قاسم متقی نیا

Wool weight is an economic trait affecting farm income for which phenotypic mean is expected to increase as the genetic selection is practiced. This research aimed to analyse phenotypic and genetic aspects of wool weight trait in Iran Black sheep using different animal models. A total of 13,175 wool weight records belonging to 3,763 Iran Black sheep breed (progeny of 104 sire and 1,122 dams) collected during 24 years (1983-2006) in Abbas Abad Breeding Centre, Mashhad was use. Genetic analysis was carried out through a set of animal models. Least square means of wool weight for male and female lambs were 864.21 and 678.95 g, respectively which were significantly different from each other (P<0.0001). Phenotypic trend was found to be 6.762 (±4.325) g per year which was statistically non-significant. Direct and maternal additive genetic variances, lamb and maternal permanent environmental variances, direct and maternal heritabilities, and repeatability of wool weight were found to be 16658.129, 6636.060, 6755.514, 3021.294, 0.142, 0.057 and 0.200, respectively. Mean predicted breeding value of wool weight for female lambs (8.09 g) was significantly (P<0.05) lower than male lambs (37.74 g). Based on model 4, direct and maternal changes were 13.1 (±0.192) and -7.15 (±0.092) g per year and were statistically significant (P<0.001). The findings of the present research indicate that selection has resulted in a positive and favorable genetic gain for the wool trait in the population under consideration.

In this research, a data set comprising 35,511 pre-weaning growth records belonging to 11,837 lambs (6,030 males and 5,807 females) resulted from 300 rams and 3,694 ewes and collected during 1986-2008 from two flocks of Abbas Abad Breeding Centre, Mashhad was used. Based on inclusion of direct additive genetic (model 1), direct additive genetic and maternal permanent environment (model 2), two above components along with maternal additive genetic and without covariance (model 3), and with taking account of covariance (model 4), genetic parameters were estimated. Based upon the best model, C2, direct and maternal heritabilities for birth weight were 0.081, 0.104 and 0.072, respectively. The corresponding figures for weaning weight were 0.073, 0.063 and 0.025, respectively and for daily gain were 0.068, 0.046 and 0.014, respectively. Genetic trends for the traits were found to be 2.688 (±0.104), 7.208 (±0.359) and 0.069 (±0.004) g per year, respectively and statistically significant (P<0.01) indicating that positive favorable changes have been resulted from selection in the population under consideration.

Effects of lamb and parents coefficient of inbreeding (CI) on wool weight were studied using 10،868 wool records belonging to 3،244 Iran Black lambs (1،633 males and 1،611 females) representing 96 rams and 995 ewes collected during 1983-2006 from Animal Breeding Station of Abbas Abad. Year and month of shearing، CI of lamb and dam، sex and birth type had significant affect on wool weight Among 3،244 pedigree animals، 3،005 heads (92. 6 percent) were found to be inbred. Mean and standard deviation of CI of lamb، sire and dam in whole population were 8. 1±6. 1، 6. 5±6. 1 and 5. 3±5. 8 percent، respectively. The corresponding figures in inbred population were 9. 0±5. 7، 7. 0±6. 1 and 5. 7±5. 8 percent، respectively. Minimum and maximum CI of lamb was 0 and 36. 4 percent، respectively. Increase of CI by one percent was accompanied with a decrease of 26. 9 g (quadruplet male)، 4. 8 g (twin female)، 4. 3 g (triple female) and 13. 1 g (quadruplet female) in wool weight. A decrease of 1. 4 g in wool weight of lamb was observed as the CI of dam was increased by one percent. Statistically significant annual change trend were estimated to be 0. 2±0. 02 percent and 0. 1±0. 02 percent for whole and inbred populations، respectively. A controlled mating is needed to reduce deleterious effects of inbreeding.

In this research, a total of 11,837 weight records of Baluchi lamb (6,030 males and 5,807 females) representing 300 rams and 3,694 ewes of Baluchi collected during 1978- 2008 from Abbas Abad breeding centre, Mashhad were utilized for investigating inbreeding trend and its effect on pre-weaning weight traits. The traits under consideration were birth weight (BW), weaning weight (WW) and pre-weaning daily gain (PWDG). Inbreeding coefficient of all animals was computed using CFC software. A linear model was applied for analyzing the data using SAS software. Among the animals, 8,903 (75.21%) were inbred. Average (standard deviation) of inbreeding coefficient were found to be 3.17 (3.94) and 4.22 (4.02) % for whole and inbred populations, respectively. Minimum and maximum inbreeding coefficients were 0 and 33.23 %, respectively. In whole population, average (standard deviation) of inbreeding coefficients were 3.20 (3.92) and 3.14 (3.95) % for male and female lambs,respectively. The corresponding figures were 3.07 (3.89) and 3.32 (4.00) % for single and twin lambs, respectively. Inbreeding depression was detected for BW, WW, W3 and PWDG in single male and single twin lambs and for BW in twin male lams (P<0.05). Annual trends of inbreeding coefficient were 0.117 and 0.022 % for whole and inbred animals which were found to be statistically significant (P<0.0001).

