محسن احمدی شاهرخت

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.

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 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 in order to estimate genetic parameters for milk yield at different milking times for Holstein cows of Razavi Khorasan، a total of 180،462 monthly test day records belonging to first lactation cows calved from 2000 to 2009 were utilized. The records were analysed by a random regression test day model. In the model، the fixed effects of contemporary group of geographical location – herd – year of recording – production season – sperm type، linear covariables of Holstein gene percentage، age at recording، as well as additive genetic and permanent random effects were included. For morning (M1) and night (M3) milking times، maximum additive genetic variances were found in month eight (0. 808 and 0. 659، respectively) while the minimum value (0. 399 and 0. 319، respectively) was found for both milking times in month two of the lactation curve. Maximum and minimum additive genetic variances for noon (M2) milking times were observed in months ten (0. 732) and two (0. 278)، respectively. Permanent and residual variance components were the greatest values at the end of the lactation course. Maximum heritability estimates of M1، M2 and M3 were found to be 0. 143 (month eight)، 0. 137 (month nine) and 0. 139 (months eight and nine)، respectively. For all milking times، minimum additive genetic correlations were found between month one and month eight and ranged from 0. 216 to 0. 285، while the maximum values were observed between month six and month seven and ranged from 0. 993 to 0. 996. For all milking times، permanent environment correlations were maximum between months five and six (ranged from 0. 992 to 0. 993) and minimum between months one and ten (ranged from 0. 411 to 0. 445).

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).