CHILLED BOVINE SEMEN: LABORATORY METHODS FOR PREDICTING FERTILITY POTENTIAL AND FIELD FERTILITY

Abstract

Bovine semen preservation is essential for artificial insemination and fixed-time artificial insemination programs. Cryopreservation enables long-term storage and genetic dissemination but may compromise sperm function. This narrative review examines fie fertility outcomes using cooled and frozen-thawed bull semen and describes laboratory methods used to assess semen quality and support fertility prediction. Evidence concerning computer-assisted sperm analysis (CASA), flow cytometry, plasma and acrosomal membrane integrity, mitochondrial function, oxidative stress, and sperm DNA fragmentation is discussed. A study of 838 Nellore cows reported pregnancy rates of 59.9% and 49.4% with cooled and frozen-thawed semen, respectively. However, a meta-analysis of 14 studies and 8,785 inseminations found an overall difference of 2.95 percentage points without conclusive statistical evidence of superiority (p = 0.075). Combining CASA and cytometric traits may improve bull fertility characterization compared with isolated assays. Preservation methods should therefore be selected according to reproductive and logistical circumstances, while field pregnancy outcomes remain essential for validating laboratory markers.