High doses of cobalt inhibited hair follicle development in Rex Rabbits

Abstract

An experiment was conducted to investigate the effect of cobalt supplementation on hair follicle development in rabbits. Rex rabbits (30-d-old, n=180) were divided randomly into five equal treatment groups: rabbits fed a basal diet (control, measured cobalt content of 0.27 mg/kg) or rabbits fed a basal diet with an additional 0.1, 0.4, 1.6 or 6.4 mg/kg cobalt (in the form of cobalt sulfate) supplementation (measured cobalt contents of 0.35, 0.60, 1.83 and 6.62 mg/kg, respectively). Treatment with 6.4 mg/kg cobalt significantly decreased hair follicle density (P<0.05), while low levels of cobalt (0.1-1.6 mg/kg) had no effect on hair follicle density (P>0.05). The addition of dietary cobalt at the highest level examined (6.4 mg/kg) significantly increased the gene expression of bone morphogenetic protein (BMP) 2 and BMP4 in skin tissue (P<0.05), while the mRNA levels of versican, alkaline phosphatase, hepatocyte growth factor, and noggin remained unchanged (P>0.05). Compared with their levels in the control group, dietary cobalt treatment significantly suppressed the protein levels of p-mechanistic target of rapamycin (mTOR) and p-ribosomal protein S6 protein kinase (P<0.05) but did not alter the protein levels of p-AMP-activated protein kinase, Wnt10b or p-β-catenin (P>0.05). In conclusion, cobalt at the highest concentration examined inhibited hair follicle development, which may have involved the mTOR-BMP signalling pathway.1 Premix provided the following per kg of diet: vitamin A 12 000 IU, vitamin D3 900 IU, vitamin E 50 mg, vitamin K3 1.5 mg, vitamin B1 1.5 mg, vitamin B2 5 mg, vitamin B3 40 mg, vitamin B5 50 mg, vitamin B6 0.5 mg, vitamin B11 2.5 mg, choline 600 mg, biotin 0.2 mg, potassium 7 mg, magnesium 3 mg, iron 60 mg, zinc 60 mg, copper 40 mg, manganese 9 mg, iodine 1 mg, stone powder 15 000 mg, sodium chloride 5000 mg, lysine 1000 mg, methionine 2000 mg. 2 Digestible energy was calculated according to the nutrition levels of ingredients by de Blas and Mateos (1998), while the other nutrient values were measured.