Broiler breeder chickens are commonly reared under strict feed-restriction regimes to reduce obesity-induced health and fertility problems during adult life, and are assumed to experience a reduced welfare due to the resulting hunger. In these conditions, feed competition could influence the growth rate, so that the individuals falling behind in growth would experience more stress and hunger. We hypothesised that these chickens are poor competitors due to a reactive coping style and experience a further reduced welfare situation before size-sorting (‘grading’) at four weeks of age. Our results from open field, tonic immobility and home pen activity monitoring show signs of lower fear and higher home-pen activity levels in smaller hens and do not support the idea of reactive coping. H/L ratios of smaller hens were also found to be lower, indicating less stress in these birds. Dissections of smaller and larger four-week breeder hens may offer an explanation in the form of a relatively larger gastrointestinal tract in smaller birds. We argue that this is a form of habituation to restricted feeding, offering these birds a physiological stress coping mechanism, and that low early growth rate may not always be a sign of poorer welfare in broiler breeders.

Choice tests may aid determining whether qualitative dietary restriction improves the welfare of feed-restricted broiler breeder chickens (Gallus gallus domesticus). However, hunger-stress may reduce competency to choose by impairing learning. The effect of chronic feed restriction on the ability of broiler breeders to learn a hunger-relevant discrimination task was investigated using a Y-maze paradigm. The task was to associate black and white arms with large and small quantities of feed. Birds were reared to three growth curves by means of severe (n = 12), moderate (n = 12) or very mild feed restriction (n = 12). Learning the task and selecting the larger food option allowed birds to increase their feed intake. Time taken to traverse the Y-maze was also measured. Birds from all treatment groups traversed the Y-maze more quickly over time, indicating that they had learnt that running down the Y-maze arms was associated with a rewarding outcome (food). However, feed restriction significantly reduced their ability to associate the black and white cues with differences in food quantity. Consequently, average pay-offs in terms of daily feed increments disproportionately accrued to the less feed-restricted treatment groups. It is concluded that feed restriction affected the performance of broiler breeders in this task, perhaps by narrowing their attention such that they ignore potentially hunger-relevant contextual cues. However, low overall group success rates demonstrate that this task was difficult to learn even for less severely feed-restricted birds. Therefore, Y-maze choice tests may not be the most appropriate method for determining hungry broiler breeder dietary preferences.

Genetics is key to the improvement of welfare in broiler chickens at both juvenile and adult (breeder) stages but progress is hampered currently by the seemingly conflicting demands of welfare, commercial production, food security and calls for increasing intensification to curb climate change. Animal welfare is therefore most likely to be improved on a commercial scale by future breeding programmes that incorporate multiple goals of different stakeholders as far as possible and give higher priority to animal welfare. These include: i) broilers with high welfare traits; ii) broiler breeders that do not need feed restriction; iii) birds that can be grown in an economically profitable way; iv) birds with low disease levels without the need for routine medication; v) chicken meat that is healthy and good for humans to eat; and (vi) broilers and breeders that thrive in systems that are environmentally sustainable. Progress towards achieving these goals is hampered currently by the assumptions that high juvenile growth rate is incompatible with good welfare and that feed restriction in adults is inevitable with fast-growing juveniles. We challenge these assumptions at both genetic and whole-animal level and argue that the conflict between good welfare and productivity can be reduced by making use of all available genetic variation from existing breeds and other sources and selecting birds in the range of environments they will encounter in commercial production.

To investigate the effects of environmental temperature and dietary Zn on egg production performance, egg quality and antioxidant status, as well as expression of heat-shock proteins (HSP) in tissues, of laying broiler breeders, we used a completely randomised design with a 2×3 factorial arrangement of treatments. The two environmental temperatures were normal (21±1°C, NT) and high (32±1°C, HT). The three dietary Zn sources were a Zn-unsupplemented basal diet (CON), and the basal diet supplemented with 110 mg Zn/kg as either the inorganic Zn sulphate (iZn) or the organic Zn proteinate with a moderate chelation strength (oZn). HT decreased (P<0·002) egg weight, laying rate, eggshell strength, thickness and weight, but increased (P≤0·05) rectal temperature, broken egg rate, misshapen egg rate, feed:egg ratio, Cu Zn superoxide dismutase activities in liver and pancreas, as well as metallothionein (MT) level in pancreas, and HSP70 mRNA levels in liver and pancreas of laying broiler breeders. Broiler breeders fed the oZn diet had higher (P<0·04) Zn content in the liver, as well as MT levels in the liver and pancreas, compared with those fed the CON diet. Under HT, broiler breeders fed the oZn diet had higher (P<0·05) Zn content in the pancreas compared with those fed the iZn and CON diets. The results from this study indicated that HT impaired egg production performance and eggshell quality possibly because of the disturbed redox balance and HSP homoeostasis, whereas the oZn is more available than the iZn for pancreatic Zn of heat-stressed laying broiler breeders.

