Mashona heifers, estrous, artificial insemination, breeding season, GnRH.
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.