Direct Heritability Estimates Research Articles

Genetic parameters for direct and maternal effects on growth traits of sheep

Abstract. The aim of the present study was to estimate (co)variance components and corresponding genetic parameters for birth weight (BW), weaning weight (WW), 6-month weight (W6), 9-month weight (W9), average daily gain from birth to weaning (WWDG), average daily gain from weaning to 6 months (W6DG) and average daily gain from 6 months to 9 months (W9DG) for a nucleus flock of Iranian Makooei sheep. Genetic parameters were estimated by REML procedure fitting six animal models including various combinations of maternal effects. The Akaike information criterion (AIC) was used to determine the most appropriate model. Estimates of direct heritability (h2) ranged from 0.13 (W6DG) to 0.32 (BW). Maternal effects were found to be important in the growth performance of the Makooei sheep, indicating the necessity of including maternal effects in the model to obtain accurate estimates of direct heritability. Estimates of maternal heritability (m2) ranged from 0.05 (W6) to 0.16 (WWDG) and the estimates of proportion of maternal permanent environmental variance to phenotypic variance (c2) were in the range between 0.05 (BW) and 0.10 (W6). Direct additive genetic correlations were positive in all cases and ranged from 0.00 (BW/W9DG) to 0.99 (WW/WWDG). Phenotypic correlations showed a broad range from −0.27 (WW/W9DG) to 0.99 (WW/WWDG). Estimates of genetic parameters showed that genetic improvement through selection programs is possible. WW would be a suitable selection criterion since it has acceptable direct heritability and relatively high genetic correlation with other traits.

Genetic evaluation of growth traits in beef cattle using random regression models

Direct- and maternal heritabilities were estimated for weight traits in Brangus cattle using random regression models. After editing, 54 924 records, from birth- (BW) to mature weight (MW) from 21 673 animals were selected for analysis. The data, which covered a period of 8 generations (1985 to 2010), were transformed to a log scale to accommodate the wide range of weights  being studied (15 to 850 kg). Traits included in the analysis were birth- (BW), weaning- (WW), yearling- (YW), eighteen month- (FW) and three measurements of mature weight (MW). Linear polynomials with intercepts were fitted using random regression models. The direct heritability estimates were moderate and ranged from 0.13 to 0.25 while maternal heritability estimates were low ranging from 0.05 to 0.06.Keywords: Heritability estimates, South African Brangus cattle

Estimation of genetic parameters for growth traits in Brangus cattle

A combination of multiple trait and repeatability models were used to estimate genetic parameters for birth weight (BW), weaning weight (WW), yearling weight (YW), eighteen month weight (FW) and three measurements of mature weight (MW) using 23 768 records obtained from the South African Brangus Cattle Breed Society. The data covered a period of 7 generations from 1985 to 2010. Direct heritability estimates obtained were 0.21 ± 0.024, 0.23 ± 0.021, 0.22 ± 0.025, 0.29 ± 0.029 and 0.24 ± 0.019 for BW, WW, YW, FW and MW, respectively. Maternal heritability estimates for birth weight and weaning weight were 0.05 ± 0.01 and 0.11 ± 0.001, respectively. The direct genetic correlations between the different traits were all positive, ranging from moderate (0.43 ± 0.081) between YW and MW to high (0.99 ± 0.043) between WW and FW.

The estimation of (co)variance components and genetic parameters for growth traits and Kleiber ratios in Malpura sheep of India

