ANBAR JOURNAL OF AGRICULTURAL SCIENCES

Abstract

This study was conducted to investigate the effect of season, parity And age at first calving on conception rate (CR) and service per conception(SPC)in Holstein cows. The study was carried out at AL-Nasr Dairy cattle Station during the period 2004-2006.One thousand and five hundred records, pertaining to 349 Holstein cows were analyzed. The General Linear model (GLM) within SAS program was employed to study the influence of fixed factor and to estimate the component of variance for random effects in mixed model estimated by the direct maximum Likelihood procedure (REML). Overall means of CR and SPC were 67.33% and 2.51 respectively. The parity and season exhibited highly significance effect on CR and SPC. An obvious significant influence of first age at calving was noticed on SPC but not on CR .Heritability of CR and SPC were 0.17 and 0.09 respectively .In conclusion , the implementation of natural mating of heifers would increase the conception rate . Moreover, reducing of artificial insemination during hot season of mature cows would enhance the conception rate of Holstein herds.