Inheritance of fertility in broiler chickens

Eggshell translucency: its relationship with specific gravity and eggshell color and its influence on broiler egg weight loss, hatchability, and embryonic mortalities

Eggshell quality is among the most important factors affecting hatchability in broiler breeders, and therefore several methods for its assessment are available in the poultry industry. Among them, eggshell translucency has received special attention in recent years due to its connection with ultrastructural disorganization of the shell layers. However, there is very limited data on the impact of translucency on hatching eggs and on the possible links between this trait and specific gravity (SG) or shell color. Thus, our study investigated associations and interactions between eggshell translucency, SG, and color on incubation parameters of eggs from the same breeding flock (Ross 308AP, 51 wk of age). To this end, light and dark eggs within 5 different SG categories (≥1.065, 1.070, 1.075, 1.080, and ≤1.085) were selected from 15,976 eggs, graded into 3 translucency scores, and later incubated to evaluate egg weight loss, hatchability and embryonic mortalities. In general, translucency scores were evenly distributed within SG categories (χ2 [8, N = 1,138] = 13.67, P = 0.090) and color (χ2 [2, N = 1,138] = 4.93, P = 0.084). No interactions between eggshell translucency and SG or between translucency and color were found for the analyzed variables. An interaction was observed between SG and eggshell color for the variable egg weight loss, where the light-shelled eggs, in most SG categories lost more weight throughout incubation than dark eggs. Eggshell translucency affected egg weight loss, hatchability, and embryonic mortality on 11 to 18 d of incubation, with highly translucent eggs showing the worst results. At the same time, eggs with SG lower than 1.070 displayed the greatest weight loss, lowest hatchability, and highest contamination. We found no influence of eggshell color on weight loss or hatchability, but light-shelled eggs exhibited higher late embryonic mortality. Together, these data suggest that despite its effects on certain hatching parameters, shell translucency bears no relationship to SG or color.

Genetic improvement of duration of fertility in chickens and its commercial application for extending insemination intervals

The growth rate of chickens has made remarkable progress in recent decades through continuous breeding efforts. However, this advancement has also led to a decline in fertility among commercially bred chickens. Therefore, it is crucial to understand and improve factors that influence fertility to ensure the continued success of the industry. Here, we conduct a 3-generation selection experiment within 2 purebred female lines, with the aim of increasing the duration of fertility (DF). Duration of fertility refers to the length of time hens remain capable of producing fertilized eggs and is a crucial factor that directly impacts chick output. The results showed that significant genetic progress was achieved in embryo survival rates and the fertility duration day during both the peak and late laying periods. Moreover, after 3 generations of selective breeding, the disparities in embryo survival and chick health rates from setting eggs between 8-d and 5-d insemination intervals in the grandparent stock were significantly reduced. The rates decreased from 1.83% and 2.39 to 0.72% and 0.33%, respectively. Surprisingly, the hatching performances of hens with an 8-d interval were comparable to those hens that had not undergone genetic selection for DF and had a 5-d interval. We further discussed the possibility of extending the insemination interval to 8 d in parent stock for commercial practices. The parental populations exhibited remarkable performance in terms of percentages of embryo survival and healthy chicks from the setting eggs, with rates exceeding 94 and 90%, respectively. Thus, it can be inferred that an extended insemination interval is feasible by genetic selection for DF. These findings will provide valuable insights into the efficacy of genetic selection in enhancing DF and its practical application in commercial breeding programs.

Fast growing broiler production from genetically different pure lines in Turkey. 1. Parental traits: growth, feed intake, reproduction, and hatching traits

