Division of Animal Science, University of Missouri, Columbia 65211, USA.
J Dairy Sci. 2010 Dec;93(12):5668-72. doi: 10.3168/jds.2010-3395.
Cattle that are not pregnant to first fixed-time artificial insemination (TAI) may be resynchronized for a second TAI if they are found nonpregnant at pregnancy diagnosis. The specific interval between first and second TAI ranges from 4 to 8 wk. The selected interval depends on the available method of pregnancy diagnosis and the efficiency of the resynchronization program. The objective of this experiment was to evaluate a pregnancy diagnosis and resynchronization system that achieved a 21-d interval between TAI. This 21-d interval approximates the natural return-to-service interval. It also enables resynchronization to be implemented within the same estrous cycle in which cattle are first inseminated. Holstein heifers were randomly assigned to a 21-d resynchronization program (21d_resynch; n = 40) or a control group in which estrus was observed for the purpose of re-insemination (control; n = 29). The 21d_resynch heifers were diagnosed for pregnancy on d 18 after a TAI (d 0) by using predetermined cut-off values for 2'-5' oligoadenylate synthetase 1 (Oas1) gene expression in leukocytes and plasma progesterone concentration. Heifers that were not pregnant to first TAI had greater expression of Oas1 at the time of PGF(2α) (d -3) than pregnant heifers, but this relationship was reversed on d 18 after TAI: the heifers that were pregnant to first TAI had almost 5-fold greater expression of Oas1 compared with nonpregnant heifers. Nonpregnant heifers in the 21d_resynch group were injected with a luteolytic dose of PGF(2α) on d 19 and were injected with GnRH on d 21 and submitted to TAI. The pregnancy per AI after first insemination was similar for 21d_resynch (50.0%; pregnancy diagnosis on d 18) and control (51.7%; pregnancy diagnosis on d 27). Likewise, no difference was detected in second insemination pregnancy per AI for 21d_resynch (36.8%; nonpregnant heifers TAI on d 21) and control (35.7%; nonpregnant heifers inseminated at return to estrus or after nonpregnant diagnosis on d 27). The interval between first and second insemination was shorter for 21d_resynch compared with control (21.0 ± 0 and 27.5 ± 2.1 d). The conclusion is that a TAI resynchronization can be programmed within 21 d of previous TAI when a d 18 pregnancy test and a rapid resynchronization are used.
未经过首次定时人工授精（TAI）怀孕的牛，如果在妊娠诊断时发现未怀孕，可以重新进行第二次 TAI。第一次和第二次 TAI 之间的特定间隔时间为 4 至 8 周。所选间隔取决于可用的妊娠诊断方法和同步化方案的效率。本实验的目的是评估一种妊娠诊断和同步化系统，该系统可实现 TAI 之间 21 天的间隔。这个 21 天的间隔接近自然的返情间隔。它还可以使同步化在第一次授精的发情周期内进行。荷斯坦小母牛被随机分配到 21 天的同步化方案（21d_resynch；n = 40）或对照组，对照组是为了重新授精而观察发情（control；n = 29）。21d_resynch 小母牛在 TAI 后第 18 天（d 0）通过白细胞中 2'-5'寡聚腺苷酸合成酶 1（Oas1）基因表达的预定截断值和血浆孕酮浓度进行妊娠诊断。首次 TAI 未怀孕的小母牛在 PGF（2α）（d -3）时 Oas1 的表达高于怀孕的小母牛，但这种关系在 TAI 后第 18 天发生逆转：首次 TAI 怀孕的小母牛 Oas1 的表达几乎是未怀孕小母牛的 5 倍。21d_resynch 组的未怀孕小母牛在 d 19 时注射黄体溶解剂量的 PGF（2α），在 d 21 时注射 GnRH，并进行 TAI。首次授精后的每一次 AI 怀孕率在 21d_resynch（50.0%；在 d 18 进行妊娠诊断）和对照组（51.7%；在 d 27 进行妊娠诊断）之间相似。同样，21d_resynch（在 d 21 时未怀孕的小母牛进行 TAI）和对照组（在 d 27 时未怀孕的小母牛返情或诊断未怀孕后进行授精）的第二次授精每一次 AI 怀孕率也没有差异，分别为 36.8%和 35.7%。21d_resynch 与对照组相比，第一次和第二次授精之间的间隔时间更短（21.0 ± 0 和 27.5 ± 2.1 d）。结论是，当使用 d 18 妊娠试验和快速同步化时，可以在首次 TAI 后的 21 天内计划进行 TAI 同步化。
