Implications of changes to commercial broiler and broiler breeder body weight targets over the past 30 years

Genetic Variance Estimation over Time in Broiler Breeding Programmes for Growth and Reproductive Traits

Monitoring the genetic variance of traits is a key priority to ensure the sustainability of breeding programmes in populations under directional selection, since directional selection can decrease genetic variation over time. Studies monitoring changes in genetic variation have typically used long-term data from small experimental populations selected for a handful of traits. Here, we used a large dataset from a commercial breeding line spread over a period of twenty-three years. A total of 2,059,869 records and 2,062,112 animals in the pedigree were used for the estimations of variance components for the traits: body weight (BWT; 2,059,869 records) and hen-housed egg production (HHP; 45,939 records). Data were analysed with three estimation approaches: sliding overlapping windows, under frequentist (restricted maximum likelihood (REML)) and Bayesian (Gibbs sampling) methods; expected variances using coefficients of the full relationship matrix; and a "double trait covariances" analysis by computing correlations and covariances between the same trait in two distinct consecutive windows. The genetic variance showed marginal fluctuations in its estimation over time. Whereas genetic, maternal permanent environmental, and residual variances were similar for BWT in both the REML and Gibbs methods, variance components when using the Gibbs method for HHP were smaller than the variances estimated when using REML. Large data amounts were needed to estimate variance components and detect their changes. For Gibbs (REML), the changes in genetic variance from 1999-2001 to 2020-2022 were 82.29 to 93.75 (82.84 to 93.68) for BWT and 76.68 to 95.67 (98.42 to 109.04) for HHP. Heritability presented a similar pattern as the genetic variance estimation, changing from 0.32 to 0.36 (0.32 to 0.36) for BWT and 0.16 to 0.15 (0.21 to 0.18) for HHP. On the whole, genetic parameters tended slightly to increase over time. The expected variance estimates were lower than the estimates when using overlapping windows. That indicates the low effect of the drift-selection process on the genetic variance, or likely, the presence of genetic variation sources compensating for the loss. Double trait covariance analysis confirmed the maintenance of variances over time, presenting genetic correlations >0.86 for BWT and >0.82 for HHP. Monitoring genetic variance in broiler breeding programmes is important to sustain genetic progress. Although the genetic variances of both traits fluctuated over time, in some windows, particularly between 2003 and 2020, increasing trends were observed, which warrants further research on the impact of other factors, such as novel mutations, operating on the dynamics of genetic variance.

Review: Current challenges in poultry nutrition, health, and welfare

The poultry industry has benefited greatly from advances in genetics, nutrition, housing and management strategies. Geneticists have made welfare and health traits important components of selection programs, and in general, modern, high-producing poultry are healthier than 30 years ago. However, increased productivity means that the birds are closer to their physiological limits, and nutrition, environment and management have become increasingly important. The move away from in-feed antibiotic growth promotors has resulted in challenges in maintaining gut health and consequently, bird performance. However, as the industry adapts to production without the use of antibiotic growth promotors, long-term benefits may be realized due to a reduction in antimicrobial resistance. Intensive selection for meat yield and efficiency are associated with an increased risk of muscle myopathies that affect bird health and meat quality. As genetic selection increased broiler production traits, it became necessary to restrict parent stock nutrient intake in order to prevent excessive muscle and fat deposition, reduce metabolic disease, and maintain ovarian control. With continued selection for broiler production traits, the degree of restriction implemented has become a welfare issue. Additionally, recent research suggests that highly efficient broiler lines may have limited fat deposition and therefore energy reserves to support sexual maturation and egg production, especially if typical broiler breeder BW targets are maintained. A re-examination of broiler breeder feeding programs is necessary to maintain productivity and welfare. Modern laying hens are capable of laying cycles in excess of 100 weeks of age. This has reduced the use of stress-inducing forced molting programs and reduces the total number of hens needed to meet the demand for egg production. The important role of the skeletal system in eggshell deposition demands that skeletal development during rearing be carefully managed to avoid shell and skeletal problems at the end of the production cycle. As the production potential of modern poultry continues to increase through genetic and genomic selection, even greater care must be paid in order to maintain bird health and welfare. The poultry industry has successfully faced many challenges in the past and is likely to overcome the existing challenges as well.

Fast growing broiler production from genetically different pure lines in Turkey. 1. Parental traits: growth, feed intake, reproduction, and hatching traits

