The effect of insemination time with sex-sorted semen after onset of estrus on conception rate in dairy heifers

The aim of this study was to determine the insemination time after to obtain the optimum conception rate with sex-sorted semen in dairy heifers. The study was carried out with nulliparous thirteen months or over aged Holstein heifers (n=299). Heifers were included in the study after estrus induction (single dose PGF2α) and natural estrus. Estrous detection was followed by the activity-rumination (SCR Dataflow II) system. Heifers were randomly divided into three groups after estrous detection. Heifers inseminated with sex-sorted semen from three different bulls between 12-16 hours, 16,1-20 hours and 20,1-24 hours after the onset of estrus in Group1 (n = 100), Group2 (n = 100) and Group3 (n = 99), respectively. At 30 ± 3 and 60 ± 3 days, pregnancy examination was performed using ultrasonography. Temperature-Humidity Index (THI) was used to evaluate the heat stress. Statistical evaluations were performed using SPSS package program. In the first pregnancy examination, conception rates were 49.0% (49/100); 49.0% (49/100) and 58.6% (58/99) in groups. While there was no statistical difference between the groups, there was about 10% difference in Group3 compared to other groups. Conception rates were 49.0% (49/100) in Group1; 47.0% (47/100) in Group2; 55.6% (55/99) in Group3 in the second pregnancy examination. When the sperm of the bull's C where compared, conception rate was higher in Bull C (65.6%) than other two bulls (Bull A 41.4%; Bull B 49.5%). It was determined that the conception rate didn't change if the THI was over 72 (50.0%) and below (52.5%). As a result, it was determined that there was a difference in fertility between the bulls. Although the insemination with sex-sorted semen between 20,1 and 24 hours after the initiation of estrus (Group3) increased the conception rate about 10%, there was no statistical difference between the groups in dairy heifers. Key words: Heifers, Sexed Semen, Conception Rate, Timing of Insemination