Μg Kg-1 Bw Research Articles

Prevalence and health risk evaluations of mycotoxins in drinking water sources in Nigeria.

Mycotoxins in drinking water are neglected pollutants that have serious health implications when ingested. Common mycotoxins with health concerns include deoxynivalenol (DON), ochratoxin A (OTA), and zearalenone (ZEN). This study considers the distribution and apparent health risks of these mycotoxins in drinking water sources (groundwater, surface water, bottled water, sachet water) in three Southwest Nigeria States: Osun, Oyo, and Lagos States, using the UHPLC-ESI-QTOF. ZEN and DON were found in all 95 water samples across all three states. ZEN in sachet water samples has the highest mean concentrations, with those from Osun, Oyo, and Lagos States having concentrations of 14.96 ± 4.46, 8.59 ± 3.86, and 10.56 ± 2.84 μg L-1, respectively. In contrast, the mean concentrations of all three mycotoxins (± Standard Error of Mean) in bottled water samples are the lowest across the three States. The mean concentrations of OTA in sachet water samples (2.93 ± 0.79, 1.24 ± 0.40, and 3.01 ± 1.50 μg L-1) are slightly higher than those in bottled water (1.47 ± 0.28, 1.53 ± 0.31, and 0.75 ± 0.31 μg L-1) for Osun, Oyo, and Lagos States, respectively. Groundwater samples across the three States had the lowest average pH values, below the WHO's lowest limit of 6.5. Principal Component Analysis studies indicate that all three mycotoxins in water samples are closely associated by source. Possible human exposure values for ZEN suggest some health concerns, especially with the use of sachet water type based on the estrogenicity of this mycotoxin. However, OTA values for all water samples analyzed, are much lower than the tolerable daily intake (TDI) of 4.73 μg kg-1 bw per day provided by European Food Safety Auhtority (EFSA). The levels of DON in all water sample types were of no serious health concern. However, human exposure levels to all three mycotoxins in bottled water fall within safe limits of health-based guidance values (HBGV) indicating that this drinking water type is better treated, unlike sachet water. Nevertheless, stakeholders need to re-examine water quality with respect to these mycotoxins and adopt stringent guidelines and new water treatment strategies to provide consumers with safe drinking water in line with the UN SDG #6.

Acute Effects of Brevetoxin-3 Administered via Oral Gavage to Mice.

Brevetoxins (BTXs) constitute a family of lipid-soluble toxic cyclic polyethers mainly produced by Karenia brevis, which is the main vector for a foodborne syndrome known as neurotoxic shellfish poisoning (NSP) in humans. To prevent health risks associated with the consumption of contaminated shellfish in France, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) recommended assessing the effects of BTXs via an acute oral toxicity study in rodents. Here, we investigated the effect of a single oral administration in both male and female mice with several doses of BTX-3 (100 to 1,500 µg kg-1 bw) during a 48 h observation period in order to provide toxicity data to be used as a starting point for establishing an acute oral reference dose (ARfD). We monitored biological parameters and observed symptomatology, revealing different effects of this toxin depending on the sex. Females were more sensitive than males to the impact of BTX-3 at the lowest doses on weight loss. For both males and females, BTX-3 induced a rapid, transient and dose-dependent decrease in body temperature, and a transient dose-dependent reduced muscle activity. Males were more sensitive to BTX-3 than females with more frequent observations of failures in the grip test, convulsive jaw movements, and tremors. BTX-3's impacts on symptomatology were rapid, appearing during the 2 h after administration, and were transient, disappearing 24 h after administration. The highest dose of BTX-3 administered in this study, 1,500 µg kg-1 bw, was more toxic to males, leading to the euthanasia of three out of five males only 4 h after administration. BTX-3 had no effect on water intake, and affected neither the plasma chemistry parameters nor the organs' weight. We identified potential points of departure that could be used to establish an ARfD (decrease in body weight, body temperature, and muscle activity).

Silica sources for arsenic mitigation in rice: machine learning-based predictive modeling and risk assessment.