Objective of the present study was to estimate the genetic parameters and (co)variance components for different economic traits in Malpura sheep. The traits analyzed were birth weight (BWT), weaning weight (WWT), 6-month weight (6WT), average daily gain from birth to weaning (ADG1), average daily gain from weaning to 6-month (ADG2), average daily gain from birth to 6-month (ADG3), Kleiber ratio from birth to weaning (KR1), Kleiber ratio from weaning to 6-month (KR2) and Kleiber ratio from birth to 6-month (KR3). Six different animal models including or ignoring maternal genetic or permanent environmental effects were fitted for all traits. Akaike information criterion (AIC) was applied to determine the most appropriate model for each trait. For BWT, WWT, 6WT, ADG1, ADG2 and KR2 the model including permanent environmental effects due to ewe over direct genetic effects was the most appropriate. Model which included only direct genetic effects was the best model for ADG3, KR1 and KR3. Direct heritability estimates of 0.21, 0.24, 0.23, 0.23, 0.13, 0.22, 0.20, 0.12 and 0.23 were obtained for BW, WW, 6MW, ADG1, ADG2, ADG3, KR1, KR2 and KR3, respectively. Ratios of phenotypic variance due to maternal permanent environmental effects were 0.24, 0.07, 0.01, and 0.05 for BW, WWT, 6WT and ADG1, respectively. Estimates of direct genetic correlation were very low to high in magnitude and varied from −0.27 for BW–KR2 to 0.97 for ADG1–KR1. Estimates of phenotypic correlation were very low to high in magnitude and varied from −0.27 for WW–KR2 to 0.96 for ADG3–KR3. The moderate estimate of direct heritability for body weight, growth rate and Kleiber ratio suggests that Malpura sheep can be improved through selection for economic mutton production.

Abordagem bayesiana multivariada para características de crescimento, fertilidade e escores visuais de rebanhos da raça Brangus

O objetivo deste trabalho foi estimar parâmetros genéticos e tendências genéticas e fenotípicas de uma população da raça Brangus. As características peso, circunferência escrotal e escores visuais de conformação, precocidade, musculatura e umbigo, padronizadas para 550 dias de idade, foram avaliadas a partir de 6.789 registros de animais nascidos de 288 touros e 5.949 vacas, entre 1991 e 2001, em 49 fazendas localizadas nas regiões Centro‑Oeste, Sudeste e Sul do Brasil. Para a estimação dos parâmetros, das correlações e das tendências genéticas, foi adotado o modelo animal linear‑limiar hexacaracterística. As estimativas de herdabilidade direta foram de 0,39 e 0,27, para peso e circunferência escrotal, respectivamente, e de 0,22, 0,20, 0,23 e 0,33 para conformação, precocidade, musculatura e umbigo, o que indica considerável variação genética aditiva e que é possível obter ganho genético por meio da seleção. As correlações genéticas entre peso e circunferência escrotal com os escores de conformação, precocidade e musculatura mostram a possibilidade de resposta correlacionada. As tendências genéticas estimadas indicam grande contribuição de fontes de variação não genéticas para todas as características no período estudado, e apontam a necessidade de melhoria das condições ambientais, para que os animais expressem todo seu potencial genético.

Genetic associations between flight speed and growth traits in Nellore cattle1

The aim of the present study was to estimate genetic parameters for flight speed and its association with growth traits in Nellore beef cattle. The flight speed (FS) of 7,402 yearling animals was measured, using a device composed of a pair of photoelectric cells. Time interval data (s) were converted to speed (m/s) and faster animals were regarded as more reactive. The growth traits analyzed were weaning weight (WW), ADG from weaning to yearling age, and yearling scrotal circumference (SC). The (co)variance components were estimated using REML in a multitrait analysis applying an animal model. The model included random direct additive genetic and residual effects, fixed effects of contemporary groups, age of dam (classes), and age of animal as covariable. For WW, the model also included maternal genetic and permanent environmental random effects. The direct heritability estimate for FS was 0.26 ± 0.05 and direct heritability estimates for WW, SC, and ADG were 0.30 ± 0.01, 0.48 ± 0.02, and 0.19 ± 0.01, respectively. Estimates of the genetic correlation between FS and the growth traits were -0.12 ± 0.07 (WW), -0.13 ± 0.08 (ADG), and -0.11 ± 0.07 (SC). Although the values were low, these correlations showed that animals with better temperaments (slower FS) tended to present better performance. It is possible to infer that longterm selection for weight and scrotal circumference can promote a positive genetic response in the temperament of animals. Nevertheless, to obtain faster genetic progress in temperament, it would be necessary to perform direct selection for such trait. Flight speed is an easily measured indicator of temperament and can be included as a selection criterion in breeding programs for Nellore cattle.