To investigate the effect of Mn on antioxidant status and on the expressions of heat shock proteins/factors in tissues of laying broiler breeders subjected to heat challenge, we used a completely randomised design (n 6) with a factorial arrangement of 2 environmental temperatures (normal, 21±1°C, and high, 32±1°C)×3 dietary Mn treatments (a Mn-unsupplemented basal diet (CON), or a basal diet supplemented with 120 mg Mn/kg diet, either as inorganic Mn sulphate (iMn) or as organic Mn proteinate (oMn)). There were no interactions (P>0·10) between environmental temperature and dietary Mn in any of the measured indices. High temperature decreased (P<0·003) Mn content, and also tended (P=0·07) to decrease Cu Zn superoxide dismutase (CuZnSOD) activity in the liver and heart. However, an increased Mn superoxide dismutase (MnSOD) activity (P<0·05) and a slight increase in malondialdehyde level (P=0·06) were detected in breast muscle. Up-regulated (P<0·05) expressions of heat shock factor 1 (HSF1) and HSF3 mRNA and heat shock protein 70 (HSP70) mRNA and protein were found in all three tissues. Broiler breeders fed either iMn or oMn had higher tissue Mn content (P<0·0001), heart MnSOD and CuZnSOD activities (P<0·01) and breast muscle MnSOD protein levels (P<0·05), and lower (P<0·05) breast muscle HSP70 mRNA and protein levels compared with those fed CON. Broiler breeders fed oMn had higher (P<0·03) bone Mn content than those fed iMn. These results indicate that high temperature decreases Mn retention and increases HSP70, HSF1 and HSF3 expressions in the tissues of laying broiler breeders. Furthermore, dietary supplementation with Mn in either source may enhance the heart’s antioxidant ability and inhibit the expression of HSP70 in breast muscle. Finally, the organic Mn appears to be more available than inorganic Mn for bone in laying broiler breeders regardless of environmental temperatures.

To investigate the effect of Mn on antioxidant status and expression levels of heat-shock proteins/factors in tissues of laying broiler breeders subjected to heat challenge, we used a completely randomised design (n 6) with a factorial arrangement of 2 environmental temperatures (normal, 21 (sem 1)°C and high, 32 (sem 1)°C)×3 dietary Mn treatments (an Mn-unsupplemented basal diet (CON), or a basal diet supplemented with 120 mg Mn/kg diet as inorganic Mn sulphate (iMn) or organic Mn proteinate (oMn)). There were no interactions (P>0·10) between environmental temperature and dietary Mn in all of the measured indices. High temperature decreased (P<0·003) Mn content, and also tended (P=0·07) to decrease copper zinc superoxide dismutase (CuZnSOD) activity in the liver and heart. However, an increased manganese superoxide dismutase (MnSOD) activity (P<0·05) and a slight increase of malondialdehyde level (P=0·06) were detected in breast muscle. Up-regulated (P<0·05) expression levels of heat-shock factor 1 (HSF1) and HSF3 mRNA and heat-shock protein 70 (HSP70) mRNA and protein were found in all three tissues. Broiler breeders fed either iMn or oMn had higher tissue Mn content (P<0·0001), heart MnSOD and CuZnSOD activities (P<0·01) and breast muscle MnSOD protein levels (P<0·05), and lower (P<0·05) breast muscle HSP70 mRNA and protein levels than those fed CON. Broiler breeders fed oMn had higher (P<0·03) bone Mn content than those fed iMn. These results indicate that high temperature decreases Mn retention and increases HSP70 and HSF1, HSF3 expression levels in tissues of laying broiler breeders. Furthermore, dietary supplementation with Mn in either source may enhance heart antioxidant ability and inhibit the expression of HSP70 in breast muscle. Finally, the organic Mn appears to be more available than inorganic Mn for bone in laying broiler breeders regardless of environmental temperatures.

Although fertility rates are dependent on both sexes, this characteristic is most often associated with males. For example, the practice of spiking, in which males with undesirable characteristics are replaced with younger males, is often used to improve fertility rates. Dietary restrictions may offset genetic shortcomings to some extent, but nutritional deficiencies due to dietary restrictions may themselves reduce the efficiency of breeding systems. Thus, the challenge is to maintain rooster fertility even when they are receiving diets that meet the nutritional requirements for females. Subjective visual selection is often used for diagnosis of roosters as being unfit for reproduction, with those deemed as overweight or underweight, or those with too small a comb and/or too slightly pigmented, among other phenotypic parameters, being removed. Diagnosis of infertility may only be confirmed after sperm quality evaluation, with reliance on visual diagnosis often resulting in discarding of roosters suitable for reproduction but with unfavourable visual characters. This review aims to characterise reproductive management of roosters in Brazil, highlight aspects of their physiological and sperm quality parameters, and explore nutritional strategies that might contribute to extending their reproductive life.

