Total Litter Weight At Weaning Research Articles

A comparative analysis of economic traits between purebred and synthesized sheep breeds in dry and harsh environments of Iran

The present study aimed to compare economic traits of Baluchi as an indigenous purebred and Iran-Black and Arman as synthesized breeds of sheep in Iran. Data of Baluchi, Iran-Black and Arman were collected from the Abbas Abad Breeding Station located in Mashhad, Iran. The studied pre-weaning traits included birth weight (BW), weaning weight (WW), and survival from birth to weaning (SU). The studied reproductive traits included litter size at birth (LSB), litter size at weaning (LSW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW). Data was analyzed using the generalized linear model (GLM) procedure in SAS software. The least square means were compared using a Tukey test at a significance level of 0.05. The least square means for BW were 3.87, 3.71 and 3.75kg, for WW were 20.06, 20.86 and 20.98kg, and for SU were 88.26, 82.94 and 90.26 percent in Baluchi, Iran-Black and Arman sheep, respectively. The least square means for LSB and LSW were 1.31, 1.59, 1.57 lambs born per ewe and 1.17, 1.31, 1.42 lambs weaned per ewe for Baluchi, Iran-Black and Arman sheep, respectively. The least square means for TLWB in purebred and synthetic breeds differed significantly, with values of 5.66kg, 6.25kg, and 6.31kg for Baluchi, Iran-Black and Arman sheep, respectively. Furthermore, the least square means for TLWW was 28.94kg, 32.16kg and 33.67kg per ewe in Baluchi, Iran-Black and Arman sheep, respectively. The results obtained in this study indicated that TLWW in Iran-Black and Arman ewes increased by approximately 11.13% and 16.34% compared to Baluchi ewes, respectively. It can be concluded that crossbreeding Baluchi sheep with foreign breeds to create synthetic breeds has had a positive impact on the efficiency of the sheep industry in Iran.

A study on the genetic and phenotypic factors affecting specific ewe productivity traits in Sangsari sheep.

The study's objectives were to assess the genetic parameters of reproductive characteristics in Sangsari sheep. A data set of reproductive information with pedigree details from 1995 to 2016 was used. Studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). Test significance of the environmental factors to be included in the model was conducted using the general linear model procedure of the SAS program. All traits were significantly affected by the year of lambing and ewe age at lambing (P < 0.01). The AI-REML procedure of the Wombat program was used to evaluate genetic parameters. A series of bivariate animal models were employed to calculate genetic (rg) and phenotypic (rp) correlations between traits. The total least square means ± standard error of LSB and LSW were 1.04 ± 0.05 and 0.96 ± 0.03, while LMWLB, LMWLW, TLWB, and TLWW were 3.12 ± 0.08, 15.40 ± 0.13, 3.28 ± 0.04, and 19.31 ± 0.16kg, respectively. The estimates of h2 were relatively low (P < 0.01) and ranged from 0.063 ± 0.028 for LSW to 0.181 ± 0.063 for TLWW. Repeatability estimates varied from 0.101 for LSW to 0.241 for TLWW. The sire service effects for LMWLB, TLWB, and TLWW were 0.012 ± 0.004, 0.023 ± 0.006, and 0.039 ± 0.009, respectively. The traits studied showed a greater magnitude of genetic correlation than phenotypic correlation, with values ranging from - 0.59 (LSB-LMWLB) to 0.87 (LMWLB-TLWB). It appears that focusing on TLWW for selection could result in more significant improvements in the reproductive performance of Sangsari ewes.

Litter size, litter weight, and lamb survivability of Doyogena sheep managed under community-based breeding program in Ethiopia

Increasing litter size and weight during the marketing time by decreasing mortality among lambs per ewe is the objective of the community-based breeding program (CBBP). This study aims to find out litter size, litter weight per ewe, and preweaning lamb mortality of Doyogena sheep managed under CBBP. The study analyzed the data records of 4530 animals for 8 years from 2013 to 2020. A logistic regression procedure was used to analyze pre-weaning lamb survival rates. Results showed that the overall least-squares means of litter size at birth (LSB), litter size at weaning (LSW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW) were 1.57 ± 0.02 lambs, 1.50 ± 0.02 lambs, 5.24 ± 0.09 kg, and 24.14 ± 0.69 kg respectively. The incidence of pre-weaning lamb mortality was 4.72%. Year and breeder cooperative vary were observed for pre-weaning lamb losses. Females had lower odds of survival as compared to males. Odds of survival were low for triplets, quadruplets, and low birth weight (≤2 kg) born lambs. The ongoing selection program which aims to improve reproductive and growth performance had a positive influence on the survival rate of lambs. Improvement of the environment in the flock, special care for multiple-born and care for small lambs would lead to further lamb survival improvements.