Genotype by region and season interactions on weaning weight in United States Angus cattle1

The objective of this study was to determine if weaning weight performance is genetically consistent across different environments in the United States. The American Angus Association provided weight and pedigree data. Weaning weights observed in the Southeast (SoE) and Northwest (NW) were the focus of this study, as these regions are perceived as opposite extremes in climate. The 2 most represented calving seasons in each region were fall and winter in the SoE and winter and spring in the NW. The original data were edited to remove weaning weight records outside of 3 SD from the respective region-season mean, contemporary groups smaller than 20, and single-sire contemporary groups. The final dataset included 884,465 weaning weight records with 64,907 from fall-born calves in the SoE, 74,820 from winter-born calves in the SoE, 346,724 from winter-born calves in the NW and 398,014 from spring-born calves in the NW. Weaning weights of calves born in different region-season classes adjusted to 205 d of age were considered different but genetically correlated traits in a multivariate analysis. The sole fixed effect was weaning contemporary group and random effects included direct, maternal, maternal permanent environment, and a residual. Direct heritability estimates differed little across environments: 0.31 and 0.35 for weight in fall- and winter-born calves in the SoE, and 0.29 and 0.32 for winter- and spring-born calves in NW. Maternal heritability estimates ranged from 0.12 in the NW to 0.16 the SoE. Genetic correlations spanned from 0.69 to 0.93 among direct effects and from 0.65 to 0.95 among maternal effects. All heritability estimates had small (0.01 to 0.04) SE. The most distinct environments appeared to be winter in SoE and spring in NW (correlations of 0.69 and 0.65 for the direct and maternal effects). Different choices of sires for different environments might be justified to achieve the growth performance expected.

Genetic analysis of ewe productivity traits in Makooei sheep

This study reports genetic and environmental (co)variance components for productivity traits of Makooei sheep, using between 2647 and 3418 records obtained from 1429 ewes. Data were collected during 1996–2009 on the Breeding Station of Makooei sheep, located in Makoo in the west-Azerbaijan province of Iran. Genetic parameters were estimated for three basic and six composite traits. The basic traits were conception rate (CR), number of lambs born (NLB) and number of lambs alive at weaning (NLAW). The composite traits were number of lambs born per ewe exposed (NLBEE), number of lambs weaned per ewe exposed (NLWEE), total litter weight at birth per ewe lambed (TLBW), total litter weight at weaning per ewe lambed (TLWW), total litter weight at birth per ewe exposed (TLBWEE) and total litter weight at weaning per ewe exposed (TLWWEE). Genetic parameters were estimated with univariate and bivariate models using restricted maximum likelihood (REML) procedures. Random effects were explored by fitting additive direct genetic effects, permanent environmental effects due to the animal as well as service sire effects in different models for ewe productivity. The most appropriate model for each trait was determined based on likelihood ratio tests and Akaike's Information Criterion (AIC). Direct heritability estimates for CR, NLB, NLAW, NLBEE, NLWEE, TLBW, TLWW, TLBWEE and TLWWEE were 0.05±0.02, 0.11±0.01, 0.06±0.01, 0.08±0.02, 0.04±0.02, 0.17±0.03, 0.12±0.02, 0.13±0.02 and 0.10±0.02, respectively. The estimate for the permanent environmental variance due to the animal ranged from 0.03±0.02 for CR to 0.12±0.01 for NLAW, whereas service sire effects ranged from 0.02±0.01 for TLWW to 0.05±0.01 for TLBW. Genetic correlation estimates among studied traits ranged from −0.13 for CR with TLWW to 0.97 for NLAW with NLWEE. Phenotypic correlation estimates were generally smaller in magnitude than genetic correlations. Service sire effects were found to be important only for litter weight traits. These estimates of genetic parameters may provide a basis for deriving selection indexes for reproductive traits.

