40 TIMING OF INSEMINATION WITH SEXED OR NONSEXED SEMEN ON PREGNANCY RATES OF JERSEY HEIFERS DETECTED IN HEAT BY RADIOTELEMETRY

Abstract

The objectives of this study were to evaluate the follicular dynamics (experiment 1) and the effects of the timing of insemination with sexed or nonsexed semen on pregnancy rates (experiment 2) of Jersey heifers detected in heat by a radiotelemetric estrus detection system. In experiment 1, 43 Jersey heifers, around 12 mo old and BCS of 2.68 ± 0.11 (1 to 5 scale) were used. The Heat Watch (HW) system was utilized to detect the onset of estrus and mounting behavior associated with estrus. Ultrasound examinations to monitor follicular dynamics occurred every 12 h from estrus onset for 48 h. Statistical analyses were performed using GLM and GLIMMIX procedure of SAS (SAS Institute, Cary, NC, USA). The results of experiment 1 indicated a mean ovulatory follicle diameter of 14.1 ± 0.3 mm, ovulation rate of 86.1% (37/43), and an interval of 31.2 ± 0.9 h from onset of heat to ovulation. In experiment 2, 753 Jersey heifers were allocated in a 2 × 4 factorial with semen (sexed and nonsexed) and AI period (0 to 6, 6 to 12, 12 to 18, and 18 to 24 h after heat onset) as parameters. Semen from 3 bulls was used, with ejaculates divided in 2 fractions: one fraction was submitted to the traditional freezing procedure and the other was submitted to the sexing process and then frozen. The statistical analysis was performed using GLIMMIX procedure of SAS. There was no interaction among the semen, bull, and AI period. There were effects on pregnancy rate by type of semen [sexed 49.5% (189/382) and nonsexed 64.2% (238/371); P = 0.001] and by bull [bull A 53.5% (107/200)^b, bull B 50.0% (108/216)^b and bull C 63.4% (211/333)^a; P = 0.008]. Semen from bull C resulted in a greater pregnancy rate for both sexed and nonsexed semen. Within semen type, there were no differences in pregnancy rates by AI moment [sexed: 0 to 6 h 48.2% (41/85), 6 to 12 h 48.7% (54/111), 12 to 18 h 49.5% (49/99), 18 to 24h 52.4% (44/84) and nonsexed: 0 to 6h 62.8% (49/78), 6 to 12h 60.6% (63/104), 12 to 18h 68.0% (68/100), 18 to 24h 64.8% (57/88); P = 0.77]. We conclude that the use of sexed semen resulted in a lower pregnancy rate than nonsexed semen, and that AI timing does not affect conception rate in Jersey heifers identified in estrus by radiotelemetric estrus detection system. However, there was a bull effect on conception rate.

The authors wish to thank Sexing Technologies and Dalhart Jersey Ranch.