Variance components and genetic parameters of growth traits and Kleiber ratio in Muzaffarnagari sheep

Genetic analysis of body weight and growth curve parameters in Muzaffarnagari sheep of India

The objective of this study was to estimate genetic effects on parameters of the Brody and Richards growth curves using body weight records from birth to 12 months of age on 2287 Muzaffarnagari lamb for a period of 29 years (1976-2004). Estimated growth curve parameters were analysed using six univariate animal models, and genetic correlations among and between the parameters of each function and between parameters of the functions and observed birth and yearling weights were estimated using bivariate analyses. Significant environmental factors including birth year, sex, season, birth status and dam parity were included as fixed effects in all models. Likelihood ratio tests indicated that maternal genetic effects were significant only for birth weight (BW) and degree of maturity at birth (u0) for the Brody and Richards functions. For these traits, direct heritabilities were similar (0.21, 0.19 and 0.17, respectively), but the estimated maternal heritability for BW (0.18) was twice that of u0 for both functions. Heritabilites for yearling weight and asymptotic final body weights for the Brody and Richards functions were 0.28, 0.17 and 0.21, respectively. The remaining growth curve parameters were lowly heritable, ranging from zero for the predicted degree of maturity at the age of maximum growth rate for the Richards function to 0.08 for the maturing rate parameter of the Brody function. Genetic correlations between corresponding parameters for different growth functions exceeded 0.88. Our results showed that the Brody and Richards functions had similar genetic architecture, but the Richards function had no apparent advantages over the more easily interpreted Brody function. Failure to identify maternal genetic effects on maturing rate parameters suggested that both functions failed to identify potentially important maternal genetic effects. Therefore, there is no usefulness of estimated growth curve parameters in selection compared to the simple multi-trait genetic evaluations of individual body weights.

Comparison of different animal models for estimating genetic parameters for early growth traits and reproductive traits in Tianmu Sainuo sheep

As the economic level of individuals rises, so too does the demand for mutton. Enhancing the breeds of mutton sheep not only boosts production efficiency and economic benefits but also fosters the sustainable growth of the mutton sheep breeding industry. Thus, this study examines the early growth and reproductive traits of Tianmu Sainuo sheep, analyzing the genetic interactions among these traits to furnish a theoretical foundation for refining breeding strategies and expediting the genetic advancement of this breed. The investigation compiled 29,966 data entries, involving 111 sires for birth weight (BWT) and 113 for other metrics. The data encompassed 10,415 BWT records from 1,633 dams, 12,753 weaning weight (WWT) records from 1,570 dams, 12,793 average daily gain (ADG) records from 1,597 dams, and 13,594 litter size (LS) records from 1,499 dams. Utilizing the GLM procedure in SAS 9.2 software, the study analyzed the non-genetic influences on lamb BWT, WWT, ADG, and LS. Concurrently, DMU software estimated the variance components across various animal models for each trait. Employing the Akaike Information Criterion (AIC) and likelihood ratio test (LRT), six models were tested, incorporating or excluding maternal inheritance and environmental impacts, to identify the optimal model for deriving genetic parameters. The findings reveal that birth year (BY), birth quarter (BQ), birth type (BT), age of mother (AM), and birth sex (BS) exerted significant impacts on BWT, WWT, and ADG (p < 0.01). Additionally, BQ and AM significantly influenced LS (p < 0.01). The most accurate genetic evaluation model determined the heritability of BWT, WWT, ADG, and LS to be 0.0695, 0.0849, 0.0777, and 0.1252, respectively.

