Direct Additive Genetic Effects Research Articles

Impact of including the cause of missing records on genetic evaluations for growth in commercial pigs.

It is of interest to evaluate crossbred pigs for hot carcass weight (HCW) and birth weight (BW); however, obtaining a HCW record is dependent on livability (LIV) and retained tag (RT). The purpose of this study is to analyze how HCW evaluations are affected when herd removal and missing identification are included in the model and examine if accounting for the reasons for missing traits improves the accuracy of predicting breeding values. Pedigree information was available for 1,965,077 purebred and crossbred animals. Records for 503,716 commercial three-way crossbred terminal animals from 2014 to 2019 were provided by Smithfield Premium Genetics. Two pedigree-based models were compared; model 1 (M1) was a threshold-linear model with all four traits (BW, HCW, RT, and LIV), and model 2 (M2) was a linear model including only BW and HCW. The fixed effects used in the model were contemporary group, sex, age at harvest (for HCW only), and dam parity. The random effects included direct additive genetic and random litter effects. Accuracy, dispersion, bias, and Pearson correlations were estimated using the linear regression method. The heritabilities were 0.11, 0.07, 0.02, and 0.04 for BW, HCW, RT, and LIV, respectively, with standard errors less than 0.01. No difference was observed in heritabilities or accuracies for BW and HCW between M1 and M2. Accuracies were 0.33, 0.37, 0.19, and 0.23 for BW, HCW, RT, and LIV, respectively. The genetic correlation between BW and RT was 0.34 ± 0.03, and between BW and LIV was 0.56 ± 0.03. Similarly, the genetic correlation between HCW and RT was 0.26 ± 0.04, and between HCW and LIV was 0.09 ± 0.05, respectively. The positive and moderate genetic correlations between BW and other traits imply a heavier BW resulted in a higher probability of surviving to harvest. Genetic correlations between HCW and other traits were lower due to the large quantity of missing records. Despite the heritable and correlated aspects of RT and LIV, results imply no major differences between M1 and M2; hence, it is unnecessary to include these traits in classical models for BW and HCW.

Genetic associations between growth traits and age at first calving in Guzera cattle using random regression models

The aim of this study was to estimate genetic associations between body weight (BW), scrotal circumference (SC), and age at first calving (AFC) in Guzera cattle using random regression models. The analyses used 159,366 and 23,780 records of BW and SC obtained between 335 and 724 days of age and divided into classes at intervals of 10 days, as well as 63,596 records of AFC. A multitrait animal model via Gibbs sampling was adopted that included random direct additive genetic, permanent environmental (only for BW and SC), and residual effects. The fixed effects considered were the contemporary group, age of cow at calving (linear and quadratic effect), and the fixed curve to model the average trend of the population on the age classes of the animals. For BW and SC, four models were compared using the deviance information criterion, with Legendre polynomials ranging from one to four coefficients (intercept, linear, quadratic, and cubic) for additive genetic and permanent environmental effects. The model with three coefficients (quadratic) was considered the most appropriate to describe the (co)variance structure of the traits analyzed. The mean heritability estimates ranged from 0.17 to 0.31 for BW and from 0.19 to 0.28 for SC across age classes. The mean heritability for AFC was 0.07. The genetic correlations between BW and SC across age classes were always positive and favorable, ranging from 0.33 to 0.39. These findings indicate that selection for higher BW should result in animals with greater SC. The genetic correlations between BW at different ages and AFC ranged from -0.56 to -0.38, while those between SC at different ages and AFC ranged from -0.55 to 0.08. Except for some genetic correlations close to zero and positive between SC close to 365 days of age and AFC, in general the results showed that the selection for either higher BW or greater SC should result in a reduction of AFC in Guzera cattle. Calculation of the relative selection efficiency indicated a greater correlated response in AFC by selection for SC, especially after 634 days of age, compared to direct selection for AFC.

Genomic Approaches Reveal Pleiotropic Effects in Crossbred Beef Cattle.

