This study aimed to determine the effects of dietary ME and BW restriction on layer pullet sexual maturation, carcass composition and reproductive organs. Two trials were conducted: a precision feeding (PF) (Experiment 1) and a conventional (CON) experiment (Experiment 2). Experiment 1 was a 2 × 4 factorial arrangement with two feed allocation (FA) levels: meal every visit (MEV) or restricted to the lower limit of Lohmann Brown-Lite recommended BW; and three dietary ME levels: Low, Standard (Std), and High (2,600, 2,800, and 3,000 kcal/kg, respectively); the fourth treatment enabled birds to choose from the three diets (Choice). Experiment 2 was a 2 × 3 factorial arrangement with two FA levels: ad libitum or restricted to the lower limit of the strain recommended BW; and three dietary ME levels: Low, Std, and High. In Experiment 1, age at first egg (AFE), BW at first egg (BWFE), and carcass composition estimations were recorded. In Experiment 2, age at 50 % of egg production (A50), BW at 50 % of egg production (BW50), and chemical carcass composition were determined. Weight of reproductive organs were measured only in Experiment 2. Data were submitted to ANOVA on each experiment with the two main effects and age as fixed factors. Differences were reported where P ≤ 0.05. The BWFE and BW50 were greater in the MEV- and ad libitum-fed compared to the feed restricted birds in Experiments 1 and 2, respectively. Carcass lean and fat percentage were greater and lower in the feed restricted compared to the MEV- and ad libitum-fed pullets at 20 and 18 wk of age, respectively. Carcass fat percentage around photostimulation age (18 and 20 wk) was greater in the High ME compared to the Low ME fed pullets. Large yellow follicles (number and weight) and ovary (weight and percentage) were greater in ad libitum-fed compared to feed restricted birds. In conclusion, pullets fed greater dietary ME increased fat deposition and feed restricted birds had delayed sexual maturation.

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.

This study aimed to evaluate the effect of early growth (EG) and time of maximum pubertal growth peak (I2) on development, feed efficiency, carcass composition, and sexual maturation of broiler breeder females. Target BW trajectories were designed by changing coefficients of a 3-phase Gompertz model fit to the recommended BW target of Ross 308 breeders, [Formula: see text] . In each phase i, biologically relevant coefficients describe the amount of BW gain (g_i), the rate of growth (b_i), and the inflection point (I_i), which is the time when the growth rate for that phase is at its maximum rate. The study consisted of a 6 × 2 factorial arrangement, with six I2 levels (I from phase 2) and two EG levels. The I2 coefficients were 15, 17, 19, 21 (standard), 22, and 23 in wk. The EG treatments were: EG0, where g₁ and g₂ coefficients estimated from the standard from the breeder recommended BW were unchanged; and EG20, where 20% of the gain (g₂) in phase 2 (pubertal phase) was shifted to phase 1 (g₁; prepubertal phase). Two-hundred-eighty-eight Ross 308 pullets were randomly assigned to the twelve BW growth trajectories and fed using a precision feeding system from 0 to 28 wk of age. Body composition variables were submitted to three-way ANOVA, with EG, I2, and age as fixed sources of variation. Analysis of covariance was conducted on the remaining dependent variables with EG as fixed effect, I2 as a continuous fixed effect, and age as continuous random effect. Differences were reported at P ≤ 0.05. The BW of females followed their target BW, and ADFI differed depending on the amount of feed required to achieve their respective BW targets. Breast fleshing score was 0.2 greater in the EG20 compared to EG0. The number of juvenile primary wing feathers and age at first egg decreased by 0.4 and 0.9 d, respectively, per wk of earlier I2. Advancing I2 resulted in birds with increased carcass fat deposition from 16 to 28 wk of age. Carcass fat was 1.3- to 1.6-fold greater in the EG20 only from 4 to 16 wk of age. Early growth increased mostly pullet muscle and skeletal characteristics whereas advancing I2 advanced sexual maturity and increased carcass fat deposition around sexual maturation time.

