Marginal deficiencies of cobalt and selenium in weaner sheep: response to supplementation

Abstract

Five groups of 30 weaner wethers were given (i) no treatment, or a supplement of either (ii) copper (injection), (iii) cobalt (intraruminal pellet), (iv) selenium (intraruminal pellet) or (v) copper, cobalt plus selenium (intraruminal, soluble glass bolus). Liveweight, wool growth and indicators of copper, cobalt and selenium status were measured over a 54-week experimental period. The provision of all 3 elements resulted in a 180 g increase (P<0.05) in clean wool growth relative to controls. With selenium or cobalt alone there was a trend towards increases in clean wool, whereas wool growth of copper treated sheep was identical to the controls. There were no persistent or significant treatment effects on liveweight. The results indicate that both wool and liveweight changes should be used to assess responses to trace elements and show that combined deficiencies, not detectable in experiments using single element supplements, may depress productivity in grazing sheep. Glass boluses were an effective method of providing selenium and raised selenium in liver and plasma for 54 weeks. Selenium pellets resulted in smaller, less persistent increases in these tissues. Glass boluses were less effective than cobalt pellets in providing cobalt and resulted in only a small increase in vitamin B12 at 26 weeks (P=0.1), compared with increases due to cobalt pellets at both 26 and 54 weeks (P<0.05).