Carcass and meat quality are two important attributes for the beef industry because they drive profitability and consumer demand. These traits are of even greater importance in crossbred cattle used in subtropical and tropical regions for their superior adaptability because they tend to underperform compared to their purebred counterparts. Many of these traits are challenging and expensive to measure and unavailable until late in life or after the animal is harvested, hence unrealistic to improve through traditional phenotypic selection, but perfect candidates for genomic selection. Before genomic selection can be implemented in crossbred populations, it is important to explore if pleiotropic effects exist between carcass and meat quality traits. Therefore, the objective of this study was to identify genomic regions with pleiotropic effects on carcass and meat quality traits in a multibreed Angus–Brahman population that included purebred and crossbred animals. Data included phenotypes for 10 carcass and meat quality traits from 2,384 steers, of which 1,038 were genotyped with the GGP Bovine F-250. Single-trait genome-wide association studies were first used to investigate the relevance of direct additive genetic effects on each carcass, sensory and visual meat quality traits. A second analysis for each trait included all other phenotypes as covariates to correct for direct causal effects from identified genomic regions with pure direct effects on the trait under analysis. Five genomic windows on chromosomes BTA5, BTA7, BTA18, and BTA29 explained more than 1% of additive genetic variance of two or more traits. Moreover, three suggestive pleiotropic regions were identified on BTA10 and BTA19. The 317 genes uncovered in pleiotropic regions included anchoring and cytoskeletal proteins, key players in cell growth, muscle development, lipid metabolism and fat deposition, and important factors in muscle proteolysis. A functional analysis of these genes revealed GO terms directly related to carcass quality, meat quality, and tenderness in beef cattle, including calcium-related processes, cell signaling, and modulation of cell–cell adhesion. These results contribute with novel information about the complex genetic architecture and pleiotropic effects of carcass and meat quality traits in crossbred beef cattle.

Multivariate quantitative genetic analysis of body weight traits in Corriedale sheep.

In the present study, an attempt was made to elucidate the genetic parameters for body weight traits of lambs from Corriedale sheep population at different ages. Data were collected from 6874 lambs born over a span of 49 years from 1969 to 2017. The traits under study included body weight atbirth (BW), weaning (WW), 6 months of age (6MW), 9 months of age (9MW) and yearling stage (YW). Data were statistically analyzed using restricted maximum likelihood (REML) algorithm in WOMBAT program. A multi-variate animal model was fitted to the data incorporating season andperiod of lambing, sex of lamb and litter size as fixed effects. Variance and covariance components were estimated using the animal model after incorporating direct additive genetic effect of animal as random factor. Genetic and phenotypic correlations with corresponding standard errors were also estimated. The heritability estimates for BW, WW, 6MW, 9MW and YW were 0.130 ± 0.023, 0.300 ± 0.029, 0.292 ± 0.030, 0.191 ± 0.025 and 0.169 ± 0.024, respectively. The genetic correlation between different traits under study was high, except between BW and 9MW for which the estimate was moderate. Phenotypic correlation ranged from low to high for different trait combinations. Among different traits under study, only two traits showed moderate heritability i.e. WW and 6MW while heritability of other traits was low. Both these traits showed high correlation with all subsequent traits. Selection programme for Corriedale sheep should be based on WW which is expressed early in life and shall lead to moderate geneticresponseto selection.

Estimation of (Co)Variance components and genetic parameters of fibre traits in Rambouillet sheep using multi-trait analysis.

The present study aimed to estimate the genetic parameters of different fibre traits, viz., greasy fleece weight, staple length, and fibre diameter in Rambouillet sheep population using a multi-trait animal model. Data, spanning over 10 years (1998-2007) and pertaining to fibre traits at first clip, were collected for a total of 4186 Rambouillet sheep maintained at an organized farm. (Co)Variance structure and genetic parameters were estimated using a multi-trait animal model. The genetic analysis of data was performed based on restricted maximum likelihood (REML) procedure using WOMBAT software. The model incorporated sex of lamb (i = 1, 2), year of birth (j = 1-10), season of birth (k = 1-2), and litter size (l = 1-2) as fixed effects while direct additive genetic and maternal genetic effects were included as random effects. The direct additive genetic heritability estimates were 0.120±0.034, 0.136±0.037, and 0.356±0.070 for greasy fleece weight, staple length, and fibre diameter, respectively. The maternal genetic heritability of all fibre traits under study was very low. Additive genetic correlation was positive and low between greasy fleece weight and staple length; and between staple length and fibre diameter. In conclusion, fibre diameter was moderately heritable which implies that selection may lead to moderate improvement in this trait. The results from the present study will help in formulating optimal breeding plans for improvement of fibre traits in Rambouillet sheep.

