奶（黄）牛卵母细胞体外受精及体外发育的研究

自屠宰场获得150头淘汰黑白花奶牛和19头黄牛的卵巢,取得优、良级卵母细胞2060枚,采用两种培养液(A.B.)和三种不同试剂(Aa、Ba、Bb),对解冻牛精子获能(capacitation)。在38.5℃和相对湿度为100％的5％CO_2箱中进行成熟、受精、发育培养至196小时,其结果表明A液所获得的效果优于B液,但差异不显著;Aa试剂获能优于Bb,差异显著。共获得桑椹胚和囊胚58枚、非手术移植10头牛16次,三头妊娠,其中二头受体在妊娠二月半月后返情,外阴流血,确认为胚胎早期死亡,一头受体妊娠产犊,于1990年4月10日产公犊1头,体长87公分、身高78公分、体重29公斤、妊娠284天,正常分娩。(移植天为0天)。     

间接免疫荧光鉴别奶牛胚胎性别的研究

本实验用H—Y抗体的间接免疫荧光方法对奶牛6—7日龄胚胎进行性别鉴别。用数排卵法获得的胚胎,共选37枚在含H—Y抗血清的M2培养液中温育30min,用M2培养液清洗后,在含FITC—荧光标记的羊抗鼠IgG二抗的M2中温育30min,经洗后的胚胎在Nikon倒置荧光显微镜下鉴别有无荧光,结果21枚胚胎有特异免疫荧光,判作雄性胚胎;16枚无特异免疫荧光,判作雌性胚胎,分别占57％和43％。这与自然出生公母犊各约50％和性比率无显著差别(P>0.25),判定为雄性的5枚胚胎移植给3头受体奶牛(每头移植1或2枚)、3枚判定为雌性胚胎移植给2头受体奶牛一头移植一枚,枚、另一头移植2枚)移植后两个月时检查有3头受体怀孕,其中,一头移植有荧光胚胎的受体返植无荧光胚胎的2头受体各产一母犊(体重皆41kg)。     

两温度梯度多重PCR鉴别牛早期胚胎性别的技术研究

稳定、可靠和快速的牛胚胎性别鉴定方法在生产应用中具有重要意义。通过两温度梯度PCR方法对牛基因组、克隆胚胎、胚胎样品进行性别鉴别实验研究,建立了稳定、简便、快速的牛早期胚胎性别鉴别两温度梯度PCR方法,鉴定时间仅为57分钟。采用两温度梯度PCR方法对30枚奶牛胚胎进行了早期性别鉴别,并将鉴别的15枚胚胎（11枚为雌性,4枚为雄性）移植到同期处理的15头受体母牛体内。60天后妊娠检查,有7个受体成功受孕,5头受体怀孕晚期流产,流产犊牛全部为母犊。结果产下1公1母两头犊牛,流产个体与出生个体的性别与PCR鉴别结果完全相符。      

云南水牛的同期发情、超数排卵和胚胎移植试验

为探讨水牛胚胎移植的效果 ,于 2 0 0 2年对云南水牛进行了胚胎移植试验 :①用国产氯前列烯醇(PG) 0 6mg/头·次处理供、受体水牛的同期发情率和可用率分别为 4 3 33% (13/ 30 )和 16 6 7% (5 / 30 ) ;同期发情率经产水牛高于青年水牛 (P =0 0 86 ) ,杂交水牛高于德宏水牛 (P =0 15 3) ,体重 4 0 1～ 5 30kg水牛显著高于体重 30 0～ 4 0 0kg水牛 (P <0 0 5 ) ;发情明显水牛的可用率极显著高于发情不明显的水牛 (P <0 0 1)。②选用河流型摩拉水牛与沼泽型德宏水牛的杂交一代 5头为供体 ,分进口激素组 (n =2 )和国产激素组 (n =3)进行超数排卵 ,共有 2头获 9枚胚胎 ;进口激素组供体的平均获胚数和可移植胚数分别为 2 0枚和 1 5枚 ,比国产激素组分别多 0 33枚 (P =0 4 5 4 )和 1 17枚 (P =0 2 88)。③所获 4枚可用鲜胚分别移植 3头受体 ,结果 90d的妊娠率为 33 33% ,但最终无一头产犊。试验结果表明使用进口FSH 2 4mg +PG (Lutalyse○R) 35mg和国产FSH 11mg +PG 0 8mg对水牛超数排卵有效 ,同时提示需要足够数量的受体 ,从中选用发情表现明显、黄体发育良好的进行胚胎移植 ,才能取得良好效果。     

