Model to predict age at sexual maturity in broiler breeders given a single increment in photoperiod

Effect of body weight at photostimulation on productive performance and welfare aspects of commercial layers

OBJECTIVE

Due to current selection practices for increased egg production and peak persistency, the production profile, age at maturity, and body weight criteria for commercial layers are constantly changing. Body weight and age at the time of photostimulation will thus always be the factors that need to be adequately addressed among various production systems. The current study was carried out to determine the effects of pullets' body weight (low, medium, and heavy) on their performance, welfare, physiological response, and hormonal profile.

METHODS

With regard to live weight, 150 16-week-old pullets were divided into three groups using a completely randomized design (CRD) and held until the 50th week. One-way analysis of variance was used to evaluate the data under the CRD, and the least significant difference test was used to distinguish between treatment means.

RESULTS

In comparison to the medium and light birds, the heavy birds had higher body weight at maturity, an earlier age at maturity, and higher egg weight, eggshell weight, eggshell thickness, egg yolk index, breaking strength, egg surface area, egg shape index, egg volume, and hormonal profile except corticosterone. However, the medium and light birds had lower feed consumption rates per dozen eggs and per kilogram of egg mass than the heavy birds. Light birds showed greater body weight gain, egg production, and egg specific gravity than the other categories. At 20 weeks of age, physiological response, welfare aspects, and catalase were non-significant; however, at 50 weeks of age, all these factors-aside from catalase-were extremely significant.

CONCLUSION

The findings of this study indicate that layers can function at lower body weights during photostimulation; hence, dietary regimens that result in lighter pullets may be preferable. Additionally, the welfare of the birds was not compromised by the lighter weight group.

Update and evaluation of the egg production model in laying hens

The egg production model (EPM) described here is a mechanistic and stochastic model that simulates the amino acid and energy requirements of laying hens. It takes into account their potential rate of laying, and egg weight over time, and the composition of the feed provided. The model predicts feed intake based on the assumption that hens will consume enough feed to reach their genetic potential. The environment is assumed to be non-limiting, although feed intake may be constrained by bulk capacity when bulky feeds are offered. The simulation model integrates a least-cost feed formulator, which enables the prediction of a feeding program that maximizes economic returns. A series of simulations were conducted to demonstrate the model behavior, external evaluation, and the economic optimization routine. The model behavior showed that as the energy content in the feed decreased, the simulated feed intake increased to compensate. Consequently, feeds with lower energy concentrations led to an overconsumption of nutrients, resulting in increased egg component weights (yolk and albumen). However, when the balanced protein was reduced while maintaining a constant energy-to-protein ratio, there was no change in egg components, consistent with published literature. The external evaluation indicated that feed intake, egg production, and egg weight were estimated with low error, and there was a similar trend observed between the estimated and observed data. This demonstrates the reliability of the model. Additionally, the paper provides a demonstration of how to use and interpret the results from the egg production model, including the economic optimization routine. The study found that a feed containing 7.8 g/kg of digestible lysine maximized economic returns. This optimization tool can be valuable in making nutritional decisions to optimize economic returns in an egg production system.

Welfare of broilers on farm

This Scientific Opinion considers the welfare of domestic fowl (Gallus gallus) related to the production of meat (broilers) and includes the keeping of day-old chicks, broiler breeders, and broiler chickens. Currently used husbandry systems in the EU are described. Overall, 19 highly relevant welfare consequences (WCs) were identified based on severity, duration and frequency of occurrence: 'bone lesions', 'cold stress', 'gastro-enteric disorders', 'group stress', 'handling stress', 'heat stress', 'isolation stress', 'inability to perform comfort behaviour', 'inability to perform exploratory or foraging behaviour', 'inability to avoid unwanted sexual behaviour', 'locomotory disorders', 'prolonged hunger', 'prolonged thirst', 'predation stress', 'restriction of movement', 'resting problems', 'sensory under- and overstimulation', 'soft tissue and integument damage' and 'umbilical disorders'. These WCs and their animal-based measures (ABMs) that can identify them are described in detail. A variety of hazards related to the different husbandry systems were identified as well as ABMs for assessing the different WCs. Measures to prevent or correct the hazards and/or mitigate each of the WCs are listed. Recommendations are provided on quantitative or qualitative criteria to answer specific questions on the welfare of broilers and related to genetic selection, temperature, feed and water restriction, use of cages, light, air quality and mutilations in breeders such as beak trimming, de-toeing and comb dubbing. In addition, minimal requirements (e.g. stocking density, group size, nests, provision of litter, perches and platforms, drinkers and feeders, of covered veranda and outdoor range) for an enclosure for keeping broiler chickens (fast-growing, slower-growing and broiler breeders) are recommended. Finally, 'total mortality', 'wounds', 'carcass condemnation' and 'footpad dermatitis' are proposed as indicators for monitoring at slaughter the welfare of broilers on-farm.