The aim of the present study was to reveal the trends in age-related growth, feed intake, reproduction, and hatchability traits in 5 pure line (PL) breeders (3 dam [A1: slow-feathering, A2: fast-feathering, A3: slow-feathering] and 2 sire [B1: fast-feathering, B2: fast-feathering]) and their reciprocal two-way cross parent stock (PS) breeders (6 female [A1♂ × A2♀; A1♂ × A3♀; A2♂ × A1♀; A2♂ × A3♀; A3♂ × A1♀; A3♂ × A2♀] and 2 male [B1♂ × B2♀; B2♂ × B1♀]) and to identify heterotic effects in two-way cross PS combinations showing superiority over PL breeders. In the rearing period, 60 females and 15 males in the each PL group, 120 females in each female PS and 120 males in each male PS breeders, and 40 females and 5 males were used in each PL and PS genotype in the laying period. Body weight (BW), average daily feed intake (ADFI), reproductive traits (age at first egg [AFE], age at sexual maturity [ASM], egg number, weekly and total %Lay, egg weight, egg mass), hatching traits (fertility, hatchability of fertile [HOF] and set [HOS] and embryonic mortality), and heterosis (%) values for some traits were assesed. Both males and females of PLs and PSs had different BW at 4 and 8 weeks of age (P < 0.01), but had similar BW from 12 to 24 weeks of age. The A2, B1, and B2 hens had a higher BW (nearly 4000 g) than the others at 31 weeks of age (P < 0.01), and B2 hens showed a BW of more than 5000 g at 64 weeks (P < 0.001). Weekly ADFI per female in rearing, laying, and overall period was not different between groups. The A1 (179 days), A3 (183 days), two-way cross (from 175.5 to 185.5 days) hens started laying at a similar age and earlier than B1 (184 days), A2 (192 days), and B2 (194 days) hens. From AFE to 64 weeks, %Lay was the highest in the A1 line (69.7%), lowest in the B1 (45.3%) and B2 (48.8%) line, and between 56.9 and 64.8% in PS breeder hens. The PS eggs tended to have higher fertility, HOF, and HOS, and less embryonic mortality compared to PL eggs. Negative and low heterosis for AFE was observed in PS eggs, while positive heterosis for fertility, HOF, and HOS was generally observed in four-way hybrid eggs. The highest heterosis for the 64-week cumulative egg number was observed in A3 × A2 hens. Our study results show that mating of B1 × B2 males with A3 × A2 females seems more favorable in terms of higher egg or chick production. However, more knowledge is also needed for the overall efficiency of each PS, including the final performance of its hybrids.

Feed Space Allowance and Perch Design Criteria for Broiler Breeders Determined by Biometric Data

Simple Summary

This investigation obtained data of broiler breeders’ body measurements to develop adjusted barn equipment, in order to realize high welfare standards and legal requirements. The broiler breeders had an average body weight of 2791.80 g (female) and 3615.88 g (male), and female broiler breeders had a body width of 20.63 cm, while it was 21.94 cm for the males. Accordingly, a trough side and perch length of 21.00 cm (female) or 22.00 cm (male), respectively, must be provided to ensure that all broiler breeders have equal access to feed and to perches. The feet showed an average length of 10.14 cm (female) and 12.05 cm (male). These measurements can be used for perch design.

Abstract

The equipment used in broiler breeder houses is an important factor in allowing the expression of the various behaviours of the animals, and thus realizing high welfare standards. Presently, detailed requirements for the equipment in broiler breeder houses are not specified in Germany, especially feed space and perch design allowance. One reason is that basic biometric data on broiler breeders are lacking. To close this gap, a pilot study was conducted, and birds’ width, weight, and feet were measured. Broiler breeders at 22 weeks of age (50 female and 17 male) were weighed and photographed digitally, and their body widths were calculated from the photographs. Female broiler breeders weighed 2791.80 ± 334.99 g on average and showed a body width of 20.63 ± 1.88 cm. For males, a mean of 3615.88 ± 432.46 g was measured with a body width of 21.94 ± 2.32 cm. Our examinations revealed that a trough side length of 21.00 cm per hen and 22.00 cm per cock must be provided to ensure that all broiler breeders have equal access to feed. The same dimensions should be planned as the perch length for each animal. Measurements of broiler breeders’ feet (506 female and 150 male Cobb 500) were performed at 60 weeks of age. The length of each toe and the width and length of the foot pad of both sexes were photographed and measured digitally. Female broiler breeders’ feet showed an average length of 10.14 cm, and male birds showed a length of 12.05 cm. Based on recommendations for the perch design for laying hens, round and oval perches for broiler breeders should have a circumference of at least 11.30 cm (female) or 13.40 cm (male). For angular perches, the upper contact area should have a width of 2.80 cm (female) or 3.40 cm (male). The obtained biometric data could be a useful basis for the development of legal requirements for broiler breeders.

Relationship among Sex, Skin Color, and Production Parameters of Broiler in Pectoral Myopathies

Breast anomalies in broilers, especially wooden breast (WB) and spaghetti meat (SM), cause high economic losses to the poultry meat sector. In order to identify the parameters that have a causal effect and to reduce the incidence of these myopathies, 141,792 broilers were analyzed in a total of 1477 batches using a visual grading system. The relationship among productive parameters such as the feed conversion ratio, live weight, growth rate, and mortality, was evaluated. Effects due to skin color (white vs. yellow), broiler sex (male, female, and mixed groups), feed presentation (grain vs. mash), and veterinary treatments (treated vs. untreated) were also included in the statistical study. Live weight was observed to have a significant effect (p < 0.001) on WB incidence, which increased by 1.11 for each 100 g of weight. Weight did not significantly affect the incidence of SM. Males had a higher incidence of WB and a lower incidence of SM than females. The incidence of both myopathies varied between samples that turned out to be significantly affected by some of the variables considered in the model, such as grain feeding and the feed conversion ratio. Controlling these factors in the broiler production could help to reduce the incidence of WB and SM.

Effect of early photostimulation at 15-weeks of age and everyday spin feeding on broiler breeder performance

To prevent broiler breeders from growing too quickly and becoming too large for optimum reproduction, their dietary intake is restricted. While current restricted feeding programs, such as skip-a-day feeding (SAD), improve the economic efficiency of broiler breeder operations, this management practice impacts bird welfare. There is an interest in finding strategies that could reduce the impact of feed restriction during broiler breeder rearing. This research investigated the effects of feeding pullets on an advanced growth curve for early photostimulation at 15 wk (15P) or standard growth curve for photostimulation at 21 wk (21P), using either an every-day-spin feeding program (EDS) or SAD feeding, on the reproductive parameters of broiler breeder hens in a 2 × 2 factorial arrangement. Overall, advancing the growth curve (15P) decreased blood corticosterone levels compared to 21P, but EDS resulted in higher blood corticosterone levels compared to SAD. At the end of rearing in both 15P and 21P, EDS pullets weighed less than SAD pullets. The onset of egg production was 20 and 24 wk of age for the 15P and 21P hens, respectively. Despite an earlier onset, 15P hens did not produce more eggs than 21P hens through 65 wk of age. Egg weight was reduced for 15P compared to 21P until 30 wk of age. The 15P hens had a greater number of double yolk eggs than the 21P hens. Fertility and hatch were not impacted by the advanced growth curve and early photostimulation. Although the current research indicates the potential to reduce feed restriction associated welfare issues by rearing broiler breeder pullets for an earlier photostimulation onset, further research in needed to determine if this management technique can be improved to optimize hen reproductive efficiency.