两温度梯度多重PCR鉴别牛早期胚胎性别的技术

稳定、可靠和快速的牛胚胎性别鉴定方法在生产应用中具有重要意义.通过两温度梯度PCR方法对牛基因组、克隆胚胎、胚胎样品进行性别鉴别实验研究,建立了稳定、简便、快速的牛早期胚胎性别鉴别两温度梯度PCR方法,鉴定时间仅为57分钟.采用两温度梯度PCR方法对30枚奶牛胚胎进行了早期性别鉴别,并将鉴别的15枚胚胎(11枚为雌性,4枚为雄性)移植到同期处理的15头受体母牛体内.60天后妊娠检查,有7个受体成功受孕,5头受体怀孕晚期流产,流产犊牛全部为母犊.结果产下1公1母两头犊牛,流产个体与出生个体的性别与PCR鉴别结果完全相符.     

供体细胞类型对体细胞克隆牛生产效率的影响

建立了中国红系冀南黄牛颗粒细胞系(YGR)、Holstein奶牛颗粒细胞系(HGR)、Holstein奶牛不同个体的成年成纤维细胞系(AFB)以及Holstein奶牛同一个体的胎儿成纤维细胞系(FFB)和胎儿输卵管上皮细胞系(FOV). 以上述不同类型的体细胞为核供体, 进行了体细胞核移植, 共成功培育出12头体细胞克隆牛. 比较了不同类型供体细胞的重构胚的发育潜能, 结果表明: (ⅰ) YGR和HGR的重构胚的囊胚发育率(33.2% vs 35.1%)无显著差异(P > 0.05), 妊娠率分别为33.3%和30.2%, 产犊率分别为16.7%和11.6%; (ⅱ) Holstein奶牛不同个体AFB的重构胚的囊胚发育率(27.9% vs 39.4%)差异显著(P < 0.05), 妊娠率分别为36.2%和36.4%, 产犊率分别为14.9%和27.3%; (ⅲ) Holstein奶牛同一个体的FFB和FOV的重构胚的囊胚发育率(37.9% vs 41.5%)差异显著(P < 0.05), 妊娠率分别为45.7%和24.1%, 产犊率分别为22.9%和10.3%. 综合比较Holstein奶牛的4种体细胞(HGR, AFB, FFB和FOV)的重构胚的发育情况, 结果显示: 在体外发育阶段, FOV的重组胚的囊胚发育率(41.5%)最高, FFB (37.9%)和HGR (35.1%)次之, AFB(29.4%)最低, 三者之间差异显著(P < 0.05). 在体内发育阶段, 4种供体细胞克隆胚胎的妊娠率分别为30.2%, 36.2%, 45.7%和24.1%, 产犊率分别为11.6%, 17.2%, 22.9%和10.3%.     

天祝白牦牛胚胎移植实验研究

选用健康成年天祝母白牦牛(Poephagus grunniens)(供体)10头、黑牦牛(受体)37头进行实验. 供体牛(组1)用CIDR-B+FSH＋PG进行同期发情和超数排卵; 受体牛(组2和组3)分别采用CIDR-B+PG和单次注射PG法进行同期发情. 结果表明, 平均黄体数、卵泡数、可移植胚胎数和退化胚胎数分别为4.75±2.19, 1.13±0.83, 2.50±1.31和1.38±0.92. 在3组中, 组1的同期发情率最高, 为80%, 组2和3分别为60%和45.5%. 处理后不同组别的发情开始时间不同, 组1的大部分白牦牛在处理结束后的25~75 h发情, 而组2和3的受体黑牦牛分别在73~96和49~72 h发情. 平均胚胎回收率55.6%. 共收集18枚可用胚胎, 将其中12枚移植到10头同期发情的受体牦牛, 最终妊娠率50%, 分娩率40%.     