Arsenic (As) is a well-known human carcinogen, and the consumption of rice is the main pathway for the South Asian people. The study evaluated the impact of the amendments involving CaSiO3, SiO2 nanoparticles, silica solubilizing bacteria (SSB), and rice straw compost (RSC) on mitigation of As toxicity in rice. The translocation of As from soil to cooked rice was tracked, and the results showed that RSC and its combination with SSB were the most effective in reducing As loading in rice grain by 53.2%. To determine the risk of dietary exposure to As, the average daily intake (ADI), hazard quotient (HQ), and incremental lifetime cancer risk (ILCR) were computed. The study observed that the ADI was reduced to one-third (0.24 μg kg-1bw) under RSC+SSB treatments compared to the control. An effective prediction model was established using random forest model and described the accumulation of As by rice grains depend on bioavailable As, P, and Fe which explained 48.5, 5.07%, and 2.6% of the variation in the grain As, respectively. The model anticipates that to produce As benign rice grain, soil should have P and Fe concentration more than 30 mg kg-1 and 12 mg kg-1, respectively if soil As surpasses 2.5 mg kg-1.

Distribution of Cadmium in Fresh Vegetables Marketed in Southeast China and Its Dietary Exposure Assessment.

This study investigated concentrations of cadmium (Cd) in 2465 vegetable samples (52 species) from 2018 to 2022 and estimated the associated health risk for local consumers. The average concentration of Cd was 0.035 mg kg-1, and the percentage of samples exceeding the Chinese maximum allowed concentration was 3.89% (96/2465). The top five species with highest Cd levels were Lilium brownii F (0.182 mg kg-1), Allium chinense G (0.117 mg kg-1), Allium macrostemon Bunge (0.105 mg kg-1), Colocasia esculenta (0.064 mg kg-1), and Amaranthus tricolor L (0.054 mg kg-1). Bulb vegetables had a higher relative accumulation of Cd compared to other vegetables. The levels of Cd in vegetables varied significantly across sampling areas and years. The mean estimated daily intake (EDI) of cadmium through consumption of vegetables was 0.519 μg kg-1 bw per day for adults and 0.217 μg kg-1 bw per day for children. The target hazard quotients (THQs) were all less than the threshold of 1 for both adults and children. This indicates that there is low health risk for Cd through vegetable consumption. However, routine monitoring of Cd levels in food is still crucial to ensure food safety and protect public health.

Microcystin-LR exposure interfered maintenance of colonic microenvironmental homeostasis in rat.

Microcystin-leucine arginine (MCLR) is a phycotoxin produced by cyanobacteria. As a hepatotoxin, increasing evidence suggests that it has some negative effects on the mammal gastrointestinal tract, but further studies are warranted. In this study, we investigated the effects of MCLR on the intestinal epithelial microenvironment by oral administration of MCLR. As expected, MCLR at doses of 200 and 400μgkg-1 bw showed hepatorenal toxicity in rats but without significant gastrointestinal symptoms. MCLR exposure decreased the thickness of the colonic epithelial mucus layer, and down-regulated the expression of main mucin protein (MUC2), cytoskeletal assembly-related genes (Arpc1a, Enah) and cytoskeletal stability-related genes (Ptk2, Prkca, Actn1, Pxn, Tln1, Cttn, Vcl) in colonic tissue to varying degrees, but did not affect the expression of cell connection-related genes including Zo1, Ocln, Cldn2 and Cdh1. In addition, MCLR exposure had a limited effect on gut bacterial diversity but clearly enriched specific bacteria. Prevotella, which plays a crucial role in balancing health and disease, was inhibited, whereas Muribaculaceae concerning the epithelial barrier, was promoted. Together, our findings demonstrate that MCLR exposure can weaken the colonic epithelial barrier by interfering with the stability of the cytoskeleton, which in turn exacerbates the homeostasis maintenance in the intestinal microenvironment.

Dietary exposure to acrylamide of university students in Ningxia of Northwest China and the effect on their neurobehavioral performance and oxidative stress in serum.

