Welfare assessment of broiler breeders that are food restricted after peak rate of lay

Is relaxing broiler breeder growth restriction cost-effective?

Broiler breeders are subjected to feed restriction programs to control excessive growth. However, current levels of feed restriction and concomitant growth restriction are becoming severe, raising welfare and suboptimal reproductive performance concerns in underfed breeders. To circumvent the issue, our previous studies investigated the effects of new strategic growth curves, with various degrees of relaxed growth restrictions, on broiler breeders and their progeny's performance. The broiler breeder study was conducted with 40 Ross 708 broiler breeder pullets reared on 1 of 10 target growth trajectories using a precision feeding (PF) system. The growth trajectories were designed with 2 levels of the amount of prepubertal BW gain and 5 levels of pubertal growth timing. The prepubertal BW gain (g1) was estimated from the breeder-recommended standard BW gain (Standard g1) target, or 10% higher (High g1). The pubertal growth timing (I2) was advanced such that it happened at I2-0% = 22.29 wk, I2-5% = 21.16 wk, I2-10% = 20.05 wk, I2-15% = 18.94 wk, I2-20% = 17.82 wk of age. Two broiler experiments with different maternal ages (35 and 42 wk) were conducted as the extension of the breeder experiment to evaluate the intergenerational effects of a reduced degree of maternal prepubertal phase growth restriction and earlier maternal pubertal phase growth on offspring growth and development. The current paper investigated the economic aspects of implementing the growth curves using the partial budget analysis. Increasing prepubertal BW gain by 10% and advancing the pubertal growth phase by 20% (scenario 10) could increase margin over feed and chick cost for the hatching egg producers by CDN$1.97/hen. For broiler chicken supply chain as a whole, the highest differential margin over feed and chick cost was for maternal growth scenario 10 from 42-wk-old hens. The latter margin over feed and chick cost was greater than that of breeder-recommended maternal growth (from 35-wk-old hens) by $0.1053/kg live chicken under the current economic situation.

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.

THE EFFECT OF DEXAMETHASONE ON HEMATOLOGIC PROFILES, HEMOSPORIDIAN INFECTION, AND SPLENIC HISTOLOGY IN HOUSE FINCHES (HAEMORHOUS MEXICANUS)

Research on host response to infectious disease often involves pharmacological induction of immunosuppression, frequently through administration of dexamethasone. Reports on the effect of dexamethasone in birds are largely restricted to poultry and pigeons. This study describes changes in white blood cell (WBC) differentials, hemoparasite counts, splenic histology, and splenic CD3 immunoreactivity in House Finches (Haemorhous mexicanus). Experimental group birds (n=9) were treated with a daily intramuscular injection of 25 µg of dexamethasone for 8 d; a control group (n=9) received daily saline solution. Smears were made with blood collected immediately before the first dose (day 0) and on d 4, 8, and 9, and stained with modified Wright. The WBC differential counts were performed by three blinded observers, parasite counts by two blinded observers, and histology by one blinded observer. Dexamethasone-treated birds experienced relative heterophilia and lymphopenia on d 4 (P=0.008); heterophilia was also present at d 8 (P=0.018). Hemosporidian counts were significantly increased in dexamethasone-treated birds on d 4 and 8 (P=0.048 and P=0.031, respectively). In contrast with control birds, all dexamethasone-treated birds lacked histologically apparent splenic lymphoid follicles (P<0.001). No significant difference was observed in splenic CD3 immunoreactivity between groups. Our results indicate that dexamethasone has an effect on the hematologic profile of House Finches and suggest that it may be a useful method to induce immunosuppression in this species.

Timing of growth affected broiler breeder feeding motivation and reproductive traits