Evaluation of animal models to explore the influence of maternal genetic and maternal permanent environment effect on reproductive performance of Jersey crossbred cattle.

The present study was conducted on 1,002 reproductive records of 430 Jersey crossbred cattle, descended from 57 sires and 198 dams, maintained at the Eastern Regional Station of ICAR-National Dairy Research Institute, Kalyani, Nadia, West Bengal, India to investigate the influence of direct genetic, maternal genetic and maternal permanent environmental effect on three most important reproductive traits viz., number of service per conception (NSPC), days open (DO) and calving interval (CI) of Jersey crossbred cattle. Six single-trait animal models (including or excluding maternal genetic or permanent environmental effects) were fitted to analyse these traits, and the best model was chosen after testing the significant increase in the log-likelihood values when additional parameters were added in the model. Direct heritability estimates for NSPC, DO and CI from the best model were 0.10, 0.14 and 0.20, respectively. The maternal permanent environmental (c2 ) effects on reproductive traits accounted for almost negligible fraction of the total phenotypic variance in this study. The maternal genetic effects (m2 ) also contributed very little (0%-3%) to the total phenotypic variance except for CI where it was important and accounted for 20% of phenotypic variance. A significantly large negative genetic correlation was observed between direct and maternal genetic effects for all traits, suggesting the presence of antagonistic relationship between dam's direct additive component and daughter's additive genetic component. Results suggest that both direct and maternal effects were important only for CI but not for other traits. Therefore, both direct additive effects and maternal genetic effect need to be considered for improving this trait by selection.

Contribution of social genetic effects in variance components estimation for body weight in Nigerian indigenous chickens raised in a tropical humid location.

Social interactions among chickens can have a great unfavourable effect on economic returns in a poultry farm. The purpose of this study was to use four models to examine the influence of social genetic influences on the variation in body weight of Nigerian indigenous chickens. Sex was treated as the fixed effect within the models. Direct additive genetic, social genetic, and family effects and covariance between direct and social genetic effects were used as random effects. Data were analysed using single-trait animal models which include or exclude social genetic effects. Model comparison revealed that inclusion of full-sib family effect in model 3 did not cause any change in residual and additive genetic variances relative to estimates obtained with model 2. In general, social genetic variance was lower than the estimate for additive genetic variance, but substantially added to the overall heritable variance. For direct hereditary, full-sib family, and residual effects, accounting for heritable social effect in model 4 had a marginal effect on the size of the variances measured. All the estimated residual, additive genetic, social genetic effect, and family variances increased in comparison with model 3. The relationship between direct and social additive effects was positive and not significantly different from 0 (P > 0.05), suggesting autonomy between the direct and social breeding values. In conclusion, the use of models that account for direct effect and social genetic effect of the individual on its group members would entail an optimal individual selection scheme to increase the body weight of chickens.

Genetic parameters for performance, feed efficiency, and carcass traits in Senepol heifers

Improving feed efficiency is a key breeding goal in the beef cattle industry. In this study, we estimated the genetic parameters for feed efficiency and carcass traits in Senepol cattle raised in tropical regions. Various indicators of feed efficiency [gain to feed ratio (G:F), feed conversion ratio (FCR), residual weight gain (RG), residual intake and body weight gain (RIG), and residual feed intake (RFI)] as well as growth [final BW, average daily gain (ADG), and DM intake (DMI)], and carcass [rib-eye area (REA), backfat thickness (BF), intramuscular fat score, and carcass conformation score] traits were included in the study. After data editing, records from 1 393 heifers obtained between 2009 and 2018 were used for the analyses. We fitted an animal model that included contemporary group (animals from the same farm that were evaluated in the same test season) as the fixed effect, and a linear effect of animal age at the beginning of the test as a covariate; in addition to random direct additive genetic and residual effects. The (co)variance components were estimated by Bayesian inference in uni- and bivariate analyses. Our results showed that feed efficiency indicators derived from residual variables such as RG, RIG, and RFI can be improved through genetic selection (h2 = 0.14 ± 0.06, 0.13 ± 0.06, and 0.20 ± 0.08, respectively). Variables calculated as ratios such as G:F and FCR were more influenced by environmental factors (h2 = 0.08 ± 0.05 and 0.09 ± 0.05), and were, therefore, less suitable for use in breeding programs. The traits with the greatest and impact on genetic progress in feed efficiency were ADG, REA, and BF. The traits with the greatest and least impact on growth and carcass traits were RG and RFI, respectively. Selection for feed efficiency will result in distinct overall effects on the growth and carcass traits of Senepol heifers. Direct selection for lower RFI may reduce DMI and increase carcass fatness at the finishing stage, but it might also result in reduced growth and muscle deposition. Residual BW gain is associated with the highest weight gain and zero impact on REA and BF, however, it is linked to higher feed consumption. Thus, the most suitable feed efficiency indicator was RIG, as it promoted the greatest decrease in feed intake concomitant with faster growth, with a similar impact on carcass traits when compared to the other feed efficiency indicators.

