Estimates of direct and maternal (co)variance components as well as genetic parameters of growth traits in Nellore sheep

Evaluation of models for estimation of genetic parameters for post-weaning body measurements and their association with yearling weight in Nellore sheep

OBJECTIVE

The objective of this study was to obtain (co) variance components and genetic parameter estimates for post-weaning body measurements such as body length (BL), height at withers (HW), and chest girth (HG) recorded at six (SBL, SHW, and SHG), nine (NBL, NHW, and NHG) and twelve (YBL, YHW, and YHG) months of age along with yearling weight (YW) in Nellore sheep maintained at livestock research station, Palamaner, Andhra Pradesh, India and also the association among body measurements with YW was studied.

METHODS

Data on 2,076 Nellore sheep (descended from 75 sires and 522 dams) recorded between 2007 and 2016 (10 years) were utilized in the study. Lambing year, sex of lamb, season of lambing and parity of dam were included in the model as fixed effects and ewe weight was kept as a covariate. Analyses were conducted with six animal models with different combinations of direct and maternal genetic effects using restricted maximum likelihood procedure. Best model for each trait was determined based on Akaike's information criterion.

RESULTS

Moderate estimates of direct heritability were obtained for the studied traits viz., BL (0.02 to 0.24), HW (0.31 to 0.49), and CG (0.08 to 0.35) and their corresponding maternal heritability estimates were in the range of 0.00 to 0.07 (BL), 0.13 to 0.17 (HW), and 0.07 to 0.13 (CG), respectively. Positive direct genetic and phenotypic correlations among the traits and they ranged from 0.07 (YBL-YW) to 0.99 (SBL-SHG, SHG-YW, and NBL-YBL) and 0.01 (SBL-YBL) to 0.99 (NBL-NHG), respectively. Further, the genetic correlations among all the body measurements and YW were positive and ranged from 0.07 (YW and YBL) to 0.99 (YW and SHG).

CONCLUSION

There was a strong association of chest girth at six months with YW. Further, it is indicated that moderate improvement of post-weaning body measurements in Nellore sheep would be possible through selection.

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.

Comparative proteomics reveals genetic mechanisms of body weight in Hu sheep and Dorper sheep

Body weight (BW) is a critical economic trait for meat production in sheep, and it is a complex trait affected by numerous elements. The aim of this study was to investigate the genetic mechanisms of sheep BW by a label-free proteomics approach. The result showed, a total of 27, 14, 61, and 65 differentially abundant proteins (DAPs) were identified in the Hu_HBW vs. Hu_LBW, DP_HBW vs. DP_LBW, Hu_HBW vs. DP_HBW, and Hu_LBW vs. DP_LBW comparisons, respectively. Five proteins (including ILK, AHCYL2, MLIP, CYB5A, and SMTNL1) related to fat synthesis and muscle development were detected in the Hu sheep group. In the Dorper sheep group, the screened DAPs strictly related to muscle development and fat synthesis were significantly enriched in MAP kinase activity (MAPK12), Arachidonic acid metabolism, and Steroid hormone biosynthesis (PGFS, LOC101107119) pathways. Several DAPs related to immune responses (SERPINA1, FGG, SERPINC1, and LOC101108131), fat deposition (APOH, GC, AHSG, SKP1, ACSL1, ACAT1, and ACADS), and muscle development (LMOD3 and LRRC39) were detected in the Hu vs. Dorper sheep comparison. These analyses indicated that the BW of sheep is regulated via a variety of pathways, and these DAPs can be further investigated as candidate markers for predicting the BW of sheep. SIGNIFICANCE: Body weight is one of the key traits in sheep and involves multiple coordinated regulatory mechanisms, but the genetic mechanism of BW is still unclear in sheep. In the current study, the label-free method was used to identify the proteins and pathways related to BW using LT muscle of Hu sheep and Dorper sheep with different BW. These findings will provide new candidate proteins and vital pathways into the molecular mechanisms involved growth traits in sheep.

Phenotypic and genetic parameter estimates for early growth, growth rate and growth efficiency-related traits of Fogera cattle in Ethiopia

BACKGROUND

Understanding the phenotypic and genetic parameter estimates of growth traits is important for an effective livestock genetic improvement programme.

OBJECTIVES

In this study, we evaluated the phenotypic performances and estimated genetic parameters for birthweight (BWT), weaning weight (WWT), pre-weaning average daily gain (PADG), pre-weaning Kleiber ratio (PKR), pre-weaning growth efficiency (PGE) and pre-weaning relative growth rate (PRGR) of Fogera cattle in Ethiopia.

METHODS

Growth data collected from 2000 to 2018 in Andassa Livestock Research Center were used for the study. General linear model of SAS 9.1 was used to estimate the least squares mean (LSM) ± standard error (SE) for phenotypic performances, and AI-REML of Wombat software combined with a series of five single-trait animal models to estimate phenotypic variance and its direct, maternal and residual components. Calf sex, calf birth season and calf birth year were the fixed effects considered.

