key: cord-287243-fm3587ww authors: Scanes, Colin G.; Butler, Leasea D.; Kidd, Michael T. title: Reproductive management of poultry date: 2020-01-24 journal: Animal Agriculture DOI: 10.1016/b978-0-12-817052-6.00020-3 sha: doc_id: 287243 cord_uid: fm3587ww Based on data from the UN's Food and Agricultural Organization, about 120 million metric tons of poultry meat were produced globally in 2016. In addition, about 82 million metric tons of eggs were produced. One of the bases for this production is the reproductive efficiency of today's poultry. This, in turn, is due to their inherent reproductive physiology, intensive genetic selection and advances in husbandry/management. The system of reproduction in males in largely similar to that in mammals except that there is no descent of testes. In females, there are marked differences with there being a single ovary and oviduct; the latter being the name of the differentiated entire Müllerian duct. Moreover, females produce eggs with a yolky oocyte surrounded by albumen, membranes and shell. Among the most successful reproductive management techniques are optimizing photoperiod, light intensity and nutrition. Widespread employment of these has allowed maximizing production. Laying hens can be re-cycled toward the end egg production. Other aspects of reproductive management in poultry include the following: artificial insemination (almost exclusively employed in turkeys) and approaches to reduce broodiness together with cage free (colony), conventional, enriched and free-range systems. Introduction Poultry production has markedly increased globally over the last 50 years. This is summarized in Table 20 .1. The increase in rate of poultry production over 50 years is over twice the rate of increase in human population. 1 Chicken production is divided into two distinct sectors: meat and eggs. There are disparate lines of birds derived from different strains with greatly different genetics. An analogous situation exists for ducks. Production of poultry meat depends on three distinct reproductive phases: with pedigree flocks undergoing intensive genetic selection for improvement. These produce grandparent stock/great grandparent stock and, following multiplication, leads to broiler breeders (or their equivalent in other poultry species). In the USA, there were 114 million broiler breeder pullets placed for broiler egg production (and hence broiler chick) in 2017. 2 Broiler breeder production of fertile eggs. In the USA, there were 1.2 billion hatching eggs produced in 2017. 2 3. Incubation of the fertile eggs in hatcheries to produce broiler chicks, turkey poults, ducklings and goslings. In the USA, there were 185 million broiler chicks placed per week in August 2018 (cf. 227 million eggs set per week) 3 and 292 million turkey poults hatched in 2017. 4 Production of eggs depends on three distinct reproductive phases: 1. Primary breeding companies with pedigree flocks undergoing intensive genetic improvement. These produce replacement pullets. In the USA, there are 115 million re-placement pullets per year. 5 The average number of layers in the USA in 2017 was 375 million. 2 In the USA, the average hen produces 281 eggs per year. 4 2. Re-cycling hens toward the end of egg production cycle. Embryonic development of the reproductive system In contrast to the situation in mammals, the sex chromosomes in male birds are ZZ (homozygous) compared to ZW (heterozygous) in females. In males, the two testes are internal and accessory organs such as the prostate and seminal vesicles are absent. The testes develop due to gene dosing with increased expression of the Z-linked transcription factor gene, doublesex and mab-3-related transcription factor 1 (DMRT1). 6, 7 Anti-M€ ullerian hormone (AMH) is synthesized and secreted by the embryonic testis with greater expression in the embryonic testes than the ovaries. 8e10 AMH directs the regression of the paired M€ ullerian ducts. 8e10 In females, only the left ovary and oviduct develop in all avian species and closely related dinosaurs; the latter based on fossil evidence from the early Cretaceous period. 11 The avian oviduct is derived from the embryonic M€ ullerian duct; the former term encompassing the entire reproductive tract from infundibulum to the cloaca. 7 Regression of the right oviduct is induced by AMH. 10 Parenthetically, AMH also plays an important role in development of tubules in the testes. 8, 9 The embryonic female gonad expresses the rate-limiting enzyme for the production of estrogens, aromatase (CYP19A1) but expression is not found in the embryonic male gonads. 12, 13 In turn, the estrogens, such as estradiol, induce growth of the oviduct. 7 The egg is comprised of the yolk, yolk membranes, egg white, shell membranes and finally the egg shell. Each of these components are developed along specific regions of the female reproductive tract together with the ovary. The egg yolk is a mature ovum (oocyte) that is produced by the ovary. The maturation of the ovum involves multiple processes including deposition of yolk proteins/lipids. Yolk protein/lipoproteins/phosphoproteins were assigned to three categories based on centrifugation of diluted yolk: • Low-density fraction with a very high lipid composition • Granules composed of heavy and light chain lipovitellins, phosvitin and a yolk glycoprotein. 14 • Soluble proteins. The soluble proteins 15 consist of the following: • a livetins (serum albumen) • b livetins (serum a 2 -globulin containing transport proteins) • g livetins (serum g -globulin predominantly immunoglobulin Y). Egg yolk livetins (a, b, and g-livetin) have recently been shown to exert anti-inflammatory properties. 