Comparison of different methods of heritability estimates for body weights and wool yield traits in avikalin crossbred sheep
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Records of body weights and wool yield traits of 1313 lambs, the progeny of 106 sires and 134 baseline dams of Avikalin crossbred sheep were used to estimate the heritability and variance components. Traits analyzed were birth weight (BWT), weaning weight (WT-3), 6-month weight (WT-6), 12-month weight (WT-12) and first greasy fleece yield (GFY1). The estimate of habitability under model 2 and 8 of least squares analysis and univariate REML animal model were found to be 0.183, 0.170 and 0.168 for BWT, 0.259, 0.252 and 0.077 for WT-3, 0.365, 0.377 and 0.162 for WT-6, 0.445, 0.453 and 0.203 for WT-12 and 0.408, 0.412 and 0.107 for GFY1, respectively. Additive genetic variance was higher under model 2 of LSA than model 8 of LSA and univariate animal model. The univariate animal model estimated higher additive genetic variance than model 8 of LSA for all the five traits except BWT. Residual and phenotypic variances for all the three methods were almost similar and showed increasing trend with advancement of the age of animal.Keywords:
Restricted maximum likelihood
Univariate
Animal model
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Data and managementData and pedigree information on Ghezel sheep collected at the Breeding Station of Ghezel sheep, over the period from 1999 to 2007 (9-years), were used in this research.This information included pedigree information (animal, sire and dam code), birth information (date of birth, lamb sex, birth type) and performance records (birth weight (BW), weaning weight (WW), and 6-months weight (6 MW)).Data which were available for analysis included 9,221 lamb records born from 180 sires and 5,060 dams for BW, 7,206 lamb records born from 167 sires and 4,497 dams for WW, and 6,112 lamb records born from 157 sires
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Genetic parameters of growth traits were estimated in the German Angora rabbit reared in the sub-temperate region of India.Estimates of (co)variance components were obtained for body weights at weaning (42 days) and post-weaning at 84, 126 and 168 days.A total of 8,324 animal records were used for the analysis of these traits.The data were analyzed by restricted maximum likelihood (REML) fitting six animal models with various combinations of direct and maternal effects.A log likelihood ratio test was used to select the most appropriate univariate model for each trait.Direct heritability estimates were observed to be moderate for the traits under study.Heritability estimates for weaning (42 d), 84, 126 and 168 d weights obtained from the best models were 0.25±0.05,0.17±0.05,0.21±0.06and 0.12±0.05.Maternal effects had higher importance at weaning, and declined with the advancement of age.Significant maternal permanent environmental effect on weaning and post-weaning weights was a carryover effect of maternal influences during pre-weaning age.The estimated repeatabilities of doe effects on body weights were 0.37, 0.22, 0.18 and 0.28 at weaning, 84, 126 and 168 d body weight, respectively.Results indicated that modest rate of genetic progress is possible for body weight traits of Angora rabbit through selection.Similarly, these growth traits could be included in selection criteria along with wool traits for early selection of the animals.
Restricted maximum likelihood
Maternal effect
Genetic correlation
Animal Breeding
Animal model
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Different genetic parameters for weaning weight and wool traits were estimated using restricted maximum likelihood (REML) in Angora rabbits.Total wool yield of first (I), second (II) and third (III) clips were taken as a separate trait under study.The records from more than 2,700 animals were analysed through fitting six animal models with various combinations of direct and maternal effects.A log likelihood ratio test was used to select the most appropriate model for each trait.Direct heritability estimates for the wool traits were found to be moderate to high across different models.Heritability estimates obtained from the best model were 0.24, 0.22, 0.20 and 0.21 for weaning weight, clip I, II and III; respectively.Maternal effects especially due to permanent environment had higher importance at clip I and found to be declining in subsequent clips.The estimates of repeatability of doe effect on wool traits were 0.44, 0.26 and 0.18 for clip I, II and III; respectively.Weaning weight had moderately high genetic correlations with clip I (0.57) and II (0.45), but very low (0.11) with clip III.Results indicated that genetic improvement for wool yield in Angora rabbit is possible through direct selection.Further, weaning weight could be considered as desirable trait for earliest indirect selection for wool yield in view of its high genetic correlation with wool traits.
