Lysine partitioning in broiler breeders is not affected by energy or protein intake when fed at current industry levels.

A study was conducted to determine the effects of dietary energy and protein intake on the partitioning of lysine in broiler breeder hens. One hundred twenty-six broiler breeders were randomly assigned to 1 of 6 dietary treatments in a 2 (390, 450 kcal/d) × 3 (22, 24, 26 g of CP/d) fashion. Thirty-six hens were administered a daily oral dose of 15 mg of (15)N-Lys for a period of 2 wk or until first egg. After the 2-wk enrichment period, no isotopes were given for 2 d. After 2 d, a daily oral dose of 15 mg of (2)D4-Lys was administered until the 2nd, 3rd, and 4th egg (saved) after the initial (2)D4-Lys was given, at which point pectoralis muscle was sampled. Weeks 25, 29, and 45 were assessed. Isotopic enrichment of pectoralis muscle, egg yolk, and albumen was determined via gas chromatography-mass spectrometry. The (15)N-Lys was intended to represent endogenous lysine, whereas the (2)D4-Lys was intended to represent dietary lysine. Greater than 78% of all labeled lysine ((15)N and (2)D4-Lys) was found in breast muscle. Endogenous muscle was the main source of lysine for yolk formation at wk 25 and 45. Diet was the main source of lysine for albumen formation at wk 25 and 29. A consistent decrease in the (15)N-Lys in breast muscle from the 2nd to the 3rd egg was observed, while also seeing an increase in the (15)N-Lys in the egg from the 3rd to the 4th egg. No difference in the partitioning of lysine was determined by energy or protein intake at levels typical for the current poultry industry. Rather, age, and possibly rate of production, appear to be the main drivers of lysine partitioning in the broiler breeder hen.