Influence of non-genetic factors on the maternal ability of Santa Inês ewes

ABSTRACT: The aim of this study was to evaluate the influence of different non-genetic effects on indicator traits for maternal ability in Santa Inês ewes. Data included performance records of 100 lambs (males and females) born from 59 dams, from 2009 to 2012. The analyzed traits were birth weight (BW), weaning weight (WW), average daily gain from birth until weaning (ADGBW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW). The effects analyzed were the year of birth of the lamb, birth season, dam age at lambing, dam weight at lambing, sex of the lamb, lamb birth type, interaction between sex and birth type, and interaction between sex and birth season. SAS® software (SAS University Edition, USA) was used for calculation of the analysis of variance, means, and Pearson correlation coefficients. With the exception of the birth season, all the other environmental effects evaluated had a significant influence on at least one of the studied traits. The correlation estimates ranged from low to high and were either positive or negative. Birth weight was negatively correlated with the birth type and influenced positively all the other performance traits evaluated. The maternal ability of Santa Inês ewes was more clearly influenced by the age and weight of the dam at lambing, and the lamb birth type.

Bayesian inference on genetic parameters for some reproductive traits in sheep using linear and threshold models

Genetic parameters for reproductive traits in Baluchi sheep were estimated on 3844 dams born during 1991 to 2012. The studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). Significant effects were determined using Logistic and GLM procedure of SAS software for threshold and continuous traits, respectively. Variance components needed for breeding were estimated using Gibbs sampling methodology of Bayesian inference. The genetic parameters for LMWLB, LMWLW, TLWB TLWW were estimated by fitting a linear model. To examine the appropriateness of fitting linear or threshold model to litter size at birth and weaning, both models were used to estimate genetic parameters on the observed data. Posterior means of the heritabilities of litter size at birth and weaning by using a threshold model were estimated to be two times higher than the heritabilities based on the linear model (0.18 versus 0.09 and 0.11 versus 0.05 for LSB and LSW, respectively). Bayesian information criterion (BIC) selected the threshold model as most appropriate model for LSB and LSW given the data. The heritability estimates for LMWLB, LMWLW, TLWB TLWW resulting from linear analysis were 0.12, 0.05, 0.06 and 0.08, respectively. Genetic correlation estimates between the traits ranged from −0.67 for LMWLB–TLWW to 0.85 for LSB–TLWB. Phenotypic correlations ranged from −0.06 for LSB–LMWLW to 0.88 for LSB–TLWB and permanent environmental correlations ranged from −0.74 for LMWLB - TLWW to 0.88 for LSB–TLWB. Results of this study showed that the threshold model seems to be reliable for genetic evaluation of litter size in Baluchi sheep.

Inbreeding effects on some reproductive traits in Markhoz goats

The objective of this study was to estimate the inbreeding coefficient and its effects on reproductive traits in Markhoz goats. The pedigree file included 5351 kids produced by 234 bucks and 1470 does. Average inbreeding coefficient for the whole population was 2.68%, and the minimum and maximum inbreeding coefficients were 0.05% and 31.25%, respectively. Average coefficient of inbreeding for inbred population was 5.17% and the number of inbred animals in the population was 2777. For investigating effects of inbreeding coefficient on reproductive traits, 3443 records were available for litter size at birth (LSB), litter size at weaning (LSW), total litter weight at birth (TLWB) and mean of litter weight at birth (MLWB). Furthermore, available records for total litter weight at weaning (TLWW) and mean of litter weight at weaning (MLWW) were 2918. Inbreeding depression was estimated as the linear regression of performance on the individual inbreeding coefficient of kids and dams using the most appropriate animal model based on Akaike’s information criterion. Furthermore, inbreeding depressions for LSB and LSW were estimated using threshold and Poisson models. Regression coefficients of LSB, LSW, TLWB, TLWW, MLWB and MLWW on inbreeding coefficient of kids were –0.035, –0.019, –0.077 kg, –0.782 kg, –0.009 kg and –0.332 kg, respectively. Furthermore, regression coefficients of LSB, LSW, TLWB, TLWW, MLWB and MLWW on inbreeding coefficient of dams were 0.064, –0.013, 0.241 kg, 0.638 kg, 0.028 kg and –1.783 kg, respectively. The obtained results from this study showed that inbreeding depression is controlled by an appropriate mating system policy.

