Summary
The U.S. broiler industry is currently facing challenges in breeder production and hatchability. Hatchability rates have recently dropped below 82 %, the lowest since 1988 (Agristats Report, 2023), alongside increased mortality in pullets, breeder hens, and roosters. To address these issues, this symposium brought together global experts to share insights and strategies. Discussions focused on breeder nutrition, management, incubation management, and epigenetic effects on progeny. While primarily targeting broiler breeders, the symposium also explored practices in layer breeders to offer additional insights. A panel of five experts presented innovative ideas to enhance breeder performance and chick quality. Emphasis was placed on revising amino acid and energy requirements for modern genetics, optimizing management practices, and leveraging epigenetics to improve sustainability and performance. Hatchery practices were also identified as crucial for increasing hatchability and chick quality. For layer breeders, the focus extends beyond egg production to maximizing chick quality and viability through lighting, feeding programs, and genetic selection.
Description of problem
As poultry meat remains a key protein source globally, production has increased by approximately 3 % annually, reaching over 100 million tons in 2020 (USDA, 2021). This growth relies on the productivity of 600 million broiler breeders, underscoring their critical role in the poultry supply chain. This implies that a relatively small number of broiler breeders (or parent stock) substantially impacts the poultry meat chain. The main task of broiler breeders is to produce first-class hatching eggs and healthy chicks; therefore, appropriate nutrition and management are essential. During the last decades, this has become more and more challenging because of the continuing genetic improvement in the growth of the offspring and the parent stock (Zuidhof et al., 2014). Besides these factors, nutrient requirements, diet composition, and feeding strategies are essential to reach this goal.
Due to genetic selection for high body weight gain and feed efficiency, the body composition of broiler breeders has changed over time. The body fat deposition has decreased since 1970, whereas the body protein deposition remained stable (Fig. 1); (Fuller et al., 1969; Bornstein et al., 1979; Leeson and Summers, 1983; Bennett and Leeson, 1990; Renema et al., 1999; de Beer and Coon, 2007; Carneiro et al., 2019). At the same time, egg production increased. The body composition, gain, and egg mass production determine the energy and amino acid requirements (Lopez and Leeson, 1994; Fisher, 1998; Pishnamazi et al., 2015), which have changed over time.
Fig. 1. Changes in broiler breeder body composition (fat = circles with dotted line, protein = squares with continuous line) over time at 20 weeks of age. All data was recalculated to body composition relative to the total body, including feathers. Only timepoint 1970 is free-feather body composition, and the fat level is therefore slightly overestimated while protein is slightly underestimated compared to other data points (Fuller et al., 1969; Leeson and Summers, 1983; Bennett and Leeson, 1990; Renema et al., 1999; de Beer and Coon, 2007; Carneiro et al., 2019).
With these changes, it is essential to discuss the amino acid and energy requirements of modern broiler breeders, considering historical changes, including the influence on offspring performance. Also, it is crucial to understand how maternal nutrition can influence the health of progeny through epigenetic modifications (Berghof et al., 2013). Specific nutrients and environmental factors can trigger these epigenetic changes during critical periods of development (Zeisel, 2017), and the role of zinc and modifications in the breeder’s crude protein (CP) is discussed. Also, we discuss new alternatives for feeding programs, broiler breeder male management, optimal male-to-female ratio, and housing equipment that can improve egg production, hatchability, and breeder welfare. With current challenges in hatchability, we reviewed the modern incubation requirements at each stage of embryo development, which play a crucial role in optimizing hatching performance. Tallentire et al. (2018) note that modern lines of fast-growing chickens have advanced so genetically that more than one-third of a broiler chicken’s life is now spent inside the egg. This highlights the importance of hatcheries in commercial operations and the critical role of monitoring egg and incubation parameters to maintain broiler production (Kroetz Neto et al., 2023). The main factors influencing the incubation process include regulating embryo temperature, maintaining optimal egg quality, ensuring proper egg turning, and providing adequate ventilation. Appropriate management of these factors ensures that embryos develop in an environment conducive to their health and growth, significantly impacting hatchability and the quality of chicks. With a focus on broiler breeders, where feed restriction is applied along the rearing and production phase, and incubation practices, we concluded with a review of the main factors that affect laying breeder performance, which are selected for laying production and are fed without restriction to reach proper body weight and production.
Amino acid and energy requirements of broiler breeders
Henk Enting and Lieske van Eck
Lysine requirements
The Lys requirements have increased over time but are relatively stable in most recent publications (Table 1). When recalculated to intake levels, the dietary Lys levels agree with the current recommendations for the first phase of the laying period in current breeder guides (Aviagen 2021a; Cobb-Vantress 2022). However, Lys requirement data is more scarce for the second half of the laying and rearing periods, while dietary Lys levels may have long-term effects (Van Emous et al., 2015; Oviedo-Rondon et al., 2021).