This study aims to investigate dietary exposure to acrylamide (AA) and also make an assessment of its effect on the neurobehavioral performance and oxidative stress in the serum of university students in Ningxia. The place primarily consists of arid, dry desert, and wheat-based foods are the staple food there. A total of 803 university students in Ningxia participated in this cross-sectional study. Diet intake of AA was estimated with FFQ. The AA risk was calculated as margin of exposure (MOE) values. NCTB questionnaires were used to assess neurobehavioral performance. The serum oxidative stress levels of the university students were measured as GSH, MDA, and SOD. The mean for AA exposure of university students was 0.515 μg kg-1 bw day-1. The highest contributor was traditional Chinese grain products, representing 34.71% of the total daily AA intake. Followed were deep-fried potato products, traditional Western grain products, soft drinks, and nuts, which accounted for 23.87%, 16.59%, 11.15%, and 11%, respectively. The median AA exposure were 480 (BMDL10=0.18 mg kg-1 bw day-1) and 827 (BMDL10=0.31 mg kg-1 bw day-1), respectively. The results indicated that diet AA may have an effect on the emotional status and neurobehavior among this population. We observed no significant differences in oxidative stress under the three levels of AA exposure (p > .05). It suggests a health concern for university students in Northwest China that should get society's attention.

Assessing the risk of human exposure to bioaccessible arsenic from total diet through market food consumption in Chengdu, China.

To assess the daily intake of total arsenic (tAs) and arsenic speciation and their potential health risks, different food groups, including vegetables, rice, meat, viscera, freshwater fish, and seafood from Chengdu, China were analyzed. The concentrations of tAs ranged from 41.3 to 1185μgkg-1 with a median of 238μgkg-1, and 26.0% of tAs in the food groups was of inorganic toxic form. The median concentration of As(V) in rice (184 ± 21.6μgkg-1) was approximately 2 to 6 times higher than those in other food groups. The bioaccessible inorganic arsenic (iAs) concentrations of the food items obtained from the local markets of Chengdu ranged from 1.07 to 24.6μgkg-1 (mean of 6.04μgkg-1). Rice contributed toward the largest amount of daily iAs intake (66.2%). The mean daily iAs intake from vegetable, meat and viscera contributed 10.7%, 12.5% and 6.04% of total iAs intake, respectively. The actual concentration of arsenic in the food exposed to the human body depends on oral bioaccessible fraction. The oral bioaccessibility estimated daily intake (μg kg-1 bw d-1) of tAs and iAs for the residents of Chengdu was 0.32 and 0.16. Health risk assessments carried out based on bioaccessible iAs concentrations showed that the food items were safe for consumption from the iAs perspective.

Lycopene Regulates Dietary Dityrosine-Induced Mitochondrial-Lipid Homeostasis by Increasing Mitochondrial Complex Activity.

Dityrosine (DT), a marker of protein oxidation, is widely found in many high-protein foods. Dietary intake of DT induces myocardial oxidative stress injury and impairs energy metabolism. Lycopene is a common dietary supplement with antioxidant and mitochondrial-lipid homeostasis modulating abilities. This study aimed to examine the effects of lycopene on DT-induced disturbances in myocardial function and energy metabolism. Four-week-old C57BL/6J mice received intragastric administration of either tyrosine (420µg kg-1 BW), DT (420µg kg-1 BW), or lycopene at high (10mg kg-1 BW) and low (5mg kg-1 BW) doses for 35 days. Lycopene administration effectively reduced oxidative stress, cardiac fatty acid accumulation, and cardiac hypertrophy and improved mitochondrial performance in DT-induced mice. In vitro experiments in H9c2 cells showed that DT directly inhibited the activity of the respiratory chain complex, whereas oxidative phosphorylation and β-oxidation gene expression is upregulated. Lycopene enhanced the activity of the complexes and inhibited ROS production caused by compensatory regulation. Lycopene improves DT-mediated myocardial energy homeostasis disorder by promoting the activity of respiratory chain complexes I and IV and alleviates the accumulation of cardiac fatty acids and myocardial hypertrophy.

Flavonoid-Like Components of Peanut Stem and Leaf Extract Promote Sleep by Decreasing Neuronal Excitability.