Changes in body composition and energetic efficiency in response to growth curve and dietary energy-to-protein ratio in broiler breeders

Body composition plays an important role in reproduction in broiler breeders. The aim of this study was to evaluate the dynamics in body composition and energetic efficiency in broiler breeders, using different dietary strategies. About 1,536-day-old pullets were randomly allotted to 24 pens in a 2 × 4 factorial design with 2 growth curves (standard or elevated (+15%)) and 4 diets, with a step-wise increment in energy (96, 100, 104, and 108% apparent metabolizable energy nitrogen corrected [AME_n]) fed on a pair-gain basis. Body composition was determined at 10 time points from 0 to 60 wk of age. Body protein mass was linearly related to body weight (BW) in growing breeders, which can be expressed as -6.4+0.184*BW (R² = 0.99; P < 0.001). Body fat mass was exponentially related to BW in growing breeders, which can be expressed as -42.2+50.8*1.0006^BW (R² = 0.98; P < 0.001). A higher energy-to-protein ratio resulted in higher body fat mass at the same BW (P < 0.001). Sexual maturation was related to body protein mass at 21 wk of age, where each 100 g of body protein mass extra advanced sexual maturation by 5.4 d (R² = 0.83). Estimates of energetic efficiency for growth (k_g) and egg production (k_e) appeared not constant, but varied with age in a quadratic manner between 0.27 and 0.54 for k_g and between 0.28 and 0.56 for k_e. The quadratic relationship could be expressed as k_g=0.408-0.0319*Age+0.00181*Age² (R² = 0.72; P < 0.001) and k_e=-0.211+0.034*Age-0.00042*Age² (R² = 0.46; P < 0.001). Body protein mass in broiler breeders is tightly regulated and mainly depended on BW and seems to be the main determinant for sexual maturation. Body fat mass is exponentially related to BW, where an increase in dietary energy-to-protein ratio results in a higher body fat mass. Treatments had minimal effects on estimated energetic efficiencies in breeders.

Early photostimulation at the recommended body weight reduced broiler breeder performance

To synchronize the onset of sexual maturity in the face of high BW variation, the age at photostimulation has been increasing in the broiler breeder industry. This experiment studied the effects of increased BW and earlier photostimulation on broiler breeder reproductive performance where within-treatment BW uniformity was very high. The experiment tested BW and age at photostimulation treatments in a 2 × 2 factorial arrangement. Hens (n = 120) were fed with a precision feeding system to allocate feed individually following the breeder-recommended target BW (Standard) or to a 22% heavier target BW curve reaching the Standard 21 wk BW at 18 wk (High). Hens were photostimulated at either 18 wk (18WK) or 21 wk (21WK) with a 16L:8D photoschedule. Age at first egg (AFE) and individual egg production to 55 wk were recorded. Differences were reported as significant if P ≤ 0.05. The AFE was decreased and maturation interval between photostimulation and AFE was shorter for hens on the High BW treatment compared to the Standard BW treatment (178.1 vs. 194.7 d and 41.8 vs. 58.2 d, respectively). Hens on the 21WK treatment had a decreased AFE compared to the 18WK treatment (177.0 d vs. 195.9 d) and their maturation interval was shorter (30.0 d vs. 69.9 d). The CV for AFE was higher in the 18WK treatment compared to the 21WK treatment (28.2% vs. 11.2%). Total egg production was higher for hens on the High BW treatment compared to the Standard BW treatment (129.4 vs. 92.8, respectively). Total egg production was higher for hens on the 21WK treatment compared to the 18WK treatment (138.4 vs. 83.8, respectively). Egg weight of Standard BW × 18WK hens was lower compared to High BW × 18WK hens. Current recommended breeder BW may be too low for optimal sexual maturation after photostimulation. It is concluded that even when BW variation is minimized, photostimulation at 18 wk of age is not recommended.

