heritability

Commercial silkworm hybrids result from the controlled crossing of the Japanese-shaped parent with the Chinese-shaped parent (direct cross) and vice versa (reverse cross). Suppose the silkworm hybrids resulting from direct and reverse crossing have a large difference in the performance of the important productive, reproductive, and viability characteristics. In that case, they are not suitable for supply to the farmers. In this research, to identify the hybrid pairs with the least differences, the traits of 72 reciprocal hybrids (36 mating pairs) were tested by statistical methods. These results will be used for the final selection of commercial hybrids. Also, the genetic analysis of reciprocal hybrids and the estimation of genetic parameters in each of the mating programs were done separately using line × tester analysis. 

The current research was done at the Iran Silk Research Center by carrying out two mating programs in the form of line-tester crosses between six Chinese lines (IRA2, IRA4, IRA6, IRA8, IRA10, and IRA12) with six Japanese lines (IRA1, IRA3, IRA5, IRA7, IRA9, and IRA11). Six lines with dumbbell-shaped cocoons (Japanese) and six lines with oval-shaped cocoons (Chinese) were crossed bilaterally. All lines (12 genotypes) and 72 hybrids (36+36) were reared in a completely randomized design with 4 replications. All stages of hatching and rearing of silkworm lines and hybrids in this project were done in the same way based on standard methods. The studied traits including the number of cocoons per liter, cocoon weight per liter, best cocoons percentage, middle cocoons percentage, cocoon weight per 10,000 larvae, hatchability percentage, cocoon weight, cocoon shell weight, cocoon shell percentage, and pupation rate were recorded and analyzed by applying of GLM procedure of SAS software. Line×tester analysis was applied to study the reciprocal crossing effect and estimate genetic parameters. Gene effects, heritability, σ2gca/σ2sca, and Baker’s ratio were investigated by applying of IML procedure of SAS software. 

The results of the comparison of reciprocal hybrids based on the total difference (∑D) showed that this parameter was more than the total average in 14 pairs of hybrids. Therefore they could not be selected for commercial level. In the other 22 pairs, either none of the traits or at most one trait had a significant difference (P<0.05). The results showed that the characteristics of cocoon weight and cocoon shell weight were more affected by reciprocal crossing. On the other hand, the number of cocoons per liter, the hatchability percentage and the middle cocoon percentage were higher in Chinese mother hybrids than in Japanese mothers. For other traits (weight per liter, cocoon weight per 10,000 larvae, pupation percentage, good cocoon percentage and pupation percentage), Japanese mother hybrids were almost superior. The comparison of crosses effect in Japanese-shape lines and Chinese-shape testers with Chinese-shape lines and Japanese-shape testers showed that four traits (cocoon weight, cocoon shell weight, cocoon shell percentage and cocoon weight per 10 thousand larvae) and for the interaction effect (line × tester), three Traits (cocoon weight, cocoon shell percentage and pupation rate) were most affected by the substitution of parents. The values of additive genetic variance, Baker's coefficient, ratio σ2gca/σ2sca and heritability in four studied traits including cocoon weight, cocoon shell weight, cocoon shell percentage and number of cocoons per liter showed that these traits are under additive genetic effect. Moreover, they had a higher value in Chinese mothers than the Japanese mother crosses. The trait of cocoon weight per 10,000 larvae was also controlled by non-additive genetic effects, and the substitution of parents did not affect their genetic parameters. The pupation rate in the direct crosses was due to additive genetic effects, but in the reverse crosses was affected by non-additive genetic effects. In general, the narrow sense heritability for all traits was higher in Chinese-shape than in Japanese-shape mothers. 

In the present study, similar and close performances of the Chinese mother and Japanese mother hybrids were determined except for cocoon weight and cocoon shell weight which was different in almost 33% of reciprocal hybrids. The crosses effect in the line × tester ANOVA supported the result of mean comparison for reciprocal hybrids evaluation. Further field investigations can be carried out to select the hybrids suitable for different geographical conditions.