Genetic Parameters and Genetic Trends for Reproductive Traits of Santa Ines Sheep Kept in Extensive Environments in Brazil

Studying the Santa Ines sheep breed is important, as it is the most prevalent breed in Brazil and can adapt to many environments. This study included data were collected over a period of 12 years from 33 flocks in 10 Brazilian States. The estimation of variance components, genetic parameters and breeding values were obtained by DFREML method, using lineal mixed model in single-trait analysis. Traits of age at first lambing (AFL), lambing interval (LI), survivability (SU), litter size at birth (LSB), litter size at weaned (LSW),total litter weight at birth (TLWB) and total litter weight at weaning (TLWW) were assessed. The significance of the fixed effects to be included in the model was performed using statistic program R. The effects of breeder and lambing year were significant (P<0.001). A remarkable phenotypic and permanent environmental variability were found in all traits. Direct heritability estimates were 0.13, 0.04, 0.01, 0.12, 0.03, 0.16 and 0.18 for AFL, LI, SU, LSB, LSW, TLWB and TLWW, respectively. The estimated fractions of variance due to the permanent environmental effects in any traits were high magnitude (0.79 to 0.97). The annual genetic gain has a slightly negative trend in all of them except for AFL and SU. Results indicate that change in environmental conditions of flock in addition to the direct selection for TLWB and TLWW, can be used as selection criteria for improving the productivity of this sheep.

Genetic parameter estimates for growth and reproductive traits in Lori sheep

Lori sheep is one of the well adapted and relatively heavy breeds in mountainous regions of Iran, primarily reared for mutton production. The current study was conducted to estimate the (co) variance components and genetic parameters by restricted maximum likelihood method using six univariate models for growth and four univariate models for reproductive traits. Data and pedigree information were collected at Agricultural Organization of Lorestan province, west of Iran from 2001 to 2012. Studied growth traits were birth weight (BW), weaning weight (WW), 6-month weight (6MW), average daily gain from birth to weaning (ADG0–3), average daily gain from birth to 6-month (ADG0–6), average daily gain from weaning to 6-month (ADG3–6), and corresponding Kleiber ratio (KR0–3, KR0–6, KR3–6). Reproductive traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lambing (LMWL), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). Moreover, multivariate analyses were performed to estimate covariance between traits. Direct heritability estimates (h2a) for growth traits ranged from 0.000 (ADG0–3 and KR0–3) to 0.156 (6MW). Maternal heritability (h2m) decreased from 0.110 at birth to 0.022 at 6-month weight. The ratio of maternal permanent environmental variance to phenotypic variance (pe2) persisted into the post-weaning growth period and it was 0.115, 0.080, 0.087 and 0.081, for BW, ADG0–6, KR0–3 and KR0–6, respectively. Estimates of h2a for reproductive traits were significant for LSB, LSW, LMWL and LMWLW being 0.175, 0.213, 0.088 and 0.034, respectively, while TLWB and TLWW were more affected by the permanent environmental effects of ewes. Service sire effects (S2) were significant for LMWL. Genetic correlations between growth traits ranged from −0.425 (BW-KR0–3) to 1.000 (6MW-ADG0–3, 6MW-KR0–3, ADG0–3–ADG3–ADG3–6-KR0–3 and KR0–3–KR0–6), and phenotypic correlations ranged from −0.341 (ADG0–3–KR3−6) to 0.990 (6MW–ADG0−6). Genetic correlations between reproductive traits were higher than phenotypic ones, and ranged from −0.986 (LSB-LMWLW) to 0.999 (LMWLW-TLWB).

