Individual egg production of Hy-Line Brown hens during the early laying phase in response to dietary CP levels

Abstract

The aim of this study was to investigate the effects of gradually increased dietary CP level on the dynamics of individual egg production of laying hens from 18 to 54 weeks of age. Forty Hy-Line Brown hens were divided into five treatments of eight replicates each and were fed diets formulated to have five different CP concentrations: 14, 15, 16, 17, and 18% CP with the same energy content. For each experimental diet, the contents of lysine, methionine + cysteine, threonine, and tryptophan were maintained at minimum requirement concentrations by supplying synthetic amino acids. Clutch characteristics were recorded (e.g., number, size, patterns, egg weight, etc.) and individual egg production curves were modeled according to Grossman and Koops (2001). Clutch size was defined as the unstopped length of individual egg production on a daily basis. BWs were also recorded every week to account for changes in BW during the experimental period. Three hens were excluded from the statistical analyses as their laying patterns were very inconsistent. Four clutch patterns with data weighted on a weekly basis were identified. Heavier hens tended to lay more regular clutch patterns when compared to their lighter counterparts within the same treatment. In contrast, irregular clutch patterns (too many pauses between clutches) were more common in hens fed low CP diets (≤16%). This could be explained by imbalances in amino acids supply according to their theoretical requirements and adverse effects caused by amino acids interactions. Low CP diets were able to maintain egg production and mean clutch size up to 54 weeks of age. The maximum clutch size and the modeled proportion of maximum production for the increasing phase (k₁) displayed a linear response to the graded addition of CP content to the diet. No differences were detected among treatments for the age at the beginning of the maximum clutch (22.6 ± 2.82 weeks). Egg weight displayed a quadratic response that was maximized when hens were fed 17% CP in the diet. Our approach appears to be promising for ranking individual laying hens based on their clutch performance to evaluate both CP and amino acids adequacy of diets.