Accurate estimation of genetic and phenotypic variance enhances the selection of superior horses and serves as a valuable tool for the long-term improvement of the sport horse population. Therefore, this study was conducted to estimate the variance components for performance traits of sport horses using the Bayesian method.

A database was created using 49,026 records from 1499 horses collected between 2017 and 2020 from the Iranian Equestrian Federation. The sport performance traits examined were race completion time (RCT), number of errors in competition (NEC), and rank at the end of the competition (REC). Analysis of variance and Duncan's multiple comparison tests were used to determine the significance of environmental effects, and genetic parameters were estimated using a Gibbs sampling method. R software was utilized to evaluate environmental effects, fit the model, and estimate reliability, variance components, heritability, and genetic correlations, with the GIBBS1F90 and THRGIBBS1F90 software used for estimation. The statistical model included fixed effects for birth year, sex, age, breed, height of obstacles, and level of difficulty of the event, as well as random effects for rider, date, city of competition, and additive genetic effect.

Heritability (h2) was estimated using single-trait and multi-trait models for the traits RCT, NEC, and REC, respectively, as 0.02 and 0.08, 0.13 and 0.23, 0.16 and 0.29. The estimated genetic correlations between the traits RCT and NEC, RCT and REC, and NEC and REC were 0.38, 0.36, and 0.65, respectively. The mean estimated reliability (r2) using single-trait and multi-trait models for the traits RCT, NEC, and REC were 0.60 and 0.69, 0.62 and 0.73, 0.58 and 0.66, respectively. The heritability values of different traits can vary, and a specific trait may exhibit different levels of heritability across various populations. The estimated heritability of RCT, NEC, and REC fell within the range of values reported in various horse populations and it was <0.01–0.41, 0.07–0.38, and 0.02–0.23, respectively. These estimates demonstrate genetic variation in the traits within the study population, and their alignment with other studies increases confidence in the estimated values.

The results of the present study indicated that the heritability of the traits studied was low. Among the performance traits, REC showed the highest heritability. Due to its positive genetic correlation with RCT and NEC, selecting for REC could potentially improve the other traits as well. These findings emphasize the importance of using multi-trait models in breeding programs, as they can provide more accurate heritability estimates and enhance the precision and reliability of breeding value predictions.

The aim of the present study was to investigate effect of additive genetic on egg weight, yolk weight and yolk fatty acid content and estimation of heritability for these traits. In this research, 150 white Japanese quails (50 males and 100 females) were used as the base population (without any pedigree information). In the F2 generation, 100 female quails were randomly selected at the fifth week of age and transferred to laying cages. The traits included egg weight, yolk weight and yolk fatty acid contents. (Co) Variance components and genetic parameters were estimated using multiple animal models by Wombat software. The estimated heritability for egg weight and yolk weight were 0.45 and 0.38, respectively. These estimates for yolk fatty acids ranged from 0.27 (Palmitoleic acid) to 0.45 (Palmetic acid). Genetic correlations between egg weight and yolk fatty acids were low, ranging from 0.01 (between egg weight and Linoleic acid) to 0.10 (between egg weight and Stearic acid). The higher genetic correlations were between yolk weight and yolk fatty acids, varying from 0.10 (between yolk weight and Linoleic acid) to 0.51 (between yolk weight and Stearic acid). The results showed that selection for increasing the yolk weight could lead to producing eggs with more contents of yolk fatty acids.

Estimates of genetic and environmental parameters of different component traits related to growth are needed to develop a proper selection program. The Kleiber ratio (KR) is defined as average daily gain as a proportion of metabolic body weight. Most studies conducted in KR ignored the effect of sex-linked chromosomes and assumed that direct genetic effects were influenced by autosomal chromosomes. Therefore, the purpose of this study was to estimate (Co)variance components of both autosomal and sex-Linked chromosomes for KR in Markhoz goat.