Estimation of genetic parameters for reproductive traits in Mehraban sheep

Genetic parameters for basic and composite reproductive traits in Mehraban sheep were estimated. Data included 10 257 records on reproductive performances of 5813 lambs from 69 sires and 603 dams which were collected from 1994 to 2011 in the Mehraban breeding station in Hamedan province, western Iran. Studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW). Test of significance to include fixed effects in the statistical model was performed using the GLM procedure of SAS. Genetic parameters were estimated with univariate and bivariate repeatability animal models using WOMBAT program. Direct heritability estimates were 0.16, 0.14, 0.03, 0.16, 0.06, and 0.18 for LSB, LSW, LMWLB, LMWLW, TLWB, and TLWW, respectively, and corresponding repeatabilities were 0.02, 0.01, 0.73, 0.41, 0.27, and 0.03. The estimate for animal-dependent permanent environmental variance ranged from 0.01 ± 0.04 for LMWLW to 0.23 ± 0.04 for LSB. Genetic correlation estimates between traits ranged from −0.98 for LSB–LMWLW to 0.99 for LSB–TLWB. Phenotypic and environmental correlations were generally lower than genetic correlations. Phenotypic correlations ranged from −0.50 for LSB–LMWLB to 0.85 for LMWLW–TLWW. Environmental correlations ranged from −0.45 for LSB–LMWLB to 0.87 for LMWLW–TLWW. The results suggested that indirect selection based on TLWW could improve the reproductive performance in Mehraban ewes more effectively than if based on the other traits.

Inbreeding effects on reproductive traits in Iranian Guilan sheep.

The objective of the present study was to evaluate the effects of inbreeding on reproductive traits in Guilan sheep. Traits included were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW). Data and pedigree information used in this study were collected during 1994 to 2011 by the Agriculture Organization of Guilan Province in the north of Iran. Data were comprised of 14,534 records of lambs from 136 sires and 2021 dams. All the animals were grouped into three classes according to the inbreeding coefficients (F) obtained by their pedigree: the first class included non-inbred animals (F = 0%), and the second and third classes included inbred animals (0 < F ≤ 5% and F > 5%, respectively). The regression coefficients of LSB, LSW, LMWLB, LMWLW, TLWB, and TLWW on lamb inbreeding for a change of 1% in inbreeding were estimated to be 0.035 ± 0.0038 (P < 0.001), -0.029 ± 0.0077 (P < 0.05), -0.333 ± 0.009 (P < 0.001), -2.21 ± 0.071 (P < 0.001), -0.254 ± 0.013 (P < 0.001), and -1.95 ± 0.093 (P < 0.001), respectively. Effect of inbreeding on reproductive traits in Guilan sheep was very pronounced in the flock. The utilization of a program for planned mating system, in the present flock, suggested keeping the level of inbreeding under control and avoiding appearance of its detrimental effects.

Genetic parameters and genetic gains for reproductive traits of Arabi sheep

The current study reports, for the first time, the genetic parameters and genetic, phenotypic and environmental correlations and trends of reproductive traits in Arabi sheep. Data were collected at Animal Science Research Station of Khuzestan Ramin Agricultural and Natural Resources University (ASRSKRANRU), south-west of Iran from 2001 to 2008. Litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW) averaged 1.11 lambs, 1.01 lambs, 3.83 kg, 19.43 kg, 4.16 kg and 20.12 kg, respectively. Genetic parameters and correlations were estimated with univariate and bivariate models using restricted maximum likelihood, breeding values of animals were estimated with best linear unbiased prediction (BLUP) and genetic- and phenotypic trends by regression of ewes? average breeding values and phenotypic least square means on year of birth respectively. Random effects were fitted by additive direct genetic effects and permanent environment related to the ewe as well as service sire effects, in addition to fixed effects of ewe age at lambing and lambing year. Heritability estimates of 0.05, 0.02, 0.13, 0.12, 0.04, and 0.06, and repeatability estimates of 0.08, 0.06, 0.17, 0.16, 0.14 and 0.21 for the six traits, respectively. Genetic correlations between traits varied from ?0.82 to 0.94. Phenotypic correlations were lower, ranging from ?0.33 to 0.52. Estimated annual genetic progress was very low; ?0.003 lambs for LSW and 15 g for TLWW. Annual phenotypic trend was only significant for LSW being 0.007 lambs. The study concluded that indirect selection based on total litter weight at weaning could be efficient for the traits studied.

