Angus sire field fertility and in vitro sperm characteristics following use of different sperm insemination doses in Brazilian beef cattle

ABSTRACT The primary objective was to determine if Angus bull fertility varied by number of sperm inseminated. A secondary objective was to characterize the potential impact of random variation on fertility using two identical sperm per dose treatments, which differed only in straw color. Computer-assisted sperm analysis (CASA) and flow cytometry (FC) were used to identify post-thaw sperm characteristics associated with field fertility differences between bulls. Ejaculates from five Angus bulls were collected, extended, and cryopreserved at 10, 20, 20 or 40 x 106 sperm per dose in color-coded 0.5-mL French straws. Multiparous cows (n = 4,866) from ten Brazilian farms were synchronized for first-service timed artificial insemination (TAI). Bull identification and straw color were recorded at TAI. Pregnancy per TAI (P/TAI) did not differ between sperm doses (43.8, 45.3, 43.8 and 47.1% for 10, 20, 20 or 40 x 106 sperm respectively; P = 0.31) nor was there an interaction between bull and dose (P = 0.53). The P/TAI differed between bulls and ranged from 40.7 to 48.1 % (P