In the present study, the data were collected from 1992 to 2014 at Markhoz goat breeding station in Kurdistan province, Iran. The traits were kleiber ratio from birth to weaning (KR1), kleiber ratio from weaning to six months of age (KR2), kleiber ratio from weaning to six months of age (KR2), kleiber ratio from six to nine months of age (KR3) and kleiber ratio from nine to twelve months of age (KR4). The GLM procedure of the SAS software was used to determine significant fixed effects. The model accounting for fixed effects included year, sex, birth type and age of doe. In addition, random effects included direct additive genetic effects of autosomal chromosomes, direct additive genetic effects of sex-linked, maternal genetic effects, maternal permanent environmental effects and residual effects. (Co)variance components and genetic parameters were estimated using six different single-trait analysis via Average Information algorithm of Restricted Maximum Likelihood method using WOMBAT software. Akaike’s Information Criterion (AIC) test was applied to select the most apropariate model for each trait.

The most suitable model for KR1, KR2, KR3 and KR4 traits were the sixth, first, fourth and first models, respectively. Based on the best models, the estimated direct autosomal heritabilities were 0.410, 0.019, 0.172 and 0.020 for KR1, KR2, KR3 and KR4, respectively. The estimated sex-linked direct heritabilities were 0.008, 0.021, 0.049 and 0.023 for KR1, KR2, KR3 and KR4, respectively. The maternal heritability for KR1 and KR3 were 0.106 and 0.057, respectively. The maternal permanent environmental effect of 0.064 was estimatedfor KR1. The autosomal, sex-chromosome and phenotypic correlations between traits were ranged from -0.518 to 0.901, -0.943 to 0.652 and -0.001 to 0.312, respectively.

The results of this study showed that a considerable ratio of the phenotypic variance is explained by sex-linked chromosome effects. Therefore, including the sex-linked chromosome effect in the model may lead to a more precise estimates of direct autosomal heritability.

Improving the performance of economic traits of domestic livestock by means of sounds breeding programs could elaborate meeting the protein demands of the human world population. The water buffalo, also called the domestic water, bears up substantial value in terms of milk and meat production. Khuzestani buffalo, the subspecies of domestic Asian water buffalo (Bubalus bubalis) has become a strategic animal species in Khuzestan province, Iran, due to its ability to adapt to adverse environmental conditions, low quality feed sources dependency and high quality products. Archaeological and ancient records show little evidence regarding the expansion of the Khuzestani buffalo. Many people in the region depend on this species for their livelihoods than on any other domestic animal. In this regards, the buffalo lactation could have crucial role in farmers' economy. In general, having knowledge of lactation curve, may shed some lights on management and farm-based operation of milk production system. The lactation curve is a graphical representation tool that reflects the effect of couple of numbers of different factors on milk production during lactation; therefore, it is useful in making better management decisions. In other words, it could summarize the pattern of milk production, biological and economic efficiency of the animal. Several models have been suggested to describe the lactation curves. In this study, in order to estimate the association between different fitted lactation curves and their comparisons on Khuzestani buffalo, six nonlinear mathematical models (Wood, Wilmink, inverse polynomial, Complex logarithm, Ali and Schaefer and Digestra) were used.

The data used in this study, consisted of 103760 test day records of milk yield of 14280 buffalu in the first parity that collected by the Agricultural Jihad Center of Khuzestan province during 1993 to 2020. The Microsoft Excel was used to edit the data. Animals with unknown birth and calving dates were removed. Those fixed effects that had significant effects on the coefficients of lactation curve (P < 5%) were included in the final model. The lactation curve parameters were estimated using the nonlinear regression procedure (NLIN) of SAS software version 9.4 on test day records. Evaluation of goodness of fit was based on the coefficient of determination (R2), root mean square error (RMSE) and Akaike information criterion (AIC). The (Co) variance components were estimated by multi-trait animal model using restricted maximum likelihood method run in WOMBAT software.