Genetic correlations between growth and reproductive traits in Zandi sheep

For the first time, the current study reports the genetic and phenotypic correlations between growth and reproductive traits in Zandi sheep. The data were comprised of 4,309 records of lamb growth traits from 1,378 dams and 273 sires plus 2,588 records of reproductive traits from 577 ewes. These data were extracted from available performance records at Khojir Breeding Station of Zandi sheep in Tehran, Iran, from 1993 to 2008. Correlations were estimated from two animal models in a bivariate analysis using restricted maximum likelihood procedure between lamb growth traits [birth weight (BW), weaning weight at 3months of age (WW), as well as six-month weight (6MW)] and ewe reproductive traits [litter size at birth (LSB), litter size at weaning (LSW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW)]. The genetic correlations between BW and reproductive traits varied from low to high ranges from 0.10 for BW-LSB to 0.86 for BW-TLWB. WW was moderately (0.37) to highly (0.96) correlated with all the reproductive traits. Moreover, the genetic correlations were observed between 6MW and reproductive traits, varied from 0.19 to 0.95. Relationships between growth and reproductive traits ranged from 0.01 for BW-LSW to 0.28 for BW-TLWB in phenotypic effects. Results indicated that selection to improve WW would have high effect on genetic response in TLWW, and also, these results could be effective for all of the reproductive traits in Zandi sheep.

Pre-Weaning Growth Traits in Nigerian Indigenous Pig Crossbreds

Forty-seven hybrid progenies from crossbreeding between the Nigerian indigenous pig (NIP) and Large white pigs were used. Body measurements and live weight were recorded weekly from first week of birth to their weaning date. Body measurements taken were Body Weight (BW), Body Length (BL), Body Height (BH), Heart girth (HG) and Rump circumference (RC) of crossbred progenies. The correlation between the reproductive parameters and growth performance of hybrid pigs were established with good management practice. The mean for weaning weight was 6.72 ± 0.02, birth weight 0.91 ± 0.13, litter size at birth 5.36 ± 1.87, litter size at weaning 5.29 ± 1.97, litter weight at birth 4.56 ± 1.57, total litter weight at weaning 33.91 ± 11.6, average daily weaning weight 0.73 ± 0.12, average litter size at birth 0.93 ± 0.11 and sex ratio 97.78% ± 8.61%. The male and female mean values for weight of animals were 6.96 ± 1.0 and 6.52 ± 0.9 with male heavier in weight and higher in morphometric traits such as body length, heart girth and rump circumference, while the female were high in morphometric traits such as snout length, ear length and body height. The correlation matrix for body weight against linear body measurements in pre-weaned NIP crossbreds indicates that all the parameters could be used to select for body weight. The linear equation generated by regressing body weight on snout length, body height, rump circumference, heart girth and body length could be used by resource poor pig farmers in the estimation of body weight of pre weaned crossbreds pigs if they cannot afford weighing scales.

Estimation of genetic parameters for reproductive traits in shall sheep

The objective of this study was to estimate genetic parameters for reproductive traits in Shall sheep. Data included 1,316 records on reproductive performances of 395 Shall ewes from 41 sires and 136 dams which were collected from 2001 to 2007 in Shall breeding station in Qazvin province at the Northwest of Iran. Studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW). Test of significance to include fixed effects in the statistical model was performed using the general linear model procedure of SAS. The effects of lambing year and ewe age at lambing were significant (P<0.05). Genetic parameters were estimated using restricted maximum likelihood procedure, under repeatability animal models. Direct heritability estimates were 0.02, 0.01, 0.47, 0.40, 0.15, and 0.03 for LSB, LSW, LMWLB, LMWLW, TLWB, and TLWW, respectively, and corresponding repeatabilities were 0.02, 0.01, 0.73, 0.41, 0.27, and 0.03. Genetic correlation estimates between traits ranged from -0.99 for LSW-LMWLW to 0.99 for LSB-TLWB, LSW-TLWB, and LSW-TLWW. Phenotypic correlations ranged from -0.71 for LSB-LMWLW to 0.98 for LSB-TLWW and environmental correlations ranged from -0.89 for LSB-LMWLW to 0.99 for LSB-TLWW. Results showed that the highest heritability estimates were for LMWLB and LMWLW suggesting that direct selection based on these traits could be effective. Also, strong positive genetic correlations of LMWLB and LMWLW with other traits may improve meat production efficiency in Shall sheep.

