Effects of a Pre-Molt Calcium and Low-Energy Molt Program on Laying Hen Physiology

Abstract

and ImplicationsThe objectives of this study were to compare stress measures and bone quality of laying hens when offered a Ca pre-molt treatment followed by low-energy molt diets versus a traditional feed withdrawal before, during, and after an induced molt. A total of 189 Hy-Line W-36 laying hens (85 wk of age, 1.7 ± 0.2 kg), housed 3 per cage, (413 cm 2 /hen) were used. Six treatments were compared in a 2 × 3 factorial design with 2 Ca (coarse and fine) pre-molt treatments (coarse and fine) and 3 molt diets: feed withdrawal (FW), soybean hulls (SH), and wheat middlings (WM). The Ca pre-molt treatment was defined as the period when the hens received either a combination of fine (0.14 mm in diameter) and coarse (2.27 mm in diameter) CaCO 3 or an all-fine CaCO 3 mixed into a commercial diet for 1 wk. Both diets were formulated to contain 4.6% Ca, such that only the particle size of the CaCO 3 differed between the 2 treatments. Hens had free access to feed and water and had a 24-h photoperiod. The 3 molt diets were applied for a total of 28 d. The hens assigned to the FW molt diet were deprived of feed for 7 d with free access to water followed by 21 d of skip-a-day feeding restricted to 60 g of feed / hen per feeding day. The hens fed the WM and SH molt diets were provided free access to feed and water during the entire 28 d molt period. Lighting was reduced to 8 h for the first 3 wk and was then increased to 12 h at the start of the last week of molt. During the 22 wk postmolt, hens were fed a laying hen diet and lighting was increased by 1 h each week to 16 h. None of the treatments resulted in an increased heterophil to lymphocyte ratio during or post-molt compared to baseline values, which would have suggested increased stress in the laying hen. Additionally, any changes reported during molt in bone quality returned to baseline values during the post-molt period. Therefore, these treatments are acceptable for inducing molt in the laying hen.