Effect of crude protein and fat content of diet on productive performance and egg quality traits of brown egg-laying hens with different initial body weight.

A trial was conducted to study the influence of CP and fat content of the diet on performance and egg quality traits of brown egg-laying hens from 22 to 50 wk of age. The experiment was conducted as a completely randomized design with 8 treatments arranged factorially with 4 diets and 2 initial BW of the hens (1,592 vs. 1,860 g). Three of these diets differed in the CP content (16.5, 17.5, and 18.5%) and included 1.8% added fat. The fourth diet also had 18.5% CP but was supplemented with 3.6% fat instead of 1.8% fat. Each treatment was replicated 4 times, and the experimental unit consisted of 21 hens allocated into groups of 7 in 3 adjacent cages. All diets were isocaloric (2,750 kcal of AME/kg) and met the recommendations of brown egg-laying hens for digestible Arg, Ile, Lys, Met, Thr, Trp, TSAA, and Val. Productive performance and egg quality were recorded by replicate every 28 d. For the entire experimental period, diet did not affect any of the productive performance traits studied, but the heavier hens had higher ADFI (120.6 vs. 113.9 g; P < 0.001), egg production (92.5 vs. 89.8%; P < 0.01), and egg weight (64.9 vs. 62.4 g; P < 0.001) than the lighter hens. Initial BW did not affect feed conversion per kilogram of eggs or hen mortality, but BW gain was higher (289 vs. 233 g; P < 0.01) and feed conversion ratio per dozen of eggs was better (1.52 vs. 1.57; P < 0.01) for the lighter than for the heavier hens. None of the egg quality variables studied was affected by dietary treatment or initial BW of the hens. It is concluded that brown egg-laying hens, irrespective of their initial BW, do not need more than 16.5% CP to maximize egg production, provided that the diet meets the requirements for key indispensable amino acids. Heavier hens produce more eggs that are larger than lighter hens but feed efficiency per kilogram of eggs is not affected.