Multiple-trait and structural equation modelling approaches to infer genetic relationships between tail length and weight traits in Merinoland sheep

Tail docking is routinely conducted in long-tailed sheep breeds to prevent flystrike infections, but it is not in agreement with legal guidelines and animal welfare issues. Selection on short tails is a sustainable alternative in this regard, but side effects on other breeding goal traits are unclear. In consequence, the present study aimed to estimate genetic parameters for tail length (TL) at birth, birth weight (BW), weaning weight (WW) and postweaning weight (PWW) at the slaughtering date considering single-trait (STM), multiple-trait (MTM) and structural equation models (SEM) with different random effects, and accordingly, different covariance structures. The SEM considered time-lagged recursive relationships among response variables in three different pathways. The first path pertained to the effect of TL on WW and of WW on PWW. The second path reflected the effect of BW on WW and of WW on PWW. The third path was the recursive effect of TL on PWW. The phenotypic data consisted of 2803 records for TL, 13,042 records for BW, 1556 records for WW and 3986 records for PWW from Merinoland lambs. Lambs were born in the period from 1995 to 2021 and kept at the university Gießen research station, Germany, with their naturally long tails. Genetic statistical model evaluation based on Bayesian and Akaike's information criteria suggested models simultaneously considering direct genetic, maternal genetic and maternal permanent environmental effects and respective covariances. For statistical models including the same random effects and covariance structures, SEM were superior over MTM. The direct heritability for TL from the best-fitting STM was 0.60 ± 0.08, indicating the potential for genetic reduction of tail length within a few generations. For growth traits, the direct heritabilities ranged from 0.16 ± 0.03 for BW to 0.31 ± 0.09 for PWW. The maternal heritabilities were 0.03 ± 0.03 for TL, 0.12 ± 0.02 for BW, 0.04 ± 0.03 for WW and 0.07 ± 0.03 for PWW, reflecting small, but the non-significant influence of uterine characteristics on the tail development. The direct genetic correlations between TL and all weight traits were positive and very similar to MTM and SEM but reflected antagonistic genetic relationships from a breeding perspective. Oppositely, the structural equation coefficients reflecting trait associations phenotypically were negative (favourable) for the time-lagged effects of TL on WW and on PWW. As an explanation, lambs with long and woolly tails have an increased risk for contamination with dirt and dust causing infections, which in turn impairs the body weight development. In conclusion, breeding on short tails should consider trait-associated environmental risk factors, for example, disease susceptibility, which can be mimicked via SEM approaches.

Growth rate and efficiency-related traits in Kermani lambs: estimations of (co)variance components and genetic parameters

Using Kermani sheep, the current study estimated (co)variance components and genetic parameters for average daily gain, Kleiber's ratio, growth efficiency, and relative growth rate. Data were analyzed by the average information restricted maximum likelihood (AI-REML) method using six animal models with different combinations of direct and maternal effects. The best-fitting model was determined after testing for improvement in log-likelihood values. The estimates of h² for average daily gain (ADG), Klieber's ratio (KR), growth efficiency (GE), and relative growth rate (RGR) in pre- and post-weaning phases were 0.13 ± 0.6 and 0.17 ± 0.02, 0.12 ± 0.04, and 0.16 ± 0.03; 0.05 ± 0.05 and 0.07 ± 0.03 and 0.06 ± 0.02 and 0.07 ± 0.01, respectively. Maternal heritabilities (m²) ranged from 0.03 ± 0.01 for relative growth rate in pre-weaning phase to 0.11 ± 0.04 for average daily gain in post-weaning period. The maternal permanent environmental component (Pe²) accounted for 3 to 13% to the phenotypic variance for all the studied traits. Estimated values of additive coefficient of variations (CV_A) ranged from 2.79% for relative growth rate at 6 months of age to 23.74% for growth efficiency at yearling age. Genetic and phenotypic correlations among traits were ranged from -0.687 to 0.946 and -0.648 to 0.918, respectively. The result indicated that selection for growth rate and efficiency-related traits would also be less effective in achieving genetic change, because there was little additive genetic variation among Kermani lambs.