Table 1. Literature overview of lysine requirements in broiler breeders.
| Reference | Lysine | Requirement | Broiler Breeder Age, week |
|---|---|---|---|
| NRC, 1966 | Total | 0.50 % | Not specified |
| Bornstein et al., 1979 | Total | 760 mg/hen/day, BW 3.5 kg, BWG 4 g/day, EM 52.7 g | Production parameter specific |
| NRC 1984 | Total | 0.64 % | Not specified |
| Wilson and Harms, 1984 | Total | 938 mg/day | 24 to 64 |
| Bowmaker and Gous, 1991 | Total | 793 mg/day | 29 to 38 |
| Harms and Ivey, 1992 | Total | 824 mg/day | 40 to 53 |
| NRC, 1994 | Total | 765 mg/hen/day | Not specified |
| Harms and Russell, 1995 | Total | 845 mg/hen/day | 32 to 40 |
| Fisher, 1998 | Total | 893 mg/bird/day | 27 to 33 |
| Mbambo, 2001 | Total | 922 mg/bird/day | 36 to 46 |
| Fakhraei et al., 2010 | Total | 0.64 % | 52 to 62 |
| Gous and Nonis, 2010 | Total | 992 mg/hen/day, 587 g body protein, 66 g egg weight | Production parameter specific |
| Ekmay et al., 2013 | Digestible | 916 mg/hen/day (0.61 %) | 32 to 38 / 30 to 40 |
| Dorigam et al., 2017 | Digestible | 915 mg/hen/day (0.602 %) 876 mg/hen/day (0.596 %) |
31 to 35 46 to 50 |
| Weil et al., 2019 | Digestible | 723 mg/hen/day (egg mass only), start lay | Start lay |
In a study testing six crude protein (CP) to energy ratios fed during week 3 to 22 in Ross 308 pullets with 27 hens per replicate and four replicates per treatment, both body composition and long-term lay were influenced (Assadi Soumeh et al., 2018). The pullets and hens received restricted feeding to achieve breed recommendation body weights, and feed allowance was adjusted when needed to maintain target body weight in all periods); a common diet was provided from week 22 onwards. In the rearing diets, both CP and Lys varied between −20 % to +5 % compared to a standard diet. Lowering dietary CP and Lys levels linearly increased body fat percentage and decreased breast percentage at the end of rearing. During the laying period, the fatter birds required less feed to maintain body weight targets than the lean breeders. Optimum laying performance was obtained with the −10 % and −15 % CP to energy ratios in the rearing period, which was mainly due to an improved laying persistency (Fig. 2), resulting in significant differences in laying rate at the end of the laying period. Similar effects were found by Van Emous et al. (2015) and Oviedo-Rondon et al. (2021) when providing different Lys levels during the rearing period.
Fig. 2. The effect of difference crude protein (CP) to metabolizable energy (ME) ratios during weeks 3 to 22 on the laying performance of Ross 308 broiler breeders from 24 to 63 weeks of age.
Body fat levels might be important to initiate reproduction, and current feed restriction probably prioritizes body protein deposition over body fat deposition (Bornstein et al., 1984; Carney et al., 2022). Apart from the function as energy storage, body fat also functions as an endocrine organ by producing adipokines (Bornelöv et al. 2018). In birds, adipokines probably have a profound effect on reproductive function, and especially adiponectin, visfatin and chemerin are of interest (Mellouk et al., 2018). This relatively new field of research should be considered in future studies to optimize Lys and energy levels for broiler breeders, especially during the rearing period.
In another trial with 27 Ross 308 broiler breeder hens and three males per replicate with six replicates per treatment, dietary crude protein and standard ileal digestible (SID) Lys were gradually decreased during the laying period compared to a control diet (14.0 % CP, 0.58 % SID Lys from week 34 to 58 in the control group vs. a gradual reduction from 13.1 % CP and 0.54 % SID Lys from week 34-40, 12.2 % CP and 0.50 % SID Lys from week 41-46, 11.4 % CP and 0.45 % SID Lys from week 47-52 and 10.5 % CP, 0.41 % SID Lys in week 53-58). No differences in laying performance were observed between treatments, but feed allowance had to be increased significantly from 151 to 156 g/day from week 47-52 and from 152 to 161 g/day from week 53-58 to maintain the breeder target body weight. Egg weight was significantly reduced. The increase in feed allowance indicated that a reduction below 12.2 % protein (0.50 % SID Lys) is too low to maintain body weight and performance.
Amino acid ratios
The required amino acid to Lys ratios show large fluctuations between studies, which could be caused by the time, method, or age of the broiler breeders (Table 2). In general, trial data about optimal amino acid ratios in broiler breeder feeds are scarce, and modeling approaches have been used to estimate optimal amino acid ratios in rearing and laying. Unfortunately, different amino acid profiles have been reported for the three main processes that determine requirements: maintenance, body weight gain and egg production (e.g. Lunven et al., 1973; Gous and Nonis, 2010; Sakomura et al., 2015). Comparing the ratios found in the literature, Aviagen (2021a) recommendations are relatively high, except for TSAA/Lys, whereas Cobb-Vantress (2022) ratios are relatively low for Arg/Lys, Val/Lys, and Ile/Lys.
Table 2. Literature overview of amino acid ratio requirements of broiler breeders.
| Empty Cell | Weil et al., 2019 | Ferreira et al., 2019 | Cerrate et al., 2019 | Ekmay et al., 2013 | Gous and Nonis, 2010 | Leeson and Summers, 2000 | Fisher, 1998 |
|---|---|---|---|---|---|---|---|
| Method | Nitrogen balance | Modeling | Modeling, breeder 1 | Dose response | Modeling | Modeling | Modeling |
| Age, weeks | 32-36 | 32 | 25-36 | 32-38 | 30-40 | Bird with 587 g of body protein and 66 g of egg weight | 27-34 |
| Lys | 100 | 100 | 100 | 100 | 100 | 100 | 100 |
| Met/Lys | 69 | 46 | 44 | 71 | 42 | ||
| TSAA/Lys | 56 | 89 | 105 | 98 | 104 | 70 | |
| Thr/Lys | 66 | 64 | 85 | 67 | 64 | 93 | 62 |
| Trp/Lys | 28 | 22 | 25 | 21 | |||
| Arg/Lys | 73 | 135 | 112 | 90 | 90 | ||
| Val/Lys | 98 | 102 | 87 | 78 | |||
| Ile/Lys | 75 | 96 | 91 | 70 | 67 |
To study the accuracy of the factorial modeling approach, Cerrate et al. (2019) compared Aviagen breeder recommendations for amino acids (Aviagen, 2013) with dietary amino acid levels that were calculated using a factorial modeling approach. Despite the lower amino acid intake, dietary treatments did not affect body weight and laying rate. Egg weight, on the other hand, was significantly lower from week 38 onwards when broiler breeders were fed diets containing lower amino acids (calculated according to the factorial model). Moreover, the factorial amino acid profile negatively impacted the feather condition from 45 weeks onwards. This indicates that the factorial models can estimate requirements for egg production, but not egg weights. Moreover, higher levels of amino acid intake are required to increase egg weight. Comparing the amino acid levels and profiles in the work of Cerrate et al. (2019) with recently performed studies with laying hens on next limiting amino acids, we hypothesize also that other amino acids are limiting than the ones mentioned in Table 2.
