1. Ovaries from a light‐bodied egg laying strain and a broiler breeder strain were compared at 26 and 82 weeks of age. 2. The rate of lay in both strains was lower in the older hens. The 82‐week‐old hens were subdivided into good and poor layers: the poor layers produced eggs at about half the rate of the good layers. 3. The yellow‐yolky ovarian follicles in both strains were smaller, more numerous and more closely ranked in hierarchies in 26‐week‐old hens than in 82‐week‐old hens. 4. No marked differences were seen between the strains at 26 or 82 weeks of age in the sizes, numbers or hierarchical arrangements of yellow‐yolky ovarian follicles. 5. The ovaries from 82‐week‐old good and poor layers from both strains contained similar numbers of yellow‐yolky follicles. 6. After feeding a fat‐soluble dye, the number of days over which eggs containing dye were laid did not differ between 26‐, 52‐ and 113‐week‐old hens from an egg laying strain. However, fewer eggs with dyed yolks were laid by the older hens. 7. These observations suggest that the decrease in egg production with age is due initially to a reduction in the rate of recruitment of yellow‐yolky follicles. Towards the end of the laying year it may also be due to an increased incidence of follicular atresia, internal ovulation and the production of membraneous or soft shelled eggs.

1. Understanding of the physiology, molecular genetics and developmental biology of avian reproduction is essential for advances in the efficient breeding of birds for commercial gain,2. Reproduction is controlled at the central nervous level by gonadotrophin releasing hormone-I (GnRH-I) and prolactin.3. The activity of GnRH-l neurones can be manipulated photoperiodically, through understanding of the physiology of photorefractoriness, to prevent premature onset, or to enhance persistency of reproductive function.4. Active immunisation against prolactin releasing hormone, vasoactive intestinal peptide, delays the development of photorefractoriness and enhances persistency of reproductive function.5. The creation of molecular maps of the chicken genome makes it possible to identify quantitative trait loci for reproductive traits, which will be used to identify DNA sequences for marker assisted selection. Polymorphisms in alleles of physiological candidate genes for reproductive efficiency might also be useful for marker assisted selection.6. New understanding of the developmental biology of the chicken opens up the prospect of developing methods to control sex ratios, and to make transgenic birds. Transgenic technology will be used to introduce genes for disease resistance, and to make proteins for biomedical applications.7. Nuclear transfer technology might be applied to save endangered species from extinction.

The aim of the study was to establish, in contemporary broiler breeders, whether delayed photostimulation at 313 d results in a reproductive response similar to that after photostimulation at 134 d (standard practice). The standard lighting program was compared with a novel program in which daily hours of light were reduced to 3 h during rearing and kept at 3 h until photostimulation at 264 d (8 h) or at 313 d (16 h). This experiment was done with hens fed ad libitum or feed-restricted hens. In photostimulated and nonphotostimulated hens, feed restriction delayed the onset of egg production and enhanced the subsequent rate of laying. Standard photostimulation advanced the onset of lay and increased the subsequent rate of lay in hens fed ad libitum and feed-restricted hens. Delayed photostimulation of hens did not impair the photoinduced increase in the concentration of plasma luteinizing hormone (LH) or egg production. Delayed photostimulation in cockerels failed to stimulate LH secretion. Unexpectedly, for feed-restricted hens, transfer from 3 to 8 h light/d at 264 d resulted in an increased in plasma LH and increased egg production. A similar increase in plasma LH was observed for cockerels subjected to the same lighting treatment. We concluded that, in broiler breeder hens, the reproductive response to photostimulation is not impaired if photostimulation is delayed for up to 313 d. Cockerels may not respond well to delayed photostimulation.

1. The administration of the anti-oestrogen, tamoxifen (TAM) to juvenile chicks results in precocious puberty. In the present study the effects of TAM administration (1 mg/kg body weight on alternate days from 12 d of age) on testicular function, hypothalamic chicken gonadotropin-releasing hormone (cGn-RH-I), plasma luteinising hormone (LH), growth hormone (GH), prolactin (PRL) and testosterone were studied in juvenile White Leghorn cockerels.2. The increase in hypothalamic GnRH-I content which occurs during sexual development was advanced in TAM-treated birds, in association with precocious testicular development, an early rise of plasma testosterone content and enhanced comb growth.3. Plasma LH concentrations behaved similarly and were higher in the TAM-treated than in control birds, during most of the experimental period. Plasma PRL concentration, which is high at hatching, decreased more quickly in TAM-treated than in control birds; plasma GH values were not consistently affected by TAM treatment.4. Both the growth and the involution of the bursa of Fabricius in the TAM-treated cockerels preceded that in the control chicks.5. It is concluded that TAM treatment induces precocious puberty in the cockerel by blocking the negative feedback action of aromatised testicular androgens on the hypothalamus.

