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1.
The Gibbs sampling under a multitrait animal model was applied to detect the single gene affecting chicken performance traits and their pleiotropic actions as well as to estimate the heritability and correlations for these traits. A total of 14 823 individuals of a Rhode Island Red line (RIR) and 18 653 individuals of a Rhode Island White line (RIW) from six generations under long-term selection were recorded. Five performance traits were studied: initial egg production (IEP; until 38th week), egg production (until 54th week), egg weight at 33rd week (EW), age at first egg (AFE), and body weight at 20th week (BW). An analysis was based on the estimated marginal densities of the following parameters: frequencies, additive and dominance effects and variances and covariances (for single gene) as well as additive genetic and residual variances and respective covariances (for polygenes). An inference concerning the mixed inheritance model is performed by visualising the marginal posterior densities of major gene variance separately for all traits. The pleiotropic effect of single locus is expressed as the single gene correlation coefficient. It shows contributions of single genes to BW (10 and 15% of total variance for A22 and K44, respectively) and EW of K44 (9% of total variance). Moreover, a small positive pleiotropic single locus effect in line K44 was also registered. The polygenic heritability estimates obtained were low, except for EW and BW of both lines. Generally, the correlation estimates were in agreement with results reported in literature.  相似文献   

2.
白羽番鸭RF系主要经济性状的遗传分析   总被引：8，自引：1，他引：7  
采用混合家系方差组分剖分法对白羽番鸭RF系的主要经济性状遗传参数进行了估计。结果初生重、 42日龄体重、 0～ 70日龄体重、 70日龄日增重、开产体重、 0～ 70日龄料重比、开产日龄、 30 0日龄产蛋量、 30 0日龄蛋重和 50 0日龄产蛋量的遗传力分别为 0 54、 0 48、 0 56、 0 37、0 2 9、 0 34、 0 55、 0 2 5、 0 55和 0 2 1。同时 ,对各性状的遗传相关和表型相关进行了估计和分析。  相似文献   

3.
1. In a closed White Leghorn flock over a 6-year period the average increase in egg weight from the start of lay to 37 weeks of age was 12.6 g. 2. The heritability of this egg weight increase was estimated at 0.36 +/- 0.06. 3. The genetic correlations of egg weight increase with other characteristics were: age at first egg -0.50, early egg weight -0.51, 37 week egg weight 0.42 and egg production to 273 d 0.44. 4. It is predicted that with unit selection intensity the direct response in egg weight increase will be -1.30 g, with correlated responses in age at first egg of 2.1 d, early egg weight 0.64 g, 37 week egg weight -0.51 g and egg production to 273 d -1.83 eggs.  相似文献   

4.
(1) The study was conducted to estimate the heritability, genetic correlations and breeding values of laying hens based on individual records and group mean records. (2) Records of two pure lines from a commercial breeding programme of White Leghorns from three generations housed in single cages and in group cages were used. A total of 8483 and 8817 individual records of lines A and D, respectively, and a total of 1358 (line A) and 1161 (line D) group mean records were analysed. (3) An animal model using Restricted Maximum Likelihood (REML) was used to estimate variance components of individual records. Group mean records were analysed using the sire model, taking heterogeneity of error variance and correlated residual effects into account. Breeding values of sires were estimated based on the BLUP method using a multivariate sire model. Spearman Rank correlations were used to compare sire breeding values estimated from individual records and from group mean records. The traits studied were monthly egg production, cumulative production and egg weight. (4) Heritability estimates based on individual records were higher than from group mean records. Heritabilities for cumulative production records were higher than for monthly production, based on individual as well as group mean records. The estimates of genetic correlations between monthly egg production and cumulative production were moderate to high. Egg production and egg weight recorded individually were highly genetically correlated with those recorded on group means. Sire breeding values estimated from individual records showed high correlations with those from group mean records. (5) Differences in the ranking of sire breeding values estimated from individual vs group mean records were negligible, indicating that no genotype x environment interaction exists. Selection based on individual performance records of laying hens housed in single cages could give a good response on performance of laying hens housed in group cages. Cumulative egg production over periods 1 to 6 is the best trait for the selection programme.  相似文献   