Energy requirement
Although body composition of broiler breeders has changed, energy requirements have remained constant over time (Table 3) and are close to current breeder recommendations. Most research focused on the ratio between amino acids (lysine) and energy, so for that reason we will mainly focus on amino acid to energy ratios. Providing low-density diets results in good performance if feed allowance is adjusted to maintain energy intake and target body weights (Mens et al., 2022; Van Emous et al., 2024).
Table 3. Literature overview of the energy requirements of broiler breeders during the production phase.
| Reference | AME requirement | Broiler Breeder Age |
|---|---|---|
| Pearson and Herron, 1981 | 413 kcal/hen/day | Weeks 21-64 (egg production) |
| Spratt and Leeson, 1987 | 385 kcal/hen/day (cages) | Week 24-40 |
| NRC, 1994 | 400-450 kcal/hen/day | Week 25-64 |
| Pishnamazi et al., 2015 | 454.8 kcal/hen/day | Week 25-41 4 kg, 2 BWG, 45 EM |
| Zaghari et al., 2018 | 458.5 kcal/hen/day | Week 40-49 |
| Salas et al., 2019 | 420 kcal/hen/day | Week 22-65 |
| Van der Klein et al., 2020 | 505.8 kcal/hen/day | 3.5 kg, 2 BWG, 45 EM |
| Teofilo et al., 2023 | 364.7 kcal/hen/day | Model 1.2, 4.0 kg., 46.3 EM, 21.1 g BWG |
BWG: Body Weight Gain, in g. EM: Egg Mass in g (egg weight x percentage production).
Offspring effect
The dietary strategy during rearing and lay might also have transgenerational effects. Feeding 15 % lower lysine to energy ratio during rearing (study design discussed above), resulted in a tendency for higher daily gain and feed intake in offspring performance (combined results of 3 grow-out trials). This effect was similar to those reported by Moraes et al., 2014. Also, Heijmans et al. (2022) observed an effect on offspring performance by feeding different energy to lysine ratios during both the rearing and laying period. A higher energy to Lys ratio resulted in lower feed and protein intake in the broiler breeder hens, to reach the target body weight curves. The offspring of these hens showed a higher feed intake and increased feed efficiency, although this result was inconsistent between different grow-out studies. The authors suggest epigenetic effects since the parental diet did not affect the egg nutrient composition.
The dietary effect of the rearing period might be more important for offspring performance than similar dietary changes in the laying period; Enting et al. (2007) found that providing low-density diets in the rearing period only had similar effects on offspring performance as providing low-density diets during both rearing and laying.
In a trial conducted at the Cargill Global Innovation Center (Velddriel, the Netherlands) with Ross 308 broiler breeders with 6 replicates per treatment of 27 hens and 3 males per replicate, lowering dietary CP and lysine levels during the second phase of lay (week 34 to 58), offspring performance was significantly reduced, as indicated by lower chick weight and 64 grams lower body weights on day 36 (P < 0.05). This was a direct effect of a 2.7 g lower egg weight. Chang et al. (2016) observed a similar effect of reduced dietary protein in breeder feed on day-old chick weight, while Van Emous et al. (2018) did not observe offspring performance effects when the crude protein level in the breeder feed was reduced by 1.5 %. This might be related to the dietary lysine level that was kept constant between treatments and could indicate that dietary lysine is more important for offspring performance than the CP level.
Recent publications on dietary energy and lysine requirements are consistent and in reasonable accordance with the broiler breeder manuals. There is less consistency in the requirements for amino acid ratios, and factorial designs might underestimate the requirements for egg weight. The broiler breeder Lys to energy ratio in both the rearing and laying phases can influence both production and offspring performance. Lowering dietary Lys to energy ratios while restricting feed to maintain breed-recommended body weight growth curves improves egg production, potentially mediated through body composition changes. Also, offspring performance might be improved with lower Lys to energy ratios in broiler breeder diets, although results are inconsistent.
The concept of feeding the hen to improve progeny performance
Hugo Romero-Sanchez
The concept of feeding the hen to improve progeny performance is well-established, yet the objectives of breeder nutrition—maximizing reproductive performance—sometimes conflict with optimizing progeny development. Two critical aspects of progeny development can be affected through maternal nutrition: growth performance and carcass yield, as well as the health and immunity of the progeny (Calini and Sirri, 2007; Santos et al., 2022). Although reducing dietary protein levels in a breeder’s diet can decrease egg size, it does not seem to impact progeny performance (Kidd, 2003). On the other hand, the cumulative energy intake in the breeder diet has been shown to improve progeny performance (Walsh and Brake, 1997). Brake et al. (2003) reported that increasing protein and energy in the breeder diet enhanced progeny performance, particularly in males. Additionally, research by Leeson and Summers (2001) and Peebles et al. (1999, 2002a) demonstrated that feeding fat sources rich in linoleic and linolenic acids, such as corn oil, resulted in better progeny performance, carcass yield, and reduced embryo mortality compared to feeding poultry fat or lard. However, this effect was not observed in younger breeders (Peebles et al., 2002b).
