Genetic Parameters For Growth Traits Research Articles

Genetic variance components of the growth curve for Isfahan indigenous chicken.

Being able to model a growth curve using three or four non-linear functional parameters could help explain the growth phenomenon in a precise way and would allow the comparison of an animal's development rate, optimize management and feeding strategies and guide animal production strategies. The goal of this study was to estimate the genetic parameters of growth traits of Isfahan indigenous chicken in Iran and to determine the best non-linear model describing the growth curve. The prediction of additive genetic parameters was performed using the REML method by WOMBAT. Direct heritability of the studied traits and genetic correlations between them were obtained. The Logistic, Gompertz, von Bertalanffy, Brody, Negative exponential, Weibull, Janoschek and Bridges models were compared based on the coefficient of determination (R2 ), mean square error (MSE) and akaike information criterion. The Gompertz model was identified as the best model for describing the growth curve for Isfahan native chicken. The heritability of maturity weights (A), initial weight (B) and maturity rate (K) parameters were 0.223±0.002, 0.016±0.005 and 0.087±0.001, respectively. This study shows that Isfahan indigenous chicken has the genetic potential for improving growth and reproduction based on their desirable heritabilities and correlations using appropriate models.

Genetic Parameters for Growth Traits of Malya Goats and Heterosis from Crossbreds of Malya and Sukuma Goats

Genetic Parameters for Growth Traits of Malya Goats and Heterosis from Crossbreds of Malya and Sukuma Goats

Direct – Maternal Genetic Parameters Estimated for Real-Time Ultrasound Scan Measures of Eye Muscle Area, Rib Fat Depth, and their Correlation with Body Weight in Male Philippine Riverine Buffaloes

Background: Ultrasound scanning is a non-invasive technique for evaluating animals based on carcass yield and meat quality traits. It has been incorporated into the beef cattle breeding program. However, little has been done in buffaloes. Thus, this study was conducted to estimate the genetic parameters for growth traits- body weights (BW) and a real-time ultrasound scan of eye muscle area (EMA) and rib fat (RF) to determine their suitability as a tool for selection.
 Methods: Four hundred thirty-eight (438) male Philippine riverine buffaloes with 1,535 BW records and 417 real-time ultrasound scans of EMA and RF scans at the 12th rib were available for the study. BW was taken and adjusted at birth, 6, 12, 18, 24, 30, and 36 months while RF and EMA scans were taken at 12 & 18 mos. Genetic parameters were estimated with a pedigree-based multi-trait animal model using ASREML software.
 Results: The average BW of buffaloes adjusted to 6, 12, 18, 24, 30, and 36 months of age were 135kg, 230.8kg, 323.0kg, 382.7, 453.6, and 502.4kg, respectively. The mean EMA and RF at 12 months were 29.7 cm2 and 3.2mm, respectively. Direct genetic heritabilities were 0.26±0.16, 0.29±0.12, 0.35±0.19 and 0.67±0.32 for birth, BW12mos, EMA12mos and RF12mos, respectively. Maternal genetic heritability for birth weight. was 0.12±0.09. Genetic correlations among traits were positive except between birth and RF.
 Conclusions: Results indicate that ultrasound scanning can be used for selection together with BW at 12mos. and suggest that early performance is an excellent predictor of performance at a later age.

Computer vision system using deep learning to predict rib and loin yield in the fish Colossoma macropomum.

