Dietary modulation of oleic and stearic acids in egg yolks

Single comb white leghorn (SCWL) hens at 28 weeks of age were fed a basal layer mash (2600 kcal metabolizable energy/kg and 16.5% crude protein) for a 14-day pretrial period to collect egg production and feed consumption data. For the experiment, hens of equivalent production and body weights were then divided into six groups of four hens each and fed one of the following dietary lipid treatments for 42 days: five combinations of olive oil:tallow (100:0, 75:25, 50:50, 25:75, and 0:100) or soybean oil. All lipid treatments were mixed on a weight basis with the basal diet (5% lipid to 95% diet). Egg production, total egg and yolk weights, feed consumption, and fatty acid composition and cholesterol content of the egg yolks were determined. Dietary lipid treatment did not affect egg production, feed/dozen eggs, or feed/hen/day. Feeding 100% tallow compared with the olive oil:tallow ratio of 75:25 significantly (P ≤ 0.05) lowered egg weights. Hens fed soybean oil had lower yolk concentrations of 16:1 and 17:0 fatty acids, but elevated 18:2n6 and 18:3n3 fatty acid concentrations compared to yolks from hens given tallow. The 18:1 fatty acid concentration in egg yolks increased proportionately with the addition of olive oil in the diet (77 mg/g of yolk for 75% olive oil compared to 67 for 100% tallow and 57 for soybean oil, respectively). The lipid treatments did not influence cholesterol concentrations in the egg which averaged 196 ± 9 mg/egg.