A series of experiments by Walsh and Brake (1997, 1999) showed that broiler breeder females reared to similar 20-week body weights (BW) with diets containing crude protein (CP) levels ranging from 11 % to 20 % exhibited reduced fertility if they consumed less than 1,180 g of CP, regardless of cumulative ME intake or 20-week BW. This suggests a specific requirement for adequate CP during the pre-lay period, which is critical for the growth and development of the reproductive tract (Yu and Marquardt, 1974). When broilers from different breeder nutritional planes were grown out, the broilers from breeders with High nutritional planes tended to have heavier BW at 21 d of age (Brake et al., 2003).
Male broiler breeders also need a minimum CP intake during growth to reach sexual maturity by 20 weeks. Inadequate CP delays maturity and reduces initial fertility, whereas a programmed feed increase maintains mating activity and flock fertility and enhances progeny growth and efficiency (Romero-Sanchez, 2006; Romero-Sanchez et al., 2008). However, broilers from flocks with lower early fertility had reduced 42 d body weight despite high male nutrition (Romero-Sanchez et al., 2008). Dixon et al. (2016) emphasized that pre-lay factors, including hen age, nutrition, and management, significantly impact offspring performance beyond genetics.
Epigenetics mechanisms and progeny performance
The mechanisms underlying parental effects are believed to involve epigenetic modifications, such as DNA methylation and histone acetylation, which regulate gene expression without altering the genetic code. Epigenetic modifications, influenced by maternal factors such as stress and nutrition, can have significant transgenerational effects on phenotypic traits in broiler breeders, impacting sexual maturity, egg production, and embryonic development. Studies, including those on quail, have shown that the maternal environment and previous generations’ diets can induce epigenetic changes affecting traits like body weight and behavior (Moresi et al., 2015). This area of research is gaining attention, with recent studies highlighting the potential for epigenetic regulation to influence traits related to thermal tolerance, metabolism, and disease susceptibility, emphasizing the need for further exploration in breeder and hatchery management.
Zinc effect in broiler breeder and progeny
Studies have shown that maternal nutrition, particularly the inclusion of specific nutrients like zinc (Zn), can enhance the immune function of progeny. For instance, Zn supplementation in breeder diets has been linked to improved embryonic development and immune response in offspring, possibly due to epigenetic modifications. These changes may persist beyond the first generation, indicating a potential for long-term improvements in flock health.
Kidd et al. (1992, 1993) demonstrated that supplementing breeder diets with organic Zn increased embryonic bone weight and enhanced both cellular immune responses and primary antibody titers to Salmonella pullorum antigen. Similarly, Virden et al. (2003) reported that feeding breeders a combination of Zn and manganese (Mn) in both organic and inorganic forms improved progeny livability, with the organic form yielding a more pronounced response.
More recent studies have delved into the mechanisms by which maternal Zn supplementation modulates offspring’s immune system. Zhang et al. (2012) documented that Zn supplementation prevented Salmonella enterica-induced loss of intestinal mucosal barrier function by upregulating the expression of key proteins responsible for maintaining gut integrity, including occludin and claudin-1. Zhu et al. (2017) further showed that maternal dietary Zn supplementation, whether from inorganic or organic sources, enhanced the antioxidant capacity of chick embryos under both standard and high maternal temperatures. This enhancement was reflected in increased mRNA and protein expressions of metallothionein IV in the embryonic liver, achieved by reducing DNA methylation and increasing H3K9 acetylation of the metallothionein IV promoter. Both Zn sources chelated Zn and ZnSO4, significantly reduced DNA methylation at the A20 promoter. However, only the chelated Zn significantly increased histone H3K9 acetylation at the A20 promoter. Because methylation represses gene expression and histone acetylation activates gene expression, lower DNA methylation and greater histone H3K9 acetylation at the A20 promoter region suggests that breeder Zn supplementation activates the A20 gene’s expression.
Li et al. (2015) evaluated the role of maternal Zn on the intestinal immunity of offspring and investigated the epigenetic mechanisms by which Zn regulates A20 gene expression, DNA methylation, and histone H3K9 acetylation at A20 promoter region was measured in the jejunum of progeny broilers at 35 d of age. In their study, broiler breeder hens (45 weeks old) were initially fed a Zn-deficient diet (0 ppm supplemental Zn) for two weeks to deplete maternal Zn stores. Subsequently, the hens were provided with either a commercial (50 ppm) or a high (300 ppm) Zn diet. The broilers were fed a similar diet with inorganic Zn. The study found that Zn content in both the egg yolk and albumen increased with Zn supplementation, with higher levels observed in the yolk than in the albumen in the chelated Zn treatments. Evidence in human literature postulated that Zn suppresses inflammation via induction of A20-mediated inhibition of the nuclear factor-κB (NF-κB) signaling pathway (Prasad et al., 2011). Zn finger protein A20 can negatively regulate the inflammatory response by affecting ubiquitin-dependent factors of NF-κB signaling cascades (Ma and Malynn, 2012; Catrysse et al., 2014). NF-κB signaling pathway is one of the major pathways to regulate inflammation induced by external stimuli such as bacteria, infection, and inflammation (Neurath et al., 1998). The A20 blocks the phosphorylation and activation of NF-κB, thereby inhibiting translocation of NF-κB and suppressing inflammation cascade.