The aim of the present study was to reveal the trends in age-related growth, feed intake, reproduction, and hatchability traits in 5 pure line (PL) breeders (3 dam [A1: slow-feathering, A2: fast-feathering, A3: slow-feathering] and 2 sire [B1: fast-feathering, B2: fast-feathering]) and their reciprocal two-way cross parent stock (PS) breeders (6 female [A1♂ × A2♀; A1♂ × A3♀; A2♂ × A1♀; A2♂ × A3♀; A3♂ × A1♀; A3♂ × A2♀] and 2 male [B1♂ × B2♀; B2♂ × B1♀]) and to identify heterotic effects in two-way cross PS combinations showing superiority over PL breeders. In the rearing period, 60 females and 15 males in the each PL group, 120 females in each female PS and 120 males in each male PS breeders, and 40 females and 5 males were used in each PL and PS genotype in the laying period. Body weight (BW), average daily feed intake (ADFI), reproductive traits (age at first egg [AFE], age at sexual maturity [ASM], egg number, weekly and total %Lay, egg weight, egg mass), hatching traits (fertility, hatchability of fertile [HOF] and set [HOS] and embryonic mortality), and heterosis (%) values for some traits were assesed. Both males and females of PLs and PSs had different BW at 4 and 8 weeks of age (P < 0.01), but had similar BW from 12 to 24 weeks of age. The A2, B1, and B2 hens had a higher BW (nearly 4000 g) than the others at 31 weeks of age (P < 0.01), and B2 hens showed a BW of more than 5000 g at 64 weeks (P < 0.001). Weekly ADFI per female in rearing, laying, and overall period was not different between groups. The A1 (179 days), A3 (183 days), two-way cross (from 175.5 to 185.5 days) hens started laying at a similar age and earlier than B1 (184 days), A2 (192 days), and B2 (194 days) hens. From AFE to 64 weeks, %Lay was the highest in the A1 line (69.7%), lowest in the B1 (45.3%) and B2 (48.8%) line, and between 56.9 and 64.8% in PS breeder hens. The PS eggs tended to have higher fertility, HOF, and HOS, and less embryonic mortality compared to PL eggs. Negative and low heterosis for AFE was observed in PS eggs, while positive heterosis for fertility, HOF, and HOS was generally observed in four-way hybrid eggs. The highest heterosis for the 64-week cumulative egg number was observed in A3 × A2 hens. Our study results show that mating of B1 × B2 males with A3 × A2 females seems more favorable in terms of higher egg or chick production. However, more knowledge is also needed for the overall efficiency of each PS, including the final performance of its hybrids.

Applicability of single-step genomic evaluation with a random regression model for reproductive traits in turkeys (Meleagris gallopavo)

Fertility and hatchability are economically important traits due to their effect on poult output coming from the turkey hatchery. Traditionally, fertility is recorded as the number of fertile eggs set in the incubator (FERT), defined at a time point during incubation by the identification of a developing embryo. Hatchability is recorded as either the number of fertile eggs that hatched (hatch of fertile, HOF) or the number hatched from all the eggs set (hatch of set, HOS). These traits are collected throughout the productive life of the bird and are conventionally cumulated, resulting in each bird having a single record per trait. Genetic evaluations of these traits have been estimated using pedigree relationships. However, the longitudinal nature of the traits and the availability of genomic information have renewed interest in using random regression (RR) to capture the differences in repeatedly recorded traits, as well as in the incorporation of genomic relationships. Therefore, the objectives of this study were: 1) to compare the applicability of a RR model with a cumulative model (CUM) using both pedigree and genomic information for genetic evaluation of FERT, HOF, and HOS and 2) to estimate and compare predictability from the models. For this study, a total of 63,935 biweekly FERT, HOF, and HOS records from 7,211 hens mated to 1,524 toms were available for a maternal turkey line. In total, 4,832 animals had genotypic records, and pedigree information on 11,191 animals was available. Estimated heritability from the CUM model using pedigree information was 0.11 ± 0.02, 0.24 ± 0.02, and 0.24 ± 0.02 for FERT, HOF, and HOS, respectively. With random regression using pedigree relationships, heritability estimates were in the range of 0.04–0.09, 0.11–0.17, and 0.09–0.18 for FERT, HOF, and HOS, respectively. The incorporation of genomic information increased the heritability by an average of 28 and 23% for CUM and RR models, respectively. In addition, the incorporation of genomic information caused predictability to increase by approximately 11 and 7% for HOF and HOS, respectively; however, a decrease in predictability of about 12% was observed for FERT. Our findings suggest that RR models using pedigree and genomic relationships simultaneously will achieve a higher predictability than the traditional CUM model.

