TY - JOUR ID - 56824 TI - Genetic study of somatic cell score using random regression test day model in dairy cattle of Iran JO - Iranian Journal of animal Science JA - IJAS LA - en SN - 2008-4773 AU - Razmkabir, Mohammad AU - Kheirabadi, Khabat AD - Assistant Professor, Department of Animal Science, University of Kurdistan, Sanandaj, Iran AD - Ph.D. Student, Ramin University of Agriculture and Natural Resources of Khuzestan, Ahvaz, Iran Y1 - 2015 PY - 2015 VL - 46 IS - 4 SP - 389 EP - 397 KW - genetic trend KW - heritability KW - random regression model KW - somatic cell count DO - 10.22059/ijas.2015.56824 N2 - Genetic parameters were estimated for somatic cell score (SCS) in dairy cattle of Iran using test day records. The records of first lactation were extracted from the database of National Animal Breeding Center for cows calved between 2001 and 2010. Data included 222923 test-day records, obtained from 29668 animals distributed in 100 different herds. Estimates were carried out through Gibbs sampling procedures and using a random regression test-day model. Lactation curve were described in the model with orthogonal Legendre polynomials on days in milk. In order to correct for heterogeneity effect of residual variance, lactation period (5 to 365 days in milk) was classified into 10 groups with unequal distances. According to the results, residual variance was highest at the beginning and it was steady and decreased slowly from the second months to the end of lactation. Low residual and permanent environment variances and high genetic variance were lead to increase of heritability at the end of lactation. The lowest and the highest of heritability were at days 68 (0.031) and 365 (0.098), respectively. Genetic correlations between individual test-day records were high for adjacent tests and decreased as the interval between tests increased. Daily breeding values and genetic curve across lactation were produced for all animals using predicted regression coefficients. Estimation of genetic and phenotypic trends for SCS were -0.0025 and -0.1075, respectively (P<0.01). The results show a desirable improvement for somatic cell score at genetic and phenotypic levels. UR - https://ijas.ut.ac.ir/article_56824.html L1 - https://ijas.ut.ac.ir/article_56824_7e3812c70726c6843c82c9cd1c33501f.pdf ER -