Safety of cypermethrin 15% in laying hens naturally infested by Ornithonyssus Sylviarum

Brazil is among the five largest egg producers in the world. Their level of production is second only to China, USA, India and Japan (USDA, 2008). In 2005 there were 58.8 million tons of eggs and it is projected that by 2015 production will reach 70.9 million tons (Paranense Poultry Association, APAVI). Commercial layers reared in confinement are constantly attacked by ectoparasites, being common and persistent the infestation by the feather mite Ornythonyssus sylviarum. The action of these mites on birds promotes stress conditions with the consequent reduction in weight gain and egg production, and the transmission of microorganisms Axtell and Arends (1990). Currently, these arthropods are controlled with insecticides, especially pyrethroids such as cypermethrin. The growing demand for safe food (uncontaminated) increasingly restricts the use of insecticides and other drugs in poultry. This has been accentuated by the creation of the Normative Instruction Nº. 56 of 2007 (Ministry of Agriculture, Livestock and Supply, MAPA, Brazil), which refers to the procedures for registration, supervision and monitoring of poultry commercial and reproduction farms. Thus, for the registration of new products or for the renewal of those already registered, it is necessary to evaluate different parameters, one of them being safety. The safety of drugs can be determined by clinicopathological tests of hematology, biochemistry and urinalysis (International Cooperation on Harmonisation of Technical Requirements for Registration of Veterinary Medicinal Products, +++International Cooperation on Harmonisation of Technical Requirements for Registration of Veterinary Medicinal Products, VICH, 2008). Despite the common use of pyrethroids in poultry, there is no information about its effects on blood biochemical profile of laying hens. Aiming to answer this question, this study evaluated the safety of cypermethrin in laying hens naturally infested with the mite O. sylviarum.

The study was performed with Hyline Brown layers (n = 30), 70 weeks old, naturally parasitized with O. sylviarum. These birds were housed in cages 45 x 45 x 25 cm, with 17 hours of daylight, balanced food and water ad libitum on the experimental farm of the Department of Animal Nutrition (NPV) of the Faculty of Veterinary Medicine from the University of São Paulo, Campus Pirassununga. Biochemical tests were performed using blood samples without EDTA by puncturing the ulnar vein to draw 2 mL. These samples were kept without refrigeration until analysis. The samples were taken on day 0 (before treatment, untreated birds), being the control group, and day 7 (seven days after treatment). Two groups of 15 birds that received the treatment T1: topical application (spraying) of cypermethrin EC (emulsifiable concentrate) at the recommended dose, or T2: cypermethrin EC three times (3X) the recommended dose. The biochemical profiles of serum function (uric acid and urea), hepatic function (aspartate aminotransferase [AST], alkaline phosphatase [FA] and γ-glutamyltransferase [GGT]), cholesterol, glucose, total protein and albumin were analyzed in serum. Levels were determined using commercial BioClin kits, processed in an automatic CELM^® SBA-200 and the reading was performed in a spectrophotometer. The statistical analysis was performed with GraphPad InStat.

The results of liver function tests (AST and GGT), renal function (urea and creatinine), protein and glucose metabolism, as well as reference values, are shown in Table 1.

Table 1. Serum biochemical profile in Hyline Brown layers before and after the spraying of cypermethrin (Cyperpour 15, Vetbrands^®) at two different doses: T1 (dose recommended by the manufacturer) and T2 (three times the recommended dose)

Cypermethrin treatments at the recommended dose (T1) and three times the dose (T2) generated values of biochemical parameters in accordance with reference (Borsa et al. 2006; Thrall, 2007), except for albumin. Blood albumin levels are considered normal 0.8 to 2.0 g/dL. However, average values ranged from 2.7 to 2.9 g/dL, with a significant difference between the group of layers before (day 0) and after treatments (day 07). Notwithstanding, it can be seen that these animals had higher albumin values​than the reference even before applying the product, showing that the insecticide was not the factor that caused this condition. In fact, there are constant variations in the levels of albumin in layers, which can be explained by the protein requirement for egg formation (Gonçalves et al., 2008), since the egg white is basically composed of albumin. In addition, according to Campbell (2004), females before laying can have estrogen-induced hyperproteinemia. There was no alteration in other biochemical parameters, indicating that the product was not toxic to animals at the doses studied. The reference values​cited in the text are from observations made​by other authors in birds (in general) and broilers. Due to the paucity of literature on the subject, this study also contributed new information on the reference values​for serum biochemical variables in commercial layers.

Cypermethrin was shown to be safe in layers, even at triple the dose recommended by the manufacturer.

Fundación de Amparo a la Investigación del Estado de São Paulo - FAPESP.

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