Peanut stem and leaf (PSL), a traditional Chinese medicine, is widely used as a dietary supplement to improve sleep quality; however, the underlying mechanism is unclear. Here, the study aims to determine whether active compounds in PSL extract exert their effects by mediating neuronal excitability. Aqueous PSL extract (500mg kg-1 BW) increases the duration of total sleep (TS), slow wave sleep (SWS) and rapid eye movement sleep (REMS) in BALB/c mice after 7 and 14 continuous days of intragastric administration. Two PSL extract components with flavonoid-like structures: 4',7-di-O-methylnaringenin (DMN, 61µg kg-1 BW) and 2'-O-methylisoliquiritigenin (MIL, 12µg kg-1 BW), show similar effects on sleep in BALB/c mice. Moreover, incubation with DMN (50µM) and MIL (50µM) acutely reduces voltage-gated sodium and potassium currents and suppresses the firing of evoked action potential in mouse cortical neurons, indicating the inhibition on neuronal excitability. Meanwhile, RNA-seq analysis predicts the potential regulation of voltage-gated channels, which is according with the molecular docking simulation that both MIL and DMN can bind to voltage gated sodium channels 1.2 (Nav 1.2). DMN and MIL are the active ingredients of PSL that improve sleep quality, suggesting that PSL promotes sleep by regulating the excitability of neurons.

Anthelmintic activity of crude powder and crude aqueous extract of Trachyspermum ammi on gastrointestinal nematodes in donkey (Equus asinus): An in vivo study.

Trachyspermum ammi has been used traditionally as a popular ethnobotanical plant in human and animal parasitic infestations. Few scientific studies have been conducted on in vitro anthelmintic activity of T.ammi against various helminths and there is no study on its in vivo/in vitro anthelmintic properties against equine helminths. The present study aimed to evaluate in vivo anthelmintic activity of crude powder (CP) and crude aqueous extract (CAE) of T.ammi seeds against gastrointestinal nematodes in the donkey. Thirty donkeys, naturally and severely infected with Strongyle-type nematodes, were randomly divided into six groups and administered orally with graded doses of CP and CAE at single dose as follow: Two groups were treated with 1 and 3 gkg-1 body weight of CP, two groups were treated with CAE at the equivalent dose rate 1 and 3 gkg-1 bw of CP and one group was treated with 200 μgkg-1 bw of Ivermectin 0.2% (Positive Control). One group received no medication (Negative Control). Efficacy was determined by faecal egg count reduction (FECR) test. The faecal samples were taken from the donkeys on days 7, 14 and 28 post-treatments (PT) and the egg per gram (EPG) of faeces was determined for each animal. FECR for donkeys treated with CP, CAE, and Ivermectin 0.2% was calculated on days 7, 14, and 28 PT. In the present study, CAE was analyzed using gas chromatography-mass spectrometry (GC-MS) to determine CAE chemical components. High-performance liquid chromatography (HPLC) using a marker (thymol) was applied to confirm the existence of thymol as an active principle. Based on the FECR findings, the maximum FECR (71.2%) was observed in the group treated with CAE3 on day 14 PT, while it was 66.2% for CP3 on the same day. The effects of different treatments (P < 0.001), time (P < 0.001) and their interactions (P < 0.05) on EPG showed a significant difference. A dose-dependent response in the anthelmintic activity of CP and CAE was observed. GC-MS analysis indicated that thymol was the major component of CAE (Area = 45.01%) with the respective peak at retention times (Rt) 10.41 min. On HPLC analysis of CAE, thymol was found to be the major constituent of CAE (Area = 58.76%) with the same Rt at 13.233 min. The present study indicated that both CP and CAE of T.ammi had the dose-dependent anthelmintic effects. Due to the development of drug resistance against synthetic anti-helminthics, T.ammi seems to be a promising alternative for the treatment and prevention of helminths in livestock.