Competition effects in breeding value prediction of forest trees

Competition is a concern for tree breeding because of its potential to reduce the genetic gain. Competition, if not accounted for in the analytical model, can potentially introduce a source of bias in genetic parameter estimation and breeding value prediction. This study modelled competition between trees in 20 Swedish progeny trials of Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and lodgepole pine (Pinus contorta Douglas ex Loudon). The competition model assumed a tree has a direct additive genetic effect, which affects the tree’s own phenotype, and an indirect additive effect, which affects the phenotypes of its neighbours. Genetic parameters were estimated via a factor analytic structure in which separate indirect effects were considered for each neighbour, or via a combined indirect effect approach. We analysed diameter, as it is the trait that can be expected to be affected most by competition. Competition at the genetic level was detected in 17 of the 20 trials analysed. In most cases, the ratio of indirect to direct additive variance was less than 20% and no major changes in ranking resulted. At this stage, there is little incentive to incorporate indirect effects into program-wide genetic evaluation models. The added complexity is not commensurate with the benefit that would be gained.

Maternal effect on body measurement and meat production traits in purebred Duroc pigs.

We investigated maternal effect on nine body measurement traits (body height, body length, front width (FW), chest width (CW), hind width (HW), chest depth, chest girth (CHG), front cannon circumference (FCC) and rear cannon circumference (RCC)) measured at the end of performance testing and five meat production traits (ages at the start and end of performance testing (D30 and D105), average daily gain (ADG), backfat thickness and loin muscle area) in purebred Duroc pigs. Genetic parameters for each trait were estimated by using six single-trait models with and without common litter environmental effect, maternal genetic effect and direct-maternal genetic correlation. The value of Akaike's information criterion was lowest with the model including direct additive genetic and common litter environmental effects for 10 traits. The estimated proportion of common litter environmental variance to phenotypic variance was approximately ≥0.1 for D30, D105, ADG, FW, CW, HW, CHG, FCC and RCC. Using a model without common litter environmental effect would overestimate the direct heritability of most traits. Standard errors of estimated genetic parameters tended to be larger in models including maternal genetic effect. The results indicate that a compromise could be made for accurate genetic parameter estimation for body measurement traits, as well as meat production traits, in pigs by considering common litter environmental effect.

Genetic Evaluation for Sexual Maturity and Egg Production Traits in Crossbreeding Experiment Involving Four Local Strains of Chickens

