Litter Mean Weight Per Lamb Weaned Research Articles

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.

Estimation of the variance due to parent-of-origin effects for productive and reproductive traits in Lori-Bakhtiari sheep

Parent-of-origin effects are often excluded from models used for estimating of additive and non-additive genetic variances. Omission of parentally-linked genetic factors, such as imprinting, from statistical models has potential to induce profound bias during the estimation. In this study, parent of origin variance for productive and reproductive traits in Lori-Bakhtiari sheep was estimated using a gametic relationship matrix approach. The data set were obtained from a total of 7568 animals, collected from 1994 to 2012 from the Lori-Bakhtiari research flock at Shooli station in Shahrekord, Iran. Growth traits were included birth weight (BWT), weaning weight (WWT), 6-month weight (WT6), 9-month weight (WT9), yearling weight (WT12), average daily gain from birth to weaning (ADGa), and from weaning to 6-month (ADGb). In addition, 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) were analyzed as basic reproductive traits, and total litter weight at birth per ewe lambing (TLWB) and total litter weight at weaning per ewe lambing (TLWW) as composite reproductive traits. Models including or excluding maternal and paternal imprinting effects were compared using the ayesian information criterion (BIC). For all growth traits, except WT6 and WT12, adding maternal imprinting effects into the models decreased BIC, with estimates ranging from 10.5% (WWT) to 23.3% (BWT) of the total phenotypic variance. Paternal imprinting effects, in the other hand, was estimated as 6.9% of the total phenotypic variance for ADGb. For reproductive traits, maternal imprinting effects explained up to 6% of total phenotypic variance for TLWW. Adding paternal or maternal imprinting to the models decreased the direct additive genetic, maternal additive genetic and maternal permanent environmental variance for the growth traits.

Genetic Analysis of Basic and Composite Reproduction Traits in Guilan Sheep

Abstract The objective of the present study was to estimate genetic parameters for reproductive traits in Guilan sheep. Data were comprised of 14,534 records of lambs from 136 sires and 2,021 dams which were collected during 1994 to 2011 by the Agriculture Organization of Guilan Province in the north of Iran. The basic reproductive 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). The composite reproductive traits were total litter weight at birth per ewe lambing (TLWB) and total litter weight at weaning per ewe lambing (TLWW). The general linear model procedure of SAS was used for determining the fixed effects which had significant effect on the traits under study. The flock-year-season of lambing had significant effect on studied traits (P<0.01). The genetic parameters were estimated with repeatability animal model using restricted maximum likelihood (REML) procedure of the Wombat program. Direct heritability estimates were 0.00, 0.00, 0.01, 0.01, and 0.03 for LSB, LSW, LMWLW, TLWB, and TLWW, respectively, and corresponding repeatabilities were 0.2, 0.00006, 0.01, 0.972 and 0.034, respectively. Genetic correlation estimates between traits ranged from -0.99 for LSB-LSW to 0.99 for LMWLW-TLWW. Phenotypic correlations ranged from -0.09 for LSB-TLWB to 0.98 for LMWLW-TLWW and environmental correlations ranged from -0.03 for LSW-TLWW to 0.98 for LMWLW-TLWW. The results showed that strong positive genetic correlations of LMWLB and LMWLW with other traits may improve meat production efficiency in Guilan sheep. The low estimates of heritability and repeatability obtained for ewe productivity traits indicate that selection based on the ewe’s own performance may result in slow genetic improvement.

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.

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.

English

Moghani sheep breed is one of the most important meat type breeds among Iranian local sheep.&nbsp;The objective of this contribution was to estimate direct and maternal genetic variance as well as covariance between direct and maternal additive genetic effects. Maternal permanent environmental variance was also estimated. The following traits were studied: Birth weight (BW), average daily gain until three months (ADG3) and average daily gain until 6 months (ADG6). Genetic parameters were estimated for conception rate (CR), number of lambs born per ewe lambing (LS), number&shy; of lambs born alive (NLBA), number of alive lambs at weaning (NLAW), litter mean weight per lamb born (LMWLB) and litter mean weight per lamb weaned (LMWLW). Three single trait linear animal models have been employed to estimate genetic parameters for production traits and one mixed model method used to analyze reproduction traits included fixed effects due to year, age of ewe and hormone treatment and also random effects due to animal direct and maternal genetic effects, permanent environmental effects due to repeated lambing by ewes and residual effects. Data were analyzed by restricted maximum likelihood method (REML). &nbsp; Key words:&nbsp;Birth weight, genetic parameters, Moghani sheep, reproductive traits.

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.

Genetic parameters of reproductive traits in sheep

Reproductive traits from 7642 ewes were recorded from 1975 to 1983. The ewes were of five breeds (Dorset (D), Finnsheep (F), Rambouillet (R), Suffolk (S) and Targhee (T)) and two composite lines [C1 (1/2F+1/4R+1/4D) and C2 (1/2F+1/4S+1/4T)]. Genetic parameters were estimated for six basic and seven composite traits. The basic traits were conception rate (CR), total number of lamb born (NLB), number of lambs born alive (NLBA), number of lambs alive at weaning (NLAW), litter mean weight per lamb born (LMWLB) and litter mean weight per lamb weaned (LMWLW). The composite traits were ratio of lambs surviving to weaning relative to NLB (LSW=NLAW/NLB), number of lambs born per ewe exposed (NLBEE=CR×NLB), number of lambs weaned per ewe exposed (NLWEE=CR×NLAW), total litter weight at birth (TLWB=NLB×LMWLB), total litter weight at weaning (TLWW=NLAW×LMWLW), total litter weight at birth per ewe exposed (TLWBEE=CR×NLB×LMWLB) and total litter weight at weaning per ewe exposed (TLWWEE=CR×NLAW×LMWLW). Year, age of ewe, breed of ewe, hormone treatment and season of breeding were used as fixed effects. Direct and maternal genetic effects, permanent environmental effects of ewe and mate of ewe were considered to be random effects. A derivative-free algorithm was used to obtain REML estimates of genetic and environmental parameters. Estimates of heritabilities for animal genetic and permanent environmental and maternal genetic effects were mainly small due to the typical high influence of environmental factors on reproductive traits and to non-normal distributions of traits. Mate of ewe effects were not important for any trait. Important genetic correlations were found between some traits. Some estimates of genetic correlations do not seem to have a biological explanation. Nevertheless, these estimates of genetic correlations among traits may provide a basis for deriving selection indexes for reproductive traits.