Effect of soy oil supplementation and protein level in laying hen diets onpraecaecal nutrient digestibility, performance, reproductive performance, fatty acid composition of yolk fat, and on other egg quality parameters

An experiment was carried out with laying hens in the age of 22-45 weeks to examine the effects of added soy oil (0%, 3.5%, 7%, 10.5%, and 14%) and di etary protein level (13.2% and 16.3%) on laying and reproductive performanc e, fatty acid composition of yolk fat, and other egg quality parameters. Mo reover, digestibility of nutrients and of energy was determined by using a marker technique. Laying intensity and feed intake were not influenced by d ietary treatments whereas egg weight and daily egg mass production were sig nificantly improved by soy oil addition in a non-linear related manner. The feed conversion ratio reached a minimum at soy oil proportions between 3.5 % and 10.5%. Reproductive performance in terms of fertilized eggs, hatchabi lity, and mortality of chicks was not affected by dietary treatments. The i ncrease of egg weights due to soy oil addition was accompanied by a simulta neous increase in the proportion of albumen and a decrease of yolk and shel l percentage. Palmitic acid (C16:0) and oleic acid (C18:1) proportions in y olk fat decreased as soy oil addition was increased whereas the proportions of linoleic acid (C18:2 n-6), linolenic acid (C18:3 n-3), and docosahexaen oic acid (C22:6 n-3) were increased at the same time. Praecaecal digestibil ity of crude fat and fatty acids of the diets were non-linearly improved by soy oil addition. Digestibility of crude protein and amino acids were not affected by either protein content of the diet or by soy oil supplementatio n. In conclusion, a decrease in dietary protein content from 16.3% to 13.2% di d not negatively influence performance of hens and egg quality under the ex perimental conditions applied. Soy oil addition improved egg quality.