5.
Native chicken breeding station of Mazandaran was established in 1988 with two main objectives: genetic improvement through selection programs and dissemination of indigenous Mazandarani birds. (Co)variance components and genetic parameters for economically important traits were estimated using (bi) univariate animal models with ASREML procedure in Mazandarani native chicken. The data were from 18 generations of selection (1988?C2009). Heritability estimates for body weight at different ages [at hatch (bw1), 8 (bw8), 12 (bw12) weeks of ages and sex maturation (wsm)] ranged from 0.24?±?0.00 to 0.47?±?0.01. Heritability for reproductive traits including age at sex maturation (asm); egg number (en); weight of first egg (ew1); average egg weight at 28 (ew28), 30 (ew30), and 32 (ew32) weeks of age; their averages (av); average egg weight for the first 12?weeks of production (ew12); egg mass (em); and egg intensity (eint) varied from 0.16?±?0.01 to 0.43?±?0.01. Generally, the magnitudes of heritability for the investigated traits were moderate. However, egg production traits showed smaller heritability compared with growth traits. Genetic correlations among egg weight at different ages were mostly higher than 0.8. On the one hand, body weight at different ages showed positive and relatively moderate genetic correlations with egg weight traits (ew1, ew28, ew30, ew32, ew12, and av) and varied from 0.30?±?0.03 to 0.59?±?0.02. On the other hand, low negative genetic correlations were obtained between body weight traits (bw1, bw8, bw12, and wsm) and egg number (en). Also, there is low negative genetic correlation (?24?±?0.04 to ?29?±?0.05) between egg number and egg weight. Therefore, during simultaneous selection process for both growth and egg production traits, probable reduction in egg production due to low reduction in egg number may be compensated by increases in egg weight.  相似文献   

6.
1. The main purpose of this study was to estimate genetic correlations between yolk proportion, chick weight and production traits using an animal model. 2. Direct-direct genetic correlations were estimated between yolk proportion and age at first egg (-0.34), body weight at 20 (0.10), 40 (0.58) and 60 (0.52) weeks of age, egg number (0.56), egg mass (0.59), feed intake (0.64) and feed conversion (-0.25). 3. Maternal-direct genetic correlations were estimated between chick weight and age at first egg (0.40), body weight at 20 (0.57), 40 (0.66) and 60 (0.56) weeks of age, egg number (-0.50), egg mass (0.21), feed intake (0.45) and feed conversion (0.17), respectively. 4. In conclusion, the results suggest that selection on a higher yolk proportion would not have any unfavourable effects on egg production. Maternal-direct genetic correlations between chick weight and production traits resembled direct-direct genetic correlations between egg weight and production traits found in other studies.  相似文献   

7.
ABSTRACT

1. The objective of the study was to investigate the influence of maternal and parent of origin effects (POE) on genetic variation of Iranian native fowl on economic traits.

2. Studied traits were body weights at birth (BW0), at eight (BW8) and 12 weeks of age (BW12), age (ASM) and weight at sexual maturity (WSM), egg number (EN) and average egg weight (AEW).

3. Several models, including additive, maternal additive genetics, permanent environmental effects and POE were compared using Wombat software. Bayesian Information Criterion (BIC) was used to identify the best model for each trait. The chance of reranking of birds between models was investigated using Spearman correlation and Wilcoxon rank test.

4. Based on the best model, direct heritability estimates for BW0, BW8, BW12, ASM, WSM, EN and AEW traits were 0.05, 0.21, 0.23, 0.30, 0.39, 0.22 and 0.38, respectively. Proportion of variance due to paternal POE for BW8 was 4% and proportion of variance due to maternal POE for BW12 was 5%.