Broiler growth and efficiency in response to relaxed maternal feed restriction

Broiler growth performance can be influenced by maternal BW, maternal age, and sex. The present study evaluated broiler growth and efficiency in response to increased maternal BW (relaxed level of maternal feed restriction). It was hypothesized that BW and fatness would increase, and efficiency would be reduced as maternal BW increased. Ten BW trajectories were applied to precision-fed Ross 708 female broiler breeders (n = 30) from 2 to 42 wk of age. Trajectories varied in prepubertal and pubertal growth phases from 2.5 to 22.5% above the recommended BW target. Additional unrestricted breeders (n = 6) were not limited to a maximum BW (fed ad libitum). Two 35 d experiments were conducted with precision-fed broilers from these breeders at 35 and 42 wk of age. Two analyses (full and restricted analysis scopes) were performed to evaluate broiler BW, feed conversion ratio (FCR) and carcass traits with maternal BW at photostimulation (22 wk of age) as a continuous effect, and maternal age and sex as discrete effects. The full scope included broilers from all hens (feed restricted and unrestricted). The restricted scope excluded broilers from unrestricted hens. Differences were reported at P ≤ 0.05. For every kilogram increase in maternal BW, cumulative FCR increased by 0.235 and 0.471 g:g for broilers from all and feed restricted hens, respectively. Proportional gut weight of broilers from feed restricted hens decreased by 0.8244% per kilogram increase in maternal BW. Males were heavier than females on day 28 and 35, and broilers from 42-wk-old breeders were heavier than broilers from 35-wk-old breeders on day 0 and 35. Males from all hens were more feed efficient (1.318 g:g) than females (1.335 g:g) from day 29 to 35. Females from all and feed restricted hens had a greater proportional fat pad and breast muscle weight than males, and proportional breast muscle yield of broilers from 42-wk-old breeders was on average 1.04 times greater than that of broilers from 35-wk-old breeders. Maternal BW did not affect offspring BW, reduced cumulative FCR, and reduced gut weight in the restricted analysis scope.

Impact of growth curve and dietary energy-to-protein ratio on productive performance of broiler breeders

The impact of growth curve (GC) and dietary energy-to-protein ratio on productive performance of broiler breeder females was investigated from 0 to 60 wk of age. One-day-old pullets (n = 1,536) were randomly allotted to 24 pens according to a 2 × 4 factorial arrangement, with 2 GC (standard growth curve = SGC or elevated growth curve = EGC, +15%) and 4 diets, differing in energy-to-protein ratio (96%, 100%, 104%, or 108% AME_n). Feed allocation per treatment was adapted weekly based on the desired GC, meaning that breeders fed the different diets within each GC were fed according to a paired-gain strategy. Linear and quadratic contrasts for energy-to-protein ratio for each GC were evaluated. Elevated growth curve breeders had an earlier sexual maturity (∆ = 4.1 d) than SGC breeders. Egg weight was higher for EGC breeders (∆ = 2.3 g) than for SGC breeders over the whole laying phase (22–60 wk). No differences between EGC and SGC breeders were observed on settable egg production. An increase in dietary energy-to-protein, at a similar BW, led to a linear increase in age at sexual maturity (β = 0.14 d/% AME_n). From 22 to 40 wk of age, an increase in dietary energy-to-protein ratio led to a linear decrease in egg weight (β = -0.06 g/% AME_n), regardless of GC. An interaction between GC and dietary energy-to-protein ratio was observed on settable egg production in this phase. An increase in dietary energy-to-protein ratio led to a linear decrease on settable egg production, which was more profound in EGC breeders (β = -0.70 eggs/% AME_n) than in SGC breeders (β = -0.19 eggs/% AME_n). From 41 to 60 wk of age, an interaction between GC and dietary energy-to-protein ratio was observed on egg weight. In the EGC, an increase in dietary energy-to-protein ratio led to a linear decrease in egg weight (β = -0.13 g/% AME_n), whereas in the SGC, a linear increase in egg weight was observed (β = 0.03 g/% AME_n). From 41 to 60 wk of age, no differences between diets were observed on settable egg production. It can be concluded that a higher GC of breeders has beneficial effects on egg weight, while maintaining settable egg production. Feeding breeders a lower dietary energy-to-protein ratio stimulated productive performance of broiler breeder hens, mainly during the first phase of lay. This effect was more profound when breeders were fed according to a higher GC.