The amount and timing of growth are important factors that affect age at first egg, body conformation, reproductive performance, and hunger in broiler breeders. To investigate the effect of growth pattern on feeding motivation and reproductive performance, 10 unique growth trajectories were designed with 2 levels of the amount of early growth and 5 levels of timing of growth around puberty. A 3-phase Gompertz model that described growth in phase 1 (prepubertal), phase 2 (pubertal), and phase 3 (postpubertal) was used to design the growth trajectories. Second growth phase inflection point (I₂) was advanced by 0, 5, 10, 15, or 20% of the coefficient estimated from the breeder-recommended target BW. The growth trajectories were designed with 2 discrete levels of total gain in the prepubertal phase (g₁); g₁ was either the prepubertal phase gain coefficient, estimated from the breeder-recommended BW (Standard g₁) target, or 10% higher (High g₁). Forty females were randomly assigned to the growth trajectories using a precision feeding (PF) system. Analysis of covariance was conducted on dependent variables in ten 4-wk periods with g₁ and periods as discrete fixed effects, I₂ as a continuous fixed effect, and age as a random effect. Differences were reported at P ≤ 0.05. For every week of earlier I₂, body weight at photostimulation (BWPS) increased by 126 g; BW at first egg (BWFE) increased by 94 g; 24 wk shank length increased by 0.038 and 1.495 mm in the Standard g₁ and High g₁ treatments; 24 wk body fat increased by 0.38%; pullets came to lay earlier by 0.49 d; egg weight (EW) increased by 0.27 g; egg production and egg mass (EM) increased by 0.33 egg/hen/d and 0.916 g/d in the High g₁ treatment but decreased by 0.27 egg/hen/d and 0.29 g/d in the Standard g₁ treatment, respectively. Increasing g₁ reduced feeding motivation index by 1.6 and 0.8 visits/meal during rearing and laying phase, respectively. Earlier pubertal growth showed prominent effects on the reproductive performance.

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.

Virus-induced immunosuppression in turkeys (Meleagris gallopavo): A review

Immunosuppression is characterized by a dysfunction of humoral and/or cellular immune response leading to increase of susceptibility to secondary infections, increase of mortality and morbidity, poor productivity, and welfare and vaccination failures. Humoral immune response depression is due to perturbation of soluble factors, as complement and chemokines in innate immunity and antibodies or cytokines in adaptive immunity. At the cellular immune response, immunosuppression is the consequence of the dysfunction of T-cells, B-cells, heterophils, monocytes, macrophages, and natural Killer cells. Immunosuppression in turkeys can be caused by numerous, non-infectious, and infectious agents, having variable pathological and molecular mechanisms. Interactions between them are very complex. This paper reviews the common viruses inducing clinical and sub-clinical immunosuppression in turkeys, and enteric and neoplastic viruses in particular, as well as the interactions among them. The evaluation of immunosuppression is currently based on classical approach; however, new technique such as the microarray technology is being developed to investigate immunological mediator’s genes detection. Controlling of immunosuppression include, in general, biosecurity practices, maintaining appropriate breeding conditions and vaccination of breeders and their progeny. Nevertheless, few vaccines are available against immunosuppressive viruses in turkey’s industry. The development of new control strategies is reviewed.

The effect of alternative feeding strategies for broiler breeder pullets: 1. Welfare and performance during rearing

Broiler breeders have impaired reproductive performance when fed to satiety but they can achieve an optimal hatching egg production under feed restriction. Feed restriction is a welfare concern due to signs of hunger, lack of satiety, and frustrated feeding motivation. The objective of this research was to examine the effect of a rationed alternative diet and non-daily feeding schedules on the performance and welfare of broiler breeder pullets reared under simulated commercial conditions. At 3 wk of age, 1,680 Ross 308 pullets were allocated to 24 pens fed with 1 of 4 treatments: 1) daily control diet (control); 2) daily alternative diet (40% soybean hulls and 1 to 5% calcium propionate); 3) 4/3 control diet (4 on-feed days per week; 3 non-consecutive off-feed days per week); and 4) graduated control diet (feeding frequency varied with age). Body weight and body weight uniformity were recorded at 3, 5, 7, 11, 17, and 21 wk of age. Pullets were scored for feather coverage, foot lesions, and hock burns biweekly. Physiological indicators (plasma glucose, corticosterone, hematology, and feather traits) and feeding motivation were also determined throughout rearing during on- and off-feed days. Data were analyzed using a linear mixed regression model, with pen nested in the model and age as a repeated measure. Compared to control, pullets under the 3 alternative feeding strategies had a lower feeding motivation during early rearing (P = 0.03), better feather coverage throughout rearing (P = 0.001), fewer feather fault bars (P = 0.006), and a delayed increase in the basophil to lymphocyte ratio (P = 0.001). These results indicate that the 3 alternative feeding strategies (the alternative, the graduated, and the 4/3 schedule) may decrease feeding motivation and alleviate stress compared to the control, suggesting an overall improvement in broiler breeder welfare without negative consequences on their performance.