Descriptive statistics of milk production of Khuzestani buffaloes based on 103760 records from different areas shown that the average milk production was 8.048 kg, standard deviation was 3.047 and coefficient of variation was 37.87 as well. Wood's mathematical model provided the best fit of the lactation curve due to the highest value for the R2 and lower values for RMSE and AIC compared to the other models and it obtained as 0.88. The a, b and c parameter values of Wood’s model were estimated 6.91, 0.057 and 0.00083, respectively. The results showed that the wood model was able to estimate the time of peak milk yield more accurately than the other models. The peak milk yield of Khuzestani buffaloes (8.30 kg/d) appeared on average in the tenth week (day 69) after calving. The heritability of lactation curve traits for initial yield (a), upward slope of the curve (b) and downward slope of the curve (c) were obtained 0.57, 0.27 and 0.48, respectively. In this study, the persistency(s) value for typical lactations were lactation curve were estimated 7.49. The genetic correlations among lactation curve parameters ranged from -0.55 (upward slope of the curve and initial yield) to 0.138 (upward and downward slope of the curve), whereas the phenotypic correlations ranged from -0.35 (Between initial yield and the upward slope of the curve) to +0.196 (b and c). The solutions of mixed model equations revealed that Buffalo with IDs 3436, 3410, 3360, 2868, 24, and 3174 had the highest breeding value for coefficient a. In other hand, buffalo 3438, 3409, 3418, 3361, 3282, and 3169 showed the highest breeding value in the coefficient b. Finally, the buffaloes that obtained the highest hereditary value in different coefficients of lactation curve were introduced as the superior buffaloes. By knowing the best buffaloes in terms of breeding value for parameters a and b, it is possible to select buffaloes to be parent for next generation. In general, evaluating lactation curve equations using nonlinear models and multi-trait analysis is an effective step in identifying buffaloes with high genetic potential to improve and increase milk production efficiency. The results of the present study showed that among the six mathematical models studied, Wood's incomplete gamma function had more viability for fitting the lactation curve of Khuzestani buffalo. The effect of calving season was not significant on lactation parameters while year of calving had a significant effect. Negative and moderate genetic correlations between initial production parameters (a) and upward slope (b) of the lactation curve indicate that keeping on with higher initial production level will have a lower rate of increase until peak production. In the present study, multivariate analysis led to the relationship of all coefficients of the lactation curve with each other and as a result more realistic parameters were estimated for them. It is suggested that in future studies, a computer-aided economic production system be designed and the economic coefficients related to the parameters of the lactation curve be estimated for integration into the selection index. Also, in order to improve the performance of Khuzestani buffalo, it is recommended to study the genomic relationship of milk production curve parameters.

The longevity of cows is crucial to the profitability of a dairy farm, and the culling of cows as a result of major health disorders is a significant risk that threatens production systems today. The possibility of taking diseases into account in the selection of dairy cows depends on the economic importance of the diseases. Mastitis and metritis are common diseases among dairy cows that are considered as risk factors for culling cows. The onset of these disorders can be attributed to factors such as environmental and managerial factors, but there is also evidence of a genetic component to each. Many genes are associated with resistance or susceptibility to mastitis and metritis in cattle, and their alleles have been reported. Subclinical mastitis seems to be one of the most important and damaging diseases threatening dairy cattle herds along with reproductive diseases, lameness and possibly some other common diseases such as Para-tuberculosis. Obviously, reducing production costs supports the profitability of dairy farms. By studying the relationship between the incidence rate and health disorders, in order to minimize the deaths due to health disorders, more emphasis has been placed on the health management of cows. The direct and adverse effects of mammary gland disorders (mastitis and nipple injury) on culling are well documented, while there are differences of results on the correlation between reproductive disorders and culling. Contradictory results may be due to differences in the purpose of the study, population, or the methods used. Many factors such as age, breed, production level, and calving season can play a role in the incidence of diseases.