Arsenic speciation in fish and shellfish from the North Sea (Southern bight) and Açu Port area (Brazil) and health risks related to seafood consumption

In North Sea and Port Açu (Brazil) coastal areas, high arsenic (As) concentrations were observed in water, soil and sediments. Therefore, the impact of this contamination on fish and shellfish species bought from local fishermen was studied. Total As was assessed with ICP-OES (Brazil) and ICP-MS (North Sea) after microwave digestion. Toxic As was assessed with liquid chromatography-ICP-MS (Brazil) and hydride generation-atomic fluorescence spectrometry (North Sea). All analytical methods comply with Quality Assurance/Quality Control procedures.Several fish species have average Total As concentrations above 1 μg g-1 wet weight (ww), but the highest concentrations are found in less spotted dogfish, lemon sole and whelks from the North Sea, with respectively 50, 49 and 50 μg g-1 ww. High Total As concentrations correspond to high Toxic As concentrations, except for scallops having increased Toxic As concentrations. Toxic As fractions are highest in scallops (almost 10%) but rarely exceeds 2% in all other species. Liver samples were only analyzed in ray, dogfish and catfish and their Toxic As fractions are between 2 and 4 times higher than in muscle.For a consumption of 150 g of seafood, only 3 samples exceed the provisional total daily intake of 2 μg kg-1 bw, however, cancer risks are non-negligible. Using mean Toxic As concentrations for each of the different fish and shellfish species studied, Lifetime Cancer Risk values at the actual global seafood consumption rate of 54 g day-1 are above 10–4 for whelks, scallops, dogfish, ray and lemon sole.

Bioaccessibility and Human Exposure Assessment of Cadmium and Arsenic in Pakchoi Genotypes Grown in Co-Contaminated Soils.

In many countries cadmium (Cd) and arsenic (As) commonly coexist in soils contaminated by mining activities, and can easily enter the human body via consumption of leafy vegetables, like the popularly consumed pakchoi (Brassica chinensis L.), causing major health concerns. In the present study, bioaccessibility and human exposure of Cd and As were assessed in twenty genotypes of pakchoi cultured at two different levels of co-contamination to identify low health risk genotypes. The bioaccessibilities of Cd and As represent a fraction of the total metals content could be bioaccessible for human, in the present study, significant differences in pakchoi Cd and As bioaccessibility were observed among all tested genotypes and co-contaminated levels. Cd and As bioaccessibility of pakchoi were in the ranges of 24.0–87.6% and 20.1–82.5%, respectively, for in the high level co-contaminated soils, which was significantly higher than for low level co-contaminated soils with 7.9–71.8% for Cd bioaccessibility and 16.1–59.0% for As bioaccessibility. The values of bioaccessible established daily intakes (BEDI) and the total bioaccessible target hazard quotients (TBTHQ) of Cd and As were also considerably higher in high level co-contaminated soils than in low level co-contaminated soils. Two genotypes (Meiguanqinggengcai and Zhenqing60F1) contained relatively low concentrations and bioaccessible Cd and As and, their BEDI and TBTHQ for Cd and As ranged below the tolerable limits set by the FAO/WHO (BEDI of Cd < 0.83 μg kg−1 bw day−1, BEDI of As < 3 μg kg−1 bw day−1) and United States Environmental Protection Agency (TBTHQ for Cd and As < 1), this applied for both levels of co-contaminated soils for adults and children. Consequently, these findings suggest identification of safe genotypes in leafy vegetable with low health risk via genotypic screening and breeding methods could be a useful strategy to ensure the safety of food crops grown in those Cd and As co-contaminated fields due to mining activities.

Determination and risk assessment of naturally occurring genotoxic and carcinogenic alkenylbenzenes in nutmeg-based plant food supplements.

A risk assessment of nutmeg-based plant food supplements (PFS) containing different alkenylbenzenes was performed based on the alkenylbenzene levels quantified in a series of PFS collected via the online market. The estimated daily intake (EDI) of the alkenylbenzenes amounted to 0.3 to 312 μg kg-1 body weight (bw) for individual alkenylbenzenes, to 1.5 to 631 μg kg-1 bw when adding up the alkenylbenzene levels assuming equal potency, and to 0.4 to 295 μg kg-1 bw when expressed in safrole equivalents using toxic equivalency factors (TEFs). The margin of exposure approach (MOE) was used to evaluate the potential risks. Independent of the method used for the intake estimate, the MOE values obtained were generally lower than 10000 indicating a priority for risk management. When taking into account that PFS may be used for shorter periods of time and using Haber's rule to correct for shorter than lifetime exposure it was shown that limiting exposure to only 1 or 2 weeks would result in MOE values that would be, with the presently determined levels of alkenylbenzenes and proposed uses of the PFS, of low priority for risk management (MOE>10000). It is concluded that the results of the present paper reveal that nutmeg-based PFS consumption following recommendations for daily intake especially for longer periods of time raise a concern. Copyright © 2017 John Wiley & Sons, Ltd.

