In this study there was evaluation of effects of different doses of equine chorionic gonadotropin (eCG: 200, 300, or 400 IU) administrated at progesterone (P4) plus estradiol-based timed AI (TAI). A total of 1080 heifers were included in the study. There was insertion of the intravaginal P4-device plus administration of 2 mg of estradiol benzoate IM. On D7, 12.5 mg of dinoprost tromethamine IM was administered and on D9, the P4 insert was removed and 0.5 mg of estradiol cypionate IM was administered. Heifers were categorized according to Reproductive Tract Status (RTS; 1−5) and were assigned to one of three treatments: 200 IU (n = 387), 300 IU (n = 357), or 400 IU (n = 336) of eCG. Estrous occurrence was evaluated at TAI 48 h later (D11). A subset of heifers (n = 213) had the largest follicle (LF) evaluated on D9 and on D11, and the formation of a new CL evaluated on D18.There was no effect of eCG treatment on LF on D11 (P = 0.79), occurrence of estrus (P = 0.92), and pregnancy at 30 days after AI (P/AI; 52.2%, 49.8%, and 51.5% for 200 IU, 300 IU, and 400 IU, respectively; P = 0.46). Regardless of the treatment, there was a greater P/AI when heifers had a functional CL, at initiation of the estrous synchronization treatment regimen. It, therefore, is efficacious to reduce the dose of eCG to 300 or 200 IU in purebred taurine and crossbred beef heifers without negative effects on ovarian, estrous or pregnancy responses.

在这项研究中，评估了在孕酮（P4）和基于雌二醇的定时AI（TAI）的情况下，不同剂量的马绒毛膜促性腺激素（eCG：200、300或400 IU）的作用。该研究总共包括1080个小母牛。插入阴道内的P4-装置，再加上2 mg的雌二醇苯甲酸酯IM。在D7上，施用12.5 mg地诺前列素三甲胺IM，在D9上，移除P4插入物，并施用0.5 mg环丙二醇雌二醇。小母牛根据生殖道状态（RTS; 1-5）进行分类，并被指定为以下三种处理之一：200 IU（n = 387），300 IU（n = 357）或400 IU（n= 336）的eCG。48小时后在TAI评估发情（D11）。在D9和D11上评估的部分小母牛（n = 213）的卵泡（LF）最大，在D18评估了新的CL的形成.eCG处理对D11的LF没有影响（P = 0.79） ，发生发情（P = 0.92）和AI后30天妊娠（P / AI; 200 IU，300 IU和400 IU分别为52.2％，49.8％和51.5％; P= 0.46）。无论采用哪种治疗方法，在发情同步治疗方案开始时，小母牛的功能性CL均具有较高的P / AI。因此，可以有效地将纯种牛磺酸和杂交牛小母牛的eCG剂量降低至300或200 IU，而对卵巢，发情或妊娠反应无不利影响。