Chelated Zn supplementation to breeder hens, showed a greater effect than ZnSO4 in: 1) reducing gene expression of NF-κB p65 as well as its downstream inflammatory cytokines such as IL6; and 2) increasing A20 gene expression in the jejunum of progeny. As A20 negatively regulates the NF-κB pathway, the increase of A20 is consistent with the reduction of NF-κB p65 gene expression. These results suggest that chelated Zn supplementation in breeder diets reduced gut inflammation in progeny birds by up-regulation of A20 expression (Li et al., 2015). These effects were confirmed by Roque et al. (2022), who measured similar biomarkers (NF-κB p65, A20) during the grow-out period in broilers from breeders receiving different sources of organic trace minerals, showing lower intestinal inflammation. In fact, the broiler performance reflected the benefits of the organic trace minerals in the breeder diet, mainly when the source was a metal methionine hydroxy analog chelate (Roque et al., 2022).
Transgenerational effects on broiler breeders
Understanding the transgenerational effects of breeder nutrition opens new avenues for improving broiler production. Producers can enhance progeny performance and health across multiple generations by targeting specific nutrients and optimizing maternal diets, potentially leading to more sustainable and efficient poultry production. Recent research has highlighted the transgenerational impact of broiler breeder nutrition on progeny performance. Nutritional interventions in breeders influence their immediate offspring and can have lasting effects on subsequent generations.
Lesuisse et al. (2017) in a study with 160 pure-line A breeder hens (F0 generation) that were fed either a control standard diet (C) or a reduced protein (RP) diet, found that RP hens consumed more feed to match the body weight gain of C hens. Also, the RP hens produced less cumulative eggs due to lower peak of production and less egg production from 24 to 40 weeks of age. Also, the RP group had significantly lower egg weight during the same period, which was reflected in lower chick weight at hatch. When broilers from this trial were grown, using a standard broiler diet, the broiler male body weight was significantly heavier at 5 weeks of age (88 g more). This effect was only observed in the broiler males, and the females showed lower BW at the same age (38 g less). Additionally, the RP broiler showed lower FCR adjusted for mortality, 4 points in males (P > 0.05) and 3 points in females (P < 0.025).
In another set of trials, Lesuisse et al. (2018a, Lesuisse et al., 2018b) studied the adaptation of the progeny to reduced crude protein diets. In this trial, the F1 generation was split to produce a factorial arrangement with two diets from their parents, the F0 generation (Control and RP), and the same two diets (Control and RP) for F1 breeders. Then, the broiler progeny from these F1 breeders also received a normal broiler diet and a low-protein broiler diet (Broiler Control and Broiler Low Protein). The broiler coming from breeders with a C/C combination showed the lowest BW and nitrogen retention rate (58 %). In comparison, the broilers from the RP/RP parental combination had the highest BW and nitrogen retention rate (64 %) (P < 0.05 and P = 0.067, respectively for BW and nitrogen retention). In broilers fed the RP diets, the broilers coming from any combination of breeders receiving RP and Control diets showed the heaviest BW and lower FCR. In contrast, broilers from groups with combinations (C/C and RP/RP) showed the lowest BW and the highest FCR.
Feeding and management programs to maximize breeder performance and hatchability
Rick. van Emous
Broiler breeders’ management practices have remained unchanged for years. However, recent research and practical observations suggest that changing the male-to-female ratio, adjusting feeding programs, and using morning and afternoon diets could improve welfare and hatchability. This section describes the state-of-art scientific knowledge on broiler breeder feeding and management.
Male-to-female ratio during the laying phase
In a study conducted under commercial conditions, a notably low rate of successful matings (44 %) and a high incidence of forced matings (90 %) were observed (de Jong et al., 2009). Predominantly, over-mating behavior is observed in commercial breeder houses, with males mating up to ten times more frequently compared to chickens in natural conditions. Over-mating leads to impaired feather cover, thigh wounds, and heightened fearfulness among females (van Emous, 2010). This is possibly one of the major reasons why females tend to remain in the slatted area or hide in the nests instead of being in the litter area avoiding the males and matings. Research indicates that the last four to five hours of the day are crucial for mating behavior. Breeder companies typically recommend starting the production phase with 8 to 11 % males, decreasing to roughly 7 % by the end of the laying phase. However, this approach is questionable as physical and physiological traits (e.g. mating activity, semen quality) of breeder males decline over time. Considering this decline, an alternative approach involving starting with a lower male percentage (4 to 5 %) and gradually adding males at specific intervals during the laying period (e.g., +1 % around 30, 40, and 50 weeks of age) is suggested. This strategy was successfully implemented in a Veranda cage system, resulting in a 16 percentage points higher (30 % vs. 14 %) rate of voluntary matings, improved feather cover, and a 2.6 % higher actual fertility in the second part of the laying period (van Emous, unpublished data).
Everyday feeding during the rearing phase
During the rearing phase, feed provision occurs either daily or through various feeding programs incorporating feed-less days (Leeson and Summers, 2009). These programs may adopt skip-a-day (alternating between feeding and fasting days), 6/1, 5/2, or 4/3 feeding regimens (indicating 1, 2, or 3 days without feed per week, with higher feed portions on feeding days). In Europe, legislative restrictions prohibit feeding programs with feed-less days, leading most farmers to adopt daily feeding systems. Conversely, feeding programs with feed-less days in North America remain prevalent (de Jong and van Emous, 2017). The rationale behind employing feeding programs revolves around achieving uniform BW in feed-restricted pullets (Leeson and Summers, 2009). Modern pullet housing facilities are outfitted with adequate feeder space and rapid chain feeders (up to 30 m per minute or more) or pan feeders, ensuring uniform feed distribution within three minutes, or better within three seconds, across the entire rearing house. Additional management measures, such as elevating the feeder system during filling or conducting feed system filling in darkness, further enhance feed distribution. Research indicates that daily feeding demonstrates up to 10 % lower feed intake for achieving target weight at the end of the rearing period compared to feeding programs (de Beer and Coon, 2007). This disparity in efficiency arises from the necessity for birds on feeding programs to store nutrients (such as fat and protein) on feeding days for utilization during feed-less days, a process that is not 100 % efficient and results in decreased efficiency and higher feed requirements (de Beer and Coon, 2007). Improved BW uniformity was observed with daily feeding (Sweeney et al., 2022). During the laying phase, de Beer and Coon (2007) noted earlier peak egg production and higher settable egg production in pullets fed daily compared to those on feeding programs.