The effect of alternative feeding strategies for broiler breeder pullets: 2. Welfare and performance during lay

Feeding broiler breeders to satiety has negative consequences on their health and reproduction. Alternative feeding strategies during rearing can improve welfare, although their implications during lay are not well understood. The objective was to examine the effect of rearing feeding treatments on the reproductive performance and feeding behavior of broiler breeders under simulated commercial conditions. At 3 wk of age, 1,680 Ross 308 pullets were allocated to 24 pens under 1 of 4 isocaloric treatments: 1) daily control diet; 2) daily alternative diet (40% soybean hulls and 1 to 5% calcium propionate); 3) 4/3 control diet (4 on-feed days, 3 non-consecutive off-feed days per week); and 4) graduated control diet. Feeding frequency of the graduated treatment varied with age and finished on a daily basis. At 23 wk of age, group sizes were adjusted to 40 hens, and 5 mature Yield Plus Males roosters were introduced to each pen. Pens were under the same daily feeding management and same diet during lay. The performance of broiler breeders (growth rate, body weight uniformity, and reproductive performance) was determined until 64 wk of age. At the end of lay, feeding motivation was examined with a feed intake test and a compensatory feeding test. Data were analyzed using linear mixed regression models, with pen nested in the models and age as a repeated measure. The laying rate of hens reared on the graduated treatment decreased slower compared to control hens, resulting in a higher cumulative egg production (178.2 ± 3.8 eggs/hen) than control hens (165.2 ± 3.8 eggs/hen, P < 0.01) by 64 wk of age. Hens reared on non-daily feeding treatments laid lighter eggs with relatively heavier yolks and had higher feed intake at the end of lay than hens fed daily during rearing (P = 0.02). In conclusion, rearing feeding treatments impacted the growth rate and body weight uniformity during lay, feeding motivation at the end of lay, and the laying rate and hatchability depending on hens' age.

Growth curve and diet density affect eating motivation, behavior, and body composition of broiler breeders during rearing

The aim of this work has been to assess the effect of diet density [control (CON) or 15% diluted (DIL)] and growth curve [recommended by the genetic line (RBW) or 15% heavier (HBW)] and their interaction on BW uniformity, feeding motivation, behavior, and body composition of broiler breeder pullets. A total of 3,000 one-day-old female breeders Ross 308, distributed in 20 pens, was randomly assigned to each treatment. Feed allowance was weekly adjusted to reach the desired BW. Feed was provided as pelleted (zero to 3 wk) and crumble (4 to 19 wk). Time eating was measured at 7, 11, and 19 weeks. A feeding rate test was performed after 11 weeks. Behavior was observed at 9 and 15 wk, by visual scan. At 6, 13, and 19 wk of age, one bird/pen was slaughtered for weighing different organs and analyzing the composition of empty whole bodies. Treatments did not affect BW uniformity; relative weights of the ovary, oviduct, or gizzard; or protein content of empty BW. Time eating varied with the growth curve at 19 wk (P < 0.05), HBW pullets spent 19 more min eating than RBW pullets. DIL led to 4 and 8 more min eating at 19 wk for pullets of RBW and HBW (P < 0.05), respectively. Pullets fed DIL consumed 30% (P < 0.05) less during the feeding rate test when kept on a restricted regimen, and they had lower compensatory energy intake after ad libitum feeding than those fed CON, indicating lower feeding motivation. Behavior was affected by the age and by the time of the d measured, but it did not change with the treatments. Birds spent most time pecking objects (50%), feeding (28%), and drinking (17%). Pullets fed DIL had 8% lower breast yield at different ages and higher empty digestive tracts at 6 weeks. Body composition varied with age; fat content increased from 12.7 to 15.9 to 19.8% for 6, 13, and 19 wk, respectively. The lowest body fat was observed for RBW pullets fed DIL (P = 0.003) at 19 weeks. Feeding DIL diets to HBW pullets could be done to increase the time spent eating and reduce their feeling of hunger without negative effects on body composition. However, its influence on behavior and BW uniformity was not proved.

Utilization of soy hulls, oat hulls, and flax meal fiber in adult broiler breeder hens

A total of 72, 65-week-old broiler breeder hens (Ross 308, BW 4,190 ± 45 g) was placed in individual cages to investigate utilization of fiber in soy hulls (SH), oat hulls (OH), and flax meal (FM). Birds were adapted to cages for 10 d prior to allocation (n = 18) to broiler breeder ration (control) or control mixed with either of the 3 fiber sources (wt/wt) added to supply equal amounts of neutral detergent fiber (NDF) ∼21% and TiO2. The daily feed allocation was based on 4% BW. Feed intake (FI) was monitored daily, and grab excreta samples were taken on d 16 and 17. On d 18, all birds were weighed and killed 2 h post feeding to measure ceca digesta pH and short chain fatty acids (SCFA). Relative to the control birds, birds receiving fiber lost (P < 0.05) BW due to decreased (P < 0.05) FI. The BW changes were respectively +80, -174, -133, and -585 g/bird for control, SH, OH, and FM, and corresponding FI was 1,062, 918, 885, and 590 g/bird. Birds fed FM retained higher (P < 0.05) NDF than birds fed either SH or OH. The ceca digesta pH was lower (P < 0.05) in birds receiving added fiber relative to control. However, ceca digesta pH of FM fed birds was lower (P < 0.05) than in birds fed either SH or OH, which were in turn similar (P > 0.05). Birds fed FM had higher (P < 0.05) concentration of butyric acid than birds fed the control diets, while birds fed SH and OH had intermediate butyric acid concentration. Acetic acid and total SCFA concentrations were higher (P < 0.05) in birds fed OH diet than in birds fed control but was similar (P > 0.05) to that in birds fed either SH or FM. In conclusion, short term feeding of fibrous feed ingredients reduced BW linked to reduced FI. Fiber sources exhibited differences in utilization reflective of chemical characteristics.