5. Estimated maternal heritability for BW0 was 0.30 and for BW8 and BW12 were 0.00 and 0.01, respectively, which shows that maternal heritability was reduced by age.

6. Based on the results, considering POE for BW8 and BW12 and maternal genetic effects for BW0 improved the accuracy of estimations and avoid reranking of birds for these traits.  相似文献   

8.

  • 1.?A study was conducted to study direct dominance genetic and maternal effects on genetic evaluation of production traits in dual-purpose chickens. The data set consisted of records of body weight and egg production of 49 749 Mazandaran fowls from 19 consecutive generations. Based on combinations of different random effects, including direct additive and dominance genetic and maternal additive genetic and environmental effects, 8 different models were compared.

  • 2.?Inclusion of a maternal genetic effect in the models noticeably improved goodness of fit for all traits. Direct dominance genetic effect did not have noticeable effects on goodness of fit but simultaneous inclusion of both direct dominance and maternal additive genetic effects improved fitting criteria and accuracies of genetic parameter estimates for hatching body weight and egg production traits.

  • 3.?Estimates of heritability (h2) for body weights at hatch, 8 weeks and 12 weeks of age (BW0, BW8 and BW12, respectively), age at sexual maturity (ASM), average egg weights at 28–32 weeks of laying period (AEW), egg number (EN) and egg production intensity (EI) were 0.08, 0.21, 0.22, 0.22, 0.21, 0.09 and 0.10, respectively. For BW0, BW8, BW12, ASM, AEW, EN and EI, proportion of dominance genetic to total phenotypic variance (d2) were 0.06, 0.08, 0.01, 0.06, 0.06, 0.08 and 0.07 and maternal heritability estimates (m2) were 0.05, 0.04, 0.03, 0.13, 0.21, 0.07 and 0.03, respectively. Negligible coefficients of maternal environmental effect (c2) from 0.01 to 0.08 were estimated for all traits, other than BW0, which had an estimate of 0.30.

  • 4.?Breeding values (BVs) estimated for body weights at early ages (BW0 and BW8) were considerably affected by components of the models, but almost similar BVs were estimated by different models for higher age body weight (BW12) and egg production traits (ASM, AEW, EN and EI). Generally, it could be concluded that inclusion of maternal effects (both genetic and environmental) and, to a lesser extent, direct dominance genetic effect would improve the accuracy of genetic evaluation for early age body weights in dual-purpose chickens.

  相似文献   

9.
Maternal effects are an important source of variation in early growth and body traits in sheep but are often excluded from genetic analyses. Maternal additive genetic, maternal environmental, and cytoplasmic effects were investigated in a large Suffolk breeding scheme using a range of models involving different combinations of these effects with the direct additive genetic effect. Weights at 8 wk of age and at scanning (mean age 146 d) and ultrasonically measured muscle and fat depth were analyzed using an animal model on 55,683 (8-wk weight) and 28,947 (scanning traits) lamb records. Simple additive models always overestimated the heritability of all traits when compared to more complex models. The successive inclusion of maternal environmental, maternal genetic, and the covariance between direct and maternal additive effects in the model significantly improved the fit for almost all models and all traits, as indicated by a likelihood ratio test. Under the full model, the heritability of both weight traits was low (0.14 and 0.20 for 8-wk and scanning weight, respectively). The maternal additive and maternal environmental effects, as a proportion of the phenotypic variance, were similar (0.10 and 0.08 for 8-wk weight and 0.07 and 0.06 for scanning weight). The two scanning traits had higher heritabilities (0.29 and 0.27 for muscle depth and fat depth, respectively) with low levels of maternal genetic and maternal environmental variance. No evidence was found of a cytoplasmic effect on any of the traits studied under the full model. Breeding schemes for early growth and body traits in sheep should account for maternal effects in their genetic evaluations in order to improve their accuracy. The exact model to use will depend on the trait and individual circumstances of the scheme.  相似文献   