Twice-a-day feeding during the rearing phase
In contrast to feeding programs with feed-less days, van Emous et al. (2021) investigated feeding once or twice a day in combination with control and diluted diets. Pullets fed twice a day exhibited a lower BW coefficient of variation (indicative of higher body weight uniformity) at 10 weeks of age, although no significant effect was observed at 20 weeks of age. Furthermore, pullets fed twice a day tended to display an earlier onset of lay, higher total egg production at 30 weeks of age, and improved fertility.
Adjusted feeding strategies during the rearing phase
Recently, a study with breeder pullets was conducted to investigate the effects of diluted diets and feeding frequency on behavior and performance (van Emous et al., unpublished data). Diets were diluted with 20 % or 30 % straw pellets and fed once or twice a day. Pullets received 50 % of the amount of feed at 7 AM and 50 % at 11 AM with lights on between 7 AM and 3 PM and followed the same BW profile. Feeding pullets twice daily resulted in the best average body weight (BW) uniformity, whereas those fed once daily exhibited the poorest BW uniformity (P = 0.003). The total mortality rates were lower in the 20 % and 30 % diluted diets, fed twice a day compared to the group on a 20 % diluted diet fed once a day p, primarily due to a reduced number of graded pullets in these groups. Pullets receiving twice a day feed displayed increased activity in eating and drinking, along with reduced sitting, object pecking, aggressive pecking, and auto feather licking behavior. Moreover, the behavior pattern during the daylight period was different with two peaks in activity for the pullets fed twice a day. Additionally, pullets on the diluted feeding strategies were less eager to approach the novel feeder and ate less feed. In summary, implementing adjusted feeding strategies, including twice-daily feeding and diets diluted by up to 30 %, led to improved behavioral outcomes characterized by decreased stereotypic pecking, prolonged feed retention in the feeder, and reduced eagerness to approach new feeding sources, while also positively impacting production performance.
Twice-a-day feeding or split feeding during the laying phase
Feeding breeders twice a day may enhance the availability of nutrients during egg and eggshell formation, potentially resulting in improved eggshell quality (Backhouse and Gous, 2006). Feeding specially formulated morning and afternoon diets, known as ‘split feeding,’ can help meet the varied nutritional requirements during egg formation in both layers and breeders. The study by van Emous and Mens (2021) concluded that twice-a-day feeding (with the same diets) improved behavior, while split feeding improved egg production and behavior in broiler breeders. However, no significant effects were observed on eggshell quality and incubation traits. In a second study of van Emous (2023), a tendency for higher egg production was observed between 45 and 65 weeks of age. They also found a lower water intake and water-to-feed ratio and a higher activity at the end of the day, which could stimulate mating activity. Similarly, on-farm studies, the twice-a-day feeding program increased mating activity during the second feeding time, with potential higher fertility and hatchability, as has been shown with spiking males during production (Cobb-Vantress, 2022).
Key factors for incubation performance with the modern broiler embryo
Felipe Kroetz Neto
The challenge of modern incubation lies in the precise understanding and fulfillment of specific embryonic requirements at each stage of development. Tallentire et al. (2018) note that modern lines of fast-growing chickens have advanced so genetically that more than one-third of a broiler chicken’s life is now spent inside the egg. This highlights the importance of hatcheries in commercial operations and the critical role of monitoring egg and incubation parameters to maintain broiler production (Kroetz Neto et al., 2023). As embryos progress through different phases, their needs evolve, making it crucial to adjust incubation practices accordingly. The main factors influencing the incubation process include regulating embryo temperature, maintaining optimal egg quality, ensuring proper egg turning, and providing adequate ventilation. From an embryonic perspective, these elements significantly impact hatchability and the overall quality of chicks. Adequate management of these factors ensures that embryos develop in an environment conducive to their health and growth, leading to successful hatch outcomes.
Several factors that go beyond the immediate incubation environment influence the quality of the incubation process and the resulting chick quality. The impact on chick quality begins even before incubation, during egg formation. The conditions under which the egg is formed, including the health and nutrition of the hen, play a crucial role in determining the initial quality of the egg, which in turn affects the entire incubation process and embryo development. Egg quality is a fundamental factor in the success of the incubation process. High-quality eggs are characterized by appropriate shell thickness, size uniformity, and healthy yolk and albumen (Peruzzi et al., 2012). Low-quality eggs, such as those with cracks, irregular shapes, or weak shells, are more susceptible to contamination, temperature fluctuations, and other issues that can reduce hatchability and chick quality. Ensuring optimal egg quality from the start is essential to achieve good incubation results.