16 Yolk precursors: Yolk precursors are synthesized in the liver. Two major yolk precursors are very-low-density lipoprotein (VLDL) and vitellogenin. Very-low-density lipoprotein (VLDL) has the following characteristics: • Globular micelle-like • Non-polar core of triglycerides and cholesterol esters • Coated with amphiphilic mix of phospholipid, free cholesterol (FC) and twp apolipoproteins. 17 Chicken vitellogenin has been purified from plasma of estrogen treated adult male chickens. 18 It is a dimer with a molecular weight 480,000. 18 It is a dimer composed of two polypeptide monomers each with a molecular weight of about 170,000. 19 There are about 220e235 phosphate moieties per monomer vitellogenin 18 and the lipid component is about 20%. Hepatic expression of vitellogenin is induced by estrogens. 19 Yolk deposition: A specific receptor is responsible for transfer of vitellogenin and verylow-density lipoprotein (VLDL) across the oocyte plasma membrane to fill the oocyte with yolk. 20, 21 Within the oocyte, vitellogenin is cleaved proteolytically to form the yolk proteins, heavy and light chain lipovitellin (20% lipid), phosvitin and a yolk glycoprotein. These are incorporated into yolk granules. Deposition of g livetins is very high in small follicles <200 mg, 22 but decreases during development of large follicles. 23 For the last four days of development of the follicles, yolk is being deposited at 2.5 cm 3 or greater per day. 24 Once the ovum (egg yolk) has matured, ovulation is stimulated by the pituitary hormone, luteinizing hormone (LH). An extensive explanation of hormonal control of female reproduction follows. If ovulation is successful the ovum is normally received into the infundibulum. The egg white or albumin of the egg is produced by the magnum of the oviduct. The magnum is the longest section of the oviduct where the ovum spends approximately 4 h accumulating egg white proteins. 25 Among the constituents of egg white are the following proteins: • Ovalbumen -50% of egg white proteins • Ovotransferrin (conalbumen) 12% (this chelates metal ions particularly iron) • Ovomucoid -11% • Lysozyme -3.5% • Ovomucin 1e3% • Avidin 0.05%. 26 Antimicrobial peptides and proteins 27e29 are present in the egg white and include the following: • Gallin or ovodefensin • b-defensin 11 • Cathelicidin • Cystatin -a cysteine protease inhibitor • Lysozyme-a bacteriolytic enzyme • Ovoinhibitor. Following albumin deposition and addition of water ("plumping fluid") to the developing egg, the eggshell membrane is added in the isthmus; this taking approximately 1 h. 25 The eggshell membranes are 93% protein 30 contains proteins including collagens, ovoalbumin, bacteriolytic enzymes such as ovotransferrin and lysozyme together with clusterin peptides and ovodefensins/defensins such as gallin. 30, 31 These are also glycosaminoglycans including galactosaminoglycan. 32, 33 Egg shell The formation of the egg shell in the uterus/ shell gland is the final yet it is of longest in duration taking approximately 19 h. 25 This is due to the extensive structure of the shell. The egg shell is 97% inorganic (calcium carbonate). 26, 34 Of the remaining 3% (the decalcified egg shell) is 79% protein with the matrix phosphoproteins including the following: ovocleidin-17, ovocleidin-116, ovocalyxin-32 and osteopontin. 30, 35 The fully formed egg is retained in the shell gland just distal to the vagina of the oviduct until oviposition. Unlike many mammals, the testes of poultry and other birds are in the abdominal cavity. 36, 37 Following sexually maturation, adult male birds produce semen containing large numbers of spermatozoa (see Table 20 .2). Production of spermatozoa is critical to fertilization of the ovulated ovum and, hence, the production of broiler chicks (see Broiler breeder reproduction section), layer pullet chicks and turkey poults (see Artificial insemination section). Spermatogenesis is a complex process that is tightly regulated by neuroendocrine and endocrine mechanisms (discussed later in hormonal control of reproduction). 36, 37 Spermatozoa are produced in the seminiferous tubules of the testes. 36, 37 Each mature spermatozoan consists of an acrosome containing the nucleus that holds the DNA information, attached to a microtubular flagella enabling it to be propelled from the cloaca of the hen to the infundibulum of the oviduct. Once spermatozoa enter the vagina of the oviduct, they are stored in the utero-vaginal junctions or the infundibular sperm storage tubules. 36 Similar number of utero-vaginal junctions can be found in commercial broiler breeders and turkeys. 38 Spermatozoa can retain their ability to fertilize the oocyte for several weeks, however fertility begins to decline post 7 days after insemination and is markedly lower 10 days after insemination. 39 Hormones are critically important to the optimal functioning of the gonads, the photoperiodic stimulation of reproduction, sexual and maternal behavior and induced molting. The major androgen produced by the testes is testosterone. Interestingly, it was demonstrated by Berthold in 1849, in the first endocrine study, that a testicular factor was essential to both male behaviors such as crowing, mating and aggression in chickens and to the development of the secondary sexual characteristics such as the rooster's comb and wattle. Pituitary gland and reproduction: The gonads are controlled by the anterior pituitary hormones, LH and follicle stimulating hormone (FSH). These gonadotropins play a critical role in the development and maintenance of the gonads. LH stimulates production of progesterone by granulosa cells from large follicles 40 and testosterone by Leydig cells of the testes. 