The purpose of this study is to report the prevalence of clinical mastitis and metritis, moreover to investigate environmental and genetic factors affecting these diseases, to estimate the heritability of disease traits and to measure the correlation between disease and production traits in a Holstein cattle herd. Due to the fact that health records are not recorded in the country's farms in a regular and uniform manner, conducting this research is an experiment to collect this type of information so that in the future models can be provided for all Holstein cows in Iran to consider disease relating traits.

Data of 5052 milk yield from 1796 Holstein-Frisian cows has been gathered that had parturition from 2005 to 2009. In this study, using the 305-day milk production variables, parity, year of calving, the frequency of occurrence of clinical mastitis and metritis in cattle diseases using SAS software, using logistic procedure is estimated. The cows have been studied for all the diseases that occurred in all milking period. In logistic regression analysis, the effect of 305 days of milk and other factors in the occurrence of the disorder was investigated as a binary model. The effect of the lactation period in which the disorder was created was included in all analyzes and the fixed effects included milk for 305 days, calving period, calving year and calving season.Log [p. (1-p)] = b0 + b1 * milk305 + b2 * parity + b3 * calveyear + b4 * calve seasonA coefficient of b1 is assigned for the risk factor of milk production, a coefficient of b2 is assigned for the parturition, a coefficient of b3 is assigned for the factor of calving year and a coefficient of b4 is assigned for the factor of calving season. b0 is the logistic regression estimate if there is no predictor other than the response variable in the model. For each estimate of regression coefficients, the probability level, standard error and 95% confidence interval are also calculated. For a particular disease b1, b2, b3 and b4 are regression coefficients. Estimated genetic parameter in this research was heritability of diseases traits that has been done with ASReml software.

Metritis incidence rate is lower than mastitis. The percentage of animals with mastitis and metritis in the herd was 3.11% and 1.67%, respectively. The average calving interval for metritis incidence was 167.3 days and 129.5 days for mastitis. Data analysis of correspondence of metritis and 305 milk yield, parity, the year and the season of calving showed none of the risk factors had relation with the occurrence of clinical mastitis. The heritability of clinical mastitis and metritis were estimated to be 0.27 and 0.23, respectively. We could not find a relationship between milk production and metritis. Can we consider the increase in milk production as a risk factor for disease occurrence? It is very difficult to prove and explain this relationship and there are many contradictions between the results of other studies. From the lack of a proven correlation between milk production and the occurrence of diseases, it can be concluded that if proper management and nutrition provided based on the biological needs of high-yielding cows, then cows with high milk production will not necessarily suffer from diseases in comparison with low-yielding cows.Genetic studies have shown a positive correlation between mastitis and milk production. Erb (1987) and Dehu and Martin (1984) concluded that high milk production could not be a risk factor for mastitis. A study of Ayrshire cows in Finland found that cows with higher milk production during the previous lactation period were at increased risk for mastitis (Grun et al. 1989 and Grun et al. 1990). There are few documented findings on the association between milk production and the incidence of disease. Of course, it should be borne in mind that "milk production" is not the only risk factor for the disease. Concerning diseases in Holstein dairy cattle it seems the occurrence of the disease can also be the result of breeding and nutrition conditions and management. However, identifying all relevant factors and determining their quality and relative importance is difficulty accessible. It is also not easy to estimate all possible interactions between production and disease traits, even with the efficiency of today's computer technology.

In dairy cattle genetic improvement programs, we suggest to record and estimate the breeding values for disease traits and consider them in multi-trait selections among elite sires. The estimated heritability of metritis was lower than clinical mastitis. Keywords: Holstein-Friesian cows, clinical mastitis, metritis, milk 305 days, heritability.