Regarding specific gravity (SG), Kibala et al. (2018) and Roque and Soares (1994) suggest that using an indirect and non-destructive method to measure eggshell quality is likely the most employed approach in the field due to its low cost, practicality, and significant correlation with shell thickness. However, as useful as it is, SG fails to detect some eggshell abnormalities that can be observed during candling, such as fine cracks and translucent spots (also known as eggshell mottling). Translucent spots on eggshells are areas where the mammillary and palisade layers are disorganized, and the shell structure becomes weaker (Galindo et al., 2022). This structural failure allows moisture from the egg content passing through the shell membranes to accumulate in the eggshell, leading to increased light transmission (Wang et al., 2017; Wong et al., 2020). Eggshell translucency can range from several tiny spots to nearly the entire shell and is associated with potential risks of bacterial penetration and cracking (Bain et al., 2006; Chousalkar et al., 2010).
Kroetz Neto et al. (2024b) studied the associations and interactions between eggshell translucency, SG, and color in the incubation parameters of eggs from the same breeding flock. A significant interaction between SG and eggshell color was observed for the variable of egg weight loss, where lighter brown-shelled eggs in most SG categories lost more weight during incubation than darker ones. Eggshell translucency results in eggs with lower SG (< 1070), higher egg weight loss, increased contamination, intermediate embryonic mortality, and lower hatchability. However, eggshell translucency is not related to SG or color.
One of the most critical points during incubation is embryonic temperature, as it directly influences embryo development. Embryos are sensitive even to small temperature variations, which can result in developmental abnormalities, delayed hatching, or even embryonic mortality. Maintaining the temperature within an optimal range (37.5°C to 38.0°C or 100°F to 101°F) is crucial for ensuring successful hatching and the health of the neonates (Lourens et al., 2005). Slight variations can negatively affect the embryo’s metabolism, leading to issues such as deformities, embryonic mortality, or chicks with reduced vigor. Elevated temperatures during incubation accelerate embryonic metabolism, leading to overly rapid development, dehydration, early hatching, and lower chick quality (French, 1997). On the other hand, temperatures below the ideal can slow development, prolonging incubation time and resulting in weak chicks or yolk absorption issues (Decuypere and Michels, 1992). Monitoring and adjusting embryonic temperature throughout the process can help identify harmful variations and improve incubation conditions, favoring uniform hatching and proper embryonic growth. This practice can also optimize feed conversion and post-hatch weight gain (Lourens et al., 2005). Additionally, precise temperature control reduces mortality and enhances immune system development, reflecting better production performance.
During natural incubation, hens regularly turn their eggs to ensure even heat distribution and prevent the embryo from sticking to the eggshell membrane. In artificial incubation, replicating this process is essential for promoting proper embryonic development. Improper or inadequate egg turning can lead to developmental defects and reduced hatchability. Egg turning during incubation is a crucial factor for healthy embryonic development and ensuring chick quality. This process, which involves periodically rotating the eggs, prevents the embryo from adhering to the eggshell membranes, promoting symmetrical development and proper vascular system growth (Deeming, 1989). If turning does not occur regularly, the embryo may become positioned improperly, resulting in deformities, embryonic mortality, and delayed hatching. Turning also contributes to the even distribution of heat and humidity within the egg, which is essential for nutrient absorption from the yolk and optimal embryonic growth (Wilson, 1991). Furthermore, this movement facilitates gas exchange, promoting proper oxygenation, which improves chick vitality post-hatching. Studies indicate that failure or insufficiency in egg turning can result in lower-quality chicks, with lower hatching weights and higher mortality rates in the early days of life (Elibol and Brake, 2004). Monitoring egg turning and adjusting the frequency and angle of rotation can optimize incubation conditions, improving hatch rates and chick performance (Tona et al., 2003).
The practice of administering vaccines via in-ovo vaccination is a significant advancement in poultry health management. This technique allows for early immunization, which helps protect chicks against diseases from hatching. It also reduces the stress associated with post-hatch vaccinations, resulting in healthier and more robust chicks. The timing and technique of in-ovo vaccination are crucial to maximizing its effectiveness and ensuring it does not negatively impact embryonic development. A study by Kroetz Neto et al. (2024a) demonstrated the impact on broiler performance when vaccination is done at the right time. Three explanations can be considered. First, vaccination after 460 h of incubation showed higher uniformity and earlier production of antibodies, compared with vaccination before this time (Avakian, 2006; Lozano, 2016), with intra-embryonic deposition, which may improve disease control and productivity (Islam et al., 2001). Second, shell puncture during vaccination increases water loss and accelerates the hatching process, potentially leading to dehydration and uniformity loss if chick removal time is not adjusted (Williams, 2011; Fernandes et al., 2016). Third, variability in temperature and embryonic development stages can impair vaccine efficacy in multi-stage incubators. Finally, another factor identified in our research as a determinant of broiler performance was the age of the breeder flocks, with broilers from older breeders showing greater weight gain, better intestinal adaptation, and more effective maternal immunity transfer, protecting the chicks during the first weeks of life (Machado et al., 2020; Nangsuay et al., 2021; Santos et al., 2022).
Chick yield, which refers to the ratio between chick weight at hatching and the incubated egg weight, indicates successful incubation and chick quality. An appropriate yield between 67 % and 68 % indicates that the chick has efficiently utilized the yolk nutrients and water during incubation, resulting in healthy embryonic development (Tona et al., 2013). Chicks with a yield below the ideal may face dehydration or underdevelopment, compromising their vitality and production performance, leading to lower weight gain and feed conversion (Oviedo-Rondón et al., 2019). On the other hand, yields above expectations may indicate excessive fluid retention, associated with failures in yolk absorption, which can hinder early external feeding, impacting gut health and initial growth (Careghi et al., 2005). Therefore, chick yield is directly linked to the incubation process, affecting neonate quality, their ability to adapt to the post-hatch environment, and their production performance during the rearing period.