Enhancing Ovulation of Malaysian Mahseer (Tor tambroides) in Captivity by Removal of Dopaminergic Inhibition

Natural spawning ground of most Malaysian streams are undergoing extreme changes as a result of human activities, pollution and climate change (extreme temperature fluctuation) which lead to dramatic decrease in mahseer (Tor tambroides, Cyprinidae) populations. An experiment was conducted to evaluate the effectiveness of salmon gonadotropin releasing hormone analogue (sGnRHa) alone or in combination with dopamine antagonist domperidone (DOM) on breeding performances of female breeders. Sixty females T. tambroides ranging in weight 2.01 to 3.96 kg while thirty males with average weight 1.38 to 1.72 kg were used in this study. The females were given pretreatment with Ovaplant (23.4-44.9 μg kg-1) for 6 weeks prior to induction. Females were tested with various treatments such as Ovatide, sGnRHa, sGnRHa+DOM and DOM. SGnRH analogue alone does not contain dopamine antagonist to block dopaminergic inhibition action. Females were given single intramuscular injection of Ovatide (0.5 mL kg-1 BW), sGnRHa (10 μg kg-1 BW), sGnRHa+DOM (10 μg kg-1 BW+5 mg kg-1 BW) or DOM (5 mg kg-1 BW). The control group was administered with 0.9% NaCl. The fish did not spawn spontaneously but through hand stripping to release eggs. Results showed that Ovatide significantly produced highest ovulation rate, total stripped eggs and stripped fecundity. Interestingly, we observed that broodstock groups injected with sGnRHa+DOM produced highest fertilization, hatching and survival rates compared to other treatments. Good egg and larval quality were recorded in the group treated with sGnRHa+DOM. No females ovulated in the group receiving DOM alone and saline solution. The combination treatment was found to be more potent in inducing ovulation as compared to sGnRHa alone or DOM alone. Our results suggest that dopaminergic inhibition is a major barrier in inducing spontaneous spawning in captive mahseer and we successful produced progeny generation of T. tambroides larvae.

Toxicity and genotoxicity in Astyanax bimaculatus (Characidae) induced by microcystins from a bloom of Microcystis spp

Studies of genotoxicity in fish caused by cyanobacterial microcystins can be useful both in determining the sensitivity of native species, as well as comparing exposure routes. The genotoxicity caused by the microcystins LR and LA from a bloom collected in a eutrophic lake, was revealed in the fish Astyanaxbimaculatus, a native species from South America. LC50 (72 h) was determined as 242.81 μg L (-1) and LD50 (72 h) as 49.19 μg kg (-1) bw. There was a significant increase of DNA damage in peripheral erythrocytes, following intraperitoneal injection (ip) with tested concentrations of 24.58 μg kg (-1) bw and 36.88 μg kg (-1) bw, as well as through body exposure to a concentration of 103.72 μg L (-1) . Micronucleus (MN) induction was observed after ip injections of 24.58 μg kg (-1) bw and 36.88 μg kg (-1) bw for 72 h, as well as following body exposure for 72 at 103.72 μg L (-1) . Thus, both exposure routes resulted in MN induction and DNA damage. Apoptosis-necrosis testing was carried out only by ip injection with concentrations of 24.58 μg kg (-1) bw and 36.88 μg kg- 1 bw. Exposure to microcystins at lower concentrations induced more apoptosis than necrosis in peripheral erythrocytes, whereas exposure at higher concentrations gave rise to both conditions. Thus, Astyanax bimaculatus can be considered as a species sensitive to the genotoxic effects caused by microcystins.

