Effect of exposure to long photoperiod during the rearing period on the age at first egg and the subsequent reproductive performance in geese

The objective of this study was to investigate the effects of photoperiods longer than 14 h of light:10 h of dark (14L:10D) during the rearing period on the age at first egg laying (AFE) and the subsequent reproductive performance in geese. Sixty-six White Roman geese (18 male and 48 female) were divided into three groups and subjected to different lighting schemes, i.e. natural lighting (NAT; 23 degrees 51'N, 120 degrees 33'E), 14L and 18L. Birds in 14L and 18L groups were exposed to 14L:10D or 18L:6D, respectively, beginning at 19 weeks of age and followed by a photoperiod of 10L:14D from 40 weeks of age. The natural photoperiod, including both dawn and dusk was between 11.5L:12.5D and 14.5L:9.5D. The results showed that the AFE was postponed (P < 0.05). Average weight of the first three eggs laid and the fertility of these eggs were improved (P < 0.05) for the geese in 14L and 18L groups when compared to those raised under natural lighting conditions. Meanwhile, the duration of laying were shifted from spring to autumn, with the peak laying rate in September and November instead of March. It was concluded that geese exposed to the photoperiod longer than 14L:10D for 21 weeks during the rearing period would suppress their AFE. Thereafter, the onset of laying could be induced by being transferred to the photoperiod of 10L:14D. The manipulation of photoperiodic regimes used in this study might have a potential benefit for geese farmers through improved weight and fertility of eggs.     

Egg fertility among vasectomized and non‐vasectomized male resident Canada geese at the Wildlife Conservation Park/Bronx Zoo

In 1991, a vasectomy program was initiated at the Wildlife Conservation Park/Bronx Zoo to minimize the population growth of resident Canada geese (Branta canadensis). Sixty‐nine males were vasectomized over a 6‐year period. From 1994 to 1998, egg fertility was examined in females paired with vasectomized and non‐vasectomized geese. Of the 340 eggs laid by females paired with vasectomized males, 12% were fertile. In comparsion, of the 526 eggs laid by females paired with non‐vasectomized males, 90% were fertile. The vasectomy procedure was easier to perform on males captured during the breeding season than on those captured during molt owing to the enlarged size of the vas deferens. Where resident Canada goose populations are small and resources available, the implementation of a vasectomy program can be effective in reducing population growth. Zoo Biol 19:35–40, 2000. © 2000 Wiley‐Liss, Inc.     

The Origin of the White Roman Goose

In order to avoid interference from nuclear copies of mitochondrial DNA (numts), mtDNA of the white Roman goose (domestic goose) was extracted from liver mitochondria. The mtDNA control region was amplified using a long PCR strategy and then sequenced. Neighbor-joining, maximum parsimony, and maximum-likelihood approaches were implemented using the 1,177 bp mtDNA control region sequences to compute the phylogenetic relationships of the domestic goose with other geese. The resulting identity values for the white Roman geese were 99.1% (1,166/1,177) with western graylag geese and 98.8% (1,163/1,177) with eastern graylag geese. In molecular phylogenetic trees, the white Roman goose was grouped in the graylag lineage, indicating that the white Roman goose came from the graylag goose (Anser anser). Thus, the scientific name of the white Roman goose should be Anser anser ‘White Roman.’     

The effect of food on laying date and clutch-size in Tengmalm's Owl Aegolius funereus