A cross experiment was carried out in Animal Production Research Institute (APRI), in cooperation with Benha University, Egypt for three years starting from February 2013 and terminated 2016. Four pedigreed local strains of chickens Matrouh (MT), Mandarah (MN), Inshas (IN) and Silver Montazah (SM) strains were used. A total of 34 sires and 230 dams from MN strain, 32 sires and 194 dams from MT strain were chosen randomly from 250 cockers and 600 pullets to produce purebreds and crossbreds progenies in the first generation. In the second generation, the crossbred hens of MNxMT were artificially inseminated with fresh semen of Inshas strain (IN), while the crossbred hens of MTxMN were artificially inseminated with fresh semen collected from cocks of Silver Montazah strain (SM) to produce three-way crossbreds (½IN×¼MN¼MT and ½SM×¼MT¼MN). Single trait animal model was used in estimating heritability and in predicting the breeding values (PBV). Crossbreeding effects of direct additive (GI), maternal effects (GM), direct heterosis (HI) and maternal heterosis (HI) were estimated using the procedure of generalized least-squares. The overall means of all genetic groups were 154 day, 1420 g, 39.38 g, 45 egg, 1957 g, 61 egg, 2727 g, 16 day, 411 g, 18 egg, 784 g, 13.5 egg and 593 g for ASM, BWSM, WFE, EN90D, EM90D, EN120D, EM120D, PF10E, EMF10E, EN2DW, EM2DW, EN1WM and EM1WM, respectively Estimates of heritability were moderate for ASM and BWSM (0.23 and 0.69), while they were low for egg production and partial egg recording traits. The GLM showed that three-way crossbreds reported the earlier ASM, heavier BWSM and WFE, the highest EN90D, EN120D and EN2DW and the heaviest EM90D, EM120D and EM2DW. The ranges of predicted breeding values (PBV) of MT strain were slightly higher than that for MN birds. Ranges of PBV recorded by ½MT½MN were nearly similar to those ranges recorded by ½MN½MT. Cross fathered by SM cocks and mothered by (½MT½MN) had higher ranges in PBV for egg production and partial egg recording traits than those cross fathered by IN cocks and mothered by (½MN½MT). The effects of GI on all traits (p≤0.01) and in favour of MN breed. The percentages of GM were significant for sexual maturity traits and non-significant for egg production and partial egg recording traits. Percentages of HI (-3.8, 28.5, -4.6, 29.3, 28.8, 24.9, 19.7, -36.1, -3.2, 17.4, 10.6 and 8.8%) and HM (-2.6, 1.2, 0.03, 7.8, 8.2, 7.8, 8.1, -10.5, 0.2, 7.2, 0.7, 3.2 and 3.3%) were mostly highly significant for all traits for ASM, BWSM, EN90D, EM90D, EN120D, EM120D, PF10E, EMF10E, EN2DW, EM2DW, EN1WM and EM1WM, respectively. We can recommend that Mandarah strain (MN) could be used as a sire and Matrouh (MT) as a dam, depending on the estimates of the direct additive genetic effect GI for the studied traits which were in favor of MN.

Evaluation of animal models for genetic analysis of growth performance in Landlly pigs

Selection of the most appropriate animal model for the estimation of genetic parameters for body weight was carried out using restricted maximum likelihood (REML) procedure at birth and thereafter at 3, 6, and 8 weeks of age in Landlly pigs. Six different models were fitted for each trait; by inclusion or exclusion of maternal additive genetic effect, maternal permanent environmental effect, and covariance between direct and maternal additive genetic effects. Records on 1968 piglets, born in 4 parities of 131 gilts/sows, sired by 68 boars during a period of 5 years from 2014 to 2018 were used. In order to determine the most appropriate model, Log likelihood values, log the likelihood ratio test and Akaike's information criterion were used. A model including direct additive genetic and maternal permanent environmental effects fitted best to data for birth weight. The best model explaining W3, W6, and W8 included direct additive genetic, maternal genetic and maternal permanent environmental effect with direct and maternal genetic covariance. Total heritability estimates for the body weights were low to moderate across best models.

Using random regression models to estimate genetic variation in growth pattern and its association with sexual maturity of Thai native chickens

ABSTRACT 1. Genetic (co)variances and parameters between body weights (BW) across the growth trajectory were estimated using a univariate random regression (RR) animal model. The effect of growth rates (GH) on age at first egg (AFE) and egg weight at first egg (EWFE) were explored using a series of univariate and bivariate analyses. 2. Body weights were taken from Thai native chickens at hatch day to 168 days of age. The model included interactions between age with hatch nested within year and sex as fixed effects, and random effects of direct additive genetic, direct permanent environmental, maternal genetic and maternal permanent environmental effects. All random effects were fitted as regressions to animals’ age via quadratic Legendre polynomials and fitting six classes of residual variances was identified as an optimal variance structure to estimate parameters. 3. Genetic and phenotypic variances for BW increased with increasing age. Estimated heritabilities for direct additive (h2 a) and maternal genetic (h2 m) effects on BW traits ranged from 0.34 to 0.54, and 0.04 to 0.06, respectively. Estimated variance ratios for direct (c2 ape) and maternal permanent environmental (c2 mpe) effects ranged from 0.19 to 0.48 and 0.10 to 0.12, respectively. Estimated correlations between weights at different ages were high for all random effects. 4. Estimated h2 a for six GH traits ranged from 0.06 to 0.28, while for AFE and EWFE these were 0.24 and 0.16, respectively. Estimated h2 m and c2 mpe were low for GH. Estimated genetic correlations between GH and AFE ranged from −0.22 to 0.02 and, between GH and EWFE, ranged from −0.05 to 0.40. These estimates suggested that selecting high GH chickens at 28 days of age can be expected to reduce AFE and to increase EWFE.

