The Effect of b-carotene on desaturation of ruminant fat

Abstract

An experiment was conducted to determine if limiting the amount of β-carotene in a diet could increase the expression of the gene responsible for the desaturation of saturated fats in a ruminant. Two groups of Iambs were raised on either a cereal grain/faba bean diet, or a pasture legume diet. The diets contained equal concentrations of protein and metabolisable energy, but the pasture legume diet contained at least 20 times more β-carotene than the cereal diet. The groups were fed so that they grew at very similar rates. After 14 weeks, a sample of subcutaneous fat was removed by biopsy. This demonstrated that newly deposited fat was distinctly different in composition between the groups. The animals were slaughtered after a further 4 weeks and internal body and subcutaneous fat was removed from the carcasses. Major differences were found in fatty acid composition and melting point of the fat. In particular, the lower β-carotene diet decreased 018:0 stearate (saturated) and increased C18:1 oleate (mono-unsaturated). Some other increases occurred C18:2 and a trans C18:1, probably as a result of the lipid present in corn. The melting point of the fat in animals fed low levels of β-carotene was almost 10°C less than that fed a high β-carotene diet. It is likely that one of the metabolites of β-carotene inhibits nuclear expression of the desaturase gene.