Characterization of Oviduct Lining, with Emphasis on the Sperm Storage Tubule Region (Uterovaginal Junction), Correlated with Fertility in Mature and Old Thai Native Hens

The effect of age on fertility was investigated in Thai native chickens. The objective of this study was to determine the effects of age (mature and old) on the morphological characteristics of the reproductive organs and the histological characteristics of the uterovaginal junction (UVJ) tissues, resident sperm in the UVJ, and fertility duration in Thai native hens. We found no differences in the morphological characteristics of the reproductive organs, except for the number of follicles and the sizes of the fifth large yellow follicle in mature hens, which were greater than those in old hens (p < 0.05). The diameter of the sperm storage tubules (SSTs) epithelium was larger in old hens than in mature hens (p < 0.05), whereas the epithelium height was lower in old hens (p < 0.05). The number of sperm in the SSTs was greater in mature hens compared with old hens (p < 0.05). Mature hens showed a higher fertility rate than old hens. Our results suggest that, in old hens, the function of the SSTs is impaired, and sperm cannot be retained. Such a deterioration of the SSTs may be one of the factors involved in the decline in fertility.

Modeling genetic components of hatch of fertile in broiler breeders

Reproductive efficiency such as fertility and hatch of fertile (HoF) are of economic importance and concern to breeding companies becaue of their effects on chick output. Similar to other traits of economic importance in poultry breeding, the rate of response for HoF is largely dependent on the use of an appropriate model for evaluating the trait. Therefore, the objectives of this study were to estimate genetic parameters from cumulative, repeatability, fixed regression, random regression, and multitrait models for HoF from a pure-line broiler breeder. The data available for this study consisted of weekly HoF records from 11,729 hens with a total pedigree record of 38,260. Estimates of heritability from the various models ranged from 0.04 to 0.22 with the highest estimate obtained from the cumulative model and the lowest from the repeatability model. Responses to selection estimated for the different models ranged from 0.03 to 0.08% gain per year of the phenotypic mean. In general, the cumulative and the repeatability models underestimated response to selection. The multitrait and random regression models gave similar results for response to selection at 0.08 percentage change in phenotypic mean. In conclusion, the cumulative model is not optimal for modeling HoF, and likewise, the repeatability model. The random regression and multitrait models should be considered instead as they offered a higher response to selection. However, if a multitrait analysis is to be considered, it is recommended to split up the production period in such a way as to avoid computational constraints due to overparameterization.

Estimation of additive genetic, dominance, and mate sire variances for fertility traits in Thai native (Pradu Hang Dam) chickens

The objective of this study was to compare the appropriate models used to estimate the value of genetic parameters in fertility traits: fertility (FER), hatchability of fertile eggs (HOF), and hatchability of eggs set (HOS) in Thai native (Pradu Hang Dam) chickens. Data were collected for each fertility trait from 3435 test-week records from 715 hens, 158 mate sires, and 972 pedigree animals. Three random regression models were analyzed: model 1 (M1: A + PE) was adjusted by using additive genetic and permanent environmental effects. Model 2 (M2: A + PE + D) was adjusted by using the dominance effect. Finally, model 3 (M3: A + MS + PE + D) was adjusted by using the mate sire effect. The results found the low heritability of FER (M1 to M3), HOF (M1 to M3), and HOS (M1 to M3) ranged from 0.031-0.040, 0.037-0.066, and 0.040-0.059, respectively. Adjustment for the dominance and mate sire effects in M3 reduced the upward bias in heritability and improved the accuracy of variance component estimates compared to M1 and M2. In conclusion, the genetic evaluation for FER, HOF, and HOS can include the dominance and MS effects to increase the accuracy of evaluation of breeding values and plan for mate selection in breeding programs.

