Assessment of selenium status in livestock from Koibatek district, Kenya

Abstract

Interest in assessing selenium status of livestock started around 1935, when it was discovered that selenium causes toxicity. Twenty three years later, selenium was proven to be an essential nutrient in animals and this rekindled the interest in assessment. In 1973, selenium was shown to be a component of glutathione peroxidase, an antioxidant enzyme found in animals [Rotruck et al, 1973]. Selenium levels in animals, plants and environment at large were found to be in low quantities. The margin between deficiency and toxicity levels is very narrow indeed. This has necessitated the investigation and development of sensitive and reliable methods for quantification, as well as the assessment of the element in human beings, livestock, plants and the environment as a whole. In Kenya, this has not been done. In this project. two methods of selenium analysis, fluorimetric and UVspectrophotometric, have been investigated. For digestion, an open ashing system using two types of acid mixtures and a closed ashing system using an oxygen flask were investigated. Nitric, perchloric and sulphuric acid mixtures in a ratio of 5:2:1 and, nitric and perchloric acid mixtures of ratio 5:2 were investigated. The three digestion procedures are discussed: The two methods of analysis used required reduction of selenium (VI) to selenium (IV). Methods 0 reduction of selenium (VI) under open system and various acid concentrations and times are presented. Complexation of selenium (IV) with either 2,3-diaminonaphthalene or 3,3'diaminobenzidine for fluorimetric measurements and pH variations were investigated. The fluorimetric spectra obtained compared well with those cited in the literature. 2,3 Diaminonaphthalene gave better fluorescence intensity than 3,3'diaminobenzidine. Complexation of selenium (Tv') with either 2-mercaptobenzothiazole or 3,3'diaminobenzidine for UV-spectrophotometric methods of analysis was investigated. These two methods of analysis are compared and discussed in this work. 2Mercaptobenzothiazole in UV-spectrophotometric was identified as a prior analytical method, to 2,3 diaminonaphthalene in fluorimetric analysis. Livestock samples that included those of dairy and beef cattle, sheep and goats were collected from Koibatek district, pig samples from Farmer's Choice slaughterhouse in Nairobi, poultry samples from a poultry farm in Kikuyu and plants from Bungoma, Sotik, Meru, Athi River, Ngong' and Mazeras from Coast province were analysed. Four main divisions, in Koibatek district were categorised into two geographical zones, low altitude with low rainfall and high altitude with high rainfall. Four representative farms in each region were visited and blood and hair samples collected from at least two animals from each animal species, dairy and beef cattle, sheep and goats. Slaughterhouses in the district were visited and blood, liver and kidney samples collected.