Growth and growth curve analysis in Dorper × Tumele crossbred sheep under a smallholder management system

This study aimed to evaluate the growth performance and Kleiber ratio (KR) and to determine the growth curve of Dorper × Tumele sheep under a smallholder management system. Growth and efficiency-related traits were analyzed by using the general linear model (GLM) procedure of SAS. Gompertz, Logistics, Brody, Monomolecular, and Negative exponential models were used to determine the growth curve, and growth curve parameters were estimated via the nonlinear regression model (NLIN) procedure of SAS. The overall least-squares means of the birth weight, weaning weight, 6-month weight, and yearling weight were 3.29, 13.7, 17.3, and 23.4 kg, respectively. Dorper × Tumele lambs grew faster during the preweaning period (115.3 ± 1.19 g day^-1) than during the postweaning periods (44.1 ± 1.26 g day^-1 to 33.5 ± 1.13 g day^-1). Likewise, a higher KR was observed during the pre-weaning age (16.1 ± 0.08 g/day/kg^0.75) than during postweaning periods (5.08 ± 0.13 g/day/kg^0.75 to 3.10 ± 0.09 g/day/kg^0.75). Brody, a model without an inflection point was the best-fitted growth function for Dorper × Tumele sheep under a smallholder management system. The highest and lowest asymptotic weight was observed for Brody (23.8 ± 0.22 kg) and Logistics (20.7 ± 0.11 kg) models, respectively. The maturation rate ranged between 0.21 (Brody) and 0.66 (Logistics). Based on the Brody model, the correlation between asymptotic weight and maturity rate was -0.92. The growth parameter estimate in this study indicates that Dorper × indigenous sheep had a better speed to achieve mature weight and the early mature crossbred sheep are less likely to exhibit high adult weight. The rapid growth of crossbred sheep during the early period can provide more profit to the farmer by reducing the cost of sheep production inputs. Therefore, crossing Tumele with Dorper sheep and integrating with improved management would be suggested to improve productivity and profit from sheep production.

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.

Genetic and phenotypic parameters for feed efficiency and component traits in American mink

Feed cost is the largest expense of mink production systems, and therefore, improvement of feed efficiency (FE) through selection for high feed efficient mink is a practical way to increase the mink industry's sustainability. In this study, we estimated the heritability, phenotypic and genetic correlations for different FE measures and component traits, including harvest weight (HW), harvest length (HL), final body length (FBL), final body weight (FBW), average daily gain (ADG), daily feed intake (DFI), feed conversion ratio (FCR), residual feed intake (RFI), residual gain (RG), residual intake and gain (RIG), and Kleiber ratio (KR), using data from 2,288 American mink (for HW and HL), and 1,038-1,906 American mink (for other traits). Significance (P < 0.05) of fixed effects (farm, sex, and color-type), a covariate (age of animal), and random effects (additive genetic, maternal, and common litter) were evaluated through univariate models implemented in ASReml-R version 4. Genetic parameters were estimated via fitting a set of bivariate models using ASReml-R version 4. Estimates of heritabilities (±SE) were 0.28±0.06, 0.23±0.06, 0.28±0.10, 0.27±0.11, 0.25±0.09, 0.26±0.09, 0.20±0.09, 0.23±0.09, 0.21±0.10, 0.25±0.10, and 0.26±0.10 for HW, HL, FBL, FBW, ADG, DFI, FCR, RFI, RG, RIG, and KR, respectively. RIG had favorable genetic correlations with DFI (-0.62±0.24) and ADG (0.58±0.21), and non-significant (P > 0.05) genetic correlations with FBW (0.14±0.31) and FBL (-0.15±0.31). These results revealed that RIG might be superior trait as it guarantees reduced feed intake with faster-growing mink yet with no negative impacts on body weight and length. In addition, the strong positive genetic correlations (±SE) between KR with component traits (0.88±0.11 with FBW; 0.68±0.17 with FBL; and 0.97±0.02 with ADG) suggested KR as an applicable indirect measure of FE for improvement of component traits as it did not require the individual feed intake to be measured. Overall, our results confirmed the possibility of including FE traits in mink breeding programs to effectively select feed-efficient animals.