10.
This study investigated the effects of genotype–environment interaction on yearling weight, age at first calving and post‐weaning weight gain in Nellore cattle using multi‐trait reaction norm models. The environmental gradient was defined as a function of the mean yearling weight of the contemporary groups. A first‐order random regression sire model with four classes of residual variance was used in the analyses and Bayesian methods were applied to estimate the (co)variance components. The heritability estimates ranged from 0.284 to 0.547, 0.222 to 0.316 and 0.256 to 0.522 for yearling weight, age at first calving and post‐weaning weight gain, respectively. The lowest genetic correlations between environment groups for each trait were 0.38, 0.02 and 0.04 for yearling weight, age at first calving and post‐weaning weight gain, respectively. Differences in the correlation estimates were observed between traits in the same environments, with the magnitude of the estimates tending toward zero as the environment improved. The results highlight the importance of including genotype–environment interactions in genetic evaluation programs considering the differences observed between environmental groups not only in terms of heritability, but also of genetic correlations.  相似文献   

11.
Genetic parameters for faecal egg count were estimated in naturally challenged Avikalin sheep developed and maintained at Central Sheep & Wool Research Institute, Avikanagar, India, over a period of 4 years (2004–2007). The data on faecal egg count for 433 animals descended from 41 sires, and 151 dams were used for the study. Genetic analyses were carried out using restricted maximum likelihood, fitting an animal model and ignoring or including maternal genetic or permanent environmental effects. Direct heritability for the trait was 0.149 ± 0.096 when maternal effects were ignored. In the model which takes in to account direct genetic, maternal genetic and maternal permanent environment effect together, it was observed that maternal heritability (m2) accounts for 0.6% of total variation whereas maternal permanent environmental effect (c2) accounts for 6.14% of total phenotypic variation. Effect of faecal egg count on the growth characteristics was observed to be significant. It was seen that wherever FEC was high, body weight or average daily gain declined in active infective stage. After termination of the infection, these effects were found to be non-significant. Result suggests that direct genetic and maternal permanent environmental effects were important for this trait; thus, they need to be considered for improvement in the trait.  相似文献   

12.
1. A selection experiment with two lines of White Leghorns originating from a common base population was carried out over 5 generations with the aims of maintaining an unchanged egg weight, reducing age at first egg and reducing adult body weight. Each line consisted of 14 male and 42 female breeders. 2. Males were mass selected for low body weight at 20 weeks of age. To compensate for the expected correlated loss in egg weight, hens were selected according to an index which counteracted this undesirable change while also reducing age at first egg and reducing body weight. 3. An index value was calculated for each individual hen from average egg weight, age at first egg and body weight at 20 weeks. Index weights had to be calculated for each generation and line in accordance with the expected change in egg weight due to male selection on body weight. 4. For control matings hens with an index near the population average were mated either to males with body weight near the population average (control C1) or to the selected males within lines (control C2). 5. Expected and observed total responses agreed well for all traits in line 1 and for body weight in line 2. 6. Phenotypic variances and covariances showed little change during the experiment. However, genetic variances and covariances estimated at the end of the experiment showed some differences, both between lines and compared to the parameters used for index construction.  相似文献   

13.

  1. Genetic parameters were estimated for 5 economically important egg production traits using records collected over 9 years in chickens reared under tropical conditions in Thailand. The data were from two purebred lines and two hybrid lines of layer parent stocks.

  2. The two purebred lines were Rhode Island Red (RIR) and White Plymouth Rock (WPR) and the hybrid lines were formed by crossing a commercial brown egg laying strain to Rhode Island Red (RC) and White Plymouth Rock (WC), respectively.

  3. Five egg production traits were analysed, including age at first egg (AFE), body weight at first egg (BWT), egg weight at first egg (EWFE), number of eggs from the first 17 weeks of lay (EN) and average egg weight over the 17th week of lay (EW).