Restricted maximum likelihood
Genetic correlation
Trait
Repeatability
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Genetic parameters were estimated for weights of lambs at birth, weaning and 6 months and fleece yield using leastsquares and univariate and multivariate animal models with REML procedure. The data considered from 1214 animals descendent from 110 sires, 422 dams, 36 paternal grandsires, 44 paternal grand mothers, 69 maternal grand sires and 131 maternal grand mother of Chokla sheep maintained at Central Sheep and Wool Research Institute, Avikanagr. Traits analyzed were birth weight (BWT), weaning weight (WWT), 6 months weight (6 WT) and first greasy fleece yield (GFY1 ). Variance components were estimated using least-squares analysis and restricted maximum likelihood computer ptogramme with an animal model including fixed effect for sex and year of birth and random effect for sire. Additive (direct), environmental and phenotypic variances estimated from univariate and multivariate animal models agreed closely for all the traits. Similarly, variance estimated from model 2 and model 8 analysis agreed for all the traits. Model 2 had slightly higher additive variance for weaning, 6 months and greasy fleece yield but lower for birth weight than model 8. For growth traits. REML analysis had lowest additive variance while model 2 had higher. Multivariate REML had estimated higher additive and enviromental covariance than model 2, among growth traits. Model 2 also had higher environmental covariance among first fleece yield and growth trails than multivariate REML analysis. The H² estimates for birth weight were 0.138,0.147.0.306 and 0.307, respectively, under model 2, model 8. univariate and multivariate analysis. The h² estimates for weaning weight were 0.238 , 0.185,0.204 and 0.216, respectively, under model 2, model 18 , univariate and multivariate analysis. The h² estimates for 6 month weight and first greasy fleece yield mvdrl 2, model 8, univariate and multivariate analysis were 0.245. 0.161, 0.240 and 0.226 and 0.242, 0.144, 0.103 and 0.097 respectively. Genetic correlations ranged from 0.391 (between birth and 6 month weight) to 0.822 (between weaning and first greasy fleece yield) in model 2 of LSA. whereas in multivariate REML it ranged from 0.245 (between 6 months and first greasy Hecce yield) to 0.909 (between weaning and 6 months weight). Multivariate REML analysis had explained more variation in genetic correlations than LSA. The phenotypic correlations ranged from 0.233 (between birth weight and first greasy fleece yield) to 0.722 (between birth weight and first greasy yield) under model 2 of LSA and from 0.220 (between birth weight and first greasy fleece weight) to 0.725 (between weaning weight and 6 month weight) under multivariate analysis. The environmental correlations ranged from 0.117 (between BWT and FGY 1) to 0.695 (between WWT and FGY 1). These estimates of genetic parameters between growth and fleece yield traits can be used to construct multiple trait selection indexes for genetic improvement of Avikalin strain of sheep.
Restricted maximum likelihood
Univariate
Sire
Mixed model
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Restricted maximum likelihood
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Domestic sheep reproduction
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Flock
Restricted maximum likelihood
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The study aimed to assess genetics of some layer performance traits in a control line of Rhode Island Red (RIR) chicken maintained at Central Avian Research Institute, Izatnagar. A total of 193 pedigreed pullet progenies of 30 sires mated with 41 dams in two hatches were investigated. Data were analyzed by least squares analysis of variance, and heritability and correlation parameters of different traits were estimated using full-sib correlation method. The least squares means of age at first egg, body weights at 20th and 40th week, egg weights at 28th and 40th week and part period egg production upto 40 weeks of age were estimated. Sires significantly (P<0.05) affected the estimates of body weights, but dam within sire could not affect (P<0.05) any estimate. Hatch influenced (P<0.05) the estimates of age at first egg and body weight at 40th week of age. Birds’ housing weight demonstrated significant regression effect on the estimates of age at first egg, body weight and egg weight at 40th week of age. The heritability estimates from sire component of variance of the traits ranged from 0.018 to 0.438. Corresponding estimates from dam component and sire plus dam component ranged from 0.060 to 0.643 and 0.102 to 0.355. The genetic and phenotypic correlations among the traits were low to high in magnitude when estimated from sire plus dam component. The investigation generated some valuable genetic information of layer performances which might be used as the pre-requisites for chalking out of breeding strategies for its genetic improvement.