41 FSH increases proliferation of granulosa cells, expression of both steroidogenic acute regulator (StAR) and inhibin a genes in granulosa cells and release of progesterone with the effect progressively greater with tissue from larger follicles. 42, 43 In addition, prolactin can exert an inhibitory effect on the chicken ovary. 44 Hypothalamic control of gonadotropin release: There are two gonadotropin releasing hormones (GnRHs) in the chicken (cGnRH-I and cGnRH-II) and two receptors for GnRH (cGnRHR1 and cGnRHR3). GnRH-II is much more potent than GnRH-I in hens in stimulating LH release by 36 fold. 45 However, GnRH-II is not detected in the median eminence. 46, 47 There is high expression of GnRHR3 in the pituitary gland. 48 Therefore, the releasing hormone for LH is chicken GnRH-I and the receptor is cGnRHR3. Chicken gonadotropin-inhibitory hormone (GnIH) is a peptide with 12-amino-acids. 49 While GnIH inhibits both the synthesis and the release of gonadotropins in chickens, 50 the physiological relevance of GnIH still requires clarification. The ovary produces the following: • Estrogens, primarily estradiol. Estrogens induce the following: development of the oviduct, production of yolk precursors (VLDL and vitellogenin) (see above) by the liver, production of egg white proteins by the oviduct and, with androgens, formation of medullary bone (a labile source of calcium). In addition, estrogens allow the expression of female behaviors and moderate the release of luteinizing hormone (LH). • Progesterone. Among its roles are stimulating production of a specific egg white protein (avidin) and stimulating the release of LH. • Androgens, predominantly testosterone. Androgens are essential to the development of medullary bone. 26, 51 Ovarian hormones and growth factors also play critical roles in follicular development. For instance, activin A increases expression of both FSH and LH receptors but decreases cell proliferation of granulosa cells. 52 Moreover, development of small follicles is suppressed by epidermal growth factor receptor ligands such as transforming growth factor a. 57 In contrast, bone morphogenetic protein 6 enhanced responsiveness to FSH. 43, 53 Testicular functioning is controlled in a similar manner to the ovary. LH stimulates the Leydig cells to produce testosterone. 41 The Sertoli cells produce nutrients to the maturing spermatozoa and are under the control of FSH. Testosterone is produced from the Leydig cells. There is seasonality of egg production in chickens when held under a natural photoperiod in the temperate zone. Egg production increases markedly after the winter solstice and declines beginning prior to the autumnal equinox. 54 The physiological basis of this annual cycle is photoperiodic stimulation of reproduction by long daylengths; these inducing the development of functioning gonads. 54 Red light is detected by photo-pigments in the hypothalamus 54e56 with the most important photoreceptor influencing the hypothalamic release of GnRH-I being red opsin. 55 The photoperiodic mechanism involves light coinciding temporarily with the light sensitive (photo-sensitive) phase of a circadian rhythm. This leads to release of GnRH-I, synthesis and secretion of LH and FSH and, hence, gonadal resurgence. 54 Chickens Pullets are reared under short daylengths (6L:18D or 8L:16D). They are transferred to longer daylengths (12L:12D) at breed specific physiological ages 45 to stimulate gonadal development. In studies where pullets were transferred to daylengths of 10L:14D or 11L:13D, plasma concentrations of LH did not increase, but marked increases in plasma concentrations of LH daylengths were observed with daylengths 13L:11D or greater. 54 Perhaps surprisingly, daylengths were interpreted differently depending on the previous photoperiod. Transfer of pullets from photoperiods of either 4L:20D or 20L:4D to 12L:12D were followed by, respectively increases and decreases in plasma concentrations of LH. 54 Thus, the same photoperiod can be interpreted as either photostimulatory or photoinhibitory. Commercially, pullets are brought into lay by increasing both the photoperiod and the light intensity (Table 20. 3). There are breed and genetic line specific differences between ages at which photostimulation is performed (see Table 20 .3). Egg production in broiler breeder hens is improved when photostimulation is delayed from 18 to 21 weeks old. 57 There is also evidence that it may be advantageous to delay photostimulation of broiler breeders to 24 weeks old. 58 Turkeys: Turkeys come into lay with increasing daylengths. 59 There are seasonal differences (see Table 20 .4). 60 There is a rapid increase in plasma concentrations of both LH and FSH when males and females are exposed to long day-lengths. 61 Photorefractoriness is the loss of the ability to respond to the stimulatory effects of long photoperiods. Photorefractoriness can be "broken" by re-exposure to short day-lengths. This is seen in turkeys with prolonged exposure to long day-lengths with the signs of photorefractoriness being decreased egg production and molting. 59, 60 The decline in egg production during the production cycle of chickens might also be attributed to photorefractoriness. Indeed, there is greater sensitivity of older hens to reduced daylength with an over 90% decrease in egg production in 105 weeks old hens compared to a 26% decline in 28 weeks old hens. 62 Moreover, plasma concentrations of LH were only decreased in the older hens. 62 While, light intensities greater than 1 lux are required for photoperiodic induction of egg production, 63 considerably higher light intensities are employed in commercial poultry production (Table 20. 