Computer vision system (CVSs) are effective tools that enable large-scale phenotyping with a low-cost and non-invasive method, which avoids animal stress. Economically important traits, such as rib and loin yield, are difficult to measure; therefore, the use of CVS is crucial to accurately predict several measures to allow their inclusion in breeding goals by indirect predictors. Therefore, this study aimed (1) to validate CVS by a deep learning approach and to automatically predict morphometric measurements in tambaqui and (2) to estimate genetic parameters for growth traits and body yield. Data from 365 individuals belonging to 11 full-sib families were evaluated. Seven growth traits were measured. After biometrics, each fish was processed in the following body regions: head, rib, loin, R + L (rib + loin). For deep learning image segmentation, we adopted a method based on the instance segmentation of the Mask R-CNN (Region-based Convolutional Neural Networks) model. Pearson's correlation values between measurements predicted manually and automatically by the CVS were high and positive. Regarding the classification performance, visible differences were detected in only about 3% of the images. Heritability estimates for growth and body yield traits ranged from low to high. The genetic correlations between the percentage of body parts and morphometric characteristics were favorable and highly correlated, except for percentage head, whose correlations were unfavorable. In conclusion, the CVS validated in this image dataset proved to be resilient and can be used for large-scale phenotyping in tambaqui. The weight of the rib and loin are traits under moderate genetic control and should respond to selection. In addition, standard length and pelvis length can be used as an efficient and indirect selection criterion for body yield in this tambaqui population.

Genetic Parameters of Growth Traits and Quantitative Genetic Metrics for Selection and Conservation of Mecheri Sheep of Tamil Nadu.

Determining the genetic and non-genetic sources of variation in a breed is vital for the formulation of strategies for its conservation and improvement. The present study was aimed at estimating the (co)variance components and genetic parameters of Mecheri sheep by fitting six different animal models in the restricted maximum likelihood method, with a preliminary investigation on the performance of animals for non-genetic sources of variation. A total of 2616 lambs were studied, and varying levels of significance were found for the effects of period, season, parity of dam, and birth type on different body-weight traits. Direct heritability estimates derived from the best animal model for body weight at birth, three months, six months, nine months, and twelve months were 0.21, 0.24, 0.10, 0.15, and 0.09, respectively, and the maternal heritability of the corresponding traits was 0.12, 0.05, 0.04, 0.04, and 0.04, respectively. The genetic correlations between the body-weight traits were all positive and moderate-to-strong, except for the correlation between birth weight and the other body-weight traits. The significance of non-genetic factors studied in this work demanded a correction to improve the accuracy of the direct selection of lambs for body-weight traits. The estimated genetic parameters identified the weaning weight as a selection criterion for the improvement in body weight of Mecheri lambs at different ages. Inbred individuals accounted for approximately 13% of the total population in the Mecheri sheep population studied. There were 877 founders in the population, and the actual effective population size was 128.48. The population's mean generation interval was 3.26. The mean inbreeding values ranged from 0.005 to 0.010 across generations. The population's average relatedness ranged from 0.001 to 0.014 across generations. Individual inbreeding was found to be 0.45 per cent for the entire population and 3.4 per cent for the inbred population.

Estimation of genetic parameters for weight and length gains in tambaqui (Colossoma macropomum).

The goal of this study was to determine the genetic parameters for growth traits in tambaqui (Colossoma macropomum) fish of similar age and weight. The data set included monthly measurements of body weight and length from120 fish for a year (1,440 measurements). The study found that weight gain had a heritability estimate of 0.01, while length gain had a heritability estimate of 0.27. There was a high positive correlation (0.84) between weight and length gains. The genetic variance and heritability of body weight decreased with age. This study suggests that breeding programs should select for body weight and weight gain to promote genetic gain in tambaqui. Selecting younger animals can also help reduce costs while still achieving genetic gains.

Environmental Effects and Genetic Parameters for Growth Traits of Lohi Sheep.

Estimating genetic parameters for growth traits is crucial to plan breeding strategies for improving meat production in indigenous sheep breeds. The study first tested the effects of environmental and maternal effects on five growth traits, including birth weight (BWT), weight at 120 days (WT120), weight at 180 days (WT180), weight at 270 days (WT270) and weight at 365 days of age (WT365) and then estimated genetic parameters for these traits using data obtained in 1215 Lohi sheep. The effects of factors, including year (YOB), season (SOB) and type of birth (TOB), age of dam (AOD) and sex on growth traits of Lohi sheep, were examined using analysis of variance (ANOVA) in R software. Sex, TOB and YOB significantly affected all studied traits. The estimates of direct and maternal heritability for BWT and WT120 were 0.15 ± 0.08 and 0.20 ± 0.06, and 0.45 ± 0.16, 0.21 ± 0.08, respectively. The direct heritability estimates for WT180, WT270 and WT365 were 0.20 ± 0.07, 0.21 ± 0.07 and 0.19 ± 0.08, respectively. Due to the high heritability estimate obtained for WT120 compared to other studied traits, and its strong genetic correlation (>0.9) with post-weaning growth traits, it is recommended that selection must be practiced on WT120 to improve the growth performance of Lohi sheep. The results could be used for the development of genetic/genomic selection programs aiming to improve the production performance of the Lohi sheep.

