Genetics aspects of reproductive performance for Holstein

A total of 16678 records were analyzed which included age at first calving and ages at next calving, in addition to 14058 records of calving interval belonged to Holstein over period from 1992 to 2003 , at the Nasr Dairy Cattle Station, United Company for Animal Resources Ltd., Al-Soueira ( 50 Km South of Baghdad ). Data was analaysed using General Linear Model within the SAS program to study the effects of some fixed factors on the studied traits . Components of variance for the random effects was estimated by the Minimum Variance Quadratic Unbised Estimation Procedure ( MIVQUE ) , also phenotypic trend was estimated for all traits . The overall means for age at first calving till the age at sixth calving were 48.17 , 62.77 , 77.41 , 91.35 , 105.53 months respectively , and the heritability for the same traits was 0.10 , 0.01 , 0.03 , 0.04 , 0.02 , 0.11 respectively . whereas the overall mean of calving interval and heritability was 458.59 days and 0.07 . The results obtained that there was a significant effect of year of birth on age at first calving , whereas the season of birth was not . All the estimates of heritability were low so it’s reflect the role of environment factors in the traits variation.Phenotypic trend was negative and significant ( p <0.01 ) for age at first calving ( - 1.05 month / year ) and calving interval (- 2.03 day / year )
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