  4. Fixed effects of year and hatch within year were significant for all 5 traits and were included in the model.

  5. Maternal genetic and permanent environmental effects of the dam were not significant, except for EN and EW in RIR and BWT and EW in WPR.

  6. Estimated heritability of AFE, BWT, EWFE, EN and EW were 0.45, 0.50, 0.29, 0.19 and 0.43 in RIR; 0.44, 0.38, 0.33, 0.20 and 0.38 in WPR; 0.37, 0.41, 0.38, 0.18 and 0.36 in RC; and 0.46, 0.53, 0.36, 0.38 and 0.45 in WC lines, respectively.

  7. The EN was negatively correlated with other traits, except for BWT in RC and AFE and BWT in WC.

  8. It was concluded that selection for increased EN will reduce other egg production traits in purebred and hybrid chicken and therefore EN needs to be combined with other egg production traits in a multi-trait selection index to improve all traits optimally according to a defined breeding objective.

  相似文献   

14.
Discovery of genes with large effects on economically important traits has for many years been of interest to breeders. The development of SNP panels which cover the whole genome with high density and, more importantly, that can be genotyped on large numbers of individuals at relatively low cost, has opened new opportunities for genome‐wide association studies (GWAS). The objective of this study was to find genomic regions associated with egg production and quality traits in layers using analysis methods developed for the purpose of whole genome prediction. Genotypes on over 4500 birds and phenotypes on over 13 000 hens from eight generations of a brown egg layer line were used. Birds were genotyped with a custom 42K Illumina SNP chip. Recorded traits included two egg production and 11 egg quality traits (puncture score, albumen height, yolk weight and shell colour) at early and late stages of production, as well as body weight and age at first egg. Egg weight was previously analysed by Wolc et al. ( 2012 ). The Bayesian whole genome prediction model – BayesB (Meuwissen et al. 2001 ) was used to locate 1 Mb regions that were most strongly associated with each trait. The posterior probability of a 1 Mb window contributing to genetic variation was used as the criterion for suggesting the presence of a quantitative trait locus (QTL) in that window. Depending upon the trait, from 1 to 7 significant (posterior probability >0.9) 1 Mb regions were found. The largest QTL, a region explaining 32% of genetic variance, was found on chr4 at 78 Mb for body weight but had pleiotropic effects on other traits. For the other traits, the largest effects were much smaller, explaining <7% of genetic variance, with regions on chromosomes 2, 12 and 17 explaining above 5% of genetic variance for albumen height, shell colour and egg production, respectively. In total, 45 of 1043 1 Mb windows were estimated to have a non‐zero effect with posterior probability > 0.9 for one or more traits.  相似文献   

15.
The objective of this study was to ascertain whether maternal additive genetic variance exists for within-litter variation in birth weight and for change in within-litter variation in piglet weight during suckling. A further objective was to estimate maternal genetic correlations of these two traits with mortality, birth weight, growth, and number of piglets born alive. Data were obtained from L?vsta research station, Swedish University of Agricultural Sciences, and included 22,521 piglets born in 2,003 litters by 1,074 Swedish Yorkshire sows. No cross fostering was used in the herd. The following seven traits were analysed in a multivariate animal (sow) model: number of piglets born alive, within-litter SD in birth weight, within-litter SD in piglet weight at 3 wk of age, mean weight at birth, mean weight at 3 wk of age, proportion of stillborn piglets, and proportion of dead piglets during suckling. Maternal genetic variance for the change in within-litter SD in piglet weight during suckling was assessed from the estimated additive genetic covariance components by conditioning on within-litter SD in birth weight. Similarly, mean growth of piglets during suckling was assessed from the additive genetic covariance components by conditioning on mean weight at birth. The heritability for within-litter SD in birth weight was 0.08 and 0.06 for within-litter SD in piglet weight at 3 wk. The genetic correlation between these two traits was 0.71. Little maternal genetic variance was found for the change in within-litter SD in piglet weight during suckling, and opportunity for genetic improvement of this trait by selective breeding seems limited. The genetic correlation of within-litter SD in birth weight with proportion of dead piglets during suckling was 0.25 and of within-litter SD in birth weight with mean growth of piglets was -0.31. The maternal genetic variance and heritability found for within-litter SD in birth weight indicates that genetic improvement of this trait by selective breeding is possible. In addition, selection for sows' capacity to give birth to homogeneous litters may be advantageous for piglet survival, piglet growth, and litter homogeneity at weaning.  相似文献   

