s.r. miraei ashtiani

To compare genetic evaluation methods for milk yield of Mashhad’s Holstein cows, two fixed and random regression test day models were used. The data set consisted of 95,510 test day milk records collected from 11,054 first parity Holstein cows calved between 1994 and 2007 Mashhad’s dairy farms. The number of sires, dams and total animals in pedigree file were 807, 8,835 and 11,054, respectively. Average daily milk was 26.92±6.91 Kg. Fixed and random regression test day models had fixed effects of herd – year – season of recording - milking times - sperm origin, as well as covariables of Holstein gene percentage, stage of pregnancy, age of cow at recording, and daily temperature. To take into account the shape of the lactation curve at phenotypic, genetic and environmental levels, orthogonal Legendre polynomials (order 4) was implemented in the random regression test day model. The models were fitted to the data by DXMRR software. There was a high positive and significant (P<0.001) rank correlation coefficient (0.939) between predicted breeding values (PBV) obtained by two models. Averages PBV were found to be 0.1695 and 0.1524 Kg for fixed and random regression test day models, respectively which were significantly (P<0.0001) different from each other. Genetic trends for daily milk were 0.044 and 0.077 Kg annually for fixed and random regression test day models, respectively.

In this research, association of the BoLA-DRB3.2 alleles with somatic cell score as an indicator of udder health, and clinical mastitis in Holstein dairy cows were investigated. Clinical mastitis occurrence was defined as the presence or absent of at least one case of mastitis diagnosed by farmer throughout the first lactation. Milk somatic cell count of the first lactation was converted to milk somatic cell score to achieve normality of data distribution. PCR-RFLP method, followed by digestion of the amplified fragments with three restriction enzymes, RsaI, BstYI and HaeIII, was used to determine BoLA-DRB3.2 alleles of the animal included in this study. Gene-substitution, general linear and logistic regression models were used to evaluate the effect of BoLA-DRB3.2 alleles on the LSCS and binary measures of clinical mastitis, respectively. The association results showed that BoLA-DRB3.2*11 was significantly associated with lower lactation somatic cell score, but no allele was found to be significantly associated with clinical mastitis. Although more studies are needed to confirm the present results, but it can be concluded that BoLA-DRB3 alleles may have potential usefulness as a genetic marker to improve bovine mastitis and udder health in dairy cows.

Genetic variation within and between five Iranian sheep populations including Sanjabi (SAN), Kordi Kordistan (KKO), Kordi Khorasan (KKH), Mehraban (MEH) and Moghani (MOG) was assessed using six microsatellite markers (McMA2, McMA26, MAF64, OarAE64, OarCP26 and OarFCB304). The PCR reactions were successfully perfomed with all primers except OarAE64. All locus-population combinations were at Hardy-Weinberg equilibrium except McMA2 in MOG population (P<0.005). Polymorphism criteria showed that the five studied loci were polymorphic in all populations. The lowest DA genetic distance (0.234) was observed between KKH and KKO and the highest (0.388) between SAN and MOG populations. The dendrograms based on DA distances were drawn using unweighted pair-group method using an arithmetic average (UPGMA) and neighbor-joining (NJ) method. KKO, KKH and SAN were grouped together at one cluster and MEH and MOG at another by both methods. The average expected heterozygosity for each populations (as interpopulation variation) ranged from 0.744 to 0.847 for KKH and MEH, respectively. The estimated time of divergence for two Kordi populations (KKO and KKH) was 445 years that complies with historical evidences. The findings of this research confirmed that microsatellite variation could be a useful tool for screening of investigating biodiversity among domestic animals.