Genetic and non-genetic parameter estimates for growth traits and Kleiber ratios in Dorper × indigenous sheep

Genetic improvement programme will only be successful when accompanied by a good understanding of the influence of different environmental factors, knowledge of the genetic parameters and the genetic relationships between the traits of interest. This study aimed to evaluate the influence of non-genetic factors on growth traits and Kleiber ratios and to estimate genetic parameters for early growth traits in Dorper × indigenous crossbred sheep. The effects of fixed factors were analysed by the general linear model procedure of statistical analysis system, while the genetic parameters were estimated using a WOMBAT computer program fitted animal model. The overall least-square mean for birth weight (BRW), weaning weight (3MW), six-month weight, nine-month weight, and yearling weight were 3.03 ± 0.02, 14.5 ± 0.18, 20.4 ± 0.26, 24.8 ± 0.31, and 28.3 ± 0.40 kg, respectively. The overall least-square mean for Kleiber ratio from birth to weaning (KR1), weaning to six months, six to nine months and nine months to yearling age were 16.8 ± 0.10, 6.41 ± 0.17, 4.55 ± 0.21 and 3.38 ± 0.20 g/kg of metabolic weight, respectively. The inclusion of maternal genetic effect had a significant influence on BRW, and it explains 20% of the phenotypic variation. The total heritability estimates for BRW, 3MW, birth to weaning average daily weight gain and KR1 were 0.10, 0.14, 0.16 and 0.12, respectively. The phenotypic correlation varied from -0.11 ± 0.05 to 0.98 ± 0.02, whereas the direct genetic correlation ranged from -0.32 ± 0.40 to 0.98 ± 0.17. The mean inbreeding coefficient was 0.105% with an annual rate of 0.02%. The heritability estimates for growth traits and Kleiber ratio suggest that slow genetic progress would be expected from the selection. However, the integration of selection with crossbreeding programme can enhance genetic gain. Therefore, selection should be conducted based on breeding values estimated from multiple information sources to increase the selection response.

Genetic analysis of sexual dimorphism in growth of Jamunapari goats of India

A genetic study of sexual size dimorphism (SSD) in Jamunapari goats was carried out to identify differences between sexes in genetic control of body weight at birth and at 3 (weaning), 6, 9 and 12 months of age. A total of 6,687 kids out of 264 sires and 1,704 dams were used in the study. Estimates of SSD were derived from male:female body weight ratios. Males were 9.9, 6.8, 9.3, 13.7 and 16.8% heavier than females at birth and at 3, 6, 9 and 12 months of age, respectively, demonstrating modest SSD. Phenotypic standard deviations were larger for male kids and tended to be proportional to body weight means. However, males also had somewhat greater phenotypic coefficients of variation and total resemblance among relatives. Additive direct genetic correlations between body weights of males and females exceeded 0.96 at birth and weaning. Corresponding additive maternal correlations exceeded 0.99. Additive direct correlations between sexes were somewhat less than unity for postweaning weights but exceeded 0.80 in multi-trait models. Our results indicated that body weights could be treated as the same trait in males and females, but the use of different phenotypic variances for the two sexes would improve accuracies of breeding value predictions. High genetic correlations between body weights in males and females suggest limited opportunity to use sex-specific selection to create or modify SSD or create divergent body weight phenotypes between sexes.

Impact of mother genetic and resource environment on her offspring's growth features in Munjal sheep

The present study evaluated maternal and additive influences that contribute to phenotypic variation in various growth traits in Munjal sheep. The targeted traits that pertained to 2278 records of 706 lambs were birth weight (BWT), weaning weight (WT3), 6-month body weight (WT6), 12-month body weight (WT12), average daily gain (ADG1: 0-3 months; ADG2: 3-6 months, ADG3: 6-12 months of age) and their corresponding Kleiber ratios designated as KR1, KR2 and KR3. The direct heritability estimates for BWT, WT3, WT6, WT12, ADG1, ADG2, ADG3, KR1, KR2 and KR3 under animal models were 0.20 ± 0.08, 0.28 ± 0.08, 0.17 ± 0.07, 0.47 ± 0.09, 0.33 ± 0.08, 0.09 ± 0.06, 0.36 ± 0.10, 0.33 ± 0.08, 0.09 ± 0.06 and 0.32 ± 0.10, respectively. The estimates of maternal genetic effects contributed significantly and were 8% and 7% for BWT and WT3 traits, respectively, which highlighted the considerable role of maternal effects on early growth traits. Genetic and phenotypic correlations ranged from moderate to high between weaning and post-weaning traits. It was concluded that early selection that considered additive as well as maternal effects at weaning age may be delivered to the desired genetic progress in Munjal sheep.