Intergenerational effects of maternal growth strategies in broiler breeders

Maternal growth patterns affect broiler growth performance. The current study investigated the impact of lesser growth restriction, compared to the breeder-recommended target growth, during the prepubertal growth phase and earlier pubertal growth in breeders on their offspring growth and carcass traits. In a randomized controlled trial, a total of 40 female broiler breeders were randomly assigned to 10 unique growth trajectories with 2 levels of maternal BW gain (MW) in prepubertal phase and 5 levels of maternal pubertal growth inflection (MI) for each level of the MW. Growth parameters (MW and MI) were estimated by fitting a 3-phase Gompertz model to the breeder-recommended BW target (Standard MW; SMW), or 10% higher (HMW). Maternal pubertal inflection was advanced by 0, 5, 10, 15, or 20% in both SMW and HMW groups. Maternal growth trajectories were implemented from 0 to 42 wk of age using a precision feeding (PF) system. The current study consisted of two cohorts that varied in maternal age (MA) of 35 and 42 wk. The broiler chicks were fed to 35 d of age, also with the PF system. Analysis of covariance was conducted on all dependent variables (BW, FCR, carcass traits) with MA, MW, and offspring sex as categorical variables and MI as a continuous predictor variable. Chicks from 42 wk old hens had higher 0 (hatch), 14, 21, and 28 d BW, liver, and heart weight, and lower FCR from 7 to 35 d of age than those from the 35 wk old hens. Compared to SMW hens, HMW hens produced female offspring with lower FCR, and male offspring with heavier gut weight. Advancing MI increased hatch BW in both sexes and 35 d BW in male broilers. For every week that the MI was advanced, hatch BW increased by 0.26 g in females and 0.39 g in males; however, 21 and 35 d BW decreased by 6.85 and 17.29 g/wk in females and increased by 10.53 and 25.94 g/wk in males, respectively. Overall, a lesser degree of growth restriction during prepubertal and earlier pubertal growth increased male offspring growth.

Feeding, feed-seeking behavior, and reproductive performance of broiler breeders under conditions of relaxed feed restriction

Broiler breeders are feed restricted to optimize reproductive performance. A randomized controlled study was conducted to investigate the effect of increasing female broiler breeder BW on feeding, feed-seeking behavior, and reproductive performance. It was hypothesized that a greater BW would decrease feeding and feed-seeking behavior, and reduce reproductive performance. Ross 708 female broiler breeders (n = 36) were fed using a precision feeding system from 2 to 42 wk of age. Ten BW trajectories were created from a multiphasic Gompertz growth model that increased growth from 0 to 22.5% in the prepubertal and pubertal phases of growth, in 2.5% increments. Six unrestricted birds were not limited to a maximum BW. Body weight was evaluated as a 2-way ANOVA. Two linear regression analyses were conducted, one which included all birds and one which excluded the unrestricted birds. For the regression analyses, BW at photostimulation (22 wk of age) was used as the continuous independent variable to represent the degree of variation between trajectories. Differences were reported at P ≤ 0.05. Body weight increased as trajectory-specific BW targets increased from 6 to 28 wk of age. Differences of BW between BW trajectories decreased during the laying period, which was a result of individual bird variation within BW trajectories. Station visit frequency decreased per kilogram increase in BW for all birds during rearing and lay, and within feed-restricted birds during lay only. The number of meals and ADFI increased with age, which reflected nutrient intake to support maintenance, growth, and reproductive requirements. Mean egg weight (EW) of all birds increased by 0.72 g per kilogram increase in BW from 22 to 41 wk of age. From 22 to 29 wk of age, mean EW of feed-restricted birds increased by 2.78 g per kilogram increase in BW. For every kilogram increase in BW, age at first egg comparing all birds decreased by 10.83 d. Two unrestricted birds came into lay before photostimulation. In contrast with the hypotheses, BW increased up to 22.5% above the recommended target did not reduce feeding and feed seeking behavior, or negatively impact reproductive performance.

Multiphasic poultry growth models: method and application

Growth and development are complex phenomena. To date, most growth modeling research has focused on a single growth phase, which is sufficient and useful for describing ad libitum fed animals processed at a prepubertal age, such as broilers or turkeys produced for meat. However, multiphase growth models are necessary to describe and predict growth and further to hypothesize about optimizing growth of reproducing animals such as broiler breeder hens. Therefore, the objective of the present study was to develop and evaluate multiphasic models to describe the growth of various types of poultry raised to reproductive age. Coefficients for monophasic, diphasic, and triphasic Gompertz model forms were estimated using a variety of BW trajectories published by primary breeders. The fit of these models was evaluated for a representative laying line hen, broiler breeder hen and rooster, and turkey hen. The coefficient of determination (R²), root mean square error, and the Bayesian information criterion were used to evaluate the fit of each model. The diphasic model was found to be the best fit for the turkey hen, while the triphasic model was the most suitable model for all the chicken lines studied. Hypotheses can be formulated based on any of the continuous model parameters, and the resulting BW trajectories can be implemented and evaluated in a systematic way. The biological relevance of the continuous parameters in multiphasic Gompertz models provides an opportunity to implement a robust hypothesis-based approach for future optimization of growth curves.

HSF3 and Hsp70 Expression during Post-Hatch Cold Stress in Broiler Chickens Subjected to Embryonic Thermal Manipulation

Decades of selective breeding for commercial purposes have rendered the broiler chicken (Gallus gallus domesticus) highly susceptible to heat and cold stress. A multitude of studies have documented the effects of thermal manipulation (TM) on broiler thermotolerance during periods of post-hatch heat stress, but very few have focused on the effect of TM on a broiler’s ability to withstand cold stress. Therefore, the primary objective of the current study is to determine the effects of TM on the acquisition of thermotolerance in broilers via their expression of the stress-associated 70 kilodalton heat shock protein (Hsp70) gene and heat shock factor 3 (HSF3) gene. Briefly, Hubbard broiler embryos were subject to TM by increasing the incubation temperature to 39 °C and 65% relative humidity (RH) for 18 h daily, from embryonic days (ED) 10 to 18. Broilers were then exposed to cold stress by decreasing the room temperature to 16 °C during post-hatch days 32 to 37. After thermal challenge, broilers were euthanized and hepatic and splenic tissues were collected. Our results showed that TM decreased the hatchability rate and body temperature but improved the body weight gain. TM generally decreased the hepatic expression but did not change the splenic expression of HSF3 during cold stress. In contrast, both hepatic and splenic Hsp70 expression decreased during cold stress. The results of the present study may suggest that TM significantly affects a broiler’s genetic response to cold stress.

