Small Ruminant Research 90 (2010) 170–173 Contents lists available at ScienceDirect Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres Short communication Effect of dietary cobalt supplementation on plasma and rumen metabolites in Mehraban lambs Shahab Bishehsari, Mohamad Mehdi Tabatabaei ∗ , Hassan Aliarabi, Daryoush Alipour, Pouya Zamani, Ahmad Ahmadi Department of animal Science, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran article info Article history: Received 6 October 2009 Received in revised form 18 January 2010 Accepted 16 February 2010 Available online 19 March 2010 Keywords: Mehraban lambs Cobalt Performance Nutrient digestibility abstract Two experiments were conducted to study the effects of different levels of dietary cobalt on performance, plasma and rumen metabolites and nutrient digestibility in Mehraban male lambs. Experiment 1: 28, 8–9-month-old lambs were randomly divided into four groups. Animals were fed a basal diet containing 0.088 mg Co/kg DM and were supplied with 0 (control), 0.25, 0.50, or 1.00 mg Co/kg DM as reagent grade CoSO 4 ·7H 2 O. The experiment lasted for 70 days. Experiment 2: four lambs from each group in Experiment 1 were ran- domly allocated to the individual metabolic crates to measure the effects of dietary Co on nutrient digestibility. Final body weight, average daily gain and gain efficiency were higher (p < 0.05) in the group supplemented with 0.50 mg Co/kg DM compared to other groups. Plasma glucose and vitamin B 12 concentrations increased (p < 0.05) at all levels of Co sup- plementation on day 68 of the experiment and for vitamin B 12 were higher (p < 0.05) at 0.50 and 1.00 mg Co/kg DM compared to 0.25 mg Co/kg DM. There was no significant difference among treatments for TVFA and ruminal fluid pH. Digestibility of dry matter, organic mat- ter, crude protein and neutral detergent fiber increased (p < 0.05) by Co supplementation, but did not differ among Co supplied treatments. The obtained results showed that lambs fed the control diet containing 0.088 mg Co/kg DM had a reduced appetite and gained less than the supplemented animals, suggesting that the level of 0.088 mg Co/kg DM was inad- equate for normal growth of Mehraban male lambs, and a total level of 0.58 mg Co/kg DM might be optimum level for enhancing performance. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Cobalt (Co) has been demonstrated to be an essential nutrient for ruminants and is required by ruminal microor- ganisms for the synthesis of vitamin B 12 (McDowell, 2000). In ruminants, a Co-induced vitamin B 12 deficiency results in reduced intake and ADG (Wang et al., 2007), decreased plasma, liver and ruminal vitamin B 12 (Tiffany and Spears, 2005), elevated plasma methylmalonic acid ∗ Corresponding author. Tel.: +98 8114424090; fax: +98 8114424012. E-mail addresses: m-tabatabai@basu.ac.ir, mmtaba@gmail.com (M.M. Tabatabaei). (MMA) and homocysteine (Stangl et al., 2000). Recent findings have demonstrated that 0.10 mg/kg DM of Co intake does not meet the rumen microbial requirements (Kisidayova et al., 2001; Johnson et al., 2004) and ADG, ADFI and nutrient digestibility had been increased in growing lambs when a diet with 0.086 mg Co/kg DM was sup- plemented with 0.50 mg Co/kg DM (Wang et al., 2007). Singh and Chhabra (1995) reported that 0.3–0.5 mg Co/kg DM enhanced ruminal microbial activity, fermentation and vitamin B 12 synthesis. The effects of dietary Co concentra- tion on growth, nutrient metabolism and ruminal microbial activity in Mehraban lambs are not well understood. There- fore, objectives of the present study were to determine effects of dietary Co levels on performance, plasma and 0921-4488/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2010.02.010