Thiago L. Noetzold

Modern poultry industry is divided into two main commercial categories: laying hens (egg-type) and broiler breeders (meat-type). They have been selected differently over the past 100 years. Despite the difference in egg production between egg- and meat-type chickens, similar physiological triggers are attributed to both during the transition from pullet to hen. In addition to the photoperiod threshold, reproduction in chickens is also connected to three main metabolic thresholds: nutrient intake, body weight (BW), and carcass composition. Much is still unknown regarding the physiological effects of these thresholds. Many differences in management and nutritional strategies have been attributed to egg- and meat-type chickens. However, not a lot of emphasis has been put on the possible physiological similarities between the main metabolic factors (body composition and nutrient intake) and thresholds (critical BW and body fat) affecting egg- and meat-type pullets during the transition to the reproduction period. Therefore, this review summarized current knowledge on the metabolic status of the pullets affecting the onset of sexual maturation, focusing on its integration with photoperiodic cues and reproductive physiology, and how the latter is affected by the metabolic status of egg- and meat-type chickens.

This study aimed to determine the effects of dietary energy and body-weight (BW) restriction on layer pullets’ growth, uniformity, and feed efficiency. Two experiments were conducted using a precision feeding (PF) system (Experiment 1) and a conventional feeding (CON) system (Experiment 2). Experiment 1 consisted of a 2 × 4 factorial arrangement (eight treatments) with two feed allocation (FA) levels: meal every visit (MEV) or restricted to the lower boundary of Lohmann Brown-Lite pullets; and three dietary metabolizable energy (ME) levels: Low, Standard (Std), and High (2600, 2800, and 3000 kcal/kg, respectively); the fourth treatment enabled birds to choose from the three diets (Choice). Experiment 2 consisted of a 2 × 3 factorial arrangement (six treatments): two FA levels (ad libitum or restricted) and three dietary ME levels (Low, Std, and High). In each experiment, BW, coefficient of variation (CV), average daily feed intake (ADFI), average daily metabolizable energy intake (MEI), and feed conversion ratio (FCR) were recorded. Diet ADFI preferences and feeding motivation were determined only in the PF experiment. ANOVA was conducted on each experiment with the two main effects as fixed factors (FA and dietary ME), and age or period as the sources of variation. Differences were reported at p ≤ 0.05. MEV (PF experiment) and ad libitum-fed (CON experiment) pullets had greater BW compared to restricted-fed pullets (p < 0.05). The lowest CV was observed in the restricted-fed pullets from the PF experiment (p < 0.05). ADFI was greater in pullets fed the Low ME diet in the PF experiment compared to all the other groups, and the lower the dietary ME, the greater the ADFI in the CON experiment (p < 0.05). Choice-feeding pullets preferred feed with greater ME content in the PF experiment (p < 0.05). The lower the dietary ME, the greater the FCR in the CON experiment (p < 0.05). Restricted-fed pullets had greater daily visits, and lower daily meals, meal size, and successful visits to the PF system (p < 0.05). In conclusion, the results of this trial indicated that lower dietary ME increased FCR and ADFI, whereas feed restriction decreased BW and increased feeding motivation. Future steps after this trial will include examining the effects of dietary energy and feed restriction on carcass composition and sexual maturation.