3). For instance, in broiler breeders, light intensity is increased from before photostimulation about 6 lux in the pullet phase to >50 lux after photostimulation at 21 or 22 weeks of age. 64 Other effects of light intensity: Light intensity has other effects. For instance, increasing light intensity in immature pullets is associated with increased plasma concentrations of FSH. 65 Moreover, the ability of a short pulse of light to photostimulate chickens is influenced by light intensity. 66 In addition, the ratio of the light intensity during the subjective day to that during the subjective night is important in entraining the rhythm of oviposition. 67 Nutrition and reproductive management Overview In poultry, nutrition is integrally linked to the hypothalamo-pituitary-gonadal axis. It has been known for 50 years that egg production in hens stops quickly following fasting. 68 The administration of mammalian or avian gonadotropin restores, albeit partially, egg production in starved hens 68 ; this suggesting that underlying cause is the lack of pre-ovulatory LH surges. Fasting is followed rapidly by decreases in plasma concentrations of LH, 69 body weight together with precipitous declines in ovarian and oviductal weights. 70 Similarly, production of eggs and plasma concentrations of LH decrease quickly after reducing calcium or sodium in the diet of hens. 71,72 In young chickens, protein deficiency also has been demonstrated to rapidly cause atrophy of gonads, decrease circulating concentrations of LH and depress responsiveness to GnRH. 73 The NRC Nutrient Requirements of Poultry has been invaluable to researchers and important to the poultry industry recommending minimum levels of nutrients in the feed. 74 These requirements are based on the published research prior to the development of the specific edition of NRC Nutrient Requirements of Poultry. Primary breeders publish age specific nutrient recommendations for each of their genetic lines. 64,75e77 Examples of such recommendations for energy, protein, lysine and calcium are summarized in Table 20 .5. It is clear that the recommendations for calcium content in laying hen diets are very high due to the demands of eggshell formation. Moreover, the levels of calcium in diets are higher as the production cycle proceeds presumably due to the increasing size of the egg. This is the case irrespective of whether the recommendations are for layer or broiler breeder hens (Table 20 .5). Feedingprogramsare designed toachievetarget body weights throughout growth with markedly lower weights at 24 weeks old (ad libitum fed 5.65 kg; restricted to achieve target weights 3.06 kg). 78 These programs not only decrease the feed needs of the broiler breeder but also reduce mortality and increase egg production. 78 Broiler breeder pullets can be fed nutrient restricted diets by programs where birds are fed daily or skip-a-day or feeding four or five or six days per week. There were greater body weights and lower liver weights in 16 week-old pullets fed daily than skip-a-day despite the birds despite their receiving the same amount of feed. 79 There were also higher hepatic concentrations of both lipid and glycogen together with the expression of lipogenic enzymes in skip-a-day fed pullets. 79, 80 Mench considered that feed restrict of broiler breeder females may be associated with physiological stresses and increased incidence of abnormal behaviors. 81 The severity of feed restriction needs to be progressively greater with generation exhibiting increased size/growth rates in broiler chickens. 82 The strategy in feed restriction is to reduce caloric intake while maintaining amount of feed consumed. This goal is achieved by increasing the percentage of crude fiber in the diet. Skip-a-day programs have been considered helpful in increasing uniformity within flocks and reducing abnormal behaviors. 83 Induced molting or re-cycling to increase egg production Hens can be induced (or forced) to molting at the end of their laying cycle resulting in improved egg production at a lower cost than using replacement pullets (Fig. 20.1 ). In the USA, 19.7 % of laying hens are molted (re-cycled) each month. 5 This process can involve severe nutritional restriction including starvation and/or withholding water and/or reduction in photoperiod. 70,84e86 Alternate methods of induced molting include an extremely high zinc diet (20,000 ppm) followed by a conventional layer feed beginning at day 12 87 and sodium/chloride-deficient diets. 88, 89 Broiler breeders are rarely molted, but under certain circumstances, molting may be performed. Most broiler breeder molt programs are achieved by restricting feed consumption and supplementing water containing essential micronutrients allowing utilization of fat stores. This reduced fat stores such that hens achieve a more pullet-like body composition before being photostimulated again. In addition to feed restriction, to induce molting in broiler breeder hens, the daylength is decreased to 8L:16D and light intensity is reduced. 85,86 Production levels with molted broiler breeders are about 10% less than their previous laying cycle. 85, 86 The lower production level appears to be due to there being fewer follicles after a forced molt compared to their initial lay cycle. 