16.
1. Data on 13,773 pullets, the progeny of 30 to 50 sires and about 135 to 220 dams per generation of a strain of White Leghorn under long term selection for part period egg production over 16 generations, were examined. 2. Realised genetic gain per generation was highly significant for egg production (2.55 eggs), egg weight (- 0.51 g), age at sexual maturity (- 2.30 d) and 40 week body weight (- 11.73 g). 3. The significant genetic response of 4.46 to 4.72 eggs per generation was realised in the first 8 generations only, which was accompanied by a marked decline in egg weight (- 1.67 and- 0.79 g per generation) and in age at sexual maturity (- 4.63 and- 6.39 d per generation). The 20 and 40 week body weights showed significant improvement in the last 4 generations. 4. Realised heritabilities were much lower in the last 8 than in the first 8 generation. 5. The additive genetic variance for most traits, except 20 week body weight and genetic covariances of egg production with egg weight and age at sexual maturity, declined significantly. 6. Natural selection did not seem to play any major role. No appreciable change in fitness traits was observed in the selected line. 7. The time trends were non-significant for all the traits in the control line, indicating its stability over generations.  相似文献   

17.
Genetic parameters of mature weight are needed for effective selection and genetic evaluation. Data for estimating these parameters were collected from 1963 to 1985 and consisted of 32,018 mature weight records of 4,175 Hereford cows that were in one control and three selection lines that had been selected for weaning weight, for yearling weight, or for an index combining yearling weight and muscle score for 22 yr. Several models and subsets of the data were considered. The mature weight records consisted of a maximum of three seasonal weights taken each year, at brand clipping (February and March), before breeding (May and June), and at palpation (August and September). Heritability estimates were high (0.49 to 0.86) for all models considered, which suggests that selection to change mature weight could be effective. The model that best fit the data included maternal genetic and maternal permanent environmental effects in addition to direct genetic and direct permanent environmental effects. Estimates of direct heritability with this model ranged from 0.53 to 0.79, estimates of maternal heritability ranged from 0.09 to 0.21, and estimates of the genetic correlation between direct and maternal effects ranged from -0.16 to -0.67 for subsets of the data based on time of year that mature weight was measured. For the same subsets, estimates of the proportions of variance due to direct permanent environment and maternal permanent environment ranged from 0.00 to 0.09 and 0.00 to 0.06, respectively. Using a similar model that combined all records and included an added fixed effect of season of measurement of mature weight, direct heritability, maternal heritability, genetic correlation between direct and maternal effects, proportion of variance due to direct permanent environmental effects, and proportion of variance due to maternal permanent environmental effects were estimated to be 0.69, 0.13, -0.65, 0.00, and 0.04, respectively. Mature weight is a highly heritable trait that could be included in selection programs and maternal effects should not be ignored when analyzing mature weight data.  相似文献   