Blastodermal development, hatchability and chick quality of Marshall® broiler breeders of different flock ages during egg storage

The blastoderm, which represents the fertilized germinal disc, undergoes cellular events of division, differentiation and organization to achieve embryonic development in chickens. In this study, blastodermal cell counts and hatching performance of Marshall^® broiler breeders as influenced by flock age and egg storage were investigated. A total of 1,520 eggs from the flock ages, 43 weeks (younger) and 65 weeks (older), under similar management and nutritional regime were incubated after storage at 16°C with 75% relative humidity for duration of 0 (fresh eggs), 4, 7 and 10 days. Results show that total blastodermal cell counts (BCC) for both ages declined with increasing storage duration, with a sharp regression at 4d storage from younger breeders. Higher percentages of fertility and hatchability were recorded for younger breeders compared to older breeders. Percentage hatchability was statistically similar (p > .05) for both 43 weeks and 65 weeks old broiler breeders under 0, 4 and 7d storage except at 10d storage which was lower for older breeders. Chick lengths were longer with younger breeders whereas older breeders had heavier chick weights. Also, significant associations were found between BCC and fertility, hatchability of fertile eggs and chick weights, respectively, under different conditions. These results indicate that fresh eggs (0d) and short-term stored eggs (4- and 7 d) from 43 weeks old breeders had higher total blastodermal cell counts, fertility, hatchability and increased chick lengths compared to 65 week old breeders which produced heavier chicks. Therefore, egg storage longer than 7 days especially from older breeders resulted in modifications to the blastoderm which subsequently affected fertility, hatchability, embryo liveability and hatched chick quality. Also, detection of BCC in fertile eggs can serve as a predictive tool in fertility and hatchability evaluations.

A genome-wide single nucleotide polymorphism scan reveals genetic markers associated with fertility rate in Chinese Jing Hong chicken

The function of the sperm storage tubules is directly correlated with the fertility of laying hens. However, little is known about the molecular mechanisms regulating the fertility traits in chicken. To identify genetic markers associated with reproductive traits, we calculated fertility rate at 61 to 69 wk (51 D) of Jing Hong chickens parent generation as the phenotype and the genotype were detected by the chicken 600K Affymetrix Axiom High Density single nucleotide polymorphisms (SNP)-array. The genome-wide association study using 190 Jing Hong hens showed that the 20 SNP in chromosomes 3 and 13 were significantly associated with fertility rate. To verify these results, a total of 1900 Jing Hong laying hens from 2 populations (P1 and P2) were further genotyped by polymerase chain reaction-restriction fragments length polymorphisms method. The association analysis results revealed that 12 polymorphisms (AX-75769978, AX-76582632, AX-75730546, AX-75730496, AX-75730588, AX-76530282, AX-76530329, AX-76529310, AX-75769906, AX-75755394, AX-80813697 and AX-76582809) out of 20 showed highly significant effects (P < 0.0001) on fertility rate in P1, P2 and P1+P2. Six haplotypes (TTAA, TTGG, TTAG, CTAA, CTGG, and CTAG) were inferred based on significant loci (AX-75730546 and AX-76530282) also showed significant association with fertility rate, where haplotype CTAG was shown to be markedly associated with the significantly highest (P < 0.0001) fertility rate (in P1, 86.42 ± 0.59; P2, 85.98 ± 0.59 and P1+P2, 86.16 ± 0.42) followed by other haplotypes for the irrespective of population studied. Collectively, we report for the first time that 12 SNP in the chromosomes 3 and 13 were significantly associated with fertility rate during the later stage of egg production, which could be used as the potential genetic markers that would be able to facilitate in the selection and improvement of fertility rate through chicken breeding.

