Two experiments were performed to determine effects of follicular ablation (FA) and GnRH treatment on conception rate and synchronization in timing of ovulation among Holstein heifers. In Experiment 1, heifers were randomly allocated to four groups: Control (n = 84): prostaglandin F_2α (PGF) IM on Day 0; FA-5/GnRH (n = 43): FA 5 days before PGF and GnRH on Day 2; FA-4/GnRH (n = 48):FA 4 days before PGF and GnRH on Day 2; andFA-3/GnRH (n = 21): FA 3 days before PGF and GnRH on Day 2. Ultrasonography was performed to determine follicular size, ovulation occurrence, and size of CL. In Experiment 2, heifers were assigned to three groups: Control (n = 264), FA-5/GnRH, and FA-4/GnRH. Pregnancy diagnosis was performed at Days 30 and 60. In Experiment 1, size of largest follicle at time of PGF was less variable (P ≤ 0.05) in all FA groups compared to the Control group. With the FA-5/GnRH and FA-4/GnRH treatments, there were greater (P ≤ 0.05) proportions of timing of ovulation synchronization (86 % and 85 %, respectively) compared to the Control (61 %) and FA-3/GnRH (62 %) groups. In Experiment 2, conception rates did not differ among groups, however, there were more pregnancies per cow when timing-of-ovulation treatments were imposed. In conclusion, follicular ablation combined with GnRH treatment resulted in an increased proportion of heifers having synchronized ovulation and, therefore, number of recipient heifers available for embryo transfer. Additionally, there was no effect on conception rate when there was greater synchronization in timing of ovulation among heifers.

进行了两个实验以确定卵泡消融 (FA) 和 GnRH 治疗对荷斯坦小母牛受孕率和排卵时间同步的影响。在实验 1 中，小母牛被随机分配到四组：对照组（n = 84）：第 0 天的前列腺素 F _2α (PGF) IM；FA-5/GnRH ( n = 43)：第 2 天 PGF 和 GnRH 前 5 天的 FA；FA-4/GnRH ( n = 48)：第 2 天 PGF 和 GnRH 前 4 天的 FA；andFA-3/GnRH ( n = 21)：第 2 天 PGF 和 GnRH 前 3 天的 FA。进行超声检查以确定卵泡大小、排卵发生率和 CL 大小。在实验 2 中，小母牛被分为三组：对照组（n= 264)、FA-5/GnRH 和 FA-4/GnRH。在第 30 天和第 60 天进行妊娠诊断。在实验 1 中， 与对照组相比，所有 FA 组中 PGF 时最大卵泡的大小变化较小（P ≤ 0.05）。FA-5/GnRH 和 FA-4/GnRH 处理后，有更大的（P ≤ 0.05) 与对照 (61 %) 和 FA-3/GnRH (62 %) 组相比，排卵同步时间的比例（分别为 86 % 和 85 %）。在实验 2 中，各组之间的受孕率没有差异，但是，当采用定时排卵治疗时，每头母牛的怀孕率更高。总之，卵泡消融结合 GnRH 治疗导致同步排卵的小母牛比例增加，因此可用于胚胎移植的受体小母牛数量增加。此外，当小母牛排卵时间更同步时，对受孕率没有影响。