The breeding of Tengmalm's Owl Aegolius funereus was studied at Umeå, Sweden, during the 1984–85. Mean clutch-size was one egg larger in 1984 than in 1985 despite the later laying in 1984. The difference in clutch-size was related to a better food supply in 1984. Daily weight increase of females during the prelaying period showed a high negative correlation with laying date in 1985, and a high positive correlation with clutch-size independently of laying date in 1984–85. This suggested that food eaten before and during laying had a great and direct influence on both laying date and clutch-size. Many females increased in weight during laying and most others decreased only moderately (relative to egg weight), suggesting that body reserves were not a main source for egg production.
Late breeding females were provided with extra food during the prelaying and laying periods in 1985. Fed females weighed more, bred eight days earlier and laid one more egg than controls. At the same laying dates in mid season, and after heavy snow-fall, clutch-size and female weight were larger in the fed birds than in controls, but this was not so near the end of the laying season. Although the earliest of the fed late breeders weighed more, and probably were less restricted by food availability just before or during laying, they did not lay more eggs than did early breeders. This result suggested some limitation on clutch-size that could not be overcome by the supplementary feeding. Weights of females during laying did not show any consistent relationship with clutch-size during successive laying date intervals, suggesting that clutch-size was not directly related to body condition.     

Association of single nucleotide polymorphism in melatonin receptor 1A gene with egg production traits in Yangzhou geese

In the present study the melatonin receptor 1A gene (MTNR1A) was proposed to be a candidate gene for egg production in Yangzhou geese. A total of 210 goose blood samples were collected to investigate the association of the MTNR1A gene with the number of eggs produced. Using a direct sequencing method, a single nucleotide polymorphism (SNP; g.177G>C) was detected in the 5? regulatory region of the MTNR1A gene (Genbank ss1985399687). Two alleles (G and C) and three genotypes were identified. Association analysis results showed that the g.177G>C SNP significantly affected the level of egg production within a 34‐week egg‐laying period (P < 0.05). Furthermore, the geese with the GG genotype produced significantly more eggs compared to the geese with the CC genotype. Quantitative real‐time PCR analysis showed that the MTNR1A gene was highly expressed in small intestine, granulosa cell and ovary compared to other examined tissues. In addition, the mRNA expression level of MTNR1A in ovary indicated that significantly higher expression levels were recorded for geese with the GG genotype compared to those with the CC genotype. Moreover, a luciferase reporter assay showed that the CC genotype had significantly lower promoter activity than did GG. These results suggest that the identified SNP in the MTNR1A gene may influence the number of eggs produced and mRNA expression levels in Yangzhou geese and could be considered as a useful molecular marker in goose selection and improvement, especially for egg production.     

Keeping up with early springs: rapid range expansion in an avian herbivore incurs a mismatch between reproductive timing and food supply

Within three decades, the barnacle goose population wintering on the European mainland has dramatically increased in numbers and extended its breeding range. The expansion has occurred both within the Arctic as well as by the colonization of temperate areas. Studies of performance of individuals in expanding populations provide information on how well species can adapt to novel environments and global warming. We, therefore, studied the availability of high quality food as well as timing of reproduction, wing moult, fledgling production and postfledging survival of individually marked geese in three recently established populations: one Arctic (Barents Sea) and two temperate (Baltic, North Sea). In the Barents Sea population, timing of hatching was synchronized with the peak in food availability and there was strong stabilizing selection. Although birds in the Baltic and North Sea populations bred 6–7 weeks earlier than Arctic birds, timing of hatching was late in relation to the peak in food availability, and there was moderate to strong directional selection for early breeding. In the Baltic, absolute timing of egg laying advanced considerably over the 20‐year study period, but advanced little relative to spring phenology, and directional selection on lay date increased over time. Wing moult of adults started only 2–4 weeks earlier in the temperate populations than in the Arctic. Synchronization between fledging of young and end of wing moult decreased in the temperate populations. Arctic‐breeding geese may gradually accumulate body stores from the food they encounter during spring migration, which allows them to breed relatively early and their young to use the peak of the Arctic food resources. By contrast, temperate‐breeding birds are not able to acquire adequate body stores from local resources early enough, that is before the quality of food for their young starts to decrease. When global temperatures continue to rise, Arctic‐breeding barnacle geese might encounter similar problems.     

