues in strawberry jam by concurrent use of gas chromatography (GC) coupled to electron capture detector (ECD) and GC tandem mass spectrometry (GC-MS/MS). Three versions were tested based on the original QuEChERS method. The results were good (overall average of 89% recoveries with 15% RSD) using the ultrasonic bath at five spiked levels. Performance characteristics, such as accuracy, precision, linear range, limits of detection (LOD) and quantification (LOQ), were determined for each pesticide. LOD ranged from 0.8 to 8.9?µg?kg^?1; LOQ was in the range of 2.5–29.8?µg?kg^?1; and calibration curves were linear (r ^2?>?0.9970) in the whole range of the explored concentrations (5–100?µg?kg^?1). The LODs of these pesticides were much lower than the maximum residue levels (MRLs) allowed in Europe for strawberries. The method was successfully applied to the quantification of OCP in commercially available jams. The OCPs were detected lower than the LOD.     

Survey of the anticoccidial feed additive nicarbazin (as dinitrocarbanilide residues) in poultry and eggs

A survey was carried out on the occurrence of dinitrocarbanilide (DNC), the marker residue for nicarbazin, in poultry produced in Ireland during 2002–2004. Liver (n?=?736) and breast muscle samples (n?=?342) were tested. DNC residues were found in 40 and 26% of liver and breast muscle samples at levels greater than 12.5 and 5?µg?kg^?1, respectively. DNC residues were found at >200?µg?kg^?1 in 12 and 0% of liver and muscle samples, respectively. Samples of breast muscle (n?=?217) imported from 11 countries were also tested for DNC residues. A lower incidence of DNC residues (6%) was found in imported breast muscle. Egg samples (n?=?546) were tested and DNC residues were found in nine samples, with levels ranging between 14 and 122?µg?kg^?1. Analysis of poultry, carried out as part of official food inspection in the period 2004–2006, indicated a reduction in the number of broiler liver samples containing DNC at >200?µg?kg^?1, to approximately 7%. Low levels of DNC residues continue to be found in <2% of egg samples.     

An LC–ESI–MS/MS method for residues of fluoroquinolones,sulfonamides, tetracyclines and trimethoprim in feedingstuffs: validation and surveillance

ABSTRACT

An increasing concern about food safety has been observed over the years. The presence of drugs residues in food is one of the major subjects of research in food safety. Feedingstuffs can be responsible for carryover into the food chain of residues of several drugs. This paper describes the development, validation and application of a fast and simple method for analysis of 24 antibiotic residues in feedingstuffs for cattle, pigs and poultry. Analytes include compounds from different antimicrobials classes, such as sulfonamides (sulfadiazine, sulfamethazine, sulfamethoxazole, sulfaquinoxaline, sulfachlorpyridazine, sulfadoxine, sulfadimethoxine, sulfizoxazole, sulfamerazine and sulfathiazole), fluoroquinolones (ciprofloxacin, enrofloxacin, norfloxacin, danofloxacin, difloxacin, sarafloxacin, flumequine, nalidixic acid and oxolinic acid), tetracyclines (tetracycline, doxycycline, oxytetracycline and chlortetracycline) and trimethoprim. Samples were extracted with methanol:water (70:30) 0.1% formic acid, followed by clean-up steps using centrifugation, low-temperature purification (LTP) and ultracentrifugation. Instrumental analysis was performed using liquid chromatography coupled to tandem mass spectrometry. Chromatographic separation was achieved using a C18 column and a mobile phase composed of acetonitrile and water, both with 0.1% formic acid. Validation parameters such as limit of detection (LOD), limit of quantification (LOQ), selectivity, linearity, accuracy, precision, decision limit (CCα) and detection capability (CCβ) were determined and meet the adopted criteria. LOD and LOQ were set to 30 and 75 µg kg^?1, respectively. Inter-day precision were in the range from 4.0 to 11.1%, and linearity provides values of r² above 0.95 for all analytes. The optimised method was applied to the analysis of more than 1500 real samples within the period 2012–2017. Non-compliant results were discussed and classified in terms of analytes, feed types and target species. Multivariate analysis of the data was performed using principal component analysis.     

Simultaneous determination of residues of trichlorfon and dichlorvos in animal tissues by LC-MS/MS

Trichlorfon is a thermally unstable insecticide that can be easily decomposed to dichlorvos at high temperatures. In this study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for simultaneous determination of the residues of trichlorfon and dichlorvos in animal tissues. Trichlorfon and dichlorvos in animal tissues were extracted with dichloromethane, homogenized/shaken, concentrated, and determined by LC-MS/MS. The two insecticides can be effectively separated and individually determined. The limits of detection (LODs) of trichlorfon and dichlorvos were 0.04 and 0.07 µg kg^?1, respectively; the limits of quantification (LOQs) of the two insecticides were both 5 µg kg^?1. The average recoveries for three spiked blank samples at 10, 20 and 40 µg kg^?1 were in the range 85–106%, with relative standard deviations (RSDs) below 10.6%, which falls in a reasonable range for the analysis of the two insecticides in animal-derived foods. The method is fit-for-purpose for the simultaneous determination of residues of trichlorfon and dichlorvos in animal tissues.     

Residues of sulfadiazine and doxycycline in egg matrices due to cross-contamination in the feed of laying hens and the possible correlation with physicochemical,pharmacokinetic and physiological parameters

In the poultry industry, the widespread use of veterinary drugs such as antimicrobial compounds may lead to the presence of residues in whole eggs, egg white and egg yolk. During this study, laying hens received experimental feed containing sulfadiazine or doxycycline at cross-contamination levels of 2.5%, 5% and 10% of the therapeutic concentration. Since the therapeutic dose is 250?mg?kg^?1 for both substances, cross-contamination concentrations in the feed of 6.25, 12.5 and 25?mg?kg^?1 were expected. Whole egg, egg white and egg yolk samples were collected during the treatment and depletion period and were analysed via liquid chromatography-tandem mass spectrometry. For both drugs, a plateau phase was reached within 3–5 days and residue concentrations were detected in all egg matrices. For the 10% cross-contamination group, residual sulfadiazine concentrations of 208, 299 and 60?µg?kg^?1 and residual doxycycline concentrations of 455, 332, 206?µg?kg^?1 were detected in whole egg, egg white and egg yolk on day 13 of the treatment period, respectively. Both sulfadiazine and doxycycline had higher concentrations in egg white than in egg yolk, but the egg white–egg yolk ratio was higher for sulfadiazine than for doxycycline. As neither drug is allowed in Belgium for use in laying hens, residues may pose food safety concerns.