Galvão K N, Santos J E P, Cerri R L, Chebel R C, Rutigliano H M, Bruno R G, Bicalho R C
Veterinary Medicine Teaching and Research Center, University of California-Davis, Tulare 93274, USA.
J Dairy Sci. 2007 Sep;90(9):4240-52. doi: 10.3168/jds.2007-0094.
The objectives of this study were to evaluate the effect of 3 methods of resynchronization of estrus and ovulation for lactating dairy cows of unknown pregnancy status on conception rate and time to pregnancy. Holstein cows (n = 495) were randomly assigned to 1 of 3 treatments: 1) control (n = 167), resynchronization with a timed AI protocol upon diagnosis of nonpregnancy on d 31 after preenrollment AI (PAI); 2) CIDR-G (n = 159), use of an intravaginal progesterone insert from d 14 to 21 after AI, with AI at estrus from d 21 to 24 and initiation of a timed AI protocol on d 24 after AI in cows not reinseminated; 3) CIDR-G + ECP (n = 169), the same treatment as CIDR-G but with an injection of 1 mg of estradiol cypionate at the time of progesterone insert removal. Cows were continuously reenrolled in the same treatment until diagnosed as pregnant, which resulted in a total of 1,148 AI (495 PAI and 653 resynchronized AI; RAI). Blood was collected from 1,001 cows on d 14, 21, and 24 after each AI for analysis of progesterone, and ovaries were scanned on d 21, 24, and 31 after AI. The presence of an active corpus luteum was presumed based on progesterone > or = 1 ng/mL. Pregnancy was diagnosed by ultrasonography on d 31 and 61 after AI. The presence of an active corpus luteum and the incidence of luteolysis were similar for all treatments from d 14 to 24; however, luteolysis increased in the CIDR-G + ECP treatment from d 21 to 24. Conception rates for the PAI and all AI were similar on d 31 and 61 after insemination. Conception rates at 31 and 61 d after the RAI were also similar among treatments. Overall pregnancy loss for the PAI, RAI, and all AI were similar for all treatments. The accuracy of estrous detection, based on progesterone concentration within 2 d of detection of estrus, was similar for all treatments for the RAI and averaged 95.3%. The estrus-detection rate (EDR) decreased for the CIDR-G and CIDR-G + ECP treatments from d 14 to 21, but increased from d 21 to 24 compared with control cows; however, the EDR was smaller for cows in the CIDR-G treatment during the entire resynchronization period compared with those in the CIDR-G + ECP and control groups. The reinsemination interval was reduced in cows receiving the CIDR-G + ECP treatment compared with control cows because of increased EDR after removal of the intravaginal insert; however, the interval from study enrollment to pregnancy was not different among treatments. These results indicate that the reproductive performance of dairy cows did not differ among the 3 resynchronization treatments evaluated.
本研究的目的是评估3种发情和排卵再同步方法对妊娠状态不明的泌乳奶牛受胎率和妊娠时间的影响。将荷斯坦奶牛（n = 495）随机分为3种处理中的1种：1）对照组（n = 167），在预登记人工授精（PAI）后第31天诊断为未妊娠时，采用定时人工授精方案进行再同步；2）CIDR-G组（n = 159），在人工授精后第14至21天使用阴道内孕酮植入物，在第21至24天发情时进行人工授精，未再次输精的奶牛在人工授精后第24天开始定时人工授精方案；3）CIDR-G + ECP组（n = 169），与CIDR-G组处理相同，但在取出孕酮植入物时注射1 mg环丙孕酮。奶牛持续接受相同处理直至诊断为妊娠，共进行了1148次人工授精（495次PAI和653次再同步人工授精；RAI）。每次人工授精后第14、21和24天从1001头奶牛采集血液分析孕酮，并在人工授精后第21、24和31天扫描卵巢。根据孕酮≥1 ng/mL推测存在活性黄体。在人工授精后第31天和61天通过超声检查诊断妊娠。从第14至24天，所有处理的活性黄体存在情况和黄体溶解发生率相似；然而，CIDR-G + ECP处理从第21至24天黄体溶解增加。人工授精后第31天和61天，PAI和所有人工授精的受胎率相似。各处理间RAI后第31天和61天的受胎率也相似。所有处理的PAI、RAI和所有人工授精的总体妊娠损失相似。基于发情检测后2天内孕酮浓度的发情检测准确性，所有处理的RAI相似，平均为95.3%。CIDR-G和CIDR-G + ECP处理从第14至21天发情检测率（EDR）下降，但与对照奶牛相比，从第21至24天增加；然而，在整个再同步期，CIDR-G处理奶牛的EDR低于CIDR-G + ECP组和对照组奶牛。与对照奶牛相比，接受CIDR-G + ECP处理的奶牛因取出阴道内植入物后EDR增加，再次输精间隔缩短；然而，各处理从研究入组到妊娠的间隔无差异。这些结果表明，在所评估的3种再同步处理中，奶牛的繁殖性能没有差异。