Model comparisons for estimation of genetic parameters of pre-weaning daily weight gains in Muzaffarnagari sheep

Variance components and genetic parameters were obtained for pre-weaning average daily body weight gains of Muzaffarnagari sheep maintained at the Central Institute for Research on Goats, Makhdoom, Mathura, India, over a period of 17 years (1976–1983 and 1996–2004). In this study, the pre-weaning average daily gains (ADG) was considered in six successive 15 day periods starting at birth and up to 90 days (ADG1–6). Records of 2930 lambs descended from 78 rams and 977 ewes were used in the study. Analyses were carried out by restricted maximum likelihood (REML) fitting an animal model and ignoring or including maternal genetic or permanent environmental effects. Six different animal models were fitted for all traits for comparisons of models in this study. The best model was chosen after testing the improvement of the log-likelihood values. Direct heritability estimates were inflated for all traits when maternal effects were ignored. Direct heritabilities estimates ranged from 0.01 to 0.26 for pre-weaning average daily weight gains in this study. The permanent maternal environmental (c2) effects on average daily weight gains during birth to 15 days (ADG1), 15–30 days (ADG2) and 30–45 days (ADG3) accounted for 5–17% of the total phenotypic variance in this breed. The very low to moderate heritability estimates of pre-weaning daily weight gains in this study indicates that only slow genetic progress may be possible for these traits from selection under the prevailing management system. Results suggest that direct and permanent environmental maternal effects were important for this trait; however, maternal additive effects had no impact on this trait.

Genetic parameters and relationships between heifers rebreeding and hip height in Nellore cattle

The objective of this study was to estimate heritability and verify the genetic correlations between heifers subsequent rebreeding with weaning hip height (WHH) and yearling hip height (YHH), using Bayesian inference. The (co)variance components and genetic parameters were estimated using an animal nonlinear (threshold) model for subsequent rebreeding and an animal linear model for WHH and YHH. The animal model included the contemporary group as the systematic effect and direct additive genetic and residual effects as random effects. Genetic maternal and maternal permanent environment effects were also considered in the model for WHH. Covariables considered were: rest period (linear effect), for subsequent rebreeding; animal age at measurement and age of cow at calving (linear and quadratic effects), for WHH and YHH. Direct heritability estimates were 0.14±0.04, 0.45±0.03 and 0.51±0.02 for subsequent rebreeding, WHH and YHH, respectively. For maternal effects, the heritability of WHH and the proportion attributed to the permanent environmental effect were 0.08±0.02 and 0.04, respectively. The posterior means of genetic correlations estimates between subsequent rebreeding with WHH and YHH were -0.16±0.05 and -0.21±0.04, respectively. Selection response for subsequent rebreeding of heifers would be low. Increase in the rate of subsequent rebreeding could be obtained with improvements in the management applied to heifers. The inclusion of hip height in selection indices, especially when measured at yearling, promotes small reduction in the rate of subsequent rebreeding of Nellore heifers.

Multiple Regression Analysis of Reading Performance Data from Twin Pairs with Reading Difficulties and Nontwin Siblings: The Augmented Model

The augmented multiple regression model for the analysis of data from selected twin pairs was extended to facilitate analyses of data from twin pairs and nontwin siblings. Fitting this extended model to data from both selected twin pairs and siblings yields direct estimates of heritability (h2) and the difference between environmental influences shared by members of twin pairs and those of sib or twin-sib pairs (i.e., c2(t) - c2 (s)). When this model was fitted to reading performance data from 293 monozygotic and 436 dizygotic pairs selected for reading difficulties, and 291 of their nontwin siblings, h2 = .48 ± .22, p = .03, and c2 (t) - c2 (s) = .22 ± .12, p = .06. Although the test for differential shared environmental influences is only marginally significant, the results of this analysis suggest that environmental influences on reading performance that are shared by members of twin pairs (.36) may be substantially greater than those for less contemporaneous twin-sibling pairs (.14).

Genetic and environmental influences on faecal nematode egg counts of Jamunapari goats in India

The present study was carried out from 1999 to 2003 to determine the genetic and environmental influences of faecal egg count (FEC), an indicator of host resistance, in adult Jamunapari...

