Assessing the Response of Laying Hens to Digestible Balanced Protein from 27 to 66 Weeks of Age

ABSTRACT: As laying hens continue to improve in egg characteristics, it is relevant to examine their response to dietary digestible balanced protein (DBP). Research using Lohmann-LSL hens, from 27 to 66 wk of age, compared DBP intake levels using diets with essential amino acids (AA) balanced to digestible lysine (Dlys) intake levels of 550, 625, 700, 775 and 850 mg/hen/day. Each treatment was replicated 10 times with 12 birds per replicate. Two base diets containing 500 or 850 mg of Dlys per 100 g of diet were blended every three wk based on previous feed intakes to produce diets that would provide treatment levels of Dlys intake. Data collection included daily hen-day egg production (HDEP), and feed intake (FI), egg weight (EW), egg mass (EM), feed efficiency (FE) and egg specific gravity (ESG) every three wk. Hens were weighed and scored for feather cover at 27, 47 and 66 wk of age. Egg components were measured at 41, 52 and 65 wk of age, including albumen height (AH), dry egg shell weight (ESW), and albumen and yolk weights (AW and YW). At the end of the experiment, pectoralis muscle (PM), abdominal fat pad (AFP), heart, liver and kidneys were collected from 10 randomly euthanized hens per treatment and weighed. Empty weight and length of gastrointestinal tract (GIT) segments were also measured. Excreta samples were collected twice from five randomly selected cages per treatment to determine total excreta nitrogen (N) content. In a completely randomized experimental design, the data were analyzed using one-way ANOVA as mixed model and by using PROC regression and PROC response surface regression procedures of SAS 9.3 (2003). Differences in means were considered significant when P ≤ 0.05. The effect of increasing DBP on hen weight, HDEP, EW, EM, FI and FE was quadratic. By using a non-linear regression model, a maximum response for HDEP, EW, EM and FE was observed at 769, 836, 903 and 839 mg/h/d intake of Dlys, respectively. Increasing Dlys levels increased AFP weight linearly and PM weight increased quadratically. Heart, liver and kidney weights were not affected by Dlys intake. Proventriculus absolute weight was increased while gizzard weight decreased linearly with increasing Dlys intakes. Intestinal segment weights decreased linearly or quadratically with increasing Dlys intake. Caeca measurements were not affected by the treatment. Feather score increased with Dlys intake level. Both percent ESW and ESG decreased linearly with increasing intake levels of Dlys. Absolute AW (linear) and YW (quadratic) increased with Dlys intake; proportional values for these criteria were affected in a quadratic manner, but the effects were small. Excreta N content increased in a quadratic manner with increasing amino acid intake. In conclusion, the response of Lohmann-LSL hens to DBP was determined and the DBP (based on diets with essential AA balanced to Dlys) level required to maximize the response varied with the criteria being assessed. Keywords: ideal protein, egg mass, body composition, plumage, egg quality, excreta nitroge