Effect of low levels of dietary cobalt on apparent nutrient digestibility in Omani goats

The effect of low levels of dietary cobalt (Co) on apparent nutrient digestibility coefficients was investigated in three breeds of Omani goats (Batina, Dhofari and Jabal Akdhar). Goats were divided into control and treated groups. Goats in both groups were fed Rhodes grass hay ad libitum and a commercially prepared diet containing 0.10 and 0.12 mg Co/kg dry matter, respectively, from 10 to 46 weeks. Animals in the treated group were supplemented with vitamin B12 by giving sub-cutaneous injections of 2000 μg of hydroxocobalamin at week 10, and at 8 weeks intervals thereafter for 46 weeks. Serum vitamin B12 levels were significantly higher (P<0.05) in goats from the treatment group from week 18 throughout the course of the experiment. The serum levels of vitamin B12 for the control group dropped to levels consistent with those of lambs considered to have a deficiency of vitamin B12. Digestibility was determined on weeks 22, 26, 30 and 34. There were significant increases (P<0.05) in digestibility coefficients of dry matter, organic matter, crude protein, ether extract and energy respectively, in goats from the vitamin B12-treated group. Compared to the Jabal Akdhar and Dhofari goats, the treated Batina goats had the largest differences in digestibility coefficients between the treated and control animals. The results of this study showed that low levels of dietary cobalt in goats resulted in lowering the apparent nutrient digestibility coefficients compared to goats supplemented with vitamin B12. This is possibly due to several factors, including a reduction in rumen microorganisms, decrease in intestinal absorption of nutrients, and inadequate synthesis of the vitamin B12-dependent methylmalonyl co-enzyme A mutase and methionine synthase, the two enzymes essential for protein and energy metabolism.