猪微注射基因胚胎的自体移植

冲取７头超排或自然发情配种的湖北白猪后备母猪１-４细胞期胚胎８６枚,显微注射ＯＭＴ／ＰＧＨ基因后,移植回原供体母猪的输卵管内。其中５头受孕,４头维持到分娩,产仔１１头,产仔率１２。８％（１１／８６）;经分子杂交检测,３头阳性,基因整合率２７。３％（３／１１）。转基因效率３。５％（３／８６）。     

转人血清白蛋白基因试管牛的研究

构建了含人血清蛋白（ｈＡＬＢ）的基因的ｃＤＮＡ全,序列,内含子１以及山羊酷蛋白基因启动子和５＇端上游调控序列在内的的乳腺载体ｐｃＤＮＡ３．１－ＧＡＬＢｍ,并通过显微将导入经过体外受精（ＩＶＦ）的奶牛受精卵中,体外培养到桑棋胚后期,取出少许细胞,应用巢式ＰＣＲ对其进行目的基因整合及性别的预鉴定,将１０枚整合胚移植于８头受体母牛,结果有３头妊娠,受孕率为３７．５％（３／８）,其中２头于妊娠中期流产,另     

利用体细胞核移植技术制作人胰岛素原转基因牛

通过体细胞核移植技术制作了人胰岛素原转基因牛。在CMV启动子指导下以内部核糖体进入位点序列（IRES）连接的新霉素抗性基因和绿色荧光蛋白基因组成了双重标记基因的筛选系统，用于转基因细胞的富集以及细胞和植入前胚胎的筛选。转基因通过电穿孔的方法（900 V/cm, 5 ms）转入体外培养的牛胎儿成纤维细胞，基因转染细胞在添加G418(800 μg/mL) 的培养基中培养10天以富集转基因细胞。选择表达绿色荧光蛋白的转基因细胞作为核供体进行体细胞核移植，重构胚经体外培养至囊胚阶段，选择表达绿色荧光蛋白的囊胚进行胚胎移植。为比较基因转染以及供体细胞所处周期对转基因细胞核移植胚胎发育的影响，用作核移植供体的转基因细胞或非转基因细胞先饥饿培养2—4天(0.5% FBS)，然后恢复培养(10% FBS)10?h使细胞同步化于G1期，以正常培养的细胞作为对照进行核移植。 结果表明，转基因细胞作为核供体得到的核移植胚胎的体外囊胚发育率低于以非转基因细胞为核供体的对照组(23.2% VS 35.2%, P<0.05)；转基因细胞周期同步化处理与否对其克隆胚囊胚发育率无显著影响（23.2% VS 18.9%, P>0.05）。胚胎移植后2个月直肠检查发现7头受体牛（每头移植2—4枚胚胎）中有一头妊娠，并最终发育足月产下一头小牛。聚合酶链反应（PCR）检测和DNA测序分析表明其为转人胰岛素原基因的转基因克隆牛。     

Detrimental effects of high plasma urea nitrogen levels on viability of embryos from lactating dairy cows

