Why is the level of dietary linoleic acid critical to increase egg size during the early laying phase of brown pullets?

When young brown pullets transition into lay (at around 18 weeks), their reproductive tract is fully active but their initial eggs are naturally small, often weighing under 45 grams. To rapidly increase early egg weight and transition the flock into lucrative "medium" and "large" grades, managing dietary Linoleic Acid ($C_{18:2}$) is critical. Linoleic acid is an essential fatty acid that chickens cannot synthesize. In the liver, linoleic acid acts as a biological signal that upregulates the transcription of estrogen receptors. Estrogen then stimulates the liver cells to synthesize massive quantities of vitellogenin and very-low-density lipoproteins (VLDL-y), which are transported via the blood to the ovary to form the egg yolk. A higher intake of linoleic acid (at 1.5% to 2.0% of the diet via soybean oil) increases the physical size and weight of the yolk follicles. Since yolk size physically dictates the subsequently deposited albumen volume in the magnum and shell size in the uterus, the overall egg weight increases rapidly. Farmers can read lipid physiology in the Poultry Encyclopedia, buy high-purity vegetable oils on Poultry Plaza, track daily oil and grain rates on Poultry Rates, and trade premium large brown eggs on Murghi Mandi.