Analysis of the laying rhythm and reproductive traits of geese

The aim of the performed investigations was to analyse the laying rhythm and reproductive traits of Ko?uda white geese from the W11 reproduction strain and to determine the heritability of these traits as well as correlations between the laying rhythm traits and reproductive traits. The total number of geese participating in the experiment included 383 one-year old layers from the control flock (the first year of reproductive utilisation). The following traits characterizing the laying rhythm were assessed individually for each layer: the number of 2 and 3-egg clutches or more, length (in days) of 2- or more egg clutches as well as the length of intervals between the laid eggs during the entire laying period. The following reproductive traits were also assessed individually for each bird: age at sexual maturity, initial number of eggs (eggs laid during the period from January, 1st to April, 30th), number of eggs during the whole laying period, laying intensity (the total number of eggs x 100/length of the laying period in days) as well as the length of the reproductive period. It was found that Ko?uda white geese laid most of their eggs (on average 70.2%) singly and not in clutches. With regard to egg clutches, it was found that 2-egg clutches constituted 85.3% of eggs laid in clutches. Moderate or high variability of traits associated with the laying rhythm and reproduction were demonstrated. The observed moderate heritability of the laying rhythm traits indicate that they may be utilised in the selection programs for geese. On the other hand, the reported high, positive genetic correlation coefficients between the number of egg clutches and the initial and total egg number as well as laying intensity confirm the existence of interactions between these traits. This fact may be helpful in breeding programs for determining the optimal selection systems for geese.     

Maturation increases early reproductive investment in Adélie Penguins Pygoscelis adeliae

Correlations between female investment in egg production and age, breeding experience and laying date have been reported in several seabird species. In general, clutch and egg sizes increase with female age and breeding experience but decrease with laying date. Positive correlations of clutch and egg size with age and breeding experience can be caused by an increase in reproductive investment with maturation or they may be an artefact of lower survival rates for individuals with poor-quality phenotypes. Negative correlations of clutch and egg size with laying date might signal an adaptive reduction in egg production or be due in part to variation among individuals. We examined the interactions of female age, breeding experience, laying date and clutch and egg size in Adélie Penguins Pygoscelis adeliae . Breeding experience strongly affected clutch size with 87.3% of all one-egg clutches laid by first-time breeders. In addition, increasing age had a positive influence on egg size and was associated with earlier laying dates. However, there was little evidence to suggest that either clutch or egg sizes are influenced by laying date. Laying dates and clutch and egg sizes did not affect a female's probability of returning to breed in the following year, indicating that increased investment is a product of maturation and not of the loss of poor-quality breeders from the population. Our results suggest that as female Adélie Penguins gain foraging and breeding experience they are able to initiate breeding earlier, to lay complete clutches of two eggs and to lay larger eggs.     

Evaluating the reproductive cost of migration for females in a partially migrating pond-breeding amphibian

Populations of animals with resident and migratory individuals provide an ideal system for addressing questions concerning the evolution of migration. Partially migratory populations may persist because residents and migrants have equal fitness or because migration is based on conditional asymmetries. Studies measuring the costs and benefits of migration provide empirical data to test hypotheses concerning the maintenance of partial migration within a population. In this study, we measured the reproductive differences between resident and migrant females in a pond-breeding amphibian, the red-spotted newt Notophthalmus viridescens . We used large field enclosures to repeatedly sample egg laying over the prolonged breeding season of this species. Resident females did not lay a greater number of eggs or begin laying eggs earlier, despite beginning the breeding season earlier and having a higher mass than migrant newts. The only difference in reproduction we detected was that the eggs of resident females hatched into larger larvae compared with the larvae of migrant females. We discuss this result in the context of other potential trade-offs between residency and migration. This study illustrates the phenology of egg laying of N. viridescens and our results contribute to understanding the population dynamics of partially migratory species.     

