Pulmonary hypertension syndrome (ascites) is a metabolic disorder in fast-growing broilers. Inconsistency of oxygen requirement and the cardiovascular ability make the birds susceptible to ascites. Incidence of ascites was accompanied by right ventricular hypertrophy, fluid accumulation in the abdominal cavity and finally mortality. The objective of the current study was to review the genetic basis of ascites syndrome and investigation of indicator traits of ascites syndrome to use in selection indices for reducing ascites susceptibility in broilers. Developing a breeding objective to increase body weight and to reduce ascites susceptibility in broilers is of ongoing interest, because the ascites syndrome is still a major challenge for poultry breeders. The blood gas parameters, which measured early in life, make it possible to design alternative selection schemes to reach birds resistance to ascites. In this way, ascites susceptibility can be effectively reduced but it might be comes at a cost, including a reduction in selection response for growth rate, due to genetic correlations. Based on the best combination of traits considered, reduction in gain for growth rate might be decreased, although with limited efficiency. Also, marker-assisted selection can be used effectively to reduce ascites susceptibility with respect to benefit-costs analysis. پرونده مقاله

Estimation of genetic trends is necessary to monitor and evaluate selection programs. The objective of this study was to estimate the genetic trends for milk yield in Iranian Holsteins cows using random regression test day model. Data set was consisted of 743205 test-day records from 1991 to 2008, which were collected by the Animal Breeding Centre of Iran. Breeding, environmental and phenotypic values were estimated using a random regression test-day model. The logarithmic form of Wood function was chosen to fit the additive genetic and permanent environmental effects of milk yield. Genetic, environmental, phenotypic trends were estimated by regressing the mean of breeding values, environmental values and phenotypic values on birth year. The genetic and phenotypic trends were positive and significant, whereas environmental trends were not significant. Genetic trends of sires and dams were estimated separately and it was positive and significant for dams, but it was not significant for sires. The phenotypic, environmental and genetic correlation between each days in milk and total 305 days were estimated. The correlations related to breeding values were weak and it showed that with the logarithmic transformation of milk yield, persistency can be improved independently from milk production. پرونده مقاله

The accuracy of genomic breeding value prediction was investigated in various levels of reference population size, trait heritability and the number of quantitative trait locus (QTL). Five Bayesian methods, including Bayesian Ridge regression, BayesA, BayesB, BayesC and Bayesian LASSO, were used to estimate the marker effects for each of 27 scenarios resulted from combining three levels for heritability (0.1, 0.3 and 0.5), training population size (600, 1000 and 1600) and QTL numbers (50, 100 and 150). A finite locus model was used to simulate stochastically a historical population consisting 100 animals at first 100 generations. Through next 100 generations, the population size gradually increased to 1000 individuals. Then the animals in generations 201 and 202 having both known genotypic and phenotypic records were assigned as reference population, and individuals at generations 203 and 204 were considered as validation population. The genome comprised five chromosomes of 100 cM length and 500 single nucleotide polymorphism markers for each chromosome that distributed through the genome randomly. The QTLs and markers were bi-allelic. In this study, the heritability had great significant positive effect on the accuracy (P<0.001). By increasing the size of the reference population, the average genomic accuracy increased from 0.64±0.03 to 0.70 ± 0.04 (P<0.001). The accuracy responded to increasing number of QTLs non-linearly. The highest and lowest accuracies of Bayesian methods were 0.40 ± 0.04 and 0.84 ± 0.05, respectively. The results showed having the greatest amount of information (i.e. highest heritability, highest contribution of gene action in phenotypic variation and large reference population size), the highest accuracy (0.84) was obtained, with all investigated methods of estimation. پرونده مقاله