Estimation of genetic parameters for growth traits and Kleiber ratios in Boer x Central Highland goat.

Accurate performance evaluation and genetic parameters estimation are the prerequisites for any successful genetic improvement program. This study was conducted to estimate genetic parameters for growth and Kleiber ratio traits in Boer x Central Highland goats. On-station data collected from 2009 to 2018 were utilized for the study. A general linear model procedure of the Statistical Analysis System (SAS, version 9.0) was used to analyze fixed effects, and genetic parameters were estimated using the WOMBAT software fitted animal model. The log-likelihood ratio test was used for selecting the best fitted model. Based on best fitted models, the total heritability (h2t) estimate for birth weight (BWT), weaning weight (WWT), six-month weight (SMWT), nine-month weight (NMWT), and yearling weight (YWT) were 0.38, 0.12, 0.05, 0.30, and 0.28, respectively. The total heritability (h2t) estimates for weight gain from birth to weaning (ADG1), 3 to 6months (ADG2), 6 to 9months (ADG3), and 9 to 12months of age (ADG4) were 0.09, 0.08, 0.16, and 0.14, respectively. The heritability estimates for Kleiber ratios in different growth phases were found to be low (0.09 to 0.18) based on the selected models. Even with this figure, including the Kleiber ratio in the selection criteria would be imperative to improve the feed efficiency of crossbred goats. The direct genetic correlation estimates among growth traits range from 0.60 ± 0.14 to 0.97 ± 0.12. Except for NMWT, ADG4, and Kleiber ratio from 9months to yearling age, the maternal effect had a significant influence on all considered traits. However, the contribution of the maternal genetic effect was more important for early growth traits. Thus, considering both the direct additive genetic effect and the maternal genetic effect is imperative for accurate genetic evaluation and for high selection response. The moderate heritability estimates for most of the growth traits implies the possibility of selection in conjunction with crossbreeding for a better genetic response. The positive and high genetic correlation estimates among growth traits confirm the possibility of a selection of goats at an early age.

Variation in autosomal and sex-linked genetic effects for growth traits in Markhoz goat using multivariate animal models.

The present study was conducted to estimate autosomal and sex-linked genetic parameters by restricted maximum likelihood method using four different multivariate models for growth traits in Markhoz goat. Data were collected over a period of 23years (1992-2014) from the breeding station of Markhoz goat. The studied growth traits were birth weight (BW), weaning weight (WW), 6-month weight (6WT), 9-month weight (9WT), and 12-month weight (12WT). The best model was determined by Akaike's information criterion. Based on the best model, direct autosomal heritabilities of 0.18, 0.10, 0.12, 0.22, and 0.24 were obtained for BW, WW, 6WT, 9WT, and 12WT, respectively. On the other hand, estimates of direct sex-linked heritability for BW, WW, 6WT, 9WT, and 12WT were 0.02, 0.01, 0.002, 0.03, and 0.04, respectively. The maternal permanent environmental component was remarkable for growth traits. Direct autosomal additive genetic correlations among the traits were positive and varied from 0.11 between BW and 9WT to 0.95 between BW and WW. The positive correlations were also estimated for direct sex-linked additive genetic effect except between BW-6WT (- 0.07) and WW-6WT (-0.19). The result of this study indicated that sex-linked chromosome effect had more considerable influence at post-weaning traits.

Crossbreeding analyses and polymorphic associations of gallinacin genes with growth traits in chickens