Genetic parameter estimates for growth traits and prolificacy in Raeini Cashmere goats

The main objectives of this study were to estimate genetic and phenotypic parameters for growth traits and prolificacy in the Raeini Cashmere goat. Traits included, birth weight (BWT), weaning weight (WWT), 6-month weight (6WT), 9-month weight (9WT), 12-month weight (12WT), average daily gain from birth to weaning (ADG1), average daily gain from weaning to 6WT (ADG2), average daily gain from 6WT to 12WT (ADG3), survival rate (SR), litter size at birth (LSB) and litter size at weaning (LSW) and total litter weight at birth (LWB). Data were collected over a period of 28 years (1982-2009) at the experimental breeding station of Raeini goat, southeast of Iran. Genetic parameters were estimated with univariate models using restricted maximum likelihood (REML) procedures. In addition to an animal model, sire and threshold models, using a logit link function, were used for analyses of SR. Age of dam, birth of type, sex and of kidding had significant influence (p < 0.05 or 0.01) all the traits. Direct heritability estimates were low for prolificacy traits (0.04 ± 0.01 for LSB, 0.09 ± 0.02 for LSW, 0.16 ± 0.02 for LWB and 0.05 ± 0.02 for SR) and average daily gain (0.12 ± 0.03 for ADG1, 0.08 ± 0.02 for ADG2, and 0.07 ± 0.03 for ADG3) to moderate for production traits (0.22 ± 0.02 for BWT, 0.25 ± 0.02 for WWT, 0.29 ± 0.04 for 6WT, 0.30 ± 0.02 for 9WT, 0.32 ± 0.05 for 12WT). The estimates for the maternal additive genetic variance ratios were lower than direct heritability for BWT (0.17 ± 0.03) and WWT (0.07 ± 0.02).

Genetic parameter estimates for growth traits of Gansu Alpine Finewool sheep

Estimation of genetic parameters for growth traits of Gansu Alpine Finewool sheep that separately identify maternal effects has not been previously conducted. (Co)variance components and corresponding genetic parameters for lamb growth traits were estimated from Gansu Alpine Finewool sheep maintained at Gansu Sheep Breeding Technology Extension Station in north-western China. Records of 17 703 lambs at birth, born over 9 years (2000–2008) and sired by 315 rams, were used in the study. Birth type, sex, dam age, record age and birth year were fitted as fixed effects. Analyses were carried out using a restricted maximum likelihood procedure (ASReml). Six different animal models were fitted for all traits and the most appropriate model was selected through log-likelihood ratio testing. After identifying the appropriate model through single-trait analysis, bivariate analyses were used to obtain the phenotypic and genetic correlations among the growth traits. In addition to the direct genetic effect, and maternal genetic effects, significant negative correlations between direct genetic and maternal genetic effects were found for all the growth traits. The maternal permanent environmental effects were only significant for birthweight, weaning weight and pre-weaning growth rate. The estimates of direct heritability for birthweight, weaning weight, pre-weaning average daily gain, post-weaning average daily gain and yearling weight were 0.22, 0.16, 0.15, 0.27 and 0.19 respectively. The maternal heritability estimates were relatively high and ranged from 0.17 to 0.27. The study provides the breed and its associated finewool sheep industry with a more encompassing basis for designing more effective breeding programs for improvement of growth traits of Gansu Alpine Finewool sheep.

Genetic relationship between growth and reproductive traits in Nellore cattle

The objective of this study was to evaluate the genetic relationship between postweaning weight gain (PWG), heifer pregnancy (HP), scrotal circumference (SC) at 18 months of age, stayability at 6 years of age (STAY) and finishing visual score at 18 months of age (PREC), and to determine the potential of these traits as selection criteria for the genetic improvement of growth and reproduction in Nellore cattle. The HP was defined as the observation that a heifer conceived and remained pregnant, which was assessed by rectal palpation at 60 days. The STAY was defined as whether or not a cow calved every year up to the age of 6 years, given that she was provided the opportunity to breed. The Bayesian linear-threshold analysis via the Gibbs sampler was used to estimate the variance and covariance components applying a multitrait model. Posterior mean estimates of direct heritability were 0.15 ± 0.00, 0.42 ± 0.02, 0.49 ± 0.01, 0.11 ± 0.01 and 0.19 ± 0.00 for PWG, HP, SC, STAY and PREC, respectively. The genetic correlations between traits ranged from 0.17 to 0.62. The traits studied generally have potential for use as selection criteria in genetic breeding programs. The genetic correlations between all traits show that selection for one of these traits does not imply the loss of the others.