Meta-analysis of genetic parameters for growth traits in meat, wool and dual-purpose sheep breeds in the world using a random-effects model.

There is large variation in genetic parameters in literature for growth traits in sheep. Reliable estimation of genetic parameters is required for developing breeding programmes. The aim of this study was to aggregate results of different studies by meta-analysis to improve reliability of estimated parameters. In the current study, 221 papers that have been published between 1995 and 2021 were reviewed. Using a random-effects model in the Comprehensive Meta-Analysis software, direct and maternal heritabilities, as well as, genetic and phenotypic correlations between growth traits were estimated in meat (M), wool (W) and dual-purpose (D) sheep breeds. The growth traits in this study were birth weight, 3-month weight, 6-month weight, 9-month weight and yearling weight. The combined direct heritability was the lowest for birth weight (0.190 ± 0.004, 0.198 ± 0.003 and 0.196 ± 0.004 for M, W and D breeds, respectively) and the highest for yearling weight (0.264 ± 0.010, 0.304 ± 0.005 and 0.285 ± 0.020 for M, W and D breeds, respectively). The maternal heritability was the lowest for yearling weight (0.085 ± 0.003, 0.055 ± 0.002 and 0.052 ± 0.005 for M, W and D breeds, respectively) and the highest for 6-month weight (0.240 ± 0.088, 0.164 ± 0.001 and 0.162 ± 0.006 for M, W and D breeds, respectively). The phenotypic and genetic correlations were lower between the weights measured at more distant intervals. The lowest genetic correlation was observed between birth weight and yearling weight (0.290 ± 0.051 for W breeds). The small standard errors could indicate that the aggregation of results from different studies improved the reliability of estimated parameters and reduced range of 95% confidence intervals. Hence, the results could be used with greater level of confidence in sheep breeding programmes.

Estimation of Genetic Parameters and Optimum Breeding Programme Design in Korean Flatfish Breeding Population

Olive flounder (Paralichthys olivaceus) is a vital aquaculture species in East Asia. However, few studies that estimate the genetic parameters of this species have been conducted. We estimated the genetic parameters of growth traits and designed an optimum breeding programme for this species. Heritability, genetic and phenotypic correlations, and breeding values were estimated for growth traits: body weight (BW), total length (TL), and condition factor (CF). A linear mixed animal model using the restricted maximum likelihood (REML) algorithm was applied to the statistical analysis of 9 traits (BW, TL, and CF at 11, 18, and 22 months of age) for a total of 54,159 animals from 7 generations. Increases of 13%, 8%, and 6.5% in BW, TL, and CF at the harvest stage were observed, respectively, after 7 generations of selection. The heritabilities of all growth traits were moderate, ranging from 0.35 to 0.46. The phenotypic and genetic correlations between BW and TL were high and positive in all three stages (0.91 and 0.92, 0.91 and 0.93, and 0.88 and 0.91). The estimated breeding values of BW and TL increased over the generations; however, the estimated breeding value of CF fluctuated. The optimum progeny number within full-sib families for an accuracy of 0.632 is suggested to be between 10 and 25. Findings indicated that a considerable response to selection and single-trait selection based on BW would be effective in olive flounder.

