Effect of Number of Days between Semen Sampling on Variance Heterogeneity of Semen Concentration of Young Simmental Bulls

Sa？etak The objective of this study was to estimate heterogeneity of genetic and environmental variances and heritabilities for semen concentration of young Simmental bulls due to different number of days between semen collections. Data utilized in this study consisted of 1132 young Simmental bulls born from 1974 to 2001 with total number of 6994 records, and 3000 animals in pedigree. The data were provided by the Performance Test Station . Vara？din. In order to analyze heterogeneity of variance, four data sets with two days periods (i.e. two and three; three and four; four and five; and five and six days) between semen samplings were derived. Similarly, three data sets with three days periods between semen samplings were derived. Variance and covariance components and associated heritabilities for such defined data sets were estimated by Restricted Maximum Likelihood from a set of single-trait animal models. Fixed effects were defined as birth year x season and number of days between collections, and animal effect was defined as a random effect. The heritability estimates ranged between 0.01 to 0.08. Days between collections influenced variance heterogeneity. An increase of days between collections increased additive and permanent environment variance, decreased error variance, thus the estimation of heritability was improved