Energy partitioning by broiler breeder hens in conventional daily-restricted feeding and precision feeding systems

An empirical linear mixed model was derived to describe metabolizable energy (ME) partitioning in broiler breeder hens. Its coefficients described ME used for total heat production (HP), growth (ADG), and egg mass (EM). A total of 480 Ross 308 hens were randomly and equally assigned to 2 treatments: precision feeding (PF) and conventional daily-restricted feeding (CON) from 23 to 34 wk of age. The PF system allowed birds to enter feeding stations voluntarily at any time, weighed them, and provided access to feed for 60 s if their BW was less than the breeder-recommended target BW. The CON birds were fed daily each morning. Energetic efficiency of hens was evaluated using residual feed intake (RFI), defined as the difference between observed and predicted ME intake (MEI). The energy partitioning model predicted (P < 0.05): MEI = A × BW0.67 + 1.75 × ADG + 0.75 × EM + ϵ. The coefficient A, a vector of age-specific HP, was 142 kcal/kg0.67/d; the energy requirement for growth and EM was 1.75 and 0.75 kcal/g, respectively. For the CON and the PF hens, respectively, MEI was 366 and 354 kcal/d (P = 0.006); RFI was -5.9 and 6.7 kcal/d (P = 0.009); HP% was 85.5 and 87.7 (P < 0.001); hen-day egg production (HDEP) was 65.5 and 55.2% (P < 0.001). Although the CON hens had higher MEI, the model predicted lower HP%; thus, CON hens had more nutrients available for egg production, increased egg production, and were more energetically efficient than the PF hens. The decreased egg production by the PF hens was likely due to these hens receiving production-related feed increases after an egg was laid. However, feed allocation increases for the CON hens resulted in increasing MEI for all CON hens at the same time. Therefore, the PF hens had lower MEI and lower HDEP than the CON hens.

Post-photostimulation energy intake accelerated pubertal development in broiler breeder pullets

The effect of ME intake (MEI) on the reproductive system was evaluated. Ross 308 broiler breeder pullets (n = 140) were assigned to 2 treatments from 22 to 26 wk of age: (1) Low-energy diet fed restricted (2,807 kcal/kg, low MEI) and (2) high-energy diet fed unrestricted (3,109 kcal/kg, high MEI). Daylength was increased from 8 to 14 h at 22 wk of age with a light intensity of 30 lux. Daily palpation was used to detect sexual maturity via the presence of a hard-shelled egg in the shell gland. Expression of gonadotropin releasing hormone-I (GnRH) and gonadotropin inhibitory hormone (GnIH) genes in the hypothalamus and GnRH receptor (GnRH-RI) and GnIH receptor (GnIH-R) genes in the anterior pituitary gland of each pullet was evaluated from 22 to 26 wk of age using quantitative real time-PCR. Blood samples were taken weekly and luteinizing hormone (LH), follicle stimulating-hormone (FSH), and 17-beta-estradiol (E2) determined using commercial ELISA kits. Carcass samples were used for determination of CP and fat content. Data were analyzed using the MIXED procedure in SAS, and differences were reported where P ≤ 0.05. High MEI treatment pullets had 2.3-fold higher GnRH and 1.8-fold higher GnRH-RI mRNA levels than low MEI pullets. MEI affected neither expression of GnIH and GnIH-R nor carcass protein content. For high MEI (489 kcal/D) and low MEI treatments (258 kcal/D), respectively, from 22 to 26 wk of age (P ≤ 0.05), LH concentration was 3.05 and 1.60 ng/mL; FSH concentration was 145 and 89.3 pg/mL; E2 concentration was 429 and 266 pg/mL, and carcass lipid was 13.9 and 10.3%. The onset of lay for pullets in the high MEI treatment advanced such that 100% had laid by 26 wk of age compared with 30% in the low MEI treatment. We concluded that higher MEI advanced the activation of the hypothalamic–pituitary–gonadal axis and also increased body lipid deposition, and moreover, stimulated reproductive hormone levels which overall accelerated puberty in broiler breeder pullets.

Effect of age at photostimulation on sexual maturation and egg-laying performance of layer breeders

The objective of this study was to determine the effect of age at photostimulation on sexual maturity and performance of layer breeders. A total of 192 fourteen-wk-old White Leghorn (WL) breeder hens were randomly allocated to 4 treatments of 48 birds each, with 2 replicates per treatment. The birds were photostimulated at 16 (PS16), 18 (PS18), 20 (PS20), and 22 (PS22) wk of age. Four birds per treatment were randomly selected to evaluate sexual organ development at 1 D before photostimulation and 2, 4, and 6 wk after photostimulation. The ovary weight, large yellow follicles number (LYF), oviduct weight, and oviduct length of PS18 increased sharply after photostimulation. Conversely, the increase in PS16 was not observed until 2 wk after photostimulation. There was no difference in age at sexual maturity between treatments (P > 0.05). The PS16 had the longest interval (28 D) from photostimulation to 5% egg production, while PS22 reached 5% egg production 7 D before photostimulation. The PS22 had lower peak production (P = 0.02) and less egg production (P = 0.02) than other treatments. The PS16 had more broken and abnormal eggs (P = 0.01) and lower hatchability (P = 0.04) than other treatments. In conclusion, photostimulation at 16 and 22 wk of age decreases hatchability and egg production, respectively, and photostimulation at 18 wk is appreciated for the WL breeder hens.