The objective of this study was to develop appropriate correction equations for dual energy X-ray absorptiometry (DXA) for total carcass composition of live meat- and egg-type chickens. Linear (bivariate linear and multivariate linear) and nonlinear (polynomial, multivariate polynomial, broken-line and Gompertz) equations were used to estimate carcass composition of DXA-scanned birds based on chemical proximate analysis. A total of 288 laying females (10-30 wk of age) and 305 broiler breeder females (4-32 wk of age) were used. The same birds scanned by DXA were dissected and utilized for whole-body proximate chemical analysis for body lean, fat, and mineral content (ash). As indicators of carcass fat and lean, abdominal fat pad and breast muscle weights were also recorded. Models were evaluated using root mean square error (RMSE), Bayesian Information Criterion (BIC), coefficient of determination (R²), Durbin Watson test for autocorrelation (DW), and residuals observation (RES). Model estimations were done separately by strain or combined. Estimations of composition responses fit at least 1 of each linear and nonlinear models for the egg- and meat-type chickens on all parameters estimated (P < 0.05). In the egg-type chickens, multivariate linear regression was the best fit for body lean with the lowest RMSE and BIC, and highest R² whereas body fat, body ash, and breast muscle were best predicted by the multivariate polynomial model. In the meat-type chickens, body lean was best predicted by the multivariate linear model with the lowest RMSE and BIC, and the highest R² whereas the multivariate polynomial was the most parsimonious model for body fat, body ash, and abdominal fat. Positive autocorrelations were observed in several models tested for body fat, body ash, breast muscle, and abdominal fat pad when both strains were analyzed combined (P < 0.05). In summary, a strain-based correction is recommended to all the parameters, with exception of the BW estimation. Correction equations developed in this study demonstrated that the DXA technique is a reliable alternative to proximate chemical analysis in egg- and meat-type chickens.

The objective of this study was to evaluate the effect of shifted gain from the pubertal to prepubertal phase (early growth; EG) and timing of maximum pubertal growth (inflection point of a second growth phase; I2) on BW, feed efficiency, carcass composition, and reproductive performance of broiler breeder hens. Target BW trajectories were designed by changing coefficients of a 3-phase Gompertz model fit to the recommended Ross 308 BW target, [Formula: see text] . In each phase i, biologically relevant coefficients describe the amount of BW gain (g_i), the rate of growth (b_i), and the inflection point (I_i), which is the age (wk) when the growth for that phase is at its peak. The study had a 6 × 2 factorial arrangement of treatments, with six I2 levels (I from phase 2) and two EG levels. The I2 coefficients were 15, 17, 19, 21 (standard), 22, and 23. The EG treatments were: EG0, where g₁ and g₂ coefficients estimated from the standard breeder recommended BW were unchanged; and EG20, where 20% of the gain (g₂) in phase 2 (pubertal phase) was shifted to phase 1 (g₁; prepubertal phase). Two-hundred-eighty-eight Ross 308 pullets were randomly assigned to the twelve BW growth trajectories and fed using a precision feeding system from 0 to 60 wk of age. Weekly BW was analyzed using three-way ANOVA (EG, I2, and age as fixed sources of variation). Analysis of covariance was conducted on the remaining dependent variables with EG as fixed effect, I2 as a continuous fixed effect, and age as continuous effect. The observed BW followed the BW target trajectories for most of the experiment duration. Dorsal feather score decreased by 0.11/wk of earlier I2. Egg production, egg weight, and egg mass increased by 0.83%, 0.09 g, and 0.54 g/d for every week of earlier I2, respectively. Total eggs produced and estimated chick number per hen increased by 3.6 eggs and 4.4 chicks for every week of earlier I2, respectively. In conclusion, advancing BW gain around the pubertal phase of growth in modern broiler breeders increased egg and chick production.