High plasma urea nitrogen (PUN) concentrations are associated with decreased fertility in lactating dairy cows. Our objective was to evaluate the quality of embryos flushed from superovulated lactating cows having moderate or high PUN concentrations. Subsequent embryo survival was determined after transfer to recipient heifers with either low or high PUN. Lactating Holstein dairy cows (n = 23; 50-120 days in milk) were randomly assigned to one of two diets designed to result in moderate or high PUN concentrations (15.5 +/- 0.7 and 24.4 +/- 1.0 mg/dl, respectively; P < 0.001) and were fed for 30 days before embryo flushing and recovery. Embryos (n = 94) were evaluated morphologically, frozen and subsequently transferred into synchronized virgin heifers that were fed one of two diets designed to result in either low or high PUN concentrations (7.7 +/- 0.9 and 25.2 +/- 1.5 mg/dl, respectively; P < 0.001; 2 x 2 factorial design). The number, quality and stage of development of recovered embryos were similar for cows with moderate or high PUN. Transfer of embryos from moderate PUN donor cows resulted in a higher pregnancy rate (35%; P < 0.02) than the transfer of embryos from high PUN donor cows (11%). Pregnancy rate was not affected by either recipient diet or the interaction of donor and recipient diets (P > 0.05). These results indicate that high PUN concentrations in lactating dairy cows decrease embryo viability through effects exerted on the oocyte or embryo before recovery from the uterus 7 days after insemination.     

Evaluation of five resynchronization methods using different combinations of PGF2α, GnRH, estradiol and an intravaginal progesterone device for insemination in Holstein cows

This study was conducted to determine the use of repeated transvaginal ultrasound-guided cumulus oocyte complex (COC) aspiration on COC recovery rate, in vitro embryo production (IVP) and subsequent pregnancy rates in Holstein Friesian (HF) and Aberdeen Angus (AA) cows (Experiment 1), and in pregnant and non-pregnant Holstein Friesian cows (Experiment 2). Cycling, non-pregnant HF (n=17) and AA (n=32) cows with 40-70 days postpartum, between 3 and 5 years of age were used in the Experiment 1. All cows were submitted to repeated transvaginal ultrasound-guided COC aspiration twice a week for 5-7 weeks. Cumulus ooctye complexes (COC) were in vitro matured, fertilized and cultured for 8 days. An overall of 100 and 350 embryos from HF and AA cows respectively were cryopreserved using a conventional slow freezing (Experiment 1). A total of 81 and 285 frozen-thawed embryos from HF and AA cows respectively were transferred to recipient cows. Pregnancy diagnosis was performed at 60 and 150 days of gestation using transrectal ultrasonography. In Experiment 2, cycling non-pregnant (n=9) and pregnant (n=8) HF cows were submitted to repeated ultrasound-guided COC aspiration and COC were in vitro matured, fertilized and cultured as in Experiment 1, except that embryos were cryopreserved but not thawed and transferred as described for Experiment 1. The results of this study indicate that COC recovery rate and blastocyts production are affected by the breed of the donor cow. The quality of blastocyts produced from both breed did not differ in terms of pregnancy and calving rates (Experiment 1). The physiologic state of pregnancy did not affect COC recovery rate and blastocysts production per donor/session (Experiment 2). The use of ultrasound-guided COC aspiration and IVP could be a powerful technique to improve the genetic of beef and dairy cattle managed under pasture-based conditions management in the southern Chile.     

Embryo yield and plasma progesterone profiles in superovulated dairy cows and heifers.