25 The terms, forced or induced molt, are open to question as it presumes that molting (loss of feathers) causes rejuvenation of reproduction performance. Molting occurs after resumption of normal feeding and is temporally shifted from ovarian recrudescence (see Fig. 20 .2). When feed is withdrawn for 8 days and water withdraw for 2 days, egg production had completely ceased by 6 days (see Fig. 20 .2). 90 Molting occurred after the resumption of feeding and there were concomitant increases in circulating concentrations of T 3 and corticosterone (see Fig. 20 .2). 90 Circulating concentrations of LH, estradiol (E 2 ) and progesterone were lower in molting hens than in laying hens or fully recycled hens. 90 The effects of an industry molting system on organ weights together with circulating concentrations of ions and corticosterone were evaluated. 91 The approach was to combine salt and protein deprivation 91 This approach is effective in stopping egg production and decreasing body weight and organ weights. 91 It is accompanied by reductions in circulating concentrations of sodium and chloride (see Table 20 .6). 91 The egg production cycle of about 21 weeks of age to 45e60 weeks old can be extended with a molt between 108 and 120 weeks old. 91 The physiological mechanism underlying induced molting included decreased release of GnRH from the median eminence and consequently lack of the pre-ovulatory LH surge. Ovulation completely ceased with 4 days of feed withdrawal. 92 Plasma concentrations of LH and progesterone were decreased with 2 days of feed withdrawal. 92 The GnRH content of the median eminence was similarly decreased but not until 4 days of feed withdrawal. 92 There are also decreases in the number of gonadotropes expressing LH. 93 Oviductal regression occurs due to lack of estrogens and is accompanied by increased expression of peptidases with, for example, expression of the peptidase, cathepsin L. 94 It is questioned whether re-cycling/forced molting of hens is consistent with one of the "The Five Freedoms," namely: "1. Freedom from hunger and thirst" and the need for "ready access to fresh water and a diet to maintain full health and vigor." 95 There is both evidence for and against the process being physiologically stressful. An indicator of stress, heterophil: lymphocyte ratio, was increased after 7 days after feed withdrawal to a forced molt. 96 Similarly, induction of molting was accompanied by increased the percentage of heterophils (day 7 and 14) and of eosinophils in one study. 97 However, the evidence of molt induction influencing plasma concentration of the stress hormone, corticosterone, is circumspect. No changes in plasma concentrations of corticosterone in force molted hens were reported (also see Table 20 .6). 91, 94 In laying hens subjected to induced molting, plasma concentrations of corticosterone were higher on day 10 in hens subjected to complete Induced molting or re-cycling to increase egg production feed withdrawal than those in which molting was induced by a high zinc diet or in a wholegrain barley diet. 98 There are also shifts in immune responses including cytokine expression. During starvation induction of molting, there is a reduced delayed type hypertensive response in the wattle. 99 Feed withdrawal for 6e8 days is associated with increased oviductal expression of the following: interleukin (IL)-6, IL 8 and interferon g. 100 Similarly, expression of cytokines in response to an endotoxin challenge increased in the uterus of molting compared to laying hens. 101 Other aspects of reproductive management in poultry Artificial insemination (AI) is used very widely in turkey production but not in the production of layer pullets or broiler chicks. 102 Hens are inseminated weekly with diluted semen (for spermatozoa concentrations in turkey ejaculate see Table 20 .2). While the technique is labor intensive, it takes advantage of the presence of spermatozoa storage glands in the oviduct. 102 These release spermatozoa after oviposition such that newly ovulated ovum can be fertilized prior to the addition of egg white, membranes and the she1l. 102 The AI techniques that were developed for poultry have been applied to the conservation of endangered wild birds when they fail to mate in captive conditions. 103 AI can be employed alone or coupled with cryopreservation. 103 It is advantageous to suppress broodiness (maternal behavior) and the consequent decrease in egg production in poultry. Broodiness has been effectively genetically eliminated in commercial chickens irrespective of whether broilers or laying hens. 104 Approaches that could reduce the unfavorable effects of broodiness in turkeys include: genetics and active or passive immunization with antisera reducing available prolactin. Administration of antisera to turkey prolactin increased egg production in turkeys. 105 An alternate approach is active immunization. Similarly, egg production was markedly increased in turkey hens actively immunized against VIP (with VIP being conjugated to keyhole limpet hemocyanin) due to impairment of prolactin release and consequently reduction in incubation behavior(s). 106, 107 It was hoped that antisera could also enhance reproduction in males. Young male chickens exhibited multiple changes after active immunization against both inhibin and VIP. These included increases in semen volume and spermatozoa mobility together with spermatozoa concentrations. 108 In contrast, this improvement in reproductive performance was not seen in old roosters actively immunized against both inhibin and VIP. 109 Antibody approaches do not appear to be widely adopted due to expense of registration. Cage free (colony), conventional, enriched and free-range systems Both egg production and bird health are influenced by the systems employed to maintain (chicken) hens. Egg production was greater in the hens in conventional caging compared to an aviary system. Much lower (w40%) mortalities were reported in hens in conventional caging compared to an aviary system. 