Quails are beneficial for their meat and eggs and have been the focus of poultry breeders in recent decades. Egg quality traits are usually divided into external (such as shell quality and egg weight) and internal (like yolk and albumen parameters) traits. Shell characteristics are important factors to determine egg quality. The breakage of quail eggs can be occurred in various processes such as collection, packaging, and transportation or in the setter and hatcher devices, and leads to serious economic problems for the breeders in the poultry industry. The size and weight of the quail egg are important factors in the marketability of this product. From an economic point of view, the yolk is the most valuable part of the egg. The yolk is a concentrated source of nutrients, as well as it has a significant effect on the weight of the chicken. The ratio of yolk to white in quail eggs has been reported to be 35 to 65, which is higher in comparison to laying hens. Egg quality can be affected by different factors such as genotype, breed, strain, age, management, nutrition, temperature, and illness. Although there have been many studies to determine the environmental factors on traits related to egg quality in quail, there are few studies to investigate the effect of genetic factors and different mating systems on the occurrence of these traits. Therefore, the present study was conducted to estimate genetic parameters of external and internal egg quality traits in wild and white strains of Japanese quails.

A total number of 570 laying quails were obtained from pure and cross-mating groups of wild and white Japanese quails. The base population was divided into four mating groups including two pure and two crossed mating groups (group 1: wild male × wild female; group 2: white male × wild female; group 3: wild male × white female, and group 4: white male × white female). The studied traits included external (egg weight, length, and width, shell weight and thickness, and egg shape index) and internal (yolk weight, albumen weight, yolk index, albumen index, and internal egg quality unit) egg quality traits. The effects of hatch and mating groups on traits related to egg quality were investigated. The means of traits related to external and internal egg quality were compared using the Duncan test. (Co)Variance components and genetic parameters of traits related to external and internal quality traits were estimated by multiple trait animal models and restricted maximum likelihood using ASREML software.

The effect of the hatch on egg weight, shell weight, and albumen weight was significant (P<0.05) and the eggs from the second and third hatches showed higher egg weight, shell weight, and albumen weight in comparison to the first hatch (P<0.05). The difference between mating groups was not significant (P>0.05) except for albumen and egg weights. The laying quails from the pure white mating group showed lower albumen and egg weights (P<0.05). The heritability estimates for traits related to external egg quality varied from 0.16 (egg shape index) to 0.39 (egg weight). These estimates for traits related to internal egg quality ranged from 0.10 (internal quality unit) to 0.31 (yolk weight). Genetic correlations were estimated from -0.33 (between egg length and egg shape index) to 0.71 (between egg length and width) for traits related to external egg quality, and from -0.37 (between yolk weight and yolk index) to 0.71 (between albumen weight and albumen height) for traits related to internal egg quality, respectively. Phenotypic correlations varied from -0.32 (between egg length and egg shape index) to 0.61 (between egg length and width) for traits related to external egg quality, and from 0.11 (between yolk index and albumen height) to 0.59 (between the internal quality unit and albumen height) for traits related to internal egg quality, respectively.

Heritability estimates for traits related to egg quality were moderate which indicates the significant effect of additive genes on the occurrence of these traits. Positive genetic correlations between egg weight and traits related to external egg quality, as well as appropriate genetic correlations between traits related to internal egg quality showed that selection based on some egg traits like egg weight and internal egg unit can effectively lead to the improvement of other egg quality traits.

Native fowl have become valuable genetic resources over the years due to their adaptation to harsh conditions in rural areas (Emamgholi et al 2009). Native fowl, despite their lower growth rate and lower egg production compared with broiler strains such as Ross and Cobb and layer strains such as Hy-Line and Lohman, perform much better in the rural system due to their good disease resistance and production under adverse nutritional and environmental conditions (Lakhi et al 2013). Breeding programs have a significant effect on improving the genetic structure of native fowl (Kiani manesh et al 2002). The purpose of this study was to combine the results of studies related to estimating genetic parameters for productive and reproductive traits in native fowl using meta-analysis method in order to improve the accuracy of estimations. In addition, the use of meta-analysis method eliminates the existing differences between studies by examining the heterogeneity between them (Field and Gillett 2010; Lortie et al 2013; Hooijmans et al 2014). Increasing the accuracy of estimates can consequently increase genetic improvement through selecting proper candidates to be parents of next generations. Higher performance will increase the courage of farmers to keep native fowl and therefore it help to keep the birds as a valuable genetic source for the future.

