Department of Animal Sciences, North Dakota State University, Fargo 58108, USA.
J Anim Sci. 2012 Dec;90(13):4823-32. doi: 10.2527/jas.2011-4778. Epub 2012 Aug 7.
Our objectives were to determine pregnancy rate, fetal loss, and number of calves born in beef cattle after a fixed-time transfer of an embryo 7 d after a fixed-time artificial insemination (TAI) of cows (Exp. 1) and after transfer of 2 demi-embryos into a single heifer recipient (Exp. 2). In Exp. 1 after synchronization of ovulation, during 2 yr, 297 suckled beef cows were assigned randomly to 1 of 3 treatments: 1) on d 2 cows received a single TAI (TAI-2; n = 99), 2) a fixed-time direct transfer, frozen and thawed embryo placed in the uterine horn ipsilateral to the ovary containing a corpus luteum (CL) on d 9 embryo transfer (ET-9; n = 99), or 3) cows received TAI on d 2 and a frozen and thawed direct transfer embryo placed in the uterine horn ipsilateral to the ovary containing a CL on d 9 (TWIN) treatments (n = 99). Fetal number and viability were determined with ultrasonography at 33 to 35 d and 90 to 100 d after insemination. In Exp. 2, 74 crossbred recipient heifers were assigned randomly to receive either 1) a single whole fresh embryo (WHOLE; n = 37) or 2) 2 identical fresh demi-embryos (SPLIT; n = 37) in the uterine horn ipsilateral to the CL 7 d after an observed estrus. Ultrasonography was used on d 33, 69, and 108 to determine presence and number of embryos or fetuses. Palpation per rectum was used to determine pregnancy status on d 180 of gestation and number of live calves was recorded at birth. In Exp. 1 pregnancy rates on d 30 to 35 were greater (P < 0.05) for TWIN- (48.5%) and TAI-2- (47.5%) than for ET-9- (33.3%) treated cows. Of the 48 pregnant cows in the TWIN treatment, 21 were twin pregnancies whereas there was 1 twin pregnancy in the TAI-2 treatment. As a result, TWIN cows had more fetuses (P < 0.05) as a proportion of all treated cows (69.7%) than TAI-2- (48.5%) or ET-9-(33.3%) treated cows, and cows in the TWIN treatment gave birth to more (P < 0.01) calves (n = 55) compared with cows in the ET treatment (n = 23) whereas cows in the TAI-2 treatment (n = 40) were intermediate. In Exp. 2 heifers receiving SPLIT (81.1%) had greater (P < 0.05) pregnancy rates on d 33 than heifers receiving WHOLE (40.5%). Of the SPLIT heifers that were confirmed pregnant at d 33 after transfer, 57% were gestating twin fetuses. Embryonic or fetal loss from d 33 to birth was greater (P < 0.01) in heifers in the SPLIT treatment (40.0%) compared with the WHOLE treatment (0.0%), but number of calves per female treated was greater (P < 0.05) in heifers in the SPLIT treatment (75.0%) compared with heifers in the WHOLE treatment (40.5%). We conclude that transferring an embryo into a cow 7 d after TAI did not increase the pregnancy rate in Exp.1. However, transferring 2 demi-embryos into a single heifer recipient increased pregnancy rate at 33 d of gestation whereas both methods of inducing twinning resulted in a greater number of calves per female treated. In addition, embryonic or fetal loss associated with unilateral twin pregnancies in heifers occurred at rates greater than those associated with single-fetus pregnancies.
我们的目标是确定牛在经过定时人工授精（TAI） 7 天后进行胚胎固定时间转移（实验 1）和将 2 个半胚胎转移到单个受体小母牛中的妊娠率、胎儿损失和小牛数量。在实验 1 中，在排卵同步后，在 2 年内，297 头哺乳期肉牛随机分配到 3 种处理之一：1）在第 2 天，奶牛接受单次 TAI（TAI-2；n = 99），2）固定时间直接转移，冷冻和解冻胚胎放置在含有黄体（CL）的卵巢同侧子宫角（ET-9；n = 99），或 3）奶牛在第 2 天接受 TAI，然后在含有黄体的卵巢同侧子宫角中放置冷冻和解冻直接转移胚胎（TWIN）处理（n = 99）。在授精后 33 至 35 天和 90 至 100 天通过超声检查确定胎儿数量和活力。在实验 2 中，74 头杂交受体小母牛随机分配接受以下处理之一：1）单个新鲜胚胎（WHOLE；n = 37）或 2）在观察到发情后 7 天，在含有黄体的卵巢同侧放置 2 个相同的新鲜半胚胎（SPLIT；n = 37）。在第 33、69 和 108 天使用超声检查确定胚胎或胎儿的存在和数量。通过直肠触诊在妊娠第 180 天确定妊娠状态，记录出生时的活小牛数量。在实验 1 中，在第 30 至 35 天的妊娠率方面，TWIN-（48.5%）和 TAI-2-（47.5%）处理的奶牛高于 ET-9-（33.3%）处理的奶牛（P <0.05）。在 TWIN 处理的 48 头怀孕奶牛中，有 21 头是双胞胎妊娠，而 TAI-2 处理中有 1 头双胞胎妊娠。因此，TWIN 奶牛的胎儿比例（P <0.05）高于 TAI-2-（48.5%）或 ET-9-（33.3%）处理的奶牛，并且 TWIN 处理的奶牛产犊数（P <0.01）多于 ET 处理的奶牛（n = 23），而 TAI-2 处理的奶牛（n = 40）则处于中间水平。在实验 2 中，接受 SPLIT（81.1%）的小母牛在第 33 天的妊娠率高于接受 WHOLE（40.5%）的小母牛（P <0.05）。在移植后第 33 天确认怀孕的 SPLIT 小母牛中，有 57%是怀有双胞胎胎儿的。从第 33 天到分娩的胚胎或胎儿损失在 SPLIT 处理（40.0%）中高于 WHOLE 处理（0.0%）（P <0.01），但 SPLIT 处理的每头小母牛产犊数（P <0.05）高于 WHOLE 处理（40.5%）（P <0.05）。我们得出的结论是，在实验 1 中，在 TAI 后 7 天将胚胎转移到奶牛中并没有提高妊娠率。然而，将 2 个半胚胎转移到单个受体小母牛中增加了妊娠第 33 天的妊娠率，而这两种诱导双胎的方法都导致每头小母牛处理的小牛数量增加。此外，在小母牛中，与单胎妊娠相关的胚胎或胎儿损失发生率大于与单胎妊娠相关的胚胎或胎儿损失发生率。