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Precise estimates of genetic parameters are required for genetic evaluation systems. This study combined data from 7 research resource flocks across Australia to estimate variance components and genetic parameters for production traits in the Australian Merino sheep. The flocks were maintained for several generations and represented contemporary Australian Merino fine, medium, and broad wool bloodlines over the past 30 years. Over 110 000 records were available for analysis for each of the major wool traits, and 50 000 records for reproduction and growth traits with over 2700 sires and 25 000 dams. A linear mixed animal model was used to analyse 6 wool traits comprising clean fleece weight (CFW), greasy fleece weight (GFW), fibre diameter (FD), yield (YLD), coefficient of variation of fibre diameter (CVFD), and standard deviation of fibre diameter (SDFD), 4 growth traits comprising birth weight (BWT), weaning weight (WWT), yearling weight (YWT), and hogget weight (HWT), and 4 reproduction traits comprising fertility (FER), litter size (LS), lambs born per ewe joined (LB/EJ), and lambs weaned per ewe joined (LW/EJ). The range of direct heritability estimates for the wool traits was 0.42 ± 0.01 for CFW to 0.68 ± 0.01 for FD. For growth traits the range was 0.18 ± 0.01 for BWT to 0.38 ± 0.01 for HWT, and for reproduction traits 0.045 ± 0.01 for FER to 0.074 ± 0.01 for LS. Significant maternal effects were found for wool and growth, but not reproduction traits. There was significant covariance between direct and maternal genetic effects for all wool and growth traits except for YWT. The correlations between direct and maternal effects ranged from –0.60 ± 0.02 for GFW to –0.21 ± 0.10 for SDFD in the wool traits and from –0.21 ± 0.03 for WWT to 0.25 ± 0.08 for HWT in the growth traits. Litter effects were significant for all wool and growth traits and only for LS in reproduction traits. The mating sire was fitted in the models for reproduction traits and this variance component accounted for 21, 17, and 8% of the total phenotypic variation for FER, LB/EJ, and LW/EJ, respectively. The implications of additional significant variance components for the estimation of heritability are discussed.
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Litter
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Genetic correlation
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(Co)variance components and genetic parameters of weight at birth (BWT), weaning (3WT), 6, 9 and 12 months of age (6WT, 9WT and 12WT, respectively) and first greasy fleece weight (GFW) of Bharat Merino sheep, maintained at Central Sheep and Wool Research Institute, Avikanagar, Rajasthan, India, were estimated by restricted maximum likelihood, fitting six animal models with various combinations of direct and maternal effects. Data were collected over a period of 10 years (1998 to 2007). A log-likelihood ratio test was used to select the most appropriate univariate model for each trait, which was subsequently used in bivariate analysis. Heritability estimates for BWT, 3WT, 6WT, 9WT and 12WT and first GFW were 0.05 ± 0.03, 0.04 ± 0.02, 0.00, 0.03 ± 0.03, 0.09 ± 0.05 and 0.05 ± 0.03, respectively. There was no evidence for the maternal genetic effect on the traits under study. Maternal permanent environmental effect contributed 19% for BWT and 6% to 11% from 3WT to 9WT and 11% for first GFW. Maternal permanent environmental effect on the post-3WT was a carryover effect of maternal influences during pre-weaning age. A low rate of genetic progress seems possible in the flock through selection. Direct genetic correlations between body weight traits were positive and ranged from 0.36 between BWT and 6WT to 0.94 between 3WT and 6WT and between 6WT and 12WT. Genetic correlations of 3WT with 6WT, 9WT and 12WT were high and positive (0.94, 0.93 and 0.93, respectively), suggesting that genetic gain in post-3WT will be maintained if selection age is reduced to 3 months. The genetic correlations of GFW with live weights were 0.01, 0.16, 0.18, 0.40 and 0.32 for BWT, 3WT, 6WT, 9WT and 12WT, respectively. Correlations of permanent environmental effects of the dam across different traits were high and positive for all the traits (0.45 to 0.98).
Genetic correlation
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Restricted maximum likelihood
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