86 86 LIGHTING PROGRAMME & EGG SIZE BODY WEIGHT & EGG SIZE In open houses, the season of the year has a significant influence on egg size. Birds reared during the summer, with more hours of light, and reaching maturity in the autumn produce larger eggs compared to those reared in winter (with fewer hours of light). In general, programmes that delay the start of laying support larger egg size and vice versa. The lighting programme (day length and intensity) therefore plays a very important role in sexual maturity and egg production. Although this topic will be discussed in depth in the corresponding section, any increase in light hours from 14–15 weeks of age will stimulate the sexual maturity of the hens. From this moment, a rapid increase in light hours will cause an early start of production with a greater number of eggs and smaller size. Conversely, a slow increase in light hours (higher hen weight) will delay the start of production and increase egg weight. As a reference, every week delay in sexual maturity that has been achieved through a lighting programme result in an increase of 1.4–1.7 g in mean egg weight. The correlation between light hours and body weight is obvious, where normally those pullets reared with a greater number of light hours have more time to consume feed and therefore achieve greater body weight . . . however, it relies on other factors as well (i.e: feed particle distribution-more selective eating). Within each genetic line, a heavier pullet at the moment of light stimulation will produce larger eggs and less egg number and vice versa. Therefore, using the standard curves of each line as a reference, regular measurement of pullets’ body weight and uniformity (≥ 85%) is paramount to modify/rectify management and nutrition practices to achieve our target. LOHMANN › MANAGEMENT GUIDE › NUTRITION › PRODUCTION PERIOD Influence of initial body weight on egg weight between 22–50 weeks Egg production (%) Egg weight (g) Egg mass (g/d) Feed intake (g/d) 1860 ± 86 g) 1592 ± 75 g Values with different letters indicate significant differences (P < 0.05), values without letters or with same letters indicate non-significant differences (P > 0.05). Pérez-Bonilla et el., 2012 92.5a 89.8b 64.9a 62.4b 60.0a 56.1b 120.6a 113.1b
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