In this research a total of 46،563 wool weight records belonging to 12،842 Baluchi sheep (represented 414 sires and 4892 dams) collected during 24 years (1983-2006) from two herds of Abbas Abad breeding centre، Mashhad were utilized to study the effects of some environmental and genetic factors. A linear mixed model was used to evaluate fixed environmental factors using SAS software. The year and month of shearing، sex، birth type، age and shearing order of lamb had statistical significant effect on wool weight. Phenotypic trend estimation was 13. 12 g per year which was statistically significant. Genetic analysis of the trait was undertaken by a repeatability animal model using DMU software. The estimates of additive genetic and permanent environment variances، heritability and repeatability were 9293. 58، 6758. 45، 0. 092 and 0. 159، respectively. The estimation of genetic trend for wool weight was 3. 49 g per year which was statistically significant. Mean breeding value for wool trait was significantly lower in male (24. 67 g) than female (32. 11 g) lambs

In this research، growth traits (birth and weaning weight، and pre-weaning average daily gain) records collected from 11،837 Baluchi lambs (represented 300 rams and 3،694 dams) during 31 years (1978-2008) in two flocks of Abbas Abad breeding station، Mashhad were used. Probability of «more than the average» was modeled for some environmental factors using logistic regression for the traits. The overall average and standard error of birth and weaning weight، pre-weaning average daily gain were 4. 32 (±0. 007)، 22. 33 (±0. 046) kg and 193. 22 (±0. 436) gr، respectively. The results indicated that year، sex and birth type of lamb had statistically significant effect on the probability of «more than the average» for all traits. Based on estimated regression coefficient، year of birth had negative effect on the probability associated with birth weight (-0. 014) while it had positive effects on the probability of weaning weight (0. 19) and pre-weaning average daily gain (0. 017). Inbreeding was found to have negative effects on the probability associated with birth (-2. 399) and weaning (-1. 495) weights. Dam age at lambing had positive effect on the probability associated with birth weight (0. 02). The probability associated with weaning weight (0. 087) was found to be positively affected by weaning age.

In this research a total of 46466 wool weight records belonging to 12821 Baluchi lambs 6334 males and 6487 females) (progeny of 413 rams and 4879 ewes) born from 1983 to 2006 in two herds of Abbas Abad breeding centre, Mashhad, Iran were utilized to study inbreeding effect on wool weight of Baluchi sheep. Inbreeding coefficient was calculated for individual lambs using pedigree software. Data were analyzed by a linear model using SAS software. Year and month of shearing, age at shearing, inbreeding coefficient, sex and birth type had statistical significant effect on wool weight (P<0.0001). In total pedigree animals, 2441 was inbred (19.4%). Average andstandard deviation of inbreeding coefficient for total and inbred population were found to be 0.669±2.60% and 3.90±5.17%, respectively. Minimum and maximum of inbreeding coefficient were 0 and 31.25%, respectively. Average inbreeding coefficients for male and female lambs were 0.708±2.69 and 0.733±2.68%, and for single and twin lambs were 0.684±2.59 and 0.785±2.84, respectively. No statistical significant difference was found between two means of inbreeding coefficients of male and female lambs while statistical significant difference was revealed between two means of twin single and twin lambs (P<0.05). Inbreeding had negative effect on performance of wool in twin male and female lams (P<0.05). Increasing 1% of inbreeding coefficient of twin male and female lambs was accompanied with decreasing 2.86 and 6.62 g in their wool weight, respectively. Annual change trend in inbreeding coefficient for total and inbred population were0.075% and -0.26%, respectively that was statistically significant (P<0.0001).

A data set consists of 6,030 weight records of Iran Black sheep (3,051 males and 2,979 females) progeny of 141 rams and 1525 ewes of Iran Black collected during 1973-2010 from Abbas Abad breeding centre, Mashhad were utilized for investigating inbreeding trend and its effect on body weight traits. The traits under consideration were birth weight (BW), weaning weight (WW), weight at 6-month (W6), weight at 9-month (W9), yearling weight (YW) and pre-weaning daily gain (PWDG). Inbreeding coefficient of all animals was computed using CFC software. A mixed linear model was applied for analyzing the data using SAS software. Among the animals, 5,333 (88.44%) were inbred indicating that the effective number of base population might be low. Average (standard deviation) of inbreeding coefficient were found to be 8.78 (6.34) and 9.33 (5.83) % for whole and inbred populations, respectively. Minimum and maximum inbreeding coefficients were 0 and 38.48 %, respectively. In whole population, average (standard deviation) of inbreeding coefficients were 8.75 (6.31) and 8.82 (6.37) % for male and female lambs, respectively. The corresponding figures were 8.69 (6.25) and 8.90 (6.37) % for single and twin lambs, respectively. Inbreeding depression was detected for WW, W3, W6, W9 and YW in twin males, for BW in twin females, and for W9 in twin females. Annual trends of inbreeding coefficient were 0.2022 and 0.1632 % for whole and inbred animals which were found to be statistically significant (P<0.0001).