Genetic parameter estimates for early growth traits in Naeini goat

The present study was carried out to estimate variance components for growth traits in Naeini goats. Bodyweight records were collected for two flocks under supervision of the Agriculture Organisation of the Esfahan province between 2000 and 2007. Investigated traits were birthweight (BW; n = 2483), weaning weight (WW; n = 1211) and average daily gain from birth to weaning (ADG; n = 1211). Environmental effects were investigated using fixed-effect models, while (co)variance components and genetic parameters were estimated with single- and three-trait analyses using REML methods and WOMBAT software. Six different animal models were fitted to the traits, with the best model for each trait determined by log-likelihood ratio tests (LRT). All traits were significantly influenced by herd, birth year, sex of the kid, birth type and dam age (P &lt; 0.01). On the basis of LRT, maternal permanent environmental effects (c2) were significant for WW and ADG, while BW was affected only by direct genetic effects. Direct heritability estimates for BW, WW and ADG were 0.25 ± 0.05, 0.07 ± 0.06 and 0.21 ± 0.11, respectively. The estimate of c2 was 0.16 ± 0.06 for both WW and ADG. Estimates of genetic correlation for BW–ADG, BW–WW and ADG–WW were 0.49, 0.61 and 0.94, respectively. The estimated phenotypic correlations were positive and were between 0.03 (BW–ADG) and 0.95 (ADG–WW). These results indicate that selection can be used to improve growth traits in this goat breed.

Genetic analysis of growth traits in Iranian Makuie sheep breed

The Makuie sheep is a fat-tailed sheep breed which can be found in the Azerbaijan province of Iran. In 1986, a Makuie sheep breeding station was established in the city of Maku in order to breed, protect and purify this breed. The genetic parameters for birth weight, weaning weight (3 months), 6-month, 9-month and yearling weight, and average daily gain from birth to weaning traits were estimated based on 25 years of data using DFREML software. Six different models were applied and a likelihood ratio test (LRT) was used to select the appropriate model. Bivariate analysis was used to define the genetic correlation between studied traits. Based on the LRT, model II was selected as an appropriate model for all studied traits. Direct heritability estimates of birth, weaning, 6-month, 9-month and yearling weights and average daily gain from birth to weaning were 0.36, 0.41, 0.48, 0.42, 0.36 and 0.37, respectively. Estimates of direct genetic correlation between birth and weaning weights, birth and 6-month weights, birth and 9-month weights, as well as between birth and yearling weights were 0.57, 0.49, 0.46 and 0.32, respectively. The results suggest there is a substantial additive genetic variability for studied traits in the Makuie sheep breed population, and the direct additive effect and maternal permanent environment variance are the main source of phenotypic variance.

(Co)variance Components for Birth and Weaning Weights of Shorthorn Beef Cattle in Australia and the United States

(Co)variance components and genetic parameters for birth (BW) and weaning weights (WW) of Shorthorn beef cattle in Australia (AU) and the United States (US) were estimated using Restricted Maximum Likelihood. Five different uni- and bivariate models were used to fit both traits within each country. In Model 1, only a direct genetic effect (a) was fitted. In Models 2 and 3, a maternal genetic effect (m) was added. A genetic covariance between direct-maternal effects [cov(a, m)] was ignored (model 2) or included (model 3). Models 4 and 5 both m and maternal permanent environment effects (pe), were allowed from model 1, and assumed cov(a,m) in the same manner as model 2 and 3, respectively. When ignoring m effect, the direct heritability estimates were inflated and differed markedly from other models. The likelihood ratio test showed that model 5 was the best fit for both traits in the US while models 2 and 4 were the fittest for BW and WW in AU, respectively. The estimates of direct, maternal, total heritabilities, and maternal permanent environment variance of the full model in AU and in the US (in parentheses) were 0.46 (0.48), 0.09 (0.05), 0.42 (0.42) and 0.00 (0.06) for BW, and 0.23 (0.32), 0.16 (0.09), 0.24 (0.26) and 0.13 (0.10) for WW, respectively. After m and pe were fitted, the estimate of total heritability decreased slightly for BW in both countries and for WW in AU, but decreased re-markedly for WW in the US. Estimate of direct-maternal genetic correlation was moderately negative and tended to be more negative after pe was fitted for both traits in the US. The parameters estimates using bivariate analysis were not different to the results from univariate analysis. This analysis yielded additive and maternal genetics correlations between BW and WW. These estimates were positive and medium to high correlation, which were higher in AU than in the US. Correlation of estimated breeding values for direct additive and maternal genetics between the full model and others were high and close to unity. The differences of some parameters between both countries indicate that joint genetic evaluation might require genotype by environment interaction to be considered.