The “Early-methionine-labelled” (Em) polypeptide is the most abundant cytosolic polypeptide found in mature wheat embryos. Using a near full-length cDNA clone as a hybridisation probe to detect genomic sequences by Southern blotting of electrophoretic separations of genomic DNA derived from Triticum aestivum L. var. Chinese Spring and a series of its aneuploid derivatives, we demonstrate that the Em polypeptide is the product of a small multigene family in which the copies are located on each of the long arms of the homoeologous group 1 chromosomes. Screening of a variety of genotypes additionally reveals a number of restriction fragment length polymorphisms associated with these loci. Screening of a library of genomic DNA cloned in the vector λEMBL 4 has resulted in the isolation of a genomic fragment containing two closely linked Em genes. These are separated by ca. 2.5 kb. Analysis of restriction enzyme digests of this clones fragment has identified it as originating from chromosome 1A.

A sensitive bioassay for inhibin based on the suppression of FSH release from cultured sheep anterior pituitary cells was used to determine whether inhibin is present in the preovulatory follicle in the domestic hen. Granulosa and thecal/stromal layers were separated from the five largest (F1-F5) yellow yolky follicles in the ovary and incubated in culture medium for 18 h. Inhibin was found predominantly in the media in which granulosa layers had been incubated. There was a progressive increase in the amount of inhibin produced per mg granulosa layer protein during the 5-6 days before ovulation. The ovary was observed to contain a growth factor which stimulated the proliferation of ovine pituitary cells. Thecal/stromal layer-conditioned medium (ThCM) but not granulosa layer-conditioned medium had a dose- and time-dependent mitogenic effect on cultured sheep pituitary cells. The maximal mitogenic effect achieved for ThCM was four to fivefold greater than control media and was significantly higher than the maximal mitogenic effects of epidermal growth factor (250 ng/ml; 1.5 x control) and transforming growth factor-beta (500 ng/ml; 1.2 x control). It is concluded that inhibin is produced by the granulosa layers in the large yellow yolky preovulatory ovarian follicles of the domestic hen. The thecal/stromal layers in these follicles produce a potent mitogenic factor, not produced by the granulosa layers, which stimulates the division of ovine anterior pituitary cells in vitro.

A β-amylase cDNA clone isolated from barley has been used to locate β-amylase encoding sequences on wheat, rye, and Aegilops umbellulata chromosomes by hybridisation to restriction endonuclease digested DNA obtained from wheat aneuploid and wheat-alien addition lines. Structural genes were identified on homoeologous group 4 and 5 chromosomes, confirming the results of isozyme studies. In addition, a further set of structural genes was found on homoeologous group 2 chromosomes. It is proposed that there are two homoeoallelic series, β-Amy-1 on group 4 or 5 chromosomes, and β-Amy-2 on group 2 chromosomes. Evidence is presented that each locus contains one or two β-amylase structural genes, and it is suggested that the large number of isozymes seen upon IEF are due to post-translational modifications.

Forty-one hexaploid wheat genotypes have been examined for RFLPs detected by a β-amylase probe using three restriction enzymes, and for mature grain β-amylase isozyme polymorphism following IEF. The two homoeoallelic series assayed for RFLPs differed: little variation was found at group 2 chromosome homoeoloci, while the group 4/5 chromosome homoeoloci displayed considerable variation. Varieties that displayed a RFLP with one RE almost always did likewise with the other two REs, suggesting that most of the polymorphisms observed were due to large DNA rearrangements. Comparison of the variation in grain β-amylase isozymes with the RFLP results indicated strong associations between particular RFLP and isozyme alleles.

Cell nuclei containing progesterone receptor were identified immunohistochemically in the hypothalamus and forebrain of the domestic hen using an antiserum to the steroid binding “B” subunit (110 kDa) of chicken oviduct progesterone receptor and the avidin-biotin complex procedure. Cell nuclei containing progesterone receptor were widely distributed in the anterior, medial and basal hypothalamus with the highest density occurring in the lamina terminalis and the preoptic area. Abundant, though less intensely reacting progesterone receptor was present in cell nuclei in the tuberal infundibular area and in the internal zone of the median eminence. A large group of cell nuclei containing progesterone receptor occurred in the dorsal anterior hypothalamus between the anterior commissure and the lateral ventricle. This group of nuclei extended anteriorly into the telencephalon. A small number of cell nuclei containing progesterone receptor was also found in the ventral telencephalon in the region of the nucleus accumbens.

Plasma luteinizing hormone (LH) levels in migratory male chaffinches exposed to natural lighting in northern Italy were seasonally high during May and June. In birds held on a fixed short day length of 8 hr light: 16 hr darkness from February to July, plasma LH levels increased slowly reaching a low plateau in July. The seasonal fall in plasma LH levels in June was not reversed by transferring the birds to continuous light in October and February: the larger increase was observed in February. It was concluded that the initiation of breeding may involve an underlying Autonomous increase in reproductive function, and that breeding is terminated by the development of absolute as opposed to relative long day refractoriness.

An individual male red kangaroo (Macropus rufus) was found to display unaligned kinetochores on one synaptonemal complex. This was the result of “synaptic adjustment” caused by heterozygosity for the size of a C-band near the centromere of this bivalent, the first report of synaptic adjustment at a C-band heterozygosity. The observation suggests a possible method of obtaining further insights into the process of synaptic adjustment.