In this meta-analysis study, previous studies in the field of estimating genetic parameters of productive and reproductive traits in Iranian native fowl were collected and used. These articles consisted of 33 articles which were published between years 2007 and 2016. Information used in current study included heritability, genetic and phenotypic correlations of productive and reproductive traits. These traits consisted of birth weight, weight at eight weeks of age, weight at twelve weeks of age, egg number, egg weight, age at sexual maturity and weight at sexual maturity. Cochran test and I2 criterion were used for testing heterogenty among used articles. The range of heterogeneity among studies could be from zero to 100 percent. Ranges of 0 to 25 percent, 25 to 50 percent, 50 to 75 percent and 75 to 100 percent indicate very low, low, moderate and high heterogeneity among studies, respectively. Fixed meta-analysis model is usually recommended for very low and low heterogeneity among studies and random meta-analysis model is normally used for moderate to high rates of heterogeneity among studies. Due to high heterogenty observed among studies in present study, random effects model meta-analysis was performed using Metacor package R software version 3,3,1 and Comprehensive Meta-Analysis (CMA) software version 3. The weighted average of the heritability, genetic and phenotypic correlations were calculated accordingly.

According to the results, the highest heritability among productive and reproductive traits was related to egg weight (0.42) and then weight at sexual maturity (0.41). The lowest heritability was related to egg number with a value of 0.20 and then birth weight with a value of 0.25. The highest positive genetic correlation between productive and reproductive traits was estimated between weight at eight and weight at twelve weeks of age (0.86) and then between weight at twelve weeks of age and weight at sexual maturity (0.64). The highest negative genetic correlation was related to the correlation between age at sexual maturity and egg number (-0.66), then egg number and egg weight (-0.19). Due to combing the results of individual studies using meta-analysis, the standard error of estimations for genetic parameters and consequently their 95% confidence interval were significantly reduced compared to individual studies (Bayssa et al 2021). This reduction indicates an increase in the accuracy of the estimates due to aggregating the results of individual studies (Field and Gillett 2010). A comparison between the results of independent studies and the results of meta-analysis shows a significant reduction in estimated standard errors for heritability and genetic and phenotype correlations in the meta-analysis method. For example, the amount of estimated standard error related to heritability of weight at twelve weeks of age in the meta-analysis was calculated to be 0.0009, while the range of reported standard error in the articles for the heritability of this trait was from 0.05 to 0.08. For weight at eight weeks of age the amount of standard error of heritability in the meta-analysis was estimated to be 0.0009, but the range reported for standard error of heritability for this trait in the articles was zero to 0.06. Similar reduction in the amount of estimated standard error were observed for reproductive traits. For example for egg number, the amount of error in the meta-analysis was estimated to be 0.0013, but the range reported in the articles was 0.01 to 0.13. The amount of estimated standard error related to egg weight in the meta-analysis was calculated to be 0.0009, while the range reported in the studied articles was from 0.004 to 0.07. This decreasing trend was similarly observed for other studied traits, which is due to the aggregation of the results obtained from independent studies.

The results of this study showed that the use of meta-analysis method by aggregating the results of individual studies, will increase the accuracy of genetic parameters of productive and reproductive traits in native fowls through increasing the sample size and reducing estimated standard errors. Therefore, by taking into consideration that Iranian native fowl are economically important animals and considerable demands for their products in the country, using genetic parameters obtained from this study with higher accuracy can play an effective role in the successful design of breeding programs for native fowls and promote genetic improvement in native fowl in Iran.