Evaluation of models for estimation of genetic parameters and maternal effects for early growth traits of Iranian Baluchi sheep

Genetic and non-genetic parameters were estimated for early growth traits of Iranian Baluchi lambs using univariate and multivariate models. The investigated traits were: birth weight (BWT), weaning weight (WWT), 6-month weight (6MW) and pre-weaning average daily gain (ADG). Data and pedigree information used in this research were collected at the Abbasabad Sheep Breeding Station during a period between 1973 and 2003 on 15,568 lambs descended from 326 sires and 4737 dams. Twelve models including different combination of direct and maternal effects (additive genetic, permanent environmental and common environmental) as well as additive genetic relationship between direct and maternal effects were used to analyze data. For each trait, the most appropriate model was chosen based on likelihood ratio tests. In addition, multivariate analysis was performed using the most appropriate models obtained in univariate analysis. Based on the most appropriate fitted models, estimates of direct heritabilities were 0.12±0.02, 0.10±0.02, 0.06±0.01 and 0.09±0.02 for BWT, WWT, 6MW and ADG, respectively. Estimates of maternal additive genetic and maternal permanent environmental variances, as a proportion of phenotypic variance (m2 and pe2, respectively) were 0.08±0.02 and 0.08±0.01 for BWT, 0.04±0.01 and 0.09±0.01 for WWT, 0.03±0.01 and 0.03±0.01 for 6MW, and, 0.01±0.01 and 0.08±0.01 for ADG, respectively. Maternal common environmental component was significant only on BWT and was estimated to be 0.19±0.02. The estimate of maternal common environmental variances as a proportion of phenotypic variance (c2) was significant only for BWT (0.19±0.02). Direct genetic correlations among studied traits were positive and ranged from 0.37 (BWT–6MW) to 0.98 (WWT–ADG). Maternal genetic correlation estimates between studied traits were positive varying from 0.11 (BWT–ADG) to 0.64 (ADG–6MW). The estimates of phenotypic and environmental correlations were positive and generally lower than those of genetic correlations. Results indicated that besides direct genetic effects, maternal effects should be included in the statistical model to obtain accurate estimates of genetic parameters for early growth traits.

Estimates of covariance components for hygienic behavior in Africanized honeybees (Apis mellifera)

Genetic and phenotypic parameters considering the genetic effect on hygienic behavior of queen and workers from 40 Africanized honeybees colonies were estimated separately. Maternal origin of queens was controlled whereas the paternal was unknown, and different groups of workers were considered in three seasons, October 2006, April 2007 and August 2007, but with the same queen. Colonies were 21 honey producers and 19 royal jelly producers. After the method of freezing capped brood, hygienic behavior was determined by the ratio between the number of dead capped brood removed at 24, 48 and 72 hours and the total number of capped brood at zero hour. Data was submitted to single and three traits analyses using Bayesian inference. Estimates of direct heritability at 24, 48 and 72 hours (0.10, 0.11 and 0.11) were identical to the motherly ones. Estimates by three trait analysis of direct heritability were 0.28, 0.15, 0.24, and of maternal heritability were 0.23, 0.29, 0.27, at 24, 48 and 72 hours, respectively. Correlations between maternal and genetic effects were 0.12, 0.09 and - 0.08 at, 24, 48 and 72 hours, respectively. Correlation between 24 and 48 hours was 0.49; between 24 and 72 hours, 0.40; and between 48 and 72 hours, 0.47. Moderate genetic correlations with the number of capped brood removed until 48 and 72 hours indicate that after the selection of a few generations, these traits can become an efficient criterion for selection in 24 hours.