Phenotypic and genetic parameter estimates for reproductive traits in Zandi sheep

This study reports on the phenotypic and genetic (co)variance components for reproductive traits in Zandi sheep, using between 1,859 and 2,588 records obtained from 577 ewes. The data were collected from the Khojir Breeding Station of Zandi sheep in Tehran, Iran from 1994 to 2008. The basic traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), and litter mean weight per lamb weaned (LMWLW), and the composite traits were total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). Genetic analyses were carried out using the restricted maximum likelihood method that was explored by fitting the additive direct genetic effects and permanent environmental effects of the ewes as random effects and the ewe age at lambing and lambing year as fixed effects for all of the investigated traits. Akaike's information criterion was used to choose the most appropriate model. LSB, LSW, LMWLB, LMWLW, TLWB, and TLWW direct heritability estimates were 0.07, 0.05, 0.12, 0.10, 0.08, and 0.14, respectively. The estimated fractions of variance due to the permanent environmental effects of the ewe ranged from 0.03 for LMWLB to 0.08 for LMWLW and TLWW. Corresponding repeatability estimates ranged from 0.10 for LSW to 0.22 for TLWW. Direct genetic correlations varied from -0.61 for LSB-LMWLB to 0.88 for LSB-LSW and LSB-TLWB. Results indicate that genetic change depends not only on the heritability of traits, but also on the observed phenotypic variation; therefore, improvement of non-genetic factors should be included in the breeding programs.

Genetic analysis of ewe productivity traits in Moghani sheep

Genetic and environmental (co)variance components for productivity traits in Moghani sheep were estimated using data from 1344 ewes. The data were collected in the Jafarabad breeding station, north-east of Iran, during a 13-year period (1995–2008). The studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). A model including direct additive genetic effects as well as permanent environmental effects related to repeated records of ewe was the most appropriate model for all the studied traits. Genetic parameters were estimated applying restricted maximum likelihood (REML) procedure. Direct heritability estimate for LSB, LSW, LMWLB, LMWLW, TLWB and TLWW were 0.11, 0.02, 0.15, 0.07, 0.07 and 0.06, respectively. Corresponding values for repeatability estimates were 0.16, 0.19, 0.18, 0.11, 0.13 and 0.09. Genetic correlations between the studied traits ranged from −0.99 for LSB–LMWLB and LSW–LMWLB to 0.99 for LSB–TLWB. Phenotypic and environmental correlation estimates were generally lower than those of genetic ones. Estimates of permanent environmental correlation among traits were positive and medium to high. Although low direct heritabilities were estimated for the reproductive traits, as these traits are of interest then they should be included in a breeding program.

Estimates of phenotypic and genetic parameters for reproductive traits in Kermani sheep

Phenotypic and genetic parameter estimates for reproductive traits in Kermani sheep were estimated using reproductive records of 860 ewes. Data were collected during 1995–2007 at the experimental breeding station of Kermani sheep, south-east of Iran. Investigated traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB) and litter mean weight per lamb weaned (LMWLW) as basic traits, total litter weight at birth (TLWB) and total litter weight at weaning (TLWW) as composite traits. Quantitative genetic analyses were performed applying restricted maximum likelihood (REML) procedure under repeatability models. Ewe age had significant effect on LMWLB, LMWLW, TLWB and TLWW ( P < 0.01). However, LSB and LSW were not affected by age of the ewe. All the studied traits were significantly affected by lambing year ( P < 0.01). Direct heritability estimates for LSB, LSW, LMWLB, LMWLW, TLWB and TLWW were 0.01, 0.03, 0.13, 0.22, 0.06 and 0.18, respectively, while the corresponding repeatabilities were 0.08, 0.10, 0.17, 0.29, 0.09 and 0.23, respectively. Genetic correlation estimates between the investigated traits ranged from −0.94 for LSB–LMWLB and LSW–LMWLW to 0.99 for LSB–TLWW. Phenotypic and environmental correlations were generally lower than those of genetic correlations. Phenotypic correlations ranged from −0.34 for LSB–LMWLB to 0.58 for TLWB-TLWW. Environmental correlations ranged from −0.33 for LSB–LMWLB and LSW–LMWLB to 0.33 for LMWLB–LMWLW. The results suggested that selection based on TLWW could be more effective than the other traits on improvement of reproductive performance in Kermani ewes.