A simple crossbreeding experiment between Fayoumi (F) and Rhode Island Red (R) and their F1 of ½R½F and ½F½R crosses was conducted. A total number of 480 chicks produced from four genetic groups was used to estimate direct additive genetic effects (GI), maternal effects (GM) and direct heterosis (HI) for growth traits by using generalized least squares procedure. The studied traits were body weights at hatch, 2, 4, 6, 8 and 10 weeks of age and daily gains during the intervals of 0-2, 2-4, 4-6, 6-8 and 8-10 weeks of age. Candidate gallinacin genes of GAL 2, GAL 3, GAL 4 and GAL 5 were genotyped using PCR-RFLP, associating the SNP with body weights and gains.Direct additive effects were mostly significantly (P≤0.01) in favour of R breed by 7.4 to 57.9 g for body weights and by 0.8 to 1.8 g for daily gains. The estimates of maternal effect were mostly significantly (P˂0.01) in favour of R breed and ranging from 0.8 to 25.1 g for body weights and 0.5 to 2.3 g for daily gains. All the estimates for direct heterosis were positive and significant (P˂0.01) and ranged from 0.15 to 35.2 g for body weights and 0.3 to 1.5 g for daily gains.The GAL 2 gene was one homozygous genotype in the four genetic groups, while in GAL 3, GAL 4 and GAL 5 genes only one homozygous genotype in Fayoumi breed was observed. The genotypes of Gal 3 gene had significant associations with most body weights and gains (p<0.05) in R, ½R½F and ½F½R genetic groups. The genotypes of GAL 4 and GAL 5 genes were associated significantly with most body weights and daily gains during the intervals of 0-2 and 2-4 weeks of age in½R½F and ½F½R genetic groups. In practice, the molecular associations obtained for GAL 3, GAL 4 and GAL 5 genes could be used in marker assisted selection programs to improve growth traits in chickens.

Random regression models for the evaluation of the growth of goats of the Anglonubian breed

ABSTRACT A total of 6593 weight records collected from 796 male and female Anglo-Nubian goats aged up to 130 days, offspring from 29 sires and 225 dams, were used to compare models and estimate genetic parameters throughout the growth curve by applying random regression models. Direct and maternal additive genetic effects and direct and maternal permanent environmental effects were included as random in the models. The contemporary groups were included as fixed effects and goat age at kidding was included as a covariable (linear and quadratic). The choice of the best model was based on the AIC, BIC and AICc criteria. Variance estimates of the four random effects increased as the animals aged. Direct heritability (h2) rose from 0.13 to 0.40 with age, whereas maternal heritability showed a low value. Genetic correlations of weight between closer ages were high. The most suitable random regression model to compare the fitting of random effects was that which employed the Legendre polynomials of quadratic order with homogeneous variance (3333-1).

Autosomal and sex-linked (co)variance components and genetic parameters for growth traits of Iranian Zandi sheep.

Separation of autosomal and sex-linked direct additive genetic effects has significant role in sheep breeding programs. Hence, this study was conducted to determine the genetic parameters of autosomal and sex-linked effects for growth traits of Zandi sheep. The data set used in this study contained 7571 Zandi lambs, descendent of 220 sires and 1481 dams, which were collected from Zandi sheep breeding Station at Khojir, Tehran, Iran from 1992 to 2011. The fixed effects included of year (20 classes), season (winter and spring), sex (male or female), birth type (single or twin), and the age of dam (seven classes, 2-8years old). The data were analyzed using REML methodology by WOMBAT software. In the most appropriate fitted model, based on Akaike's information criterion (AIC) and Bayesian information criterion (BIC), the values of direct autosomal heritabilities of birth weight (BW), kleiber ratio at weaning (KR), 6-month weight (6MW), and 9-month weight (9MW) were 0.12 ± 0.03, 0.29 ± 0.05, 0.14 ± 0.04, and 0.15 ± 0.04, respectively. Furthermore, weaning weight (WW), average daily gain from birth to weaning (ADG), and 12-month weight (12MW) showed the values of 0.19 ± 0.03 and 0.22 ± 0.03, 0.13 ± 0.05 and 0.15 ± 0.03, and 0.15 ± 0.05 and 0.18 ± 0.05, respectively. Based on the best models through all traits, estimates of the direct sex-linked heritability ranged from 0.0 (WW, ADG, KR, and 6MW) to 0.02 ± 0.03 (12MW). The average of autosomal and sex-linked breeding values (BVs) of body growth traits except KR (for autosomal) and 9MW and 12MW (for sex-linked) were greater than zero. The Pearson's/Spearman's correlation coefficients varied between 0.344 and 0.599/0.30 and 0.61 for autosomal and sex-linked BVs. Direct autosomal and sex-linked additive correlations for growth traits were ranged from - 0.02 (BW-KR) to 0.98 (WW-ADG) and 0.04 (KR-9MW) to 0.99 (WW-ADG), respectively. Our results revealed that the genetic parameters related to growth traits in Zandi sheep could be more useful in selection strategies.