The ability of synthetic vertebrate luteinising hormone releasing hormones (LHRHs) and their long-acting analogues to maintain elevated plasma luteinising hormone (LH) concentrations and to stimulate ovarian growth was investigated in incubating bantam hens. Chicken LHRH-II (pGlu1-His2-Trp3-Ser4-His5-Gly6-Trp7-Tyr8-Pro9-G ly10-NH2) was more effective than chicken LHRH-I (pGlu1-His2-Trp3-Ser4-Tyr5-Gly6-Leu7-Gln8-Pro9-Gly10-N H2) or porcine LHRH (pGlu1-His2-Trp3-Ser4-Tyr5-Gly6-Leu7-Arg8-Pro9-Gly10-N H2) in stimulating the release of LH. Long-acting analogues of chicken LHRHs (chLHRHs) were created by substituting D-amino acids in position 6. An intravenous injection (10 micrograms/bird) of D-Arg6-chLHRH-II or of a long-acting mammalian analogue of LHRH (buserelin) resulted in a sustained release of LH for up to 8 h. Less sustained releases of LH were observed after the same doses of D-Ala6-chLHRH-I or of D-Trp6-chLHRH-I. Repeated subcutaneous injections of D-Arg6-chLHRH-II or buserelin at 7 to 9 h intervals for 9 d resulted in loss of pituitary gland responsiveness to these analogues. For this reason, the treatment failed to maintain elevated plasma LH concentrations and did not stimulate the growth of the ovary or oviduct.

Seasonal changes in the concentrations of plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin were measured in serial samples taken from seven captive wild mallard drakes exposed to natural lighting and temperature in Kiel, West Germany (54 degrees N), for 20 months. The seasonal pattern of plasma LH levels was characterized by high titers during the reproductive phase in the spring, a steep decrease toward the end of this phase (May/June), low levels during the summer, and a second annual peak in the fall. Plasma FSH levels increased during February and March, the period of rapid testicular growth, and reached the highest values at the end of March/beginning of April. Later in the spring FSH levels decreased and remained low for the rest of the year. The concentrations of plasma prolactin increased progressively during April and May, reaching their highest values at the end of the breeding season, coinciding with the steep fall in the levels of plasma gonadotropins. Prolactin concentrations fell during July and August and were at their lowest level in the autumn. It is concluded that the development of photorefractoriness is associated with an increase in the concentrations of plasma prolactin.

The luteinizing hormone-releasing activities of synthetic chicken luteinizing hormone-releasing hormone (chLH-RH), synthetic porcine LH-RH (pLH-RH), and an analogue of LH-RH (buserelin, d-Ser-(But)6-des-Gly10-LH-RH ethylamide) were compared in the domestic fowl. In adult cockerels, intravenous injections of 0.5 or 1 μg chLH-RH/kg released the same amount of LH as the same doses of pLH-RH; subcutaneous injections of 0.5 or 1 μg buserelin/kg were about twice as effective as the same doses of pLH-RH. In laying hens, injections of 1, 10, 20, and 50 μg buserelin induced more sustained releases of LH than the corresponding doses of pLH-RH. Daily injections of 1 or 10 μg buserelin/bird or of 10 μg pLH-RH/bird for 12 days synchronized the timing of most ovipositions showing that the injections of releasing hormone could induce preovulatory surges of LH. In contrast with mammals, daily injections of buserelin in laying hens did not reduce pituitary responsiveness to the analogue. It is concluded that the structural difference between mammalian and chicken LH-RH does not affect their LH-releasing activities in the domestic fowl. Although the LH-releasing activity of buserelin in the hen is greater than that of pLH-RH, the difference in activity is not as great as that observed in most mammals. This view is strengthened by the finding that chronic treatment with buserelin, which exerts an antagonistic effect on ovulation in mammals, does not do so in the domestic hen.

Changes in concentrations of plasma luteinising hormone (LH), follicle stimulating hormone (FSH), androgen, growth hormone (GH), prolactin (Prl), thyroxine (T4) and triiodothyronine (T3) were measured during growth and sexual maturation in broiler cockerels reared in continuous light to 7 weeks and 14 h light/d thereafter. Concentrations of LH and FSH began to increase between 13 and 15 weeks, while those of androgens increased between 16 and 17 weeks. FSH concentration increased faster than that of LH. Concentrations of GH and Prl were high at 3 weeks; that of GH decreasing progressively between 3 and 14 weeks of age and thereafter remaining low, while that of Prl was low between 5 and 9 weeks, relatively high between 10 and 13 weeks, and then temporarily decreasing before increasing progressively during sexual maturation. Concentrations of T3 and T4 were higher in juvenile than in adult birds.

Using a double immunohistochemical technique, LH releasing hormone (LHRH) neurones and 110kDa nuclear progesterone receptor were localized in the hypothalamus of the laying hen. Nuclear progesterone receptor was widely distributed throughout the hypothalamus, occurring in the preoptic, septal, anterior and basal areas. The region where progesterone receptor was revealed in nuclei of neurones overlapped that containing LHRH neurones. However, LHRH cell bodies did not contain progesterone nuclear receptor. It is concluded that the positive feedback action of progesterone on LH release is not mediated by a genomic mechanism within the LHRH neurone.