Description of a model to optimise the feeding of amino acids to growing pullets

1. A nutrition model is described that may be used to optimise the amino acid nutrition of laying-type pullets prior to the onset of lay. It is not a method of optimising lifetime laying performance. 2. The potential growth and composition of the body, feathers, ovary and oviduct are described from hatching to the age at which sexual maturity is attained, from which the daily amino acid and energy requirements for the average individual in the population can be calculated. 3. There are two parts to the approach used, the first being a description of the model itself and the second being a description of how the required information was gathered. A number of assumptions made in developing the model are discussed. 4. The rates of maturing of the body, feather-free body and body protein of the DeKalb pullets used were shown to be constant at 0.017/d and those of feathers at 0.02/d. These are considerably slower than those of the oviduct and ovary (0.139 and 0.084/d respectively). The ovary attained a higher mature weight (78.4 vs. 58.7 g) than the oviduct. 5. The age at which the growth of the reproductive organs is initiated in the model is defined by the user. The daily amount of threonine required to meet the requirements for maintenance and potential growth of the developing tissues and organs is calculated for each day of the growing period from hatching to the age at which the first egg is laid. A method of calculating the required daily concentration of threonine in the feed is described, from which a feeding programme may be derived. 6. For the model to produce an optimum economic feeding programme for a population of laying-type pullets, more information than is available from this study is required. These issues are discussed in the paper.

Effects of feeding programme and feeder space change at photo-stimulation using maize- or wheat-based diet on growth and reproductive performance of female broiler breeders

1. This study was carried out to determine the effects of breeder feeding programme to 29 weeks of age, and feeder space change at photo-stimulation using two sources of grain on breeder hen reproductive efficiency and egg characteristics. 2. Fast-feathering Cobb 500 pullet broiler breeders were housed in 16 pens of 81 females each during rearing, and fed on either maize- or wheat-based diet, formulated to have similar nutrient composition. Two feeding programmes, Fast and Slow, were used from 14 to 29 weeks of age. At 22 weeks of age, 69 females that represented the body weight (BW) distribution from each pen were placed in a layer house where feeder space either remained very similar (from 6.3 to 6.5 cm/female) or was increased (from 6.3 to 8.4 cm/female). Breeder growth performance, reproductive efficiency and egg characteristics were evaluated. 3. Data were analysed as a 2 × 2 × 2 factorial design with diet type, feeding programme and feeder space change as the main factors. The main effects of the treatments were found but there were no treatment interactions. 4. Breeders fed on wheat were consistently heavier than breeders fed on maize from 10 to 52 weeks of age and exhibited greater hen mortality during the layer phase. Breeders fed on wheat diets exhibited improved egg production while laying eggs with a greater yolk:albumen ratio compared to the maize group. 5. The Fast feeding programme increased female mortality and increased BW during the layer phase. Breeders fed according to the Slow feeding programme had better fertility, and laid eggs with lower percentage eggshell that might be associated with the lower early embryonic mortality observed in these hens as compared with the Fast feeding programme. 6. Breeders having increased feeder space at photo-stimulation matured earlier and produced more eggs compared to breeders with no change in feeder space. 7. It was concluded that the feeding of wheat, the use of the Slow feeding programme and an increase in feeder space improved some aspects of hen productivity and egg characteristics.

Modelling changes in the components of eggs from broiler breeders over time

1. Because the components of the egg differ in nutrient content, and the proportions of these components change over time, the daily intake of nutrients required to produce an egg will also change with time. Information on these relationships is essential when attempting to determine the nutrient requirements of a broiler breeder hen at different stages of lay, and in predicting performance when the hen is supplied with a given amount of food with a given nutrient composition. 2. Yolk weight is related to hen age and may be predicted using a linear-by-linear function, the coefficients of which are the same for Cobb and Ross breeders. Allometric functions may be used to predict albumen weight from yolk weight, and shell weight from the weight of the egg contents. Egg weight is given by the sum of the three components. 3. The proportion of yolk increased with advancing age whilst the proportions of albumen and shell decreased. However, at a given age, larger eggs contain proportionally more albumen. Eggs from Cobb hens had proportionately more albumen than Ross eggs towards the end of lay. 4. A stochastic population model verified that these functions accurately reflect the proportional changes in the egg components with advancing hen age and at a given age, over a range of egg weights.

Temporary exposure of prepubertal, somatically-mature broiler breeder females to stimulatory photoperiods

1. Individually-caged Ross 308 broiler breeders were transferred temporarily at 147 d from 8 to 14-h photoperiods and back to 8 h at 5-d intervals from 5 to 25 d and at 32 d. Control birds were maintained on 8 h or transferred permanently to 14 h. 2. Five long days had minimal effect on age at first egg, between 10 and 25 long days progressively accelerated sexual development, and maximum advance was achieved by 32 long days. However, a model involving the ogive of a normal distribution with a mean of 14 long days and an SD of 5.3 indicated that 28 long days would be sufficient to maximise sexual development. 3. The similarity of this model for broiler breeders with one previously produced for egg-type pullets suggested a common physiological mechanism for photosexual responses to two opposing changes in photoperiod.