Genetic analyses of live weight and carcass composition traits in purebred Texel, Suffolk and Charollais lambs

Lamb live weight is one of the key drivers of profitability on sheep farms. Previous studies in Ireland have estimated genetic parameters for live weight and carcass composition traits using a multi-breed population rather than on an individual breed basis. The objective of the present study was to undertake genetic analyses of three lamb live weight and two carcass composition traits pertaining to purebred Texel, Suffolk and Charollais lambs born in the Republic of Ireland between 2010 and 2017, inclusive. Traits (with lamb age range in parenthesis) considered in the analyses were: pre-weaning weight (20 to 65 days), weaning weight (66 to 120 days), post-weaning weight (121 to 180 days), muscle depth (121 to 180 days) and fat depth (121 to 180 days). After data edits, 137 402 records from 50 372 lambs across 416 flocks were analysed. Variance components were derived using animal linear mixed models separately for each breed. Fixed effects included for all traits were contemporary group, age at first lambing of the dam, parity of the dam, a gender by age of the lamb interaction and a birth type by rearing type of the lamb interaction. Random effects investigated in the pre-weaning and weaning weight analyses included animal direct additive genetic, dam maternal genetic, litter common environment, dam permanent environment and residual variances. The model of analysis for post-weaning, muscle and fat depth included an animal direct additive genetic and litter common environment effect only. Significant direct additive genetic variation existed in all cases. Direct heritability for pre-weaning weight ranged from 0.14 to 0.30 across the three breeds. Weaning weight had a direct heritability ranging from 0.17 to 0.27 and post-weaning weight had a direct heritability ranging from 0.15 to 0.27. Muscle and fat depth heritability estimates ranged from 0.21 to 0.31 and 0.15 to 0.20, respectively. Positive direct correlations were evident for all traits. Results revealed ample genetic variation among animals for the studied traits and significant differences between breeds to suggest that genetic evaluations could be conducted on a per-breed basis.

Impact of inbreeding on milk fatty acids of a Brazilian Holstein cattle

Context Reproductive technologies may either contribute to the increase of genetic gains or inbreeding levels in dairy cattle breeding programs and herds. In general, studies have evaluated the impacts of inbreeding on traditional traits, such as production and reproduction. However, studies on novel traits, such as milk fatty acids profile, are scarce in the literature. Aim We aimed to evaluate the impact of inbreeding levels on milk fatty acids profile measured in a Brazilian Holstein cattle population. Methods Monthly records of the percentages (%) of palmitic, stearic, oleic, total saturated, unsaturated, monounsaturated and polyunsaturated fatty acids in milk were collected from 2047 Holstein cows between May and December 2012. The pedigree file contained 7963 animals over seven generations. The inbreeding trend was evaluated by linear regression of inbreeding coefficients on generations. The inbreeding impacts on breeding and phenotypic values were evaluated by linear regression of breeding values and phenotypic values on generations respectively. Breeding values were obtained by a Bayesian approach based on an animal model that included the systematic effect of contemporary group, cubic effect of days in milk as a covariate, and the random direct additive genetic and animal permanent environmental effects. Key results The average inbreeding coefficient was 0.28% for all animals, and 1.39% for inbred animals. Inbreeding tended to increase 0.24% per generation (P-value &amp;lt;0.0001). The regression coefficients of phenotypic values on inbreeding were not significant for saturated, unsaturated, monounsaturated, palmitic, stearic and oleic fatty acids (P-values &amp;gt;0.18, 0.10, 0.16, 0.26, 0.51 and 0.09 respectively); whereas for polyunsaturated fatty acids, they were significant (P-value &amp;lt;0.04), with an increase of –0.000978% on phenotypic values for each 1% increase in inbreeding. The regression coefficients of breeding values on inbreeding were not significant for unsaturated, monounsaturated, polyunsaturated, stearic and oleic fatty acids (P-values &amp;gt;0.33, 0.78, 0.48, 0.32 and 0.07 respectively). However, they were significant for saturated and palmitic fatty acids (P-values &amp;lt;0.03 and 0.0001 respectively), presenting an increase of 0.000689% and 0.000283% respectively on breeding values for each 1% increase in inbreeding. Conclusions There was a significant increase in inbreeding coefficients over the studied generations; however, the impacts on both breeding and phenotypic values were small, when significant. Implications Our study may contribute to the understanding of how inbreeding levels may affect the fatty acids profile in a Brazilian Holstein cattle population, as well as encourage future research on this subject.