Influence of male-male competition on reproductive performance and mortality of broiler breeders following intra-spiking

The study was conducted to determine the influence of male-male competition on reproductive performance and male mortality of Cobb 500 broiler breeder flocks following double intra-spiking. Broiler breeders were housed in 3 open-sided houses each accommodating 8,200 females and 820 males. Males of the same age on the same farm were exchanged between the houses (intra-spiking) to stimulate competition thereby changing the social hierarchy of each house. Intra-spiking was performed by replacing 25, 35, and 45% of males between the houses at 40 and 48 weeks of age (WOA), respectively. Eggs were collected from 36 to 55 WOA, when egg fertility and male mortality were recorded. Data was analyzed using repeated measures techniques of SAS 9.4, modeling the covariance structure of the observed data. Male-male competition (intra-spiking), age and their interaction significantly (P < 0.05) influenced egg fertility, hatchability, and male mortality. Average fertility and hatchability were increased in the 45% intra-spiked flocks (P < 0.05) (95.89 and 85.83%) compared with the 35% (95.13 and 86.30%) and 25% (94.42 and 0.23%) intra-spiked flocks. Fertility and hatchability with the 45% double intra-spiked flocks was consistently higher (P < 0.05) over time than the other double intra-spiked flocks. Male mortality was lower (P < 0.05) in the 45% intra-spiked flock (0.23%) than in the 35% (0.40%) and 25% (0.44%) intra-spiked flocks. After double intra-spiking, the male mortality in the 25 and 35% double intra-spiked flocks significantly increased (P < 0.05), whereas that of 45% intra-spiked flocks remained relatively low. Male mortality in the 45% intra-spiked flocks was consistently low over time than other double intra-spike levels from 45 WOA until the end of the trial. Noteworthy, egg fertility and hatchability gradually decreased, and mortality increased with increasing flock age toward the end of the productive life cycle. High level of male-male competition (45%) showed great promise as a tool to slow down the decrease in egg fertility and hatchability, and reduce male mortality in aging broiler breeder flocks.

Review: Genomics of bull fertility

Fertility is one of the most economically important traits in both beef and dairy cattle production; however, only female fertility is typically subjected to selection. Male and female fertility have only a small positive genetic correlation which is likely due to the existence of a relatively small number of genetic variants within each breed that cause embryonic and developmental losses. Genomic tools have been developed that allow the identification of lethal recessive loci based upon marker haplotypes. Selection against haplotypes harbouring lethal alleles in conjunction with selection to improve female fertility will result in an improvement in male fertility. Genomic selection has resulted in a two to fourfold increase in the rate of genetic improvement of most dairy traits in US Holstein cattle, including female fertility. Considering the rapidly increasing rate of adoption of high-throughput single nucleotide polymorphism genotyping in both the US dairy and beef industries, genomic selection should be the most effective of all currently available approaches to improve male fertility. However, male fertility phenotypes are not routinely recorded in natural service mating systems and when artificial insemination is used, semen doses may be titrated to lower post-thaw progressively motile sperm numbers for high-merit and high-demand bulls. Standardization of sperm dosages across bull studs for semen distributed from young bulls would allow the capture of sire conception rate phenotypes for young bulls that could be used to generate predictions of genetic merit for male fertility in both males and females. These data would allow genomic selection to be implemented for male fertility in addition to female fertility within the US dairy industry. While the rate of use of artificial insemination is much lower within the US beef industry, the adoption of sexed semen in the dairy industry has allowed dairy herds to select cows from which heifer replacements are produced and cows that are used to produce terminal crossbred bull calves sired by beef breed bulls. Capture of sire conception rate phenotypes in dairy herds utilizing sexed semen will contribute data enabling genomic selection for male fertility in beef cattle breeds. As the commercial sector of the beef industry increasingly adopts fixed-time artificial insemination, sire conception rate phenotypes can be captured to facilitate the development of estimates of genetic merit for male fertility within US beef breeds.

Comparative effects of zinc oxide, zinc oxide nanoparticle and zinc-methionine on hatchability and reproductive variables in male Japanese quail