Photoperiods for broiler breeder females during the laying period

Ross 308 broiler breeder females, maintained in litter-floor pens, were reared from 2 d of age on 8-h photoperiods and transferred abruptly to an 11-, 12-, 13-, or 14-h photoperiod at 20 wk of age and at a mean BW of 2.09 kg. Four qualitative dietary treatments were superimposed upon each photoperiodic treatment, but, in the absence of any significant interactions of photoperiod with diet, only photoperiodic means are reported. Age at 50% egg production (ASM) was progressively advanced as photoperiod increased from 11 to 13 h but was similar for 13-h and 14-h birds. Egg production was significantly related to ASM, with peak egg numbers being stimulated by a transfer to 13-h photoperiods. Rate of lay after 48 wk of age declined more rapidly in the 14-h birds than in any of the other groups, suggestive of an earlier onset of adult photorefractoriness. More eggs were laid outside the nest box and more cracked and dirty eggs were produced by birds on 11- and 12-h photoperiods than on 13- or 14-h photoperiods. Mean egg weight was positively correlated with ASM but negatively related to photoperiod; the number of eggs thought to be double-yolked was not significantly affected by photoperiod. Total egg mass output was not significantly affected by photoperiod. Birds exposed to 11-h and 12-h photoperiods were heavier at 60 wk than birds transferred to 13- or 14-h photoperiods. These findings show that a transfer from 8 to 13 h at 20 wk optimizes egg-laying performance in broiler breeder females, especially when they are kept beyond 60 wk of age.

Stochastic modelling of optimum initial body weight, daily weight gain and effect of genetic changes in ovulation rate and age at sexual maturity on total egg production of broiler breeders

1. A model that simulates the total production of eggs (TEP) in broiler breeders was used to predict the optimum initial (20 week) body weight (IBWexp), daily weight gains from 20 to 30 (DWGexp(20-30)) and 31 to 62 weeks of age (DWGexp(31-62)), age at photostimulation (affecting age at first egg, AFEexp), coefficients of variation of initial body weight (CV-IBWexp) and age at first egg (CV-AFEexp), and the effect of genetically increasing the numbers of yellow follicles at the onset of lay. 2. The results suggest that TEP in broiler breeders is very sensitive to changes in body weight gain during the first 10 weeks of the production period and body weight at the start of egg production, whereas changes in body weight gain after peak rate of lay showed only minor effects on TEP. Increasing CV-IBWexp was associated with a linear decrease in the mean and increased variability of TEP. 3. Decreasing AFEexp was negatively associated with TEP, whereas higher CV-AFEexp increased variability of TEP and had a trivial affect on the mean. 4. Results of the simulation suggested that reducing ovarian yellow follicle numbers by means of genetic selection could reduce the degree of feed restriction currently used in broiler breeder commercial stocks while maintaining total egg production. Higher numbers of yellow follicles associated with selection for higher growth rate would not result in lower egg production if the body weight target was maintained at the currently recommended commercial level and the effect on TEP of increasing the target in proportion to potential body weight may be relatively small.

Illuminance, sexual maturation, and early egg production in female broiler breeders

1. Broiler breeders were reared at an initial illuminance of 13, 21 or 44 lux and transferred at 20 weeks and a mean body weight of 2.06 kg to floor pens at 25, 55 or 71 lux, or to individual cages at various intensities between 3 and 138 lux. 2. Rate of sexual maturation was not significantly affected by the light intensity experienced during the rearing period, but was progressively accelerated by the provision of a brighter illuminance after 20 weeks, up to a ceiling of about 14 lux. There was no interaction between the pre- and post-20-week illuminance. 3. Cumulative egg numbers to 39 weeks were unaffected by illuminance in the rearing period, positively correlated with illuminance post 20 weeks up to an asymptote at about 8 lux, and highly correlated with age at sexual maturity. Peak rate of lay was both delayed and depressed at 3 lux. 4. It is concluded that the minimum light intensity required at bird-head height to achieve satisfactory photostimulation and an optimal peak rate of lay in broiler breeders is 10 lux, but that a higher illuminance would be prudent for broiler breeders kept in floor pen facilities to maximise nest-box usage.