In this study external fat-tail dimensions (upper, middle and lower width, length, length of gap, depth and upper circumference) and fat-tail weights collected on 724 Lori-Bakhtiari sheep were used to study external fat-tail dimensions and their relationships with fat-tail weights. Sheep were 3 months to 6 years old and slaughtered at the industrial slaughter house of Joneghan in Chaharmohal and Bakhtiari province in 2003. The mean of fat-tail dimensions were estimated as 15.83, 23.85, 24.73, 26.52, 14.96, 14.12 and 52.59 cm for upper width, middle width, lower width, length, length of gap, depth and upper circumference, respectively. Fat-tail weight varied from 0.10 to 20.60 with overall mean of 2.71 kg. Fat-tail percentage varied from 1.18 to 37.18 with overall mean of 11.87 percent. The effects of fixed factors of age, sex and body condition of sheep on all of traits were highly significant (p<0.0001). The least square means of all traits except fat-tail percentage were increased with increasing age of sheep. Lowest least square mean (± s.e) of 2.12 ± 0.25 kg fat-tail weight and 7.91 ± 0.72% fat-tail were observed for sheep having body condition score of 1 and the highest least square mean with fat-tail weight of 9.84 ± 0.56 kg and fat-tail percentage of 20.59 ± 1.63 were observed for sheep having body condition score of 5. Estimation of correlation coefficients among external fat-tail dimensions and fat-tail weight were positive and varied from 0.60 between upper fat-tail width and fat-tail weight to 0.83 between upper circomference of fat-tail and fat-tail weight. Upper circumference of fat-tail accounted for %69.5 of variation of fat-tail weight. This study showed that fat-tail weight in live sheep of Lori-Bakhtiari could be estimated using external fat-tail dimensions with very high accuracy (r = 0.904).

This research was carried out to investigate the heterogeneity of milk yield variance components in different production levels of holstein cattles. The first lactation milk yield records of 95945 Holstein cattles, which had calved in 651 herds through years 1991 to 2000, were used in this research. Data was collected by the Animal Breeding Center of Iran and adjusted for two-time milking per day. Records were classified into three classes: low (less than 5275 kg), average (5275-6874 kg), and high (more than 6874 kg) based on the level of production. Variance components and genetic parameters were estimated using single and three-trait animal models for each class and three classes with Derivative Free Restricted Maximum Likelihood methods (DF-REML). Bartlett test showed significant differences for variance components between classes. Milk yield heritability was estimated as 0.205, 0.276, and 0.196 for low, average, and high class, respectively, in both single and three-trait analysis. The gentic correlation coefficient between classes ranged from 0.80 to 0.85, Phenotypic correlation coefficients between classes were low and ranged from 0.17 to 0.19. The highest rank correlation coefficient between estimated breeding value by single and three-trait model was obtained in average class. The average changes in the rank of common animals in the top 1% of cows were greather than the top 5% of bulls. Adjustment for heterogeneity of variance components suggested selecting more top cows from herds with high level of production.

Improvement of feed efficiency in dairy farming economically has a great importance. In this study, the genetic parameters of net energy efficiency and its relationships with milk yield, 3.2% fat corrected milk, body weight, gross income and income over feed costs were investigated, by the 2589 monthly records collected from the 723 lactating cows in the 3 herds. The different requirements of energy were estimated, by the National Research Council (NRC) models. A general linear model was employed for determining significant factors affecting each trait. The genetic parameters were estimated by a multivariate analysis with the derivative free approach of restricted maximum likelihood algorithm. The animal models contained the fixed effects of herd-year-season, parity number and stage of lactation, the regression coefficients of each trait on the dietary levels of rumen undegradable protein and metabolizable energy, and the random effects of animal additive genetic, permanent environment and residuals. The heritability of milk yield, 3.2 percent fat corrected milk, body weight, net energy efficiency, gross income and income over feed cost, were estimates 0.31, 0.32, 0.30, 0.34, 0.24 and 0.29 respectively. The results of this study indicated that the direct selection for net energy efficiency might genetically improve the feed efficiency. It also seems that the selection for fat corrected milk may be effective for the indirect improvement of feed efficiency and economic performance of dairy cows.