Use of equine chorionic gonadotropin (eCG) in Mashona heifers, under a J-Synch synchronization protocol, and its effect in pregnancy rate: Use of equine chorionic gonadotropin in a J-Synch protocol in heifers

Objective: The objective of the present study was to evaluate the J-Synch protocol with two doses of eCG in beef heifers during the summer in Northeast Mexico. Design/methodology/approach: In this experiment, 218 heifers of the Mashona breed (109/treatment) with a live weight of 350 ±12.1 kg were used. On Day 0, all heifers received an intravaginal device (1.2 g P4) plus 2 mg, i.m., EB; On day 5, it was withdrawn and 0.15 mg of D-Cloprostenol was applied; where treatment 1 (T1) consisted of the application of 250 IU of eCG; in treatment 2 (T2), 300 IU of eCG was applied. Subsequently, the total number of heifers from both treatments were inseminated at a fixed time (FTAI) at 72 hours after the removal of the device with frozen bull semen; likewise, at the time of the FTAI, 10.5 µg of GnRH was applied to each heifer. Results: There were no significant differences (p > 0.05) in the percentage of estrus at the first service (T1 = 91%; T2 = 96%; as well as in the percentage of repeaters (T1 = 25.2% vs T2 = 19 .2%). For the inseminating technician and the color of the heifers' coat, there was an effect on the percentage of heifers repeating estrus. For the percentage of pregnancy at first service, it was 64.8% for T1 and 70.1 % for T2 (p > 0.05) There was only an effect of the inseminator technician in terms of pregnancy percentage, varying from 63.4% for the best-qualified technician vs. 48.6% for the one with the lowest percentage. Limitations on study/implications: At least in this study, the pregnancy rate in beef heifers will depend mainly on the experience and skill of the inseminator technician. Findings/conclusions: According to the present investigation, the indistinct application of 250 or 300 IU of eCG can be used with the same results of the presence of estrus and gestation during the summer season in beef heifers, however, the inseminator technician has an important role on pregnancy outcomes.O Objective: To evaluate the J-Synch protocol with two eCG doses in beef heifers during the summer in northeastern Mexico. Design/Methodology/Approach: 218 heifers (109/treatment) with a body weight of 350 ± 12.1 kg were used. A J-Synch protocol was applied in order to evaluate two eCG doses: T1 (250 IU) and T2 (300 IU). Subsequently, the total number of heifers from both treatments were inseminated at a fixed time (FTAI): 72 h after removing the device. Results: No significant differences (p>0.05) were recorded in the estrous percentage at first service (T1 = 91%; T2 = 96%) and in the repeating heifers (T1 = 25.2%; T2 = 19.2%). The insemination technician and coat color variables impacted the estrous percentage in repeating heifers. The pregnancy percentage at first service was 64.8% and 70.1% for T1 and T2 (p>0.05), respectively. The insemination technician had a variable effect on the pregnancy percentage, from 63.4% (the best-qualified technician) to 48.6% (the technician who obtained the lowest percentage). Study Limitations/Implications: The pregnancy rate in beef heifers will depend mainly on the experience and skill of the insemination technician. Findings/Conclusions: The same results were obtained regarding the presence of estrous and pregnancy in beef heifers during the summer season, either with 250 or 300 IU of eCG