110 Moreover, there was a greater incidence of keel deformities in hens in a cage free system compared to those in conventional cages. 111 There are also differences in leg bone characteristics with hens under the cage free conditions having increased cortical cross-sectional area and cortical density of their humerus and tibia compared to those maintained in conventional cages. 112 Moreover, there was there was greater stiffness of both humerus and tibia and increased percentage ash in the humerus in hens in a cage free system. 112,113 20 . Reproductive management of poultry However, in another study, there were little differences between tibia and humerus parameters between hens in cage-free or conventional cage systems. 111 In laying hens at the end of the laying cycle, there were differences in bone characteristics depending on the environment under which the pullets were raised. 112 Production has been compared between Lohmann Brown layer hens in convention layer housing, enriched convention layer housing and free-range systems. Perhaps unexpectedly, egg production was greater in hens in a freerange system (average production over cycle 89.3%) compared to conventional layer housing (87.3% with enrichment and 87.1% without). 94 In contrast, there was greater feed intake and higher feed conversion ratios in hens in a freerange system. 114 In another study, egg production was greater in hens with an enriched environment compared to conventional caging. 110 Broiler breeders are prone to ovulation issues. Examples include internal ovulation and double ovulation of a (double "yolked" eggs). The latter is due to pair of large yellow follicles in the follicular hierarchy. 25 Duplicate ovulation is considered to be a result of "over-stimulated" hens coming into production or pullets not ready for light stimulation or to over-feeding. 113, 115 Internal lay of the ovum is followed the constituents of ovum being absorbed, but can result in a substrate for bacterial growth like Escherichia coli. 116 Uses of components of eggs Yolk as source of antibodies A major soluble protein type in yolk are the g livetins or the immunoglobulins (discussed section above). Yolk IgY from chicken immunized against pathogens (rotaviruses, bovine coronavirus, enterotoxigenic E. coli and Salmonella spp.) offers potential to replace antibiotics in livestock production. This may be particularly important with the restriction of antibiotic use and growing consumer resistance to their use. A meta-analysis of 22 studies determine that hyperimmune yolk IgY was effective against diarrhea in piglets. 117 Similarly, oral administration of IgY was efficacious in poultry and calves. 117, 118 Other products of eggs Egg white and its constituents have important functional properties. Examples include the following. Avidin is used in multiple biochemical tests. Lysozyme (bacteriostatic and bactericidal) has been used as a preservative, for instance, in cheese making. 27 Egg shell membranes or egg shell membrane powder have been used as natural bandage for burns and injuries in traditional Asian medicine. Egg shell membrane powder and its carbohydrate constituents have been recently been demonstrated to exert anti-inflammatory effects 119, 120 supporting their effectiveness. In the chick embryo, primordial germ cells migrate from the germinal crescent to the genital ridge ultimately becoming male or female gametes. The primordial germ cells carry the genetics to the next generation and, thus, if this can be manipulated we have a multi-generational method of producing transgenic animals. Chicken primordial germ cells can be obtained from blood of chick embryos and maintained in culture. 121 This has been used to both insert and/or "knock out" genes. 121 Transgenic hens can be used as bioreactors to produce pharmaceutical proteins in their egg white when oviduct specific promoters are used. 122 This concept has been applied to the production of human erythropoietin 123 and tumor necrosis factor receptors. 115 USDA National Agricultural Statistics Service (NASS) UN Food and Agriculture Organization e FAOStat USDA National Agricultural Statistics Service (NASS) Chicken and Eggs 2017 Summary The avian Zlinked gene DMRT1 is required for male sex determination in the chicken The avian ovary and follicle development: some comparative and practical insights Anti-M€ ullerian hormone is required for chicken embryonic urogenital system growth but not sexual differentiation Overexpression of anti-M€ ullerian hormone disrupts gonadal sex differentiation, blocks sex hormone synthesis, and supports cell autonomous sex development in the chicken Identification, expression, and regulation of anti-M€ ullerian hormone type-II receptor in the embryonic chicken gonad Ovarian follicles shed new light on dinosaur reproduction during the transition towards birds Expression of P450(17 alpha) hydroxylase and P450 aromatase genes in the chicken gonad before and after sexual differentiation Sites of estrogen receptor and aromatase expression in the chicken embryo Precursorproduct relationship between chicken vitellogenin and the yolk proteins: the 40 kDa yolk plasma glycoprotein is derived from the C-terminal cysteine-rich domain of vitellogenin II Serum proteins and the livetins of hen's-egg yolk Anti-inflammatory effects of egg yolk livetins (a, b, and g-livetin) fraction and its enzymatic hydrolysates in