Linoleic acid as a mediator of egg size

ABSTRACT Diets supplemented with 5 % of tallow or safflower oil were fed to White Leghorn pullets during the initial 14 wk of production. The diets contained.6 % and 4.3 % of linoleic acid, respectively. Egg weight was consistently greater with the diet high in linoleic acid. Yolk weights relative to egg weights were similar in each sample, as were the yolk concentrations of total, neutral, and polar lipids. The fatty-acid profiles for both the neutral and the polar fractions were also similar for the large and small eggs within treatment, but there were differences between treatments. The lipid concentrations in the liver at the conclusion of the experiment were greater in the birds fed the diet low in linoleic acid as a result of increases in the neutral lipids. As with the yolk fatty acids, the substitution of safflower oil for tallow in the diet decreased the concentrations of oleic acid and increased the concentrations of linoleic acid in both lipid fractions. The constancy of the proportions of protein, neutral lipid, and polar lipid in the yolk, despite the effect of dietary linoleic-acid concentration on yolk size, supports the hypothesis that linoleic acid, or longer-chain fatty acids of the linoleic-acid family, is required for the synthesis of the lipoproteins that can be transported to the ovary for uptake by the developing ova. Egg size cannot be maximized if the amount of linoleic acid available is not adequate to support the maximum rate of synthesis by the lipoproteins. (Key words: egg size, dietary linoleic acid, yolk weight, yolk lipid composition, liver lipid composition