Karyotypes and morphological and histological alterations of the genital tracts of repeat breeder heifers with known breeding history.

Forty-two repeat breeder heifers (RBH) and 27 virgin heifers (VH) were used in the study. The breeding history and the occurrence of chromosomal aberrations were investigated in the RBH. The genital tracts of the RBH and the VH were investigated at slaughter 3 to 35 days after artificial insemination and/or embryo transfer for the presence of morphological and histological changes. According to AI data the mean number of inseminations per RBH in the herd of origin was 4.9 and 110 interservice intervals out of 141 calculated were normal (17–24 days) or twice normal (34–48 days). Two RBH out of 28 investigated demonstrated the 1/29 translocation. The post mortem examination revealed corpus lutea and follicles normal for the stage of the cycle in all animals. In three RBH abnormalities of the uterus or cervix were found. A higher incidence of cystic glands and of focal accumulation of erythrocytes and lymphocytes in the endometrium was found in the RBH than in the VH (P ≤ 0.05). The relation between the embryonic survival and the histological alterations of the uterus was not significant. It is suggested that errors in heat detection, abnormal karyotypes and morphological defects of the genital tract play a minor role in the repeat breeding complex in heifers.