Effects of chlortetracycline and Synovex-S® on growth rate and on plasma growth hormone and thyroid hormone concentrations following administration of thyrotropin-releasing hormone and GH-releasing hormone in beef steers

Twenty-four Angus steers (365 kg ± 4) were assigned randomly to a 2 × 2 factorial arrangement of treatments of either 0 or 350 mg chlortetracycline d-1, with or without Synovex-S to test the effects of chlortetracycline (CTC) and estrogenic implant on release of growth hormone (GH) and thyroid hormones. Steers received ad libitum a concentrate-forage diet over a 112-d feeding study, and growth and carcass characteristics were determined. On days 30, 56, and 106, steers received an injection, via jugular catheter, of 1.0 µg kg-1 BW thyrotropin-releasing hormone (TRH) + 0.1 µg kg-1 BW GH-releasing hormone (GHRH) and blood was collected from -30 to 360 min post-injection. Overall, compared with non-implanted steers, Synovex-S increased (P ≤ 0.009) rate and efficiency of gain, decreased (P = 0.05) time to peak for GH concentrations, whereas baseline concentrations of thyroid-stimulating hormone (TSH) were increased (P = 0.03). Additionally, the TSH response curve (P ≤ 0.05) and magnitude of triiodothyronine (T3; P = 0.01) response were greater following TRH + GHRH challenge for implanted versus nonimplanted steers. There were no main effects of CTC; however, CTC attenuated (P ≤ 0.05) the effects of implant on T3 release, slaughter weight, and carcass composition. In conclusion, Synovex-S alone increased BW gain and enhanced the response of GH, TSH, and T3 to a TRH + GHRH challenge, whereas CTC alone did not affect rate and composition of gain or release of pituitary and thyroid hormones. However, CTC appeared to mitigate the effects of implant on T3 release and carcass composition. Key words: Growth hormone, thyroid, estrogen, chlortetracycline, bovine, growth

Organochlorine pesticide residues in cow's milk from a tropical region of Mexico

A monitoring study was conducted to assess the magnitude of DDT [(1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane)] and HCH (hexachlorocyclohexane) contamination of bovine milk from the central tropical region of Mexico as the chemicals are extensively used in livestock and public-health programmes. Among pesticide residues analysed, the milk samples collected from Tlalixcoyan showed a mean level of γ-HCH (0.128 mg kg-1), which was significantly higher than residues in milk samples from Medellin (0.049 mg kg-1) and Paso San Juan (0.022 mg kg-1). The mean level of pp'-DDE in Medellin samples (0.039 mg kg-1) was significantly higher than in Paso San Juan (0.018 mg kg-1) and Tlalixcoyan (0.024 mg kg-1) milk samples. The pp '-DDT mean level from Medellin milk samples (0.089 mg kg-1) was significantly higher than the levels detected in the other two areas. The highest mean Σ-DDT level detected in Medellin samples (0.146 mg kg-1) was three times the FAO/WHO tolerance level. The highest acceptable daily intakes calculated for Σ-DDT were 0.017 μg kg-1 bw day-1 for adults and 0.530 μg kg-1 bw day-1 for infants; for γ-HCH residues, they were 0.021 μg kg-1 bw day-1 for adults and 0.666 μg kg-1 bw day-1 for infants, indicating that infants are more exposed to pesticide residues. Results indicate that cattle exposure to HCH and DDT results in high levels in dairy milk and a potential health risk for consumers.

Effects of Low Doses of Oestradiol, Testosterone and Dihydrotestosterone on the Immune Response of Broiler Chicks

Administration of either 1 μg kg-1 BW oestradiol 17β (E2), 0.1 mg kg-1 BW testosterone (T) or 0.2 mg kg-1 BW dihydrotestosterone (DHT) in feed to broiler chicks for 50 days caused increased serum concentration of the hormones compared to the control birds that were given no drugs. E2 and T but not DHT resulted in a significant decrease of the total number of leukocytes, lymphocytes and the weight of bursa of Fabricious. The hormones significantly reduced the macrophage phagocytic activity compared to controls. It is suggested that prolonged administration of low doses of E2 and T but not DHT to chicken may induce immunosuppressant effect.