Reproductive management of poultry

Based on data from the UN's Food and Agricultural Organization, about 120 million metric tons of poultry meat were produced globally in 2016. In addition, about 82 million metric tons of eggs were produced. One of the bases for this production is the reproductive efficiency of today's poultry. This, in turn, is due to their inherent reproductive physiology, intensive genetic selection and advances in husbandry/management. The system of reproduction in males in largely similar to that in mammals except that there is no descent of testes. In females, there are marked differences with there being a single ovary and oviduct; the latter being the name of the differentiated entire Müllerian duct. Moreover, females produce eggs with a yolky oocyte surrounded by albumen, membranes and shell. Among the most successful reproductive management techniques are optimizing photoperiod, light intensity and nutrition. Widespread employment of these has allowed maximizing production. Laying hens can be re-cycled toward the end egg production. Other aspects of reproductive management in poultry include the following: artificial insemination (almost exclusively employed in turkeys) and approaches to reduce broodiness together with cage free (colony), conventional, enriched and free-range systems.

Identification of selection signatures involved in performance traits in a paternal broiler line

BACKGROUND

Natural and artificial selection leads to changes in certain regions of the genome resulting in selection signatures that can reveal genes associated with the selected traits. Selection signatures may be identified using different methodologies, of which some are based on detecting contiguous sequences of homozygous identical-by-descent haplotypes, called runs of homozygosity (ROH), or estimating fixation index (FST) of genomic windows that indicates genetic differentiation. This study aimed to identify selection signatures in a paternal broiler TT line at generations 7th and 16th of selection and to investigate the genes annotated in these regions as well as the biological pathways involved. For such purpose, ROH and FST-based analysis were performed using whole genome sequence of twenty-eight chickens from two different generations.

RESULTS

ROH analysis identified homozygous regions of short and moderate size. Analysis of ROH patterns revealed regions commonly shared among animals and changes in ROH abundance and size between the two generations. Results also suggest that whole genome sequencing (WGS) outperforms SNPchip data avoiding overestimation of ROH size and underestimation of ROH number; however, sequencing costs can limited the number of animals analyzed. FST-based analysis revealed genetic differentiation in several genomic windows. Annotation of the consensus regions of ROH and FST windows revealed new and previously identified genes associated with traits of economic interest, such as APOB, IGF1, IGFBP2, POMC, PPARG, and ZNF423. Over-representation analysis of the genes resulted in biological terms of skeletal muscle, matrilin proteins, adipose tissue, hyperglycemia, diabetes, Salmonella infections and tyrosine.

CONCLUSIONS

Identification of ROH and FST-based analyses revealed selection signatures in TT line and genes that have important role in traits of economic interest. Changes in the genome of the chickens were observed between the 7th and 16th generations showing that ancient and recent selection in TT line may have acted over genomic regions affecting diseases and performance traits.

Energy partitioning by broiler breeder pullets in skip-a-day and precision feeding systems

An empirical nonlinear mixed model was derived to describe metabolizable energy (ME) partitioning in Ross 308 broiler breeder pullets. Its coefficients described ME used for total heat production (HP) and growth. A total of 630 pullets were randomly and equally assigned to 2 treatments: precision feeding (PF) and conventional skip-a-day feeding (CON) from 10 to 23 wk of age. The PF system allowed birds to enter voluntarily at any time, weighed them, and provided access to feed for 60 s if their BW was less than the target BW. Birds in the CON treatment were fed as a group on alternate days. Energetic efficiency of pullets was evaluated using residual total heat production (RHP), defined as the difference between observed and predicted total HP. Additionally, ME intake (MEI), ADG, HP, and cumulative feed conversion ratio (FCR) were calculated for the entire experimental period. The energy partitioning model (P < 0.05) predicted MEI = (120+u)BW0.68 + 1.52(ADG) + ε. Total HP was (120 kcal/kg0.68 + u); the energy requirement for each g of BW gain was 1.52 kcal/d. The random variable u ∼ N (0, σu2) indicated a pen level HP standard deviation σu = 12.1 kcal/kg0.68. Over the experimental period, for CON and PF treatments, respectively, MEI was 194 and 174 kcal/d (P < 0.001); ADG was 15.3 and 15.4 g/d (P = 0.94); HP was 129 and 111 kcal/kg0.68 (P < 0.001); FCR was 4.888 and 4.057 (P < 0.001); and RHP was 0.12 and -0.12 kcal/kg0.68 (P = 0.73). The CON pullets had similar ADG, but higher MEI relative to PF, consistent with levels of heat production predicted by RHP. The PF pullets had lower cumulative FCR compared to CON pullets. The PF pullets lost less energy as heat, likely because they were fed continuously, reducing the need to store and mobilize nutrients compared to CON pullets. Thus, increased feeding frequency likely increased PF pullet efficiency.