With different variables affecting the incubation process and hatchability performance, data analysis is crucial for detecting early issues, such as uneven temperatures or poor ventilation, which can cause embryonic malformations, mortality, and growth delays (Lourens et al., 2005.) Collecting and interpreting data, such as temperature, humidity, incubation time, egg weight, and chick yield, also allows the identification of variations and trends that directly impact embryonic development (Decuypere and Michels et al., 1992), improving hatchability, uniformity, and chick vitality and broiler performance (Tona et al., 2003).
Focus points for feeding and management practices to support hatchability in layer breeders
Estella Leentfaar
Layer breeders have been selected for a high egg production rate (peak and persistency) and internal and external egg quality (Thiruvenkadan et al., 2010). Therefore, reproductive performance values, like the number of cumulative hatching eggs per hen, are much higher than the broiler breeder hens (Table 4). Meanwhile, the male line is selected for fertility and hatchability traits. However, the hatchability trait has a low heritability. Therefore, other traits, like semen quality and mating behavior, are considered to maximize the number and quality of day-old chicks (Hendrix Genetics, 2019), and new changes to adapt to new production environments have been considered (Leenstra et al., 2016).
Table 4. Estimated reproductive performance in broiler breeders and layer breeders.
| Variable | Broiler Breeder | Layer Breeder |
|---|---|---|
| Hen-Day Egg Production, % | 78-89 at peak | 90-95 at peak |
| Total Eggs per Hen | 160-187 | 250-300 |
| Fertility Rate, % | 85-95 | 90-96 |
| Average Hatchability, % | 78-85 | 85-92 |
| Shell Breakage, % | 2-4 | 1-3 |
Incubation practices are critical, and the biggest difference is that the eggs are, on average -due to smaller flock size-, stored for a longer time than in broiler breeders, increasing early embryo mortality (Fasenko et al., 2001). Therefore, practices like heating eggs for short periods during the storage (SPIDES) period are more frequent in broiler breeders. Using SPIDES allows the embryo to grow by increasing the viability of the blastoderm (Dymond et al., 2013), reducing embryo mortality, allowing longer storage time, and reducing the hatching window.
Feed quality is vital to maintain egg quality and keep flocks free of health issues. Laying breeders are fed ad libitum or with moderate feed restriction, having better uniformity than broiler breeder flocks. Besides, the males do not suffer from being overweight like the broiler breeders and tend to have good mating behavior. In contrast to broiler breeders, the body weight difference between males and females in layer breeders is limited; for white layer breeders, there is a 400-gram body weight difference at 30 weeks of age (Hendrix Genetics, 2024). In laying breeders, the males and females are fed using the same feeding equipment and the same diets in both rearing and production phases. Although the male should have different requirements, high-calcium diets are fed to male breeders without causing kidney problems or fertility issues as reported in male broiler breeders (Moyle et al., 2011).
Like in broiler breeders, the highest mating frequency is in the afternoon, 13 to 15 h after lights are on (Duncan et al., 1990); during this period, it is recommended to prevent disturbances to the flock, like feeding and weighing. Therefore, the feeding times should be in the morning, before the mating period, and shortly after, just before the lights are off. When local legislation allows it, a maximum of two hours of light could be given to the laying breeder flock three hours after the lights are turned off. During this period, one feed distribution is provided, which is useful during the hot seasons to maintain proper feed intake. Laying breeders require dense diets and feed stimulation to reach feed intake; therefore, fiber and diet concentration support gastrointestinal tract development, stimulate feed intake, reaching daily nutrient requirements (Hendrix Genetics, 2024).
Like broiler breeders, the mating frequency is reduced with age (Duncan et al., 1990), and the sperm can be stored in the sperm storage glands for up to 3 weeks. Worldwide there are still several flocks that use artificial insemination, practice that we see in broiler breeders located in India (Romero-Sanchez H, personal communication, January 25, 2025). This practice allows lower feed intake and better fertility. Finding the right balance in the male-to-female ratio will help to improve fertility; however, this depends on the housing and management system (Hendrix Genetics, 2019). Adding more males in case of low fertility is, in most cases, not the most effective strategy. Females can get stressed by too many matings; they might lose their back feathers, resulting in painful and stressful mating experiences. In laying breeders, starting with a male-to-female ratio, of five to six males per 100 females in aviary systems, has improved hatchability (Hendrix Genetics, 2019, 2024). This lower male-to-female ratio will create less male competition and aggressiveness improving mating activity.
Conclusions and applications
Broiler and layer breeder fertility, hatchability, and progeny performance can be optimized via a holistic approach, including nutrition, management, genetics, biosecurity, health program, egg handling management, and incubation practices. Selection for growth and feed conversion, increased the challenges for broiler breeders, while selection for egg production in layer breeders, despite the longer storage time of fertile eggs, reduced hatchability issues.
In broiler breeders, different recommendations in amino acid levels might reflect differences over time with genetic improvement, strain, and trial conditions, while recommendations in energy levels are less variable. Recent studies align with the Lys and energy recommendations in the broiler breeder manuals, while the amino acids ratios remain variable. The Lys-to-energy ratio affects production and offspring performance; and lowering this ratio, at the same body weight target through feed restriction, may affect egg production and offspring performance, though results are variable. Nutrition and hatchery environment influence phenotypic variation, offering opportunities for sustainable poultry production. The source and amount of zinc and methyl donors in the breeder diet support progeny gut health by modulating inflammation, while the transgenerational effects of CP may enhance the progeny adaptation to low CP diets. Also, different feeding systems and management practices like male-to-female ratio, splitting diets, and hatchery practices might improve the broiler breeder’s performance. Some of these practices are commonly used in laying breeders, and could bring opportunities to mitigate current hatchery issues.
Source: Science Direct