lipopolysaccharide-induced RAW 264.7 macrophages Relationships of plasma and very-low-density lipoprotein lipids and subfractions with abdominal fat in chickens Vitellogenin synthesis in the avian liver. Vitellogenin is the precursor of the egg yolk phosphoproteins Estradiol-induced synthesis of vitellogenin. III. The isolation and characterization of vitellogenin messenger RNA from avian liver A single chicken oocyte plasma membrane protein mediates uptake of very-low-density lipoprotein and vitellogenin The receptor for yolk lipoprotein deposition in the chicken oocyte Changes in specific sequestration of protein during transport into the developing oocyte of the chicken The macromolecular composition of hen's egg yolk at successive stages of maturation Modeling ovarian follicle growth in commercial and heritage Single Comb White Leghorn hens Roles of body weight and feed intake in ovarian follicular dynamics in broiler breeders at the onset of lay and after a forced molt Reproduction in the female The chicken egg white proteome Gallin; an antimicrobial peptide member of a new avian defensin 20. Reproductive management of poultry family, the ovodefensins, has been subject to recent gene duplication Characterization of egg white antibacterial properties during the first half of incubation: a comparative study between embryonated and unfertilized eggs Chemical composition of chicken eggshell and shell membranes Chicken egg shell membrane associated proteins and peptides Extraction of glycosaminoglycans from chicken eggshell Galactosaminoglycan composition in chicken eggshell The eggshell: structure, composition and mineralization Functional proteins and peptides of hen's egg origin Reproduction in the male Comparisons of sperm storage tubule distribution and number in 4 strains of mature broiler breeders and in turkey hens before and after the onset of photostimulation Analysis of sperm storage ability using duration of fertility in hens Effects of mammalian LH, cyclic AMP and phosphodiesterase inhibitors on steroidogenesis, lactate production, glucose uptake and utilization by avian granulosa cells Genistein affects testosterone secretion by Leydig cells in roosters (Gallus gallus domesticus) Follicle-stimulating hormone regulation of inhibin alpha-and beta (B)-subunit and follistatin messenger ribonucleic acid in cultured avian granulosa cells Granulosa cell responsiveness to follicle stimulating hormone during early growth of hen ovarian follicles Effects of nonglycosylated and glycosylated prolactin on basal and gonadotropinstimulated steroidogenesis in chicken ovarian follicles Sex differences in the LH responses to chicken LHRH-I and -II in the domestic fowl Physiological roles of chicken LHRH-I and -II in the control of gonadotrophin release in the domestic chicken Distribution of luteinizing hormone-releasing hormones I and II (LHRH-I and -II) in the quail and chicken brain as demonstrated with antibodies directed against synthetic peptides The chicken type III GnRH receptor homologue is predominantly expressed in the pituitary, and exhibits similar ligand selectivity to the type I receptor A novel avian hypothalamic peptide inhibiting gonadotropin release Gonadotrophin inhibitory hormone depresses gonadotrophin and follicle-stimulating hormone subunit expression in the pituitary of the domestic chicken The role of hormones in the regulation of bone turnover and egg shell calcification Effect of activin A and inhibin A on expression of the inhibin/activin beta-B-subunit and gonadotropin receptors in granulosa cells of the hen Bone morphogenetic protein-6 enhances gonadotrophindependent progesterone and inhibin secretion and expression of mRNA transcripts encoding gonadotrophin receptors and inhibin/activin subunits in chicken granulosa cells Photoperiodic control of reproduction in the domestic hen The role of retinal and extra-retinal photostimulation in reproductive activity in broiler breeder hens Red light is necessary to activate the reproductive axis in chickens independently of the retina of the eye Early photo-stimulation at the recommended body weight reduced broiler breeder performance Effect of strain, feed allocation program, and age at photostimulation on reproductive development and carcass characteristics of broiler breeder hens The relationship of plasma thyroid hormone and prolactin concentrations to egg laying, incubation behavior, and molting by female turkeys exposed to a one-year natural daylength cycle Critical day lengths for egg production and photorefractoriness in the domestic turkey Effect of photoperiod on gonadotrophin concentrations in domestic fowl Neuroendocrine control of reduced persistence of egg-laying in domestic hens: evidence for the development of photorefractoriness Light intensity and age at first egg in pullets Breeder Management Supplement: Fast Feather Female: Cobb 500 Light intensity can influence plasma FSH and age at sexual maturity in domestic pullets Time of lay in hens exposed to intermittent lighting Entrainment of oviposition in the fowl using bright and dim light cycles The induction of ovulation in starving pullets using mammalian and avian gonadotropins The effect of shortterm starvation on pituitary and plasma LH, plasma estradiol and progesterone, and on pituitary response to LH-RH in the laying hen (Gallus domesticus) Physiological changes in caged layers during a forced molt. 1. Body temperature and selected blood constituents Response of laying hens to low salt diet Effects of gradation in protein-calorie restriction on the hypothalamo-pituitary-gonadal axis in the young domestic fowl Nutrient requirements of poultry publication: history and need for an update W-36 Commercial Layer Management Guide Ross 308 Nutrition Specifications Ross 708 Nutrition Specifications Effects of low dietary protein and different allocations of food during rearing and restricted feeding after peak rate of lay on egg production, fertility and hatchability in female broiler breeders An examination of the role of feeding regimens in regulating metabolism during the broiler breeder grower period. 