INFLUENCE OF DIETARY COBALT ON PERFORMANCE, NUTRIENT DIGESTIBILITY AND RUMEN ACTIVITY IN LAMBS

Mohamed Emad Abd El-Wahab Nasser

Abstract
The present study was conducted to study the effects of different inclusion levels of dietary cobalt (Co) on performance, nutrient digestibility and rumen activity in lambs. Twenty, 5.0 month-old weaned lambs (Egyptian native breed) were randomly divided into four groups which were fed with the basal diet containing 0.0486 mg Co/kg DM, the basal diet supplied, respectively, with 0.35, 0.70 and 1.00 mg Co/kg DM reagent grade CoSO4 · 7H2O for 100 days. In the end of experimental period, three lambs from each group were allocated to the individual metabolic cages to measure the effects of dietary Co on apparent nutrient digestibility. Samples of rumen content were taken once a week for seven consecutive weeks, two times daily (before feeding and 3 hours after feeding). Average daily gain and average daily feed intake for the fourth group were higher than control group (P<0.05). However, there was no difference in gain/feed. Supplemental 1.0 mg Co/kg DM resulted in highest digestibility of dry matter, organic matter, crude protein and crude fiber (P<0.05). Nitrogen free extract was higher for third group (0.7 mg Co/mg DM) than the other three groups (P<0.05). The pH values and ammonia nitrogen were low in supplemented groups than in the control. The concentrations of volatile fatty acids were increased after feeding and peaked at 3-h post-feeding in the third group. The number of total protozoa was significantly increased for third group than other groups. In conclusion, supplementation of the basal diet with 0.70-1.00 mg Co/kg DM (the total dietary Co level of 0.749 -1.049 mg/kg DM) in the basal diet enhanced growth performance and improved nutrient digestibility and rumen activity of lambs.

Key words: Cobalt, digestibility, volatile fatty acids, protozoa and lambs