Bayesian estimate of genetic parameters for growth traits in Lori Bakhtiari sheep

The information of birth (10,017 records), weaning (9439 records), 6 months (7669 records), 9 months (4536 records), and yearling weights (417 records) collected from 1989 to 2016 by the Lori Bakhtiari (Sholi) sheep breeding station located in Shahrekord were used to estimate the genotypic and phenotypic parameters of growth traits of Lori Bakhtiari sheep. The components of variance and genetic parameters were estimated by the Bayesian statistical method based on the Gibbs sampling technique due to the high accuracy of this method. Factors including birth year, lamb sex, birth type, and maternal age at lambing have significant effects on all of these traits (P < 0.01) and were considered fixed effects in the statistical model for estimation of genetic parameters. Lamb weight at weaning was used as a covariate in the model. Based on the models with the lowest Akaike information criterion, direct heritability for birth, weaning, 6-month, 9-month, and yearling weights were 0.36, 0.18, 0.21, 0.27, and 0.32, respectively. The moderate heritability obtained for the studied traits pointed up the effectiveness of selection in genetic improvement, but the environmental conditions should be improved for better performance of weight traits.

Evaluating animal models comprising direct and maternal effects associated with growth rates and the Kleiber ratio in Harnali sheep

The present work evaluated animal models comprising direct and maternal effects to estimate (co)variance components and genetic parameters of growth rates and Kleiber ratio in Harnali sheep. The information on pedigree and targeted traits of 1862 lambs born to 144 sires and 591 dams was collected for the period from 1998 to 2018. The traits studied were average daily gain from birth to 3 months of age (ADG1), 3 months to 6 months of age (ADG2), and 6 months to 12 months of age (ADG3) and their corresponding Kleiber ratios as KR1, KR2 and KR3, respectively. The statistical methods included the general linear model for analyzing the effects of fixed factors and animal models for deriving variance components for targeted traits. According to best model evaluated on the basis of likelihood ratio test, the estimated direct heritability was low in magnitude and ranged from 0.04 to 0.14. Direct heritability estimates for ADG1, ADG2, ADG3, KR1, KR2 and KR3 were 0.06, 0.14, 0.05, 0.04, 0.11 and 0.05, respectively. The maternal genetic effects contributed (4-7%) significantly for ADG1, KR1 and KR2 traits. The genetic correlations ranged from -0.35 ± 0.11 (ADG1-KR2) to 0.98 ± 0.01 (ADG2-KR2 and ADG3-KR3) and phenotypic correlations ranged from -0.36 ± 0.02 to 0.98 ± 0.01 for ADG1-KR2 and ADG2-KR2, respectively. The significant maternal effects along with low levels of direct effects for average daily gain and Kleiber ratio at different age group should be considered while setting selection and managerial strategies to achieve anticipated growth rates in Harnali sheep.

Genetic Selection for Resistance to Gastrointestinal Parasitism in Meat Goats and Hair Sheep through a Performance Test with Artificial Infection of Haemonchus contortus

Simple Summary

Internal parasitism has been an important constraint to small ruminant production and anthelmintic resistance has become a worldwide issue. This study evaluated a 3-year genetic selection program through activities on-farm and a centralized performance test and also provided estimates of genetic parameters of growth and response to artificial infection with Haemonchus contortus by goats and sheep in the southcentral USA. Considerable species as well as breed differences were found in average daily gain and response to parasite infection. Average daily gain was greater for Boer than for Kiko and Spanish goats and slightly greater for Dorper than for St. Croix sheep. Infection level (number of eggs found in feces) of Spanish and St. Croix were relatively low each year, whereas that of Kiko and Dorper was lower after selection. An indicator of anemia (packed cell volume) did not always reflect infection level, which is probably reflective of differences among animals in resilience and susceptibility to haemonchosis. Moderate to high heritabilities were found for growth performance and response to parasite infection for growing meat goat and hair sheep males under a standardized environment that suggests considerable potential for genetic improvement through selection.