Lifetime productivity of conventionally and precision-fed broiler breeders

A precision feeding (PF) system was developed to increase broiler breeder lifetime reproductive performance through improved flock uniformity. The current study consisted of 2 rearing and 3 laying treatments. From 0 to 22 wk of age, 480 Cobb male grandparent line pullets and 80 Cobb MX males were fed once daily as a group (CON), or individually with a PF system. Pullets were housed in 6 replicate pens of 40 birds, and cockerels in one pen per treatment. During lay, CON and PF treatments continued, and a third treatment was added, where PF-reared birds were transitioned to conventional feeding (PFCON; n = 3 pens). At photostimulation (22 wk of age), all pens had 24 hens and 2 roosters. Birds were allowed to mate naturally to 52 wk. Analysis of variance was conducted, and Tukey-adjusted means were reported as different where P ≤ 0.05. Mean BW was near the target BW in all treatments. At photostimulation, PF pullet BW CV was 2% vs 14% in CON pullets. Cumulative feed conversion ratio during rearing was lower in PF treatment pullets, which ate 3% less than CON pullets. Pullets in the PF treatment received 10 meals spread throughout each day, compared with one meal per day in the CON treatment. Increased feeding frequency would reduce diurnal fluctuations in nutrient supply, which may explain why PF pullets had 1.2 times the breast muscle weight of CON pullets at 22 wk. There was no treatment difference in abdominal fatpad weight at 22 wk. The PF treatment had 3.8% higher fertility and 1.3% lower egg weight CV compared with the CON treatment. Egg production in PF and PFCON treatments was 0.73 and 0.89 times that of the CON treatment, respectively. It is hypothesized that metabolic changes in PF pullets provided an insufficient metabolic trigger for sexual maturation. It follows that relaxing feed restriction may increase fat deposition and egg production in PF broiler 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.

The effect of rearing photoperiod on broiler breeder reproductive performance depended on body weight

Body weight (BW) and rearing photoperiod are important factors affecting sexual maturation rate and reproductive performance in broiler breeders. The current experiment used a 2 × 3 factorial arrangement of treatments to study the interaction between BW and rearing photoperiod on reproductive performance in group housed broiler breeder hens, while minimizing variation in BW. Hens (n = 180) were fed with a precision feeding system to allocate feed individually to achieve the breeder-recommended target curve (Standard) or to a target curve that reached the 21 wk BW at 18 wk (High). Hens were on 8L:16D, 10L:14D, or 12L:12D photoschedules during rearing and were photostimulated at 21 wk with a 16L:8D photoschedule. Sexual maturity (defined as age at first egg) and individual egg production to 55 wk were recorded. At 55 wk, proportional weights of individual body components were determined by dissection. Differences were reported as significant at P ≤ 0.05. A significant interaction between BW and rearing photoschedule affected age at sexual maturity and egg production. In the High BW treatment, age at sexual maturity did not differ between hens under the 8L:16D and 10L:14D photoschedules (173 vs. 172 d, respectively). In the Standard BW treatment, the 12L:12D rearing photoperiod delayed sexual maturity compared with the 8L:16D rearing photoperiod (266 vs. 180 d, respectively). All hens on the High BW treatment laid at least 1 egg before the end of the experiment. Conversely, 3.3, 18.1, and 37.6% of Standard BW hens on the 8L:16D, 10L:14D, and 12L:12D photoschedules, respectively, never commenced egg production. At the end of the experiment, proportional breast weight was higher and proportional fatpad weight was lower in Standard compared to High BW hens (25.8 vs. 27.5% and 2.4 vs. 1.5% of BW, respectively). We conclude that increased BW partially counters the effect of longer photoschedules on sexual maturity in broiler breeders and that dissipation of the photorefractory state depends on BW.

Hormonal levels of estradiol, testosterone, and progesterone at entry into lay of year 1980 vs. 2000 broiler breeder females under fast and slow release from feed restriction

In the mid-1960s egg production, fertility, and hatchability of broiler breeder females dropped precipitously. Due to disrupted follicle hierarchies and development of the erratic oviposition and defective eggs (EODES) syndrome. EODES was controlled by restricting feed. In the 1990s, another set of problems arose at entry of broiler breeders into lay and characterized by high mortality followed by lower peak lay and reduction in egg and chick production. These problems are induced by even slight over-feeding, and hence we termed it the "Over Feeding Complex" (OFC). We have speculated that OFC is a quasi-EODES condition, induced by the intense selection for increased breast proportion. To test this, we compared, under fast (FF) and slow (SF) release from feed restriction, body composition and reproductive performance of a broiler breeder from year 1980 (B1980) and kept without selection for performance traits since then, to a line hatched in 2000 (B2000). During the first 16 d of lay, feeding treatment had little effect on egg mass or Laying % for the B1980 birds, while for the B2000 birds, SF treatment resulted in significantly greater egg mass and Laying % compared to FF, showing that the OFC indeed manifested in this experiment. However, contrary to hypothesis, follicle hierarchies were normal for both lines under both feeding treatments. To gain further insight into the OFC syndrome, we here report levels of estradiol, testosterone, and progesterone for these line and treatment groups in the time period leading up to and into lay. A significant line × feeding treatment interaction effect was found for estradiol and testosterone, to a lesser extent for progesterone. For all 3 hormones, for B1980 levels 2 to 3 wk post entry into lay were similar and intermediate under FF and SF, but differed significantly for B2000, being much greater under SF than under FF. Thus, the hormonal effects were parallel and may explain the egg mass and Laying % effects of FF and SF in the 2 genetic types.