18.
Genetic parameters for nuclear and cytoplasmic genetic effects were estimated from preweaning growth data collected on three synthetic lines of beef cattle differing in mature size. Lines of small-, medium-, and large-framed calves were represented in each of two research herds (Rhodes and McNay). Variance components were estimated separately by herd and size line for birth weight and 205-d weight (WW) by REML with an animal mode using an average of 847 and 427 calf records from Rhodes and McNay, respectively. Model 1 included effects of fixed year, sex of calf, age of dam, and random additive direct (a), additive maternal genetic (m), covariance (a,m), permanent environment affecting the dam, and residual error. Model 2 differed from Model 1 by including random cytoplasmic lineage effects and by ignoring permanent environmental effects. Model 1--direct (maternal) heritability estimates for birth weight at Rhodes were .62(.03) for small, .67(.06) for medium, and .30(.11) for large lines. Genetic correlations between direct and maternal effects for birth weight were .67, -.16, and .48 for the respective size groups. For WW at Rhodes, direct (maternal) heritability estimates were .30(.29), .30(.14), and .10(.16) for small, medium, and large lines, respectively, with genetic correlations of -.34 (small), -.12 (medium), and .17 (large). Heritability estimates at McNay were similar to those at Rhodes, except that maternal genetic heritabilities for WW were smaller (.10, small; .01, medium; .00, large). Model 2--estimates for nuclear genetic effects were consistent with the estimates from Model 1. Cytoplasmic variance accounted for 0 to 5% of the total random variance in birth weight. For WW, cytoplasmic variance was negligible at Rhodes and accounted for 4% of the total random variance in the large line at McNay, averaging less than the permanent environment. Results failed to indicate that cytoplasmic variance was important for preweaning performance.  相似文献   

19.
1. The objective of this study was to investigate the strength of the genetic association between growth and reproduction traits in turkeys selected for body weight, conformation and egg production. 2. Two distinct populations but derived from the same heavy turkey female line and situated in different locations (UK and USA), were used to estimate genetic parameters using multivariate REML for the following traits: body weight at 14 (BW14), 19 (BW19) and 24 (BW24) weeks of age and total egg number (EGG). 3. A Box-Cox transformation was applied to egg production data to reduce the impact of non-normality. 4. The heritability estimates for each trait for the UK and USA populations, respectively, were: BW14 0.37 and 0.48; BW19 0.34 and 0.43; BW24 0.28 and 0.43; EGG 0.22 and 0.34. 5. The genetic correlation between the body weight at all ages and the total egg production was strongly negative, reaching a value of -0.75 for the UK and -0.55 for the USA population. 6. The comparison of our results with published estimates in turkeys suggests that the genetic correlation may get stronger in magnitude following selection for increased body weight. 7. This could arise from fixation during selection of genes favouring larger weights but with minimal effect on egg production, leaving the segregating genetic variation dominated by pleiotropic loci with antagonistic effects on the traits. 8. Thus, in order to avoid continued selection for body weight reducing egg production to a point where natural selection offsets selection gains, alternative selection strategies should be considered.  相似文献   

20.
Direct and maternal (co)variance components and genetic parameters were estimated for growth and reproductive traits in the Kenya Boran cattle fitting univariate animal models. Data consisted of records on 4502 animals from 81 sires and 1010 dams collected between 1989 and 2004. The average number of progeny per sire was 56. Direct heritability estimates for growth traits were 0.34, 0.12, 0.19, 0.08 and 0.14 for birth weight (BW), weaning weight (WW), 12-month weight (12W), 18-month weight (18W) and 24-month weight (24W), respectively. Maternal heritability increased from 0.14 at weaning to 0.34 at 12 months of age but reduced to 0.11 at 24 months of age. The maternal permanent environmental effect contributed 16%, 4% and 10% of the total phenotypic variance for WW, 12W and 18W, respectively. Direct-maternal genetic correlations were negative ranging from −0.14 to −0.58. The heritability estimates for reproductive traits were 0.04, 0.00, 0.15, 0.00 and 0.00 for age at first calving (AFC), calving interval in the first, second, and third parity, and pooled calving interval. Selection for growth traits should be practiced with caution since this may lead to a reduction in reproduction efficiency, and direct selection for reproductive traits may be hampered by their low heritability.  相似文献   

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