Identification of novel candidate genes for follicle selection in the broiler breeder ovary

BACKGROUND

Broiler breeders fed ad libitum are characterised by multiple ovulation, which leads to poor shell quality and egg production. Multiple ovulation is controlled by food restriction in commercial flocks. However, the level of food restriction raises welfare concerns, including that of severe hunger. Reducing the rate of multiple ovulation by genetic selection would facilitate progress towards developing a growth profile for optimum animal welfare.

RESULTS

The study utilised 3 models of ovarian follicle development; laying hens fed ad libitum (experiment 2) and broiler breeders fed ad libitum or a restricted diet (experiments 1 & 3). This allowed us to investigate gene candidates for follicular development by comparing normal, abnormal and "controlled" follicle hierarchies at different stages of development. Several candidate genes for multiple ovulation were identified by combining microarray analysis of restricted vs. ad libitum feeding, literature searches and QPCR expression profiling throughout follicle development. Three candidate genes were confirmed by QPCR as showing significant differential expression between restricted and ad libitum feeding: FSHR, GDF9 and PDGFRL. PDGFRL, a candidate for steroidogenesis, showed significantly up-regulated expression in 6-8 mm follicles of ad libitum fed broiler breeders (P = 0.016), the period at which follicle recruitment occurs.

CONCLUSIONS

Gene candidates have been identified and evidence provided to support a possible role in regulation of ovarian function and follicle number. Further characterisation of these genes will be required to assess their potential for inclusion into breeding programmes to improve the regulation of follicle selection and reduce the need for feed restriction.

Effect of quantitative feed restriction on broiler performance

The objective of the current study was to determine the effect of quantitative feed restriction on the performance of broilers. A total of 270 unsexed broilers were randomly allocated to three treatments: with no feed restriction (T1), one week (T2) and two (T3) weeks of feed restriction from 22 days of age and then fed ad libitum until the age of 42 days. Treatments were replicated three times with 30 birds per replicate. Birds were fed with starter, grower and finisher diets. The feed consumed and body weights were recorded every week from the third to the sixth week. The average daily gain (ADG), average daily feed intake (ADFI) and the feed conversion ratio (FCR) were computed for each week. At Week 6, body weights of T3 birds were similar (P>0.05) to those of T1 and T2 birds. There were also no treatment effects on the ADG at Week 6. In addition, no treatment effects (P>0.05) were observed on ADFI at each stage of growth. Since ADFI and FCR were similar among the three groups, it was concluded that feed restriction by limiting the time to eat was not successful. There was also no evidence of compensatory growth in the restricted groups.

The effect of diet change on the behaviour of layer pullets

Frequent diet change has been identified as a risk factor for feather pecking in commercial flocks but the mechanism underlying this association is not known. In this experiment we simulated a commercial change of diet between high quality (HQ) 19% protein, and low quality (LQ) 15% protein, diets. Twelve pairs of birds were fed both diets simultaneously for 38 days to determine whether clear preferences for the diets existed. A further 12 triplets of birds were fed either HQ or LQ diets for 38 days to examine any absolute effects of quality on behaviour. The remaining triplets received, on day 29, either a LQ to HQ diet change (n = 12 groups) or an HQ to LQ diet change (n = 12 groups). Half of the groups in these diet change treatments received oregano oil as a potential ‘masking’ agent to disguise the diet change. No dietary preferences were detected and there were no absolute effects of diet on behaviour. Diet change provoked significant increases in beak-related activity. Specifically, affiliative pecking (allopreening directed towards comb or beak) was increased after diet change. Masking the diet reduced the effects of diet change. Injurious pecking remained at low levels throughout the experiment and was not affected by diet change, but the relationship between affiliative pecking and subsequent injurious pecking requires further investigation.