Abstract

Internal parasitism has been the leading cause of morbidity and mortality in small ruminants in many areas such as the southcentral USA. Among the different approaches and management practices to cope with internal parasitism, genetic selection for internal parasite resistance is recognized as one with considerable potential long-term impact. A central performance test with artificial infection of Haemonchus contortus for selection of growing meat goats and hair sheep for breeding to increase resistance to internal parasitism and on-farm selection of females was conducted for 3 years. The results varied considerably among breeds of goats and flocks of sheep. Spanish goats and St. Croix sheep maintained relatively low fecal egg count (FEC) each year, whereas for goats categorized as being of high resistance and Dorper sheep FEC decreased with advancing year. Packed call volume (PCV) and total serum immunoglobulin (Ig) levels were not strongly related to FEC. Genetic parameters varied between the two species, which might be related to previous selection pressure exerted for parasite resistance. Heritability of FEC was higher in goats than sheep. The genetic correlation between FEC and IgM and IgG was negative for both species, which suggests possible genetic association. Genetic and phenotypic correlations between ADG and FEC were nonsignificant for both species. In conclusion, different relationships of FEC and PCV between species require careful attention during selection and the lack of relationship between ADG and FEC suggests that selection of growing male meat goats and hair sheep for resistance to internal parasitism will not adversely affect growth performance.

Genetic analysis of sexual size dimorphism in Markhoz goat

Genetic bases of sexual size dimorphism (SSD) in Markhoz goat (5268 kids descended from 242 sires and 1499 dams) were unraveled as it was thought that sex-specific genetic mechanism is in the place governing SSD of birth weight (BW), weaning weight at 90 days of age (WW_90d), and post-weaning weights at 6 (W6), 9 (W9), and 12 (W12) months of age. Male kids excelled for BW, WW_90d, W6, W9, and W12 than their female counterparts in the tune of 10, 17, 14, 17, and 23%, respectively. Estimates of sexual dimorphism levels (expressed as M/F) were 1.09, 1.17, 1.14, 1.17, and 1.23 for BW, WW_90d, W6, W9, and W12, respectively, which indicated relatively low levels of sexual size dimorphism in the studied traits. Though the additive genetic, residual and phenotypic variances were higher in males than females, for mostly all studied traits, but the heritability estimates for all traits except birth weight were higher in females. Differences in direct and maternal effects between male and female kids indicated that body weights traits could be treated as separate trait for male and female kids. Cross-sex genetic correlations revealed that almost all ages, genetic correlations between the two sexes, were high, and the lowest estimate (0.88) was for W6, which highlighted this trait as the most dimorphic trait in this breed. High and positive genetic correlations between the sexes indicated that selection for body weight in males would result in a correlated response in females and vice versa and, consequently, would prevent phenotypic divergence.

Analysis of X chromosome and autosomal genetic effects on growth and efficiency-related traits in sheep