"Comparison of Reliability of Animal Models and Bayesian Approach for Estimation of Genetic Parameters of Growth Traits in Chokla Sheep"

"Comparison of Reliability of Animal Models and Bayesian Approach for Estimation of Genetic Parameters of Growth Traits in Chokla Sheep"

Estimation of genetic parameters for growth relevant traits in adult Pacific abalone ( Haliotis discus hannai )

Pacific abalone (Haliotis discus hannai) is one of the most valuable aquaculture species in China. However, the rapid development of the aquaculture industry has caused problem of germplasm degeneration. It is important to carry out genetic improvement of economic traits for H. discus hannai. This study was conducted to estimate genetic parameters of growth traits in Pacific abalone to provide a database for selective breeding programs. Data of 10 growth-related traits—shell length (SL), shell width (SW), shell height (SH), shell weight (SWT), wet weight (WW), foot muscle weight (MW), soft tissue weight (STW), visceral mass weight (VW), foot muscle weight/wet weight ratio (MWR) and soft tissue weight/wet weight ratio (SWR)—were collected from 1059 adults sampled from 115 families. Significant growth differences existed between abalone under different culture modes. Abalone with red shell colour presented poorer growth performance than the normal shell colour group, and their hybrids displayed mid-parent heterosis. The heritability values of SL, SW, SH, SWT, WW, MW and STW were 0.65 ± 0.06, 0.63 ± 0.06, 0.51 ± 0.08, 0.59 ± 0.09, 0.54 ± 0.05, 0.43 ± 0.08 and 0.43 ± 0.08, respectively, indicating high heritability. The heritabilities of VW and MWR were moderate, with estimates of 0.36 ± 0.07 and 0.21 ± 0.06, respectively, and SWR had low heritability with value of 0.17 ± 0.06. Genetic and phenotypic correlations among the growth traits were positive, in the ranges 0.24–0.99 and 0.12–0.99 respectively. Genetic correlation coefficients among most of the growth traits were close to or higher than 0.9. The results of this study demonstrate the genetic improvement potential of Pacific abalone in selective breeding. Traits such as SL, SW, SH and WW could be selected and improved simultaneously.

Response to selection for growth in successive mass selected generations of Iwagaki oyster Crassostrea nippona

The Iwagaki oyster (Crassostrea nippona) is a potential aquaculture species with delicious taste and edibility in summer when the Pacific oyster (Crassostrea gigas) suffer from low meat quality. Although there is an increasing interest in hatchery mass production and field grow-out among farmers, large-scale expansion of C. nippona aquaculture has been compromised by unimproved growth performance. To improve the growth rate of C. nippona, we initiated the mass selective breeding program for fast growth in 2014 and estimated the genetic parameters of growth traits in the first three successive mass-selected generations. Each selected line exhibited better growth performance than the corresponding control group at all sampling dates. At grow-out stage, the average selection response (SR), realized heritability (hR2) and genetic gain (GG) for shell height was 0.45–0.56, 0.27–0.42 and 9.20–11.12% in the three mass selected lines, respectively. A significant increase in GG for shell height was observed in the third-generation selected line compared with that in the first-generation (P < 0.05). Meanwhile, the average SR (0.44–0.49) and GG (11.07–12.46%) for body weight of C. nippona were observed in the selective breeding program after three successive generations of mass selection. The encouraging results obtained in this study suggest that genetic variances still remain at a relatively high level in the breeding populations of C. nippona, and demonstrate the feasibility of improving the growth traits by selective breeding for C. nippona.

Genetic parameters for productive traits and skin quality in Nile tilapia

Tilapia skin has been considered an important biomaterial in the treatment of burns and tissue reconstruction in vaginoplasty. Improvements in tilapia skin quality are of great interest to regenerative medicine. This study aimed to (i) estimate variance components and genetic parameters for growth traits, fillet yield, and skin quality; (ii) assess genetic associations between productive traits and skin thickness; and (iii) investigate the effect of groups with high (HGM) and low (LGM) genetic merit for skin thickness on the expression of genes encoding the α2 and α3 chains of type I collagen in Nile tilapia (Oreochromis niloticus). Components of variance, heritability, and genetic correlations were estimated for skin thickness (ST, measured in millimeters), fillet yield (FY, measured in percentage), and weight at harvest (WH, measured in grams). The database contained records of 1221 mean values of three measurements for ST, 1213 measurements for FY, and 3171 measurements for WH. The sample included animals from the tenth generation of selection of the Nile tilapia breeding program of the State University of Maringá, Brazil. For analysis of gene expression, skin samples were collected from fish with LGM and HGM for ST. Heritability estimates were high for WH (0.71), intermediate for ST (0.59), and moderate for FY (0.21). The repeatability coefficient of ST was high (0.66). The genetic correlation between ST and WH was high and strong (0.77), whereas that between ST and FY was not significant (−0.02). There was a significant difference (p = 0.038) in COL1A3 expression between HGM (7.38 AU) and LGM (4.88 AU) groups. The results indicated that it is possible to increase the thickness and amount of type I collagen fibers in tilapia skin through selection. Genetic correlations indicated that selection for WT positively impacts ST without influencing FY. Selection for weight gain proved to be an effective tool for the production of Nile tilapia skins more suitable for use as xenografts.