1. Hepatic lipid metabolism Feed restriction significantly alters lipogenic gene expression in broiler breeder chickens Broiler breeders: feed restriction and welfare. World's Implications of changes to commercial broiler and broiler breeder body weight targets over the past 30 years. World's The effect of dietary alterations during rearing on growth, productivity, and behavior in broiler breeder females The effects of alternative forced-molting methods on the performance and egg quality of commercial layers Molting layers-alternative methods and their effectiveness Review: feed withdrawal and non-feed withdrawal moult. World's Recrudescence mechanisms and gene expression profile of the reproductive tracts from chickens during the molting period The potential use of dietary salt deficiency for the force resting of laying hens Effectiveness of low sodium diets for recycling of egg production type hens Changes in plasma thyroid hormones, luteinizing hormone (LH), estradiol, progesterone and corticosterone of laying hens during a forced molt Morphological and Physiological Changes in Various Stages of Non-Feed Withdrawal Molt (Ph.D. dissertation) Median eminence and anterior pituitary degradation of luteinizing hormone releasing hormone in hens undergoing changes in luteinizing hormone secretion Cell proliferation and apoptosis in the anterior pituitary of chicken during inhibition and resumption of laying Expression and regulation of avian cathepsin L in the oviduct during molting Farm Animal Welfare Council. Five Freedoms The effects of long-term caging and molt of Single Comb White Leghorn hens on heterophil to lymphocyte ratios, corticosterone and thyroid hormones Physiological changes in caged layers during a forced molt. 4. Leucocytes and packed cell volume Effects of different forced molting methods on postmolt production, corticosterone level, and immune response to sheep red blood cells in laying hens Effects of induced moulting on immune responses of hens Cytokines in reproductive remodeling of molting White Leghorn hens Effects of lipopolysaccharide on the expression of proinflammatory cytokines and chemokines and the subsequent recruitment of immunocompetent cells in the oviduct of laying and molting hens Success in Artificial Insemination: Quality of Semen and Diagnostics Employed Implementing artificial insemination as an effective tool for ex situ conservation of endangered avian species Genetic loci inherited from hens lacking maternal behaviour both inhibit and paradoxically promote this behaviour Prevention of the expression of incubation behaviour using passive immunisation against prolactin in turkey hens (Meleagris gallopavo) Increased egg production by active immunization against vasoactive intestinal peptide in the turkey (Meleagris gallopavo) Active immunization with vasoactive intestinal peptide in turkey hens The effect of active immunization against vasoactive intestinal peptide and inhibin on reproductive performance of young White Leghorn roosters The effect of active immunization against vasoactive intestinal peptide (VIP) and inhibin on reproductive performance of aging White Leghorn roosters Impact of commercial housing system and nutrition on egg quality parameters Comparisons of bone properties and keel deformities between strains and housing systems in end-of-lay hens Housing conditions alter properties of the tibia and humerus during the laying phase in Lohmann white Leghorn hens Influence of age and housing systems on properties of tibia and humerus of Lohmann White hens 1: bone properties of laying hens in commercial housing systems Egg production and welfare of laying hens kept in different housing systems (conventional, enriched cage, and free range) Production of recombinant tumor necrosis factor receptor/Fc fusion protein by genetically manipulated chickens Colibacillosis in caged layer hens: characteristics of the disease and the aetiological agent Effect of chicken egg yolk antibodies (IgY) against diarrhea in domesticated animals: a systematic review and meta-analysis Passive immunization with hyperimmune egg-yolk IgY as prophylaxis and therapy for poultry diseases-a review The extracellular matrix of eggshell displays anti-inflammatory activities through NF-kB in LPS-triggered human immune cells Processed eggshell membrane powder regulates cellular functions and increase MMP-activity important in early wound healing processes Germline transmission of genetically modified primordial germ cells Competitive bioreactor hens on the horizon Production of recombinant human erythropoietin/Fc fusion protein by genetically manipulated chickens Performance and profitability of second-cycle laying hens as influenced by body weight and body weight reduction during molt Sperm production and testicular development of broiler breeder males reared on shortened growth cycles Biochemical characteristics and sperm production of turkey semen in relation to strain and age of the males Management Guidelines Turkey Breeders Breeder Management Supplement: Female: Cobb 700 Reproductive management of poultry We are grateful to Ann (Ryn) Laster McDonald for her invaluable input.