Abstract Context It is believed that the X chromosome plays an important role in influencing quantitative traits. Despite this, until recently, X-linked genetic effects have not been considered in models to estimate genetic parameters for economically important traits of livestock. Aims A large dataset was analysed to quantify autosomal additive genetic, X-linked additive genetic and maternal effects on growth and efficiency-related traits in Baluchi sheep. Methods Traits included bodyweight at birth, weaning (WW), 6 months (W6), 9 months and yearling age, pre- and post-weaning average daily gain, pre- and post-weaning Kleiber ratio, pre- and post-weaning efficiency of growth (EFb), and pre- and post-weaning relative growth rate. Each trait was analysed using the REML procedure fitting a series of eight univariate animal models. For each trait, the most appropriate model was selected by the Akaike information criterion and Bayesian information criterion. Key results The X-linked genetic effect was significant only in models fitted to EFb, where the estimate of X-linked heritability was 0.02 ± 0.01 from the best model. Other traits were not affected significantly by X-linked genetic effects. Estimates of autosomal heritability () for growth traits were between 0.06 ± 0.02 (post-weaning average daily gain, pre-weaning relative growth rate) and 0.22 ± 0.04 (bodyweight at yearling age), and ranged between 0.02 ± 0.01 (EFb) and 0.08 ± 0.02 (pre-weaning Kleiber ratio) for efficiency-related traits. Maternal effects significantly contributed to phenotypic variation of most traits, with larger effects on traits measured early in life. For EFb, the Spearman’s correlation between breeding values including and excluding X-linked effects was 0.95. It was 1.00 for traits that were not affected by X-linked genetic effects. Conclusions Although the proportion of phenotypic variance attributed to X-linked loci for most traits was zero, the importance of X-linked genetic effects should be at least tested in models when estimating variance components for growth and efficiency traits of Baluchi sheep. Implications As estimates of genetic parameters are breed-specific, we recommend for growth and efficiency traits of sheep that the importance of X-linked genetic effects should be evaluated to assess if these effects should be included in models used in genetic evaluation.

Genetic and non-genetic parameters of Kleiber ratio in Pantja goat under field conditions of Tarai region of Uttarakhand

A study was conducted to estimate the Kleiber ratio of 805 Pantja kids of 514 goats sired by 26 bucks maintained by registered farmers under All India Co-ordinated Research Project on Goats (Pantja field unit) during 2015–16. The overall least-squares mean and their standard error for Kleiber ratio at 0–3, 3–6, 6–9 and 9–12 months of age were 15.29±0.16, 5.50±0.15, 4.24±0.09 and 3.53±0.37 g respectively. The random effect of sire had a highly significant effect on KR1 (0–3 months) and KR2 (3–6 months) whereas, the effect was significant on KR3 (6–9 months) and KR4 (9–12 months). The heritability estimate for Kleiber ratio was 0.28±0.09, 0.27±0.09, 0.22±0.08 and 0.04±0.03 at 0–3, 3–6, 6–9 and 9–12 months of age respectively. Most of the genetic and phenotypic correlations of Kleiber ratio were negative between different periods. It may be concluded that the pre-weaning Kleiber ratio was higher which indicated that the kids were given full care during this period. The post-weaning Kleiber ratio can be improved through better management of kids after weaning.

Direct and maternal variance components and genetic parameters for average daily body weight gain and Kleiber ratios in Nellore sheep

The objective of the present study was to estimate variance components and genetic parameters for average daily gain from birth to weaning (ADGa), birth to 6 months (ADGb) and 3 to 6 months (ADGc) and corresponding Kleiber ratios (Ka, Kb, and Kc) in Nellore sheep. Data were collected from the records maintained at Livestock Research Station, Palamaner, for analysis and the data spread from 1993 to 2016 (23 years). 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. Six animal models were fitted with various combinations of direct and maternal genetic effects using restricted maximum likelihood procedure. The Akaike's information criterion was employed to determine the best model for each trait. Direct heritability estimates obtained in the study for ADGa, ADGb, ADGc, Ka, Kb, and Kc were 0.37, 0.41, 0.34, 0.48, 0.46, and 0.37, respectively, and their corresponding maternal heritabilities ranged from 0.11, 0.21, 0.11, 0.24, 0.22, and 0.11, respectively. (Co)variance among the direct and maternal effects were found to be negative in all the traits. Direct genetic correlations among the studied traits were positive with few exceptions, and they ranged from - 0.03 (Ka-Kc) to 0.99 (ADGa-Ka); similarly, the phenotypic correlations ranged from low to high - 0.18 (ADGa-Kc and Ka-Kc) to 0.95 (ADGa-Ka). These results indicated the importance of maternal effects in affecting the growth rate and efficiency of feed utilization traits and also suggested the possibility of moderate genetic progress for these traits through selection.