A deterministic model based on the gene flow method, considering the features of Iranian Holstein cattle population, was implemented in this study to evaluate the effect of altering the number of age-classes in the dams of future sire (DS) path and the number of dams required for breeding a young bull (YB), to be evaluated as future sire, on genetic gain and resultant economic efficiency of a genomic selection program for milk production as a selection goal. Based on the simulation, changing the number of age-classes from 10 to 1 resulted in higher replacement rate of DS path (from 0.22 to 1) and shorter generation interval. Consequently, the economic efficiency of the program increased up to a maximum point and then a descending trend was observed. The maximum economic efficiency (25.68) was obtained when 7 age-classes in DS path was assumed. By chaining the number of dams required for breeding a YB from 7 to 1, the genetic gain in selection goal increased from 0.0232 to 0.0264 kg per dairy cattle and therefore, the economic efficiency rose from 25.42 to 28.52. The results revealed that a decrease in generation interval does not necessarily result in maximum economic efficiency and there is an optimum level for generation interval. Less number of required dams per YB could result in higher economic efficiency and therefore should be considered as an effective management strategy to improve the economic efficiency of a genomic selection program for milk production. پرونده مقاله

Two selection goals of inclusion or exclusion of calving interval (CI) in the selection goal function for Holstein cows in Iran, besides milk yield, milk fat percentage, and milk protein percentage, were studied. Four selection indices were composed of using the information on production traits, CI and / or days from calving to first insemination (DFI). The results of the predicted genetic growth in selection goals showed that the index composed of all production and reproduction traits generated the greatest genetic growth. Although CI had a negative coefficient in the selection goal, it is genetic mean increased in any case. However, the magnitude of this undesirable increase was lower in the CI included selection goal. This implies that the inclusion of CI in the selection goal is necessary to control the undesirable growth of this trait. The comparison of indices in this goal reflected that the inclusion of CI along with the production traits resulted in a smaller undesirable change in this trait. Constraining the genetic change in CI in the selection goal impaired the selection efficiency. So, this constraint is not recommended for breeding programs. پرونده مقاله

The objective of the present study was to estimate genetic trends for lactation milk yield, persistency of milk yield, somatic cell count and interval between first and second calving in Holstein dairy cows of Iran. The dataset consisted of 210,625 test day and 25,883 first parity cows with milk yield recorded from July 2002 to September 2007 comprising 97 herds in Iran. Breeding values of animals were predicted with Best Linear Unbiased Prediction methodology under multi-trait animal model. Model included region, herd–year–season of calving and age at first calving as fixed effects and Holstein percentage (covariate) and random animal additive effect. Genetic trends of studied traits were estimated by regressing mean of breeding values on calving year. Phenotypic trends were estimated using annual averages of first lactation traits on calving year weighted by the number of animals in each year. Genetic trend was positive and significant for lactation milk yield (21 kg/yr; p < 0.01).Although not significant, favorable genetic trends for most studied traits were reported. Considering that selection emphasis in Iran was on lactation milk yield, progress for this trait was low during the years of the study. پرونده مقاله

The present study was carried out to estimate (co)variance components and genetic parameters for some productivity traits of Baluchi ewes. The data were collected during a 31 year period (1984-2014) at the experimental breeding station of Baluchi sheep, which is located in north-east of Mashhad, Iran. The analysis was based on 14030 records of lambs and 4371 records of ewes. Investigated traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB) and litter mean weight per lamb weaned (LMWLW) as basic traits, total litter weight at birth (TLWB) and total litter weight at weaning (TLWW) as composite traits. Genetic analysis of the studied traits was performed applying restricted maximum likelihood (REML) procedure by fitting a linear mixed animal model. Direct heritability estimate for LSB, LSW, LMWLB, LMWLW, TLWB and TLWW were 0.10, 0.08, 0.13, 0.07, 0.12 and 0.05, respectively. Corresponding values for repeatability estimates were 0.18, 0.17, 0.19, 0.15, 0.18 and 0.15, respectively. Direct genetic correlation estimates among the studied traits varied from -0.52 for LSW and LMWLB to 0.99 for TLWB and TLWW. Phenotypic and environmental correlation estimates were generally lower than those of genetic ones. Although low direct heritability’s were estimated for the reproductive traits, as these traits are of interest then they used as the primary selection criterion to bring about genetic improvement in ewe productivity traits. پرونده مقاله