This study was conducted to compare the superovulatory (SOV) response of dairy cows (n=172) and heifers (n=172), with two SOV treatments started at the mid-luteal-phase of the estrus cycle. Donors were randomly treated either with equine chorionic gonadotrophin (eCG) plus neutra-eCG serum (eCG+N group, n=167) or follicle stimulating gonadotrophin (FSH-P group, n=177).No significant differences were observed among groups in the percentage of superovulatory responsive donors (SR donors; corpora lutea (CL) >/=2), the mean number of total ova, fertilized ova and viable embryos recovered. Cows yielded significantly less total ova and less fertilized ova (P<0.05) and tended to yield less viable embryos (P<0.06) than heifers.Plasma progesterone (P4) concentrations (n=135 donors) on the day of PGF(2alpha) (PGF) injection and on the day of SOV estrus were significantly higher (P<0.01) in eCG+N than in FSH-P donors and, the increase between those 2 days was also significantly higher (P<0.05) in group eCG+N than in group FSH-P, suggesting a higher luteotrophic effect of eCG than FSH-P. SR donors had P4 levels significantly higher (P<0.001) than non-SR donors only on day 5 after the SOV estrus and on the day of embryo recovery. Plasma P4 concentrations at 5 days after the SOV estrus and at embryo recovery correlated significantly (r=0.76, P<0.001).Heifers had significantly higher P4 levels than cows at gonadotrophin injection (P<0.01), PGF injection (P<0.001), 5 days (P<0.01) and 7 days (P<0.001) after the SOV estrus. At day 7 after the SOV estrus, P4 concentrations per ova recovered were significantly higher in heifers than in cows (P<0.01). The increase of plasma P4 per ova recovered, between days 5 and 7 after the SOV estrus, was significantly (P<0.01) higher in heifers than in cows. Also, the increase of plasma P4 between injections of gonadotrophin and PGF was significantly higher (P<0.05) in heifers than in cows.These results suggest that heifers have higher plasma P4 concentrations at diestrus (either before or after the SOV treatment) and this is associated with a higher embryo yield and quality, as compared to lactating cows. These higher plasma P4 concentrations reflect not only differences in ovulation rate as well as the competence of the corpus luteum, which is potentialized by gonadotrophin stimulation.     

Using hormone-treated pregnant cows as a potential source of oocytes for in vitro fertilization

In vivo collection of oocytes during pregnancy may be alternative method of obtaining gametes for in vitro fertilization (IVF) from genetically superior gestating cattle. The objectives of this experiment were to induce follicular growth in mature beef cows during each trimester of pregnancy, and then to collect oocytes and verify oocyte competency by IVF and subsequent embryo culture in vitro. Cyclic beef cows in Treatment A and pregnant cows in Treatment B were administered a total dose of 40 mg of FSH in descending dose levels (6, 5, 4, 3 and 2 mg) twice daily for 5 consecutive days. Cows in Treatment A were administered 25 mg of PGF(2)alpha and in Treatment B an equal volume of 0.9% saline at the seventh FSH injection. Pregnant cows in Treatment C were administered neither FSH nor PGF(2)alpha and served as a control group. Following a gonadotropin treatment, the ovaries of each female were evaluated for follicular development by ultrasonography. Oocytes were collected by follicle aspiration from cows in the first trimester. Following IVF procedures, the embryos were co-cultured on caprine oviductal cells, or in the chicken embryo co-culture system, or were placed in goat oviducts in vivo. The mean number of follicles per ovary 12 hours after FSH treatment was not different for cows in Treatments A and B, (8.1 vs 7.7) and both numbers were greater (P<0.05) than the 1.1 follicles per ovary for the control cows in Treatment C. Oocytes collected in vivo and exposed to IVF, resulted in 20% cleaving, and of these embryos 50% developed to the morula stage in culture. In summary, stimulating supplemental follicular development with FSH treatment during pregnancy and collecting the oocytes for IVF may be an alternative method for obtaining supplemental gametes from valuable donor cattle.     

Attenuation of premature estrous behavior in postpartum beef cows synchronized to estrus using GnRH and PGF2alpha

The efficacy of GnRH and PGF2alpha (7-day injection interval) for estrus synchronization is diminished by estrous expression before PGF2alpha (premature estrus; PE). Effects of modifications to GnRH-PGF2alpha protocols on the incidence of PE and other indicators of reproductive performance were evaluated. In Experiment 1, Angus-based crossbred cows (n=51) received 25 mg of PGF2alpha i.m. on Day 0. Animals were randomly assigned by parity and interval postpartum to receive GnRH 100 microg i.m. on either Day -7 or Day -6. Estrous detection and AI were conducted from Day -3 to Day 5