Under current practices, broiler parent stock (broiler breeders) encounter several welfare problems, such as feed restriction and injury during mating. Intensive selection for production traits, especially growth rate, is associated with increased nutritious requirement and thus feed consumption, but also reproductive dysfunctions and decreased sexual activity in broiler breeders. A resulting serious welfare problem is the subsequent severe feed restriction which is applied during rearing, in order to prevent health problems and to achieve better egg production. This severe feed restriction has negative effects on bird welfare as it causes chronic stress resulting from hunger. Recent research has focused on management practices to alleviate the negative effect of this feed restriction. Using both a more fibrous feed and an appetite suppressant seems most successful. There are welfare concerns involved in the mating of broiler breeders. In many countries mutilations (beak trimming, despurring and toe clipping) are carried out in male broiler breeders as a standard procedure to prevent excessive damage to the hens during mating. It has been reported that broiler breeder males show low libido but, at the same time, may be aggressive and show rough behaviour during mating, which can cause severe injuries to the hens, although some injuries may be caused by over-mating hens. Current studies aim to develop management practices to reduce hen injury due to over-mating and improve the sexual behaviour in both males and females. In the last part of the review, an examination of how breeding companies are taking welfare into consideration in their commercial selection scheme is made. In practice, although for example reduced mortality and some health criteria are included in selection programs and some alternative breeds as used, other welfare issues remain, such as feed restriction during rearing.

In chickens and in animals in general, growth is influenced by genotype as well as by environmental factors including nutrition. Hormonal changes form, in part, the causal link between these interacting factors and the physiological processes leading to growth. It is well established that growth-related hormones (GH, SS) play different roles in different tissues. Several studies have investigated the nutritional and/or genetic effects on growth in chickens, leading to the general conclusion that the improvement of growth in modern broiler chickens is largely influenced by the genotype. In addition, it has been shown that the nutrition-determined regulation of tissues is also genotype-specific.

Besides growth, genotype-nutrition interactions also influence reproductive parameters (sexual maturation, egg production) and their endocrine control (hormone levels), apparently having long lasting (or epigenetic) effects for the entire lifespan. Especially for broiler breeders, these interactions are of importance in terms of a long-term solution for the broiler breeder paradox. Indeed, broiler breeders need the genetics for rapid growth and yet have to show a high rate of egg production, in spite of the long recognized negative relation between growth and reproductive fitness. Currently, restricted feeding is the only practical tool available to obtain an optimal equilibrium between growth and reproduction. This has the potential for the impairment of welfare (hunger, behaviour, health, viability). Recent studies suggest that modifying the timing of restriction programmes, the quantity/quality of the diet or the use of genotypes that tolerate ad libitum feeding may achieve a good balance between growth and reproductive performance on the one hand and breeder welfare on the other.

Feeding time has the potential to influence the performance of adult broilerbreeder flocks and is thus of great importance. Aliterature review is presented concerning the responses of adult broilerbreeders to feeding time. It appears that there is no benefit in feeding broiler breeders later in the day with regard to egg numbers oregg weight.

There is a potential improvement in shell quality that results from feeding laterin the day or from splitting the daily feed allocation across more frequent feeding periods throughout the day. However, anticipated improvements in shell quality due to delayed feeding times may not be realised, particularly when birds are housed on litter floors. Furthermore, improvements in shell quality may not be translated into improvements in hatchability due to increases in shell thickness adversely affecting the watervapourconductance of the eggshell.

Broiler hatching egg producers should be aware that later feeding times may delay the time of oviposition, which may demand changes in farm procedures. Furthermore, delayed feeding times may result in feeding activity coinciding with other important periods of activity, such as mating and oviposition, resulting in a reduction in fertility and an increase in the production of eggs with abnormal shells. The current commercial practice of feeding adult broiler breeders early in the day, at, ornear, lights-on, is justified, as feeding at this time has positive consequences for other aspects of hatching egg production. However, afternoon feeding is not necessarily detrimental and may be an option to consider in cases where improvements in shell quality are required, although this may not be the solution for hatchability problems. If a change in feeding time is under consideration, environmental conditions, particularly the photoperiod and ambient temperature, must be taken into account, and any changes should be made gradually, as broiler breeders may be sensitive to abrupt changes in feeding time. Furthermore, changes in the feeding schedule should be accompanied by close monitoring of performance parameters, including the number of settable, abnormal and floor eggs, percentage of fertile eggs, and hatch of fertiles.

A series of factors have contributed to the progressive diversification of reproduction strategies to produce day-old chicks in distinct geographical locations. Some of these strategies are adaptable by simple technology transfer and education (e.g. darkout housing to control photoperiod, appropriate feeding and management of breeder flocks) while others require continued efforts from geneticists and physiologists to develop new genetic lines and tools (eg. selection of breeds adapted for hot climates and gene banking). Reproduction strategies in broiler breeders will also probably continue to diversify depending on economic and social components, including labour and feed costs as well as local regulations. As a consequence, the final choice between natural mating or artificial insemination (for caged or floored breeders) is itself multifactorial and may lead to the selection of parent stock lines optimised for one or the other strategy, according to country and living standards. Finally, the diversity in consumer demand for poultry will itself favour the emergence of specialised birds and management techniques directly adapted to local needs.