Growth and development responses of Gallus gallus domesticus embryos to in ovo bromide exposure

Abstract

Collated data showed that the concentration range of bromide (Br-) in groundwater (GW) was between 0 – 132mg/L in selected provinces in South Africa where livestock production occurs. The no observed adverse effects level (NOAEL) of 0.01 mg/L was proposed and validated using the chicken embryo model. The objective was to investigate the effect of a range of 0 – 1 mg/L Br- on the pre-hatch growth and development of the chicken embryo to demonstrate the risk that Br- exposure may pose to livestock and humans residing in the regions where livestock production depends on GW as main drinking water source. The chicken embryo model was used to investigate the effects of Br- on the growth and development of the heart, liver and brain because the thyroid hormone (TH) receptors are similar to that in mammals and the effects on TH are independent of maternal TH fluctuations. A volume of 200 μL NaBr at concentrations of 0, 0.01, 0.05, 0.5 and 1 mg/L was administered by in ovo injection and the wet mass of the whole embryo and the heart, liver and brain were measured on embryonic day (ED) 14 and 20, and on hatch day (HD) using a sensitive balance. The relative organ mass for each organ was calculated as individual organ mass over whole embryo mass and expressed as a percentage. Crown-rump (CR) and shank length were measured on ED 14, 20 and HD using callipers. These were not found to be reliable measures of pre-hatch growth. Data were analysed using the GLM and REML procedures of SAS®. There was a significant treatment effect of Br- on the relative heart mass, with the relative mass decreasing with increasing concentrations of Br- (P ≤0.1). It appeared that Br- may have interfered with the pre-hatch growth of the heart. The null hypothesis that different concentrations of Br- do not have an effect on pre-hatch growth and development was rejected. The implication of this conclusion is that Br- concentrations present in GW in excess of 0.01 mg/L could potentially pose a risk to livestock and human populations that are chronically exposed to the element in their drinking water.