Using different levels of glycerine, glucose, or sucrose in broiler starter diets to overcome negative effects of delayed feed access on growth performance

Two trials were conducted to evaluate the inclusion of glycerine, glucose, or sucrose in broiler starter diets to overcome negative effects of delayed feed access. In trial 1, 2160 newly hatched chicks (mixed sexed) were randomly assigned to two feeding programs (immediate vs. 36 h delayed feed access). Nine starter diets prepared with crude glycerine, glucose, or sucrose fed at 0%, 4%, or 8% levels were fed during the first 14 d post hatch (PH). In trial 2, 720 male and 720 female newly hatched chicks were randomly assigned to two feeding programs (immediate vs. 48 h delayed feed access). Starter diets fed during the first 14 d of feed access, consisted of a control, 8% glycerine, or 8% glucose. In both trials, a common grower and finisher diet were fed during days 14–24 and 25–35, respectively. Body weight and feed consumed were measured on 7, 14, 24, and 35 d. In trial 1, all 8% diet-fed birds were heavier compared with the control on day 35 PH (2259 vs. 2198 g, P < 0.01). Birds fed glycerine starter diets had improved feed conversion ratio (FCR) during 22–35 d (P < 0.01). In trial 2, glycerine diet resulted in heavier birds after 35 d of feed access, compared with birds fed control and glucose diets immediately after hatch (2373 vs. 2276 g, P < 0.01). Dietary inclusion of 8% glycerine can assist newly hatched broiler chicks to overcome delayed feed access induced growth suppression.

Walking Behaviour and Spatial Use of Broiler Chickens

Modern broiler chickens are genetically selected for reaching higher weights in shorter life spans. In addition to this, they are raised in crowded housing conditions with less opportunity for movement. Understanding movement patterns, migration and use of space is essential in determining welfare of the birds in commercial farms. In this study, migration behaviour of broiler chickens in semi-commercial farms of 1800 chickens was studied. Observations were repeated in six growth periods each on 12 chickens once a day during their growth period of 42 days. It was seen that the activity of broilers was not decreasing during the growth period. Travelled distances of the chickens in total were not reduced in the last 3 weeks of their growth period (p > 0.05 in 89% of the observed birds, Mann-Whitney U test). Chickens preferred to be in the zones next to the wall farthest to the entrance of the house. The observed birds did not restrict themselves only around the feeders and the drinkers but used the whole surface area available during the whole growth period. The results of the study seem to be encouraging in achieving welfare of broiler chickens even in commercialised houses with high stocking density. Reported mobility of chickens is important for their survival and has therefore considerable impact on efficient production on farms.

Molecular and metabolic profiles suggest that increased lipid catabolism in adipose tissue contributes to leanness in domestic chickens

Domestic broiler chickens rapidly accumulate fat and are naturally hyperglycemic and insulin resistant, making them an attractive model for studies of human obesity. We previously demonstrated that short-term (5 h) fasting rapidly upregulates pathways of fatty acid oxidation in broiler chickens and proposed that activation of these pathways may promote leanness. The objective of the current study was to characterize adipose tissue from relatively lean and fatty lines of chickens and determine if heritable leanness in chickens is associated with activation of some of the same pathways induced by fasting. We compared adipose gene expression and metabolite profiles in white adipose tissue of lean Leghorn and Fayoumi breeds to those of fattier commercial broiler chickens. Both lipolysis and expression of genes involved in fatty acid oxidation were upregulated in lean chickens compared with broilers. Although there were strong similarities between the lean lines compared with broilers, distinct expression signatures were also found between Fayoumi and Leghorn, including differences in adipogenic genes. Similarities between genetically lean and fasted chickens suggest that fatty acid oxidation in white adipose tissue is adaptively coupled to lipolysis and plays a role in heritable differences in fatness. Unique signatures of leanness in Fayoumi and Leghorn lines highlight distinct pathways that may provide insight into the basis for leanness in humans. Collectively, our results provide a number of future directions through which to fully exploit chickens as unique models for the study of human obesity and adipose metabolism.

Transcriptomic and metabolomic profiling of chicken adipose tissue in response to insulin neutralization and fasting

BACKGROUND

Domestic broiler chickens rapidly accumulate adipose tissue due to intensive genetic selection for rapid growth and are naturally hyperglycemic and insulin resistant, making them an attractive addition to the suite of rodent models used for studies of obesity and type 2 diabetes in humans. Furthermore, chicken adipose tissue is considered as poorly sensitive to insulin and lipolysis is under glucagon control. Excessive fat accumulation is also an economic and environmental concern for the broiler industry due to the loss of feed efficiency and excessive nitrogen wasting, as well as a negative trait for consumers who are increasingly conscious of dietary fat intake. Understanding the control of avian adipose tissue metabolism would both enhance the utility of chicken as a model organism for human obesity and insulin resistance and highlight new approaches to reduce fat deposition in commercial chickens.

RESULTS

We combined transcriptomics and metabolomics to characterize the response of chicken adipose tissue to two energy manipulations, fasting and insulin deprivation in the fed state. Sixteen to 17 day-old commercial broiler chickens (ISA915) were fed ad libitum, fasted for five hours, or fed but deprived of insulin by injections of anti-insulin serum. Pair-wise contrasts of expression data identified a total of 2016 genes that were differentially expressed after correction for multiple testing, with the vast majority of differences due to fasting (1780 genes). Gene Ontology and KEGG pathway analyses indicated that a short term fast impacted expression of genes in a broad selection of pathways related to metabolism, signaling and adipogenesis. The effects of insulin neutralization largely overlapped with the response to fasting, but with more modest effects on adipose tissue metabolism. Tissue metabolomics indicated unique effects of insulin on amino acid metabolism.

CONCLUSIONS

Collectively, these data provide a foundation for further study into the molecular basis for adipose expansion in commercial poultry and identify potential pathways through which fat accretion may be attenuated in the future through genetic selection or management practices. They also highlight chicken as a useful model organism in which to study the dynamic relationship between food intake, metabolism, and adipose tissue biology.