THE INFLUENCE OF HIGH AND LOW ERUCIC ACID RAPESEED OILS ON THE PRODUCTIVE PERFORMANCE OF LAYING HENS AND ON THE LIPID FRACTION OF EGG YOLK

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Abstract
The effects of including 5 or 15% of high (regular) and low (Span) erucic acid rapeseed oils or soybean oil on productive performance, total lipid and fatty acid content of egg yolk, and distribution of fatty acids in egg yolk fat were studied. Feed intake varied according to the dietary energy content. However, 15% high erucic acid rapeseed oil decreased feed intake and egg production in comparison with 15% low erucic acid rapeseed oil or soybean oil. Hens receiving rations containing soybean oil produced larger eggs in the treatment than in the pre-treatment period. Five percent regular rapeseed oil in the diet led to a small increase in egg weight, whereas inclusion of 15% regular rapeseed oil in the diet led to a decrease in egg weight. Diets containing the Span oil gave intermediate results. Although the total lipid and total fatty acid content in egg yolk remained constant, the fatty acid composition changed significantly with the experimental diets. The concentration of saturated fatty acids in eggs produced by hens fed diets containing the regular rapeseed oil or low erucic acid rapeseed oil (Span oil) decreased only to a small extent and not in proportion to the amount of these fatty acids present in the diets; but the oleic acid concentration in eggs produced by the hens fed diets containing the rapeseed oil was high. Only 0.2% of erucic acid was found in eggs when 15% regular rapeseed oil was fed to laying hens. The laying hen seems to be able to maintain the level of saturated and monounsaturated fatty acids in yolk lipids in a physiological range. The results indicate that in the laying hen, a partial degradation of erucic acid to gadoleic acid and oleic acid takes place.

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