RESULTS

The overall LSM ± SE BWT, WWT, PADG, PKR, PGE and PRGR were 21.28 ± 0.05 kg, 97.99 ± 0.67 kg, 320.29 ± 2.79 g, 10.10 ± 0.04, 3.51 ± 0.35 and 1.95 ± 0.00, respectively. All the fixed effects considered significantly (p < 0.001) affected all the traits. The direct heritability estimates for BWT, WWT, PADG, PKR, PGE and PRGR were 0.21 ± 0.07, 0.26 ± 0.01, 0.55 ± 0.19, 0.53 ± 0.18, 0.33 ± 0.00 and 0.50 ± 0.00, respectively. The genetic correlations among the traits ranged from negative (-0.20 ± 0.04; BWT-PKR) to positive (0.99 ± 0.00; BW-PGE, BW-GR, WWT-PGE, WWT-PGR, ADG-PGR, PKR-PGR, PKR-PGE and PGE-PGR). Similarly, the phenotypic correlations ranged from -0.03 ± 0.20 to 0.99 ± 0.01; BWT-PGE, BWT-PRGR, WWT-PGE, WWT-PRGR, PKR-PGE, PKR-PRGR and PGE-PRGR).

CONCLUSION

The positive and larger phenotypic and genetic correlations between most of the traits implied that selection based on one trait could improve the other traits. However, the negative phenotypic and genetic correlation between BWT-PKRA implies that selection of Fogera calves based on either of the traits has an adverse effect on the other. Therefore, caution should be taken when designing the selection criteria for growth improvement.

Genetic parameters and direct and maternal effects for important traits in late-feathering Qingyuan partridge hens in China

Qingyuan partridge chicken is an important indigenous chicken in China. In its breeding schemes, chickens are usually selected at the age of 105-day-old for five traits, including body weight (BW), shank length (SL), shank girth (SG), comb height (CH) and feather maturity (FM). At present, genetic parameters of the aforementioned traits have still not been studied in Qingyuan partridge chickens. The objectives of this study were the following: (1) to investigate whether the optimal statistical models of these traits need to consider maternal genetic and permanent environmental effects in late-feathering Qingyuan partridge hens, and (2) to estimate genetic parameters for these traits based on the optimal models. The numbers of records for BW, SL, SG, CH and FM were 13,721, 13,671, 13,670, 13,669 and 13,672, respectively. Variance components were estimated using average information-restricted maximum likelihood method, and the optimal model was determined based on Bayesian information criterion. More specifically, the optimal model for BW considered maternal genetic and permanent environmental effects in addition to direct additive genetic effect; SL, SG and FM considered direct and maternal genetic effects; and CH considered direct and maternal genetic effects, and the covariance between them. The direct heritabilities of these traits estimated using the optimal models were 0.21 ± 0.04, 0.30 ± 0.05, 0.40 ± 0.05, 0.59 ± 0.09 and 0.09 ± 0.04, respectively; the maternal heritabilities were 0.01 ± 0.04, 0.05 ± 0.05, 0.04 ± 0.05, 0.09 ± 0.09 and 0.03 ± 0.04, respectively. Maternal genetic effect evidently played an important part in FM and maternal heritability accounted for 30 per cent of total heritability. Furthermore, the direct and maternal genetic effects for CH were estimated to be negatively and moderately correlated (-0.51 ± 0.11). For all traits, neglecting existent maternal effects biased the estimation of direct heritability. Therefore, to implement optimum breeding strategies for improvement of these traits in Qingyuan partridge hens, maternal effects should be taken into consideration.

Evaluation of selection program by assessing the genetic diversity and inbreeding effects on Nellore sheep growth through pedigree analysis

Objective

The main objectives of the present study were to assess the genetic diversity, population structure and to appraise the efficiency of ongoing selective breeding program in the closed nucleus herd of Nellore sheep through pedigree analysis.

Methods

Information utilized in the study was collected from the pedigree records of Livestock Research Station, Palamaner during the period from 1989 to 2016. Genealogical parameters like generation interval, pedigree completeness, inbreeding level, average relatedness among the animals and genetic conservation index were estimated based on gene origin probabilities. Lambs born during 2012 and 2016 were considered as reference population. Two animal models either with the use of F_i or ΔF_i as linear co-variables were evaluated to know the effects of inbreeding on the growth traits of Nellore sheep.

Results

Average generation interval and realized effective population size for the reference cohort were estimated as 3.38±0.10 and 91.56±1.58, respectively and the average inbreeding coefficient for reference population was 3.32%. Similarly, the effective number of founders, ancestors and founder genome equivalent of the reference population were observed as 47, 37, and 22.48, respectively. Fifty per cent of the genetic variability was explained by 14 influential ancestors in the reference cohort. The ratio f_e/f_a obtained in the study was 1.21, which is an indicator of bottlenecks in the population. The number of equivalent generations obtained in the study was 4.23 and this estimate suggested the fair depth of the pedigree.

Conclusion

Study suggested that the population had decent levels of genetic diversity and a non-significant influence of inbreeding coefficient on growth traits of Nellore lambs. However, small portion of genetic diversity was lost due to a disproportionate contribution of founders and bottlenecks. Hence, breeding strategies which improve the genetic gain, widens the selection process and with optimum levels of inbreeding are recommended for the herd.