Cavalieri J, Rabiee A R, Hepworth G, Macmillan K L
Department of Veterinary Science, The University of Melbourne, Werribee, Australia.
Anim Reprod Sci. 2005 Nov;90(1-2):39-55. doi: 10.1016/j.anireprosci.2005.01.011.
This study investigated the hypothesis that a reduction in submission rates at a resynchronised oestrus is not due to the resynchrony treatment involving intravaginal progesterone releasing devices (IVDs) and oestradiol benzoate (ODB) but is associated with artificial insemination (AI) at the first synchronised oestrus. In Experiment 1, cows were synchronised for first oestrus with IVDs, with ODB administered at the time of device insertion (Day 0, 2 mg IM) and 24 h after removal (Day 9, 1 mg IM) and PGF(2alpha) injected at the time of device removal. Cows were then either inseminated (I) for 4 days or not inseminated (NI) following detection of oestrus (first round of AI). Every animal was resynchronised for a second round of AI by reinsertion of IVDs on Day 23 with administration of ODB (1 mg IM) at the time of insertion as well as 24 h after removal (Day 32). Cows detected in oestrus and inseminated for 4 days at the second round of AI were resynchronised for a third round by repeating the resynchrony treatment starting on Day 46 and inseminating cows on detection of oestrus for 4 days. In Experiment 2 the same oestrous synchronisation and resynchronisation treatments were used, but the timing of treatments differed. The cows had their cycles either presynchronised (treatment start Day -23) without AI and then resynchronised, starting on Day 0, for the first round of AI for AI at detected oestrus for 4 days, or they were synchronised (treatment start Day 0) for the first round of AI. In Experiment 1, 91.4% (64/70) and 92.6% (63/68) (P = 0.79) of cows in the I and NI treatments, respectively, were detected in oestrus after the initial synchronisation. At the second round of AI, submission rates for insemination were lower in the I group compared to the NI cows (74.5%, 35/47 versus 92.6%, 63/68, respectively; P = 0.007). Pregnancy rates (proportion treated that were classified as becoming pregnant) in I and NI cows 4 weeks (61.4%, 43/70 versus 63.2%, 43/68) and 7 weeks (77.1%, 54/70 versus 69.1%, 47/68) after the AI start date (AISD) did not differ significantly between treatments. In Experiment 2, presynchronisation and then resynchronisation of oestrous cycles before the first round of AI did not affect oestrous detection rates at the first round of AI (100%, 44/44 versus 98.0%, 50/51; P = 0.54), or pregnancy rates 1 week (63.6%, 28/44 versus 60.8%, 31/51; P = 0.70), 4 weeks (72.7%, 32/44 versus 76.5%, 39/51; P = 0.76) and 7 weeks (81.8%, 36/44 versus 88.2%, 45/51; P = 0.40) after AISD compared to cows that had their cycles synchronised for the first round of AI. These findings support our hypothesis that a reduction in submission rates at a resynchronised oestrus is associated with AI at the first synchronised oestrus and not due to a resynchrony treatment involving IVDs and ODB. This study supports the concept that early embryonic loss following AI at a synchronised oestrus could cause a reduction in submission rates following resynchronisation of oestrus, although investigation of the effect of passing an AI catheter or semen components were not studied per se.
再同步发情时受孕率降低并非由于采用阴道内孕酮释放装置（IVD）和苯甲酸雌二醇（ODB）的再同步处理，而是与首次同步发情时的人工授精（AI）有关。在实验1中，母牛通过IVD进行首次发情同步处理，在装置插入时（第0天，肌肉注射2毫克）和取出后24小时（第9天，肌肉注射1毫克）给予ODB，并在装置取出时注射前列腺素F2α（PGF2α）。然后，在检测到发情（第一轮AI）后，母牛要么接受4天的授精（I组），要么不进行授精（NI组）。每头动物在第23天通过重新插入IVD进行第二轮AI的再同步处理，在插入时以及取出后24小时（第32天）给予ODB（肌肉注射1毫克）。在第二轮AI中检测到发情并接受4天授精的母牛，从第46天开始重复再同步处理进行第三轮再同步，并在检测到发情时对母牛进行4天授精。在实验2中，采用相同的发情同步和再同步处理，但处理时间不同。母牛的周期要么在不进行AI的情况下预先同步（处理开始于第-23天），然后从第0天开始进行再同步，用于第一轮AI，在检测到发情时进行4天AI；要么直接同步（处理开始于第0天）用于第一轮AI。在实验1中，I组和NI组分别有91.4%（64/70）和92.6%（63/68）（P = 0.79）的母牛在初始同步后检测到发情。在第二轮AI中，I组的授精受孕率低于NI组母牛（分别为74.5%，35/47和92.6%，63/68；P = 0.007）。在AI开始日期（AISD）后4周（61.4%，43/70对63.2%，43/68）和7周（77.1%，54/70对69.1%，47/68），I组和NI组母牛的妊娠率（分类为怀孕的处理比例）在处理之间没有显著差异。在实验2中，在第一轮AI之前对发情周期进行预先同步然后再同步，并不影响第一轮AI时的发情检测率（100%，44/44对98.0%，50/51；P = 0.54），也不影响AISD后1周（63.6%，28/44对60.8%，31/51；P = 0.70）、4周（72.7%，32/44对76.5%，39/51；P = 0.76）和7周（81.8%，36/44对88.2%，45/51；P = 0.40）的妊娠率，与第一轮AI时直接同步周期的母牛相比。这些发现支持了我们的假设，即再同步发情时受孕率降低与首次同步发情时的AI有关，而非由于涉及IVD和ODB的再同步处理。本研究支持了这样一种观点，即同步发情时AI后早期胚胎损失可能导致发情再同步后受孕率降低，尽管未单独研究通过AI导管或精液成分的影响。
