Grazing Kajli Pakistani sheep (30 in number) with mean body weight of 35 kg and of 36 months old were investigated to evaluate seasonal influence on Se levels of three different sheep classes including lactating and non-lactating ewes and male sheep. Samples of forage and blood were obtained four times after one month interval during summer and winter seasons and these were analyzed to assess the Se contents. Forage Se content was higher in winter than that in summer, while the reverse was true during summer. Blood plasma Se contents were higher in summer, particularly in male sheep compared to those in lactating and non lactating ewes. High incidence of deficiency was found in lactating ewes compared to the other groups of animal. The plasma concentrations of all sheep classes were found in the acceptable range required for normal metabolism and reproduction. Although there is no urgent need for supplementing the animals with mineral mixture with higher availability of selenium, forage plants and lactating sheep in some instances were found deficient in Se during this investigation, therefore, their low Se concentrations may pose a threat for grazing ruminants at this livestock farm. So, a Se supplementation in the form of forages with high Se contents or mineral mixture is required at this animal ranch to prevent the potential hazards of Se deficiency. (C) 2010 Elsevier B.V. All rights reserved.