FACTORS AFFECTING THE EGG SIZE OF RED-BILLED GULLS LARUS NOVAEHOLLANDIAE SCOPULINUS

The factors influencing the egg size of the Red-billed Gull Larus novaehollandiae scopulinus were studied at Kaikoura, New Zealand, between 1964 and 1972. In two- and three-egg clutches there was a trend for the eggs to become smaller in the sequence of laying. Length, breadth and volume of eggs of one-, two- and three-egg clutches declined significantly as the season progressed. The size of eggs from single-egg clutches tended to be smaller than eggs from two-egg clutches laid at the same time. There were correlations between the proportions of one-egg and of three-egg clutches being laid at a given period and the mean egg volume of two-egg clutches. When the mean egg volume of two-egg clutches increased there was a corresponding increase in the proportion of two- and three-egg clutches laid. When the mean egg volume of two-egg clutches decreased there was an increase in the proportion of single-egg clutches laid. The egg size of the Red-billed Gull showed no direct correlation with the abundance or availability of food; the largest eggs were produced early in the season when food was in short supply. In spite of an increase in the food supply in the middle of the breeding season, birds laying at this time produced smaller eggs than birds which laid earlier in the season. However, early breeders which relayed at the peak in food abundance on average produced a larger replacement clutch than originals laid early in the season. It is suggested that the birds nesting early in the season are able to produce the largest eggs because they are the most efficient foragers for food, and those which nest later in the season produce smaller eggs, even at peak food abundance, because of their inefficiency or inexperience. Early breeders laying replacement clutches tended to lay larger eggs and larger clutches than birds which are producing their first clutches at the same time. Two-year-old females laid eggs which were significantly shorter than older aged birds while the breadth and volume of the egg increased with the age of the female up to the fifth year. There was a trend for females to lay larger eggs when mated with older rather than younger males. No statistical differences in egg size were detected between females changing or retaining the partner of the previous season. Female body weight and egg volume were positively correlated in females weighing less than 275 g but not for heavier females. It is suggested that the seasonal decline in egg size and clutch size results from a decrease in the availability of food and the ability of the individual to exploit the resource.     

Nicarbazin OvoControl G Bait Reduces Hatchability of Eggs Laid by Resident Canada Geese in Oregon

Abstract: Expanding populations of resident Canada geese (Branta canadensis) are resulting in increased conflicts with humans. Nonlethal and humane means are needed for managing Canada goose flocks at a variety of sites, including golf courses, industrial parks, government sites, and city parks. Decreased egg production and hatching are side effects of nicarbazin, a veterinary drug used to treat coccidiosis in chickens. Capitalizing on these effects, we developed nicarbazin as a reproductive inhibitor for Canada geese and conducted a field efficacy study. We recruited study sites in 2002 and 2003. Following laboratory testing, we conducted a field efficacy trial of nicarbazin for reducing the hatchability of Canada goose eggs in spring 2004 in Oregon, USA. The study began in February 2004 at 10 sites in Oregon, with 2 control and 3 treated sites on each side of the Cascades. We fed bait daily to resident Canada geese for approximately 6 weeks. We located and monitored nests until hatching or ≥5 days beyond the expected hatching date to determine hatchability. We completed data collection in May 2004. Geese consumed 8,000 kg of bait, with 5,100 kg of OvoControl G® (Innolytics, LLC, Rancho Santa Fe, CA) 2,500-ppm nicarbazin bait consumed among 6 treated sites and 2,900 kg of untreated bait consumed among 4 control sites. We monitored 63 nests at treated sites and 46 nests at control sites to determine hatching success of eggs. There was a 62% reduction in the percentage of nests with 100% hatchability at treated sites as compared to controls. There was a 93% increase in the percentage of nests at treated sites with 0% hatchability as compared to nests with no eggs hatching at control sites. Hatchability from treated sites versus control sites was reduced 36% (F = 5.72, P = 0.0622). We submitted results from this study to support Environmental Protection Agency registration of nicarbazin as a reproductive inhibitor for use in Canada geese. We have shown that treatment of resident Canada geese with OvoControl G 2,500-ppm nicarbazin bait by licensed, trained applicators immediately prior to and during the breeding season can reduce hatchability of eggs laid by treated geese, thereby reducing recruitment of goslings into problem resident Canada goose populations.     

The reliance on distant resources for egg formation in high Arctic breeding barnacle geese Branta leucopsis

Breeding in the high Arctic is time constrained and animals should therefore start with their annual reproduction as early as possible. To allow for such early reproduction in migratory birds, females arrive at the breeding grounds either with body stores or they try to rapidly develop their eggs after arrival using local resources. Svalbard breeding barnacle geese Branta leucopsis have to fly non‐stop for about 1100 km from their last continental staging site to the archipelago making the transport of body stores costly. However, environmental conditions at the breeding grounds are highly unpredictable favouring residual body stores allowing for egg production after arrival on the breeding grounds. We estimated the reliance on southern continental resources, i.e. body stores for egg formation, in barnacle geese using stable isotope ratios in the geese's forage along the flyway and in their eggs. Females adopted mixed breeding strategies by using southern resources as well as local resources to varying extents for egg formation. Southern capital in lipid‐free yolk averaged 41% (range: 23–65%), early laid eggs containing more southern capital than eggs laid late in the season. Yolk lipids and albumen did not vary over time and averaged a southern capital proportion of 54% (range: 32–73%) and 47% (range: 25–88%), respectively. Our findings indicate that female geese vary the use of southern resources when synthesising their eggs and this allocation also varies among egg tissues. Their mixed and flexible use of distant and local resources potentially allows for adaptive adjustments to environmental conditions encountered at the archipelago just before breeding.     

The effects of age and weather on egg laying inDanaus plexippus L. (Lepidoptera: Danaidae)

The effects of age and weather conditions on egg laying in D. plexippus were determined for caged females. Age (measured in physiological time), temperature and solar radiation influence egg laying in this species of butterfly. An algorithm taking these factors into account in presented and accounts for 88% of the daily variation in egg laying. Caged D. plexippus begin to lay eggs six—seven days after emergence, peak egg production (about 60 eggs/♀) occurs about 15 days later. Females continue to lay eggs throughout their adult life, which in a flight cage was about 40 days. This egg laying pattern is compared with other published fecundity schedules. The effect and importance of a female being prevented from laying her eggs, on her life-time egg production, is also discussed.     

Consequences of a changing environment on the breeding phenology and reproductive success components in a long-distance migratory bird

Migratory birds have a narrow time window to breed, especially in the Arctic, where early nesting typically yields the highest reproductive success. We assessed temporal changes (1991–2015) in reproductive success components in relation to timing of breeding in greater snow geese (Chen caerulescens atlantica). This species breeds in the Canadian Arctic, a region that has experienced a strong warming trend. We tested the effect of laying or hatching date, year and their interaction on six reproductive components: Total clutch laid, nesting success, egg survival, hatching success, prefledging, and postfledging survival. Over 25 years, mean laying date changed little, even though it advanced 1.8 days in early breeders and was delayed 3 days in late breeders. Likewise, the number of eggs in nests initiated early in the season decreased by 0.6 egg, whereas in late nests it increased by 0.3 egg. Success of nests initiated early and late in the season was lower than nests initiated near the population mean, and consistently increased over time. The proportion of eggs surviving to partial predation and postfledging survival decreased with laying date but the pattern did not change over time. In contrast, prefledging survival was not affected by laying date initially but declined in nests initiated late in the season toward the end of the study. Overall, nests initiated close to the population mean showed little temporal change for most components of reproductive success and seem to be less affected by environmental change than nests initiated early and late in the season.     

Resource use for reproduction depends on spring arrival time and wintering area in an arctic breeding shorebird

Resources for egg production may come from body reserves stored before breeding (“capital breeders”) or from food acquired at the breeding site (“income breeders”). Arctic migrants were long thought to be capital breeders, because they often arrive at a time when local food availability is still limited. However, later evidence suggested that arctic breeding shorebirds are primarily income breeders, or that they use a mixed strategy depending on laying date. We explored the relationship between laying date and resource use for reproduction in the pectoral sandpiper Calidris melanotos breeding in the Alaskan arctic by contrasting carbon isotope (δ¹³C) values of the local diet and of maternal plasma, cellular blood, feather and claw with those of the eggs produced. Our results revealed that early breeding females utilize resources for egg production that were acquired recently at staging areas, whereas later breeding females mostly relied on nutrients derived from local food sources. These findings suggest that the resource allocation strategy used for reproduction differs among females, and varies depending on the timing of arrival and the start of reproduction. The arrival date at the breeding ground and laying date may critically depend on non‐breeding season events such as winter habitat choice, staging areas or migration routes. By comparing maternal feather δ¹³C, claw δ¹³C and feather δD, we examined whether non‐breeding season events influenced the use of resources for egg production through variation in capture date or clutch initiation date. Female pectoral sandpipers originating from moulting areas characterized by higher (more positive) δD signatures were caught earlier and started laying earlier, and they used stored resources for reproduction. Using regional maps of δD values for precipitation in the wintering sites in South America, we compared the spatial variation in the observed feather δD signatures. This analysis indicated that female pectoral sandpipers with higher δD signatures, presumably coming from more north‐easterly wintering sites in southern America, started laying earlier and used mostly stored resources for egg production, compared to females that wintered (or at least moulted) further south. Our results thus show that winter moulting habitat is linked to breeding resource allocation strategy in this high‐arctic breeding shorebird.     

Reproductive behavior and spawning success of female Amblyglyphidodon leucogaster (Pisces: Pomacentridae) from the Red Sea

The reproductive behavior of female whitebelly damselfish, Amblyglyphidodon leucogaster, was investigated in the Gulf of Aqaba, Red Sea over two breeding seasons. Females were promiscuous, mating with 7–10 different males throughout the season. Females lay eggs in distinct batches, defined as the total number of eggs laid in a day. Generally females deposit a batch of eggs with one male (87.2%) and are capable of laying a new batch every other day. Egg batch size averaged 4009 eggs and females laid from 2 to 22 egg batches per season. The variation in spawning success was not correlated to body size. Females preferred to deposit eggs in nests that already contained early stage eggs (0–2 days old). Within a nest, females chose to lay eggs contiguous to the youngest egg batch, regardless if the nest contained either a single batch or multiple batches of different ages. Female within-nest spawning patterns appear to be a consequence of between nest preferences for nests with young eggs. It is proposed that the strong within-nest preference is a consequence of mate selection where females may use new egg batches as a visual cue as part of a copying style. Such a style may reduce the risk of predation and increase feeding opportunities, because less time is expended in mate selection, which would provide additional resources for egg production and ultimately increase female spawning success over the breeding season. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature and egg-laying experience influence breeding performance of captive female houbara bustards

The influence of climate, age and egg-laying experience on reproductive performance (propensity, fecundity, timing) of a flock of captive houbara bustards was determined. The flock, established in Saudi Arabia for reintroduction purposes, was housed in outdoor pens, and fed food and water ad libitum. Birds were artificially inseminated when they came into breeding condition and eggs were removed soon after laying. Winter temperatures, rather than rainfall, synchronized reproduction in the captive flock. Cooler winter temperatures led to higher proportions of females laying, an earlier start to laying, and greater numbers of eggs laid per season. The first significant rainfall of the season stimulated some females to lay their last egg. Age per se had little effect on breeding performance independent of egg-laying experience. Females with no previous egg-laying experience laid fewer eggs than similarly aged females with previous experience. This difference, in combination with a pattern of increasing recruitment into the breeding population between 1 and 5 years of age, led to improved breeding performance in the population with age. The inferior performance of first-time egg-layers, despite ad libitum food, indicates restraint in the onset of breeding, which may be an adaptation for optimizing life-time fitness.     

Reproductive behavior in captive California condors (Gymnogyps californianus)

From the fall of 1987 to the spring of 1994, data on reproductive behavior were collected on seven different pairs of California condors (Gymnogyps californianus) housed at the San Diego Wild Animal Park. Behavioral data were collected from videotaped activities in their flight pens. Behaviors for this report include male and female displays and incomplete and complete copulations. Data on the time it took for females to recycle and lay another egg after egg removal were acquired from the California Condor Studbook. Male display rates were significantly higher than female rates throughout the breeding season. Males began displaying 52–132 days before the start of copulations. Copulations slowly increased from Day -51 and peaked ∼ Day -8, prior to egg laying. Female display rates were significantly more frequent at the end of the season after the last egg was laid. An average of 26.8 (±3.1 SEM) copulations occurred prior to egg laying. Copulations occurred throughout the day, with the higher mean percentages occurring between 0700 and 0900 hours. After egg removal, the interval between laying of the first and second eggs and between the second and third eggs had a mean of 34.1 (±10.1 SD) days. © 1996 Wiley-Liss, Inc.     

Dark-bellied brent geese Branta b. bernicla breeding near snowy owl Nyctea scandiaca nests lay more and larger eggs

Several studies have demonstrated that snowy owls Nyctea scandiaca defend an area around their nests against predators, hereby inadvertently creating safe havens for breeding dark-bellied brent geese Branta b. bernicla . However, studies investigating brent goose breeding ecology within the predator-exclusion zones of the snowy owls are absent. In 1999 and 2005, years of high lemming abundance Lemmus sibiricus and Dicrostonyx torquatus , brent geese were primarily breeding in association with snowy owls in the Medusa river catchment on western Taimyr, Russia. Goose nest failure, either as a result of nest abandonment by the adult birds or of nest depredation, increased with increasing distance from the owl nests. Within the brent goose colonies, clutch size as well as egg size increased with decreasing distance from the snowy owl nest, indicating an increasing adult quality closer to owl nests. However, as a result of the abandonment of eggs and goslings, the increasing clutch size did not result in a higher nest success during this study. Apparently brent geese compete for breeding sites close to owl nests, but details of this process remain unknown.     

Endocrine regulations of reproductive seasonality, follicular development and incubation in Magang geese

This study investigated the regulatory mechanisms of seasonal breeding, developments of ovarian follicles and incubation in Magang geese, a short day breeding bird. Throughout the year, plasma PRL concentrations increased in non-breeding season in spring and summer (from April to early August), and remained low in the rest of the year, while LH concentrations peaked in August and September and remained low in non-breeding season (March to June). Lengthening photoperiod increased PRL and decreased LH secretions, which inhibited follicular development, terminated lay and induced moulting, while shortening photoperiod decreased PRL and increased LH secretion and reinitiated lay. Long photoperiod stimulated PRL secretion occurred with increased gene expressions of PRL in the pituitary gland and VIP in the hypothalamus, but inhibition of LH secretion was without decreases in gene expressions of LH beta subunit and GnRH. Under breeding conditions, terminating incubation decreased PRL but increased LH concentrations and resumed lay in 24 days following recruitment of about 10 large white follicles into hierarchical development. Plasma concentrations of progesterone and inhibin peaked at peak lay, whereas LH concentrations exhibited a bi-phasic pattern with troughs at peak lay and incubation when PRL concentrations were high. Ninety percent geese exhibited incubation behaviour after laying one clutch of approximately eight eggs in approximately 30 days. In conclusion the seasonal reproductive activities in Magang geese is directly inhibited by long photoperiod and directly stimulated by short photoperiod via PRL and LH secretions, whose interplays also cause occurrences of four to five lay and incubation cycles in the breeding season.