The objective was to examine the effect of different dietary zinc sources on reproduction of male Japanese quail. A total of 512 quail chicks (day-old) were divided into four groups with four replications for a period of 42 days. After this period, excess chicks were removed to attain the ratio of one male to three females and 16 quail in each subgroup. At 52 to 60 d of age, the eggs were collected and incubated. The basal diet (control) contained no zinc and the other three experimental diets were supplemented with 25 and 50 mg/kg zinc from zinc oxide (ZnO), zinc oxide nanoparticles (ZnONP) and zinc-methionine (Zn-Met) for 1 to 35 and 36 to 60 days, respectively. On day 42, two males from each replicate were euthanized. Males from the ZnO and Zn-Met treatments had an increase (P < 0.05) in seminiferous tubule diameters (STD) and germinal epithelium thickness (GET) compared with the control and ZnONP treatments. Cloacal gland index (CGI) was greatest (P < 0.05) for the Zn-Met compared with the other groups. Testosterone concentration was greater (P < 0.05) in the ZnO and Zn-Met compared with the other groups. Addition of Zn-Met to the diet enhanced (P < 0.05) fertility, hatchability and hatched chick weight compared with the other groups. Early and late embryonic death was greater (P < 0.05) in the control and ZnONP groups, respectively, compared with the other groups. This study indicated that supplementing diets with the Zn-Met source improves male Japanese quail reproductive performance and hatchability traits while zinc oxide nanoparticles have detrimental effects on male Japanese quail reproduction and reduces hatchability.

Reproductive soundness is higher in chickens selected for low as compared with high antibody response

White Leghorn chickens were selected for 36 generations for high (HAS) or low (LAS) antibody response to SRBC 5 d after an intravenous challenge. The aim of this study was to investigate possible changes in reproductive soundness resulting from that selection. Age and BW at onset of lay (first egg), along with weight of the first egg, were recorded on 45 hens from each line. Intensity of lay was measured as the number of ovulations within a 15-d period over 15 sequential intervals (total 225 d). Three cycles of fertility also were assessed, coinciding with early, middle, and late production stages. For fertility of males and females within a line to be independently evaluated, roosters and hens were mated by artificial insemination to an unrelated control line of White Plymouth Rocks. Twenty roosters from each antibody line were considered, as well as the 45 hens. Pooled semen from the control line was used for mating the hens from the antibody lines. Hens from the LAS line commenced lay at a younger age (11.67±3.53 d; P<0.001), lighter BW (-169.46±40.20 g; P<0.001), and with greater intensity (2.68±0.25%; P=0.001) than those from the HAS line. Any differences in intensity thereafter were trivial between lines (P=0.42), with intensity decreasing sharply toward the end of the 7-mo production period in both lines. Length of fertility differed between hens of the antibody lines during the first cycle (3.35±0.85 d; P=0.002) and between roosters during the first (3.58±1.06 d; P=0.02) and second (3.38±1.07 d; P=0.03) cycles, with chickens from the LAS line having the longer length of fertility in both sexes. A correlated response in reproductive soundness to divergent selection for antibody response was observed. This may in part be due to differences in resource allocations, with particular impact on duration of fertility.

Effect of crossbreeding on fertility, hatchability and embryonic mortality of Nigerian local chickens

A total of 970 eggs were collected from matings involving three genotypes of Nigerian local chickens (Normal-feathered, Frizzle-feathered and Naked neck) and one exotic broiler breeder strain (Anak Titan) to evaluate the effect of crossbreeding on fertility, hatchability and embryonic mortality. Mating was achieved through artificial insemination. Sire genotype significantly (P < 0.05) affected percent fertility and percent dead-in-shell. Naked neck sire genotype had the highest dead-in-shell (19.5%) with the least being 7.5% for Frizzle-feathered chickens. Frizzle-feathered sire genotype had the highest fertility (90.5%) and hatchability (91.4%). Dam genotype had a significant effect (P < 0.01) on fertility and hatchability, with Anak Titan dam having the highest fertility and hatchability of 88.2% and 94.6%, respectively. Fertility and hatchability were significantly (P < 0.05) influenced by the interactive effect of sire and dam genotypes with Frizzle-feathered × Anak Titan having 98.5% fertility and 96.8% hatchability. Both straight and reciprocal crosses involving Frizzle-feathered genotype and Anak Titan resulted in higher mean values for fertility and hatchability when compared to crosses involving the other two local chicken genotypes. This result suggests that the use of the Frizzle-feathered genotype appears to be more desirable in fertility and hatchability trials.