Genetic parameters of growth traits, trend of production and reproduction traits, and meat quality status of Ghagus, an indigenous chicken of India.

Indigenous chickens play a vital role in providing nutritional security and economic support for the rural and tribal people in tropical countries like India. Ghagus, an indigenous chicken breed of India, was characterized for growth, production, and reproduction (fertility and hatchability) traits over different generations and for carcass and meat quality traits. Heritability, and genetic and phenotypic correlations among growth traits were estimated using mixed model least squares and maximum likelihood methods. Estimates of heritability of growth traits such as bodyweights at different age and 8-week shank length were high (0.32 to 0.39) in initial generation and moderate to high during latest generation (0.20 to 0.42). The correlations of growth traits with 40-week egg production were positive and significant (P < 0.001). There was improvement in 8-week bodyweight (559.3 ± 4.40g) by 177g over the generations. The average egg production up to 40weeks over the generations was 35.66 eggs. There was also a significant (P < 0.001) increase in egg weights over the generations. The fertility (mean 89.3%) ranged from 85.2 to 92.3%. The hatchability on fertile egg set (mean 90.8%) ranged from 86.5 to 94.1% and it was improved by 3.9% over the generations. The carcass and meat quality study revealed that this breed has the lean meat, high protein, and attractive meat color with desirable meat quality characteristics. The study concluded that the Ghagus breed with self-propagation capacity has the potential to be improved as an indigenous meat-type breed to meet the ever-increasing demand for indigenous chickens' meat in the country.

Genetic studies on the estimates of (Co) variance components for growth traits in Barbari goat

The objectives of the current study were to evaluate the genetic progress and variability for growth traits and also to suggest a suitable direction to the existing breeding program of the Barbari goat population in India. The analysis included 10,648 animals descended from 2697 dams and 420 sires at the ICAR-Central Institute for Research on Goats, Makhdoom between 1993 and 2020 (28 years). The effect of fixed factors such as period and season of kidding, sex of the kid, type of birth, parity of doe, and doe weight at kidding on live weights were significant (P < 0.05). Animal models with average information restricted maximum likelihood (AIREML) approach were used to estimate genetic parameters for growth traits. The mean of inbreeding coefficient for the whole pedigree was 2.16%. For the inbred animals it was 3.32%, indicating within normal estimate for average inbreeding in a nucleus flock. Results suggested that the genetic model for additive direct effects of animal and dam and their covariance, as well as dam's permanent environment, was best for birth weight (BW), weaning weight (WW), weight at six months (6 W), and weight at nine months (9 W), whereas the model with direct effects of animal and dam and their covariance was best for weight at 12 months (12 W). The estimates of direct heritability (h2) for Barbari goat were 0.31 ± 0.04, 0.23 ± 0.03, 0.18 ± 0.03, 0.13 ± 0.03 and 0.21 ± 0.04 for BW, WW, 6 W, 9 W, and 12 W, respectively. However, the estimates were influenced by negative correlation between direct additive effects of animal and dam. We also observed substantial variance for additive maternal effect (0.09–0.15) and maternal permanent environment effect (0.11–0.17) across traits analysed. Pre-weaning growth traits had a significant maternal effect that receded as age advanced. The prospect of selecting Barbari goats for growth traits is indicated by moderate h2 estimates. The positive and desired genetic trend revealed favourable response to selection in the nucleus of the Barbari goat for growth traits. The significant and positive genetic and phenotypic correlation between post-weaning weights (6–9 W= 0.89) suggests scope for early selection of Barbari goats by decreasing the age for selection from 9 to 6 months.

Estimates of (co)variance components and phenotypic and genetic parameters of growth traits and wool traits in Alpine Merino sheep.

The (co)variance components and corresponding phenotypic and genetic parameters for growth traits and wool traits of economic importance were estimated in the Alpine Merino sheep population maintained at Gansu Provincial Sheep Breeding Technology Extension Station in northwestern China. Data from a maximum of 49,474 animals sired by 526 rams and born from 22,531 ewes over 20years from 2000 to 2019 were used in this study. Birth type, age of dam, birth year, sex and/or management group, and age at measurement were initially fitted as fixed effects in an animal model with various random effects. Genetic groups were defined for all animals by the sire breed and breed genotype interacted with dam-strain flocks and were fitted as one of the random effects. Analyses were conducted using a residual maximum likelihood procedure (ASReml). Seven different animal models were fitted for all traits, and the most appropriate model with relevant random effects 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 traits. The estimates of additive direct heritability for birth weight (BWT), weaning weight (WWT), preweaning growth rate (prwADG), postweaning growth rate (powADG), yearling body weight (YWT), average fibre diameter (AFD), greasy fleece weight (GFW), clean fleece weight (CFW), yield (YLD), yearling wool staple length (YSL), coefficient of variation of average fibre diameter (FDcv) and wool visual fineness counts (VFC) were 0.30, 0.18, 0.18, 0.20, 0.29, 0.20, 0.19, 0.20, 0.35, 0.19, 0.16 and 0.13, respectively, with standard errors ranging from 0.02 to 0.05. The corresponding ratios of genetic group variance to additive genetic variance were significant and, respectively, 0.35, 0.80, 0.62, 0.26, 0.13, 1.06, 0.38, 0.64, 0.09, 0.12, 0.06 and 0.58. These results suggest for these traits that there is potential to exploit both the additive genetic variation and between genetic group variation although for most traits the between group variation was smaller than the variation within groups. Favourable genetic correlations were found among the growth traits, and between growth traits and fleece production traits, and among wool traits GFW, CFW, YSL and YLD. This study provides the required estimates of genetic parameters of both growth and wool traits of the new breed for the design of more effective breeding programmes.

English

The objective of this study is to estimate variance-covariance components and genetic parameters for growth traits in Tswana cattle. Genetic analyses for average daily gain (ADGs) and growth traits were conducted using 7223 records of animals which were born between 1996 and 2013 from 1662 dams and 188 sires in 54 contemporary groups. Both univariate and bivariate animal models were used. Heritability estimates for growth traits ranged from 0.12&plusmn;0.03 for BWT to 0.45&plusmn;0.03 for EWT while those obtained for ADGs were 0.24&plusmn;0.03 and 0.31&plusmn;0.04 for ADG1 and ADG2, respectively. Permanent maternal environmental effects were significant for WWT and ADG1. Substantial maternal genetic effects were observed in BWT, WWT and ADG1. Genetic correlations among growth traits and ADGs ranged from 0.19&plusmn;0.07 between BWT and ADG1 to 0.99&plusmn;0.02 between WWT and ADG1. Phenotypic correlations among growth traits and ADGs ranged from 0.19&plusmn;0.01 between BWT and ADG1 to 0.94&plusmn;0.01 between WWT and ADG1. The two selected lines significantly improved annual genetic gain for all the growth traits and ADG1. Genetic gain for EWT was optimally enhanced in S2 than in S1. The control line exhibited significant annual genetic gain in WWT which was not anticipated and perhaps attributed to asymmetry of selection response. Substantial genetic variations were observed in all growth traits and ADGs suggesting that growth improvement can be attained through selection for growth rate. High genetic correlations between growth traits and ADGs indicated that selection for one of these traits may result in indirect correlated response on the other traits. Key words: Bivariate analysis, genetic correlations, heritability, indigenous cattle, maternal effects, genetic variation.

RESISTÊNCIA DO SOLO E ANÁLISES MULTIVARIADAS COMO UM MÉTODO A UXILIAR PARA A SELEÇÃO DE PROGÊNIES DE Calophyllum brasiliense

ABSTRACT Precision silviculture is being developed to manage and improve Calophyllum brasiliense, a tree species associated with wet and swampy soils. This study estimated genetic parameters for growth traits in response to soil resistance as an auxiliary tool for identifying and selecting progenies adapted to water-saturated soils. This was undertaken in a progeny test of C. brasiliense in which 1,200 seedlings grown from seeds collected from a natural population were planted in a randomized complete block design for single-tree plots. Genetic statistical analysis was conducted using the REML/BLUP method. Significant differences (p&lt;0.01) in diameter at breast height were observed among the progenies. The coefficients of genetic variation and heritability at the individual and progeny levels were low for diameter at breast height and height, indicating low genetic control for these traits, while high positive and significant genetic and phenotypic correlations were detected between diameter at breast height and height. Theoretical genetic gains and multivariate statistical analysis indicated three groups of progenies with different degrees of tolerance and adaptability to flooded soils, which could be useful in future breeding programs for this species, although further analysis at advanced ages is still required. The mean heights of tolerant and sensitive progenies were 12 and 58%, respectively, lower than the theoretical values, indicating that constant soil flooding is harmful to this species.

Meta-analysis of performance and genetic parameter estimates for growth and body weight traits of sheep in the tropics

A meta-analysis on 68 articles was performed to combine the estimates of genetic parameters of growth traits in sheep from the tropics. 10 traits were included which met the quality control criteria. Weighted estimates were obtained by combining 275 means, 442 heritability estimates (255 direct, 98 maternal, and 62 common environmental), and 765 correlation estimates (381 phenotypic and 384 genetic). A random-effects model was used and the heterogeneity of parameter estimates was evaluated using the I2-statistic. Direct heritability increased with age from 0.196 at birth to 0.388 at 18-months of age while maternal and common environmental effects decreased with age and ranged between 0.116 to 0.186 and 0.060 to 0.115 respectively. Phenotypic correlations ranged from 0.233 to 0.944 and genetic correlations ranged from 0.356 to 0.922. Weighted least-squares analysis was done to study the effects of non-genetic factors where the distance from the equator was found to significantly affect all the heritability traits. Weighted estimates obtained from this study could be beneficial during the implementation phase of a breeding program which is designed for the genetic improvement of sheep breeds in the tropics.

Dynamic changes in the genetic parameters of growth traits with age and their associations with heterosis in hybrid Liriodendron

Liriodendron plants have been cultivated in many regions of the world for both wood production and landscape ornamentation. Hybrid Liriodendron varieties show obvious growth and resistance heterosis; thus, interspecies hybridization and heterosis utilization constitute the major breeding strategy for Liriodendron plants. Choosing superior crossing parents/combinations and predicting the heterosis of potential hybrid combinations will greatly improve breeding efficiency and accelerate the breeding process. To explore the relationships between genetic parameters and heterosis, we investigated dynamic changes in the genetic parameters of growth traits with age by testing 57 progeny combinations derived from six cross types in Liriodendron. Tree height (H) and diameter at breast height (DBH) were under intermediate to strong genetic control and varied among combinations, indicating that parent-pair selection or combination selection is feasible. Both heritability and combining ability (general combining ability, GCA; specific combining ability, SCA) changed with age, with narrow-sense heritability fluctuating greatly in the early stage and increasing in the late stage, and the combining abilities varied among combinations. Additionally, the GCA of Liriodendron chinense parents was higher than that of Liriodendron tulipifera and hybrid Liriodendron parents, and the SCA of L. tulipifera × L. chinense combinations fluctuated less than that of other combinations. Further, midparent heterosis (MPH) and SCA were significantly positively correlated, suggesting that SCA could be a suitable criterion for predicting growth heterosis. Our findings provide useful clues for selecting parent pairs/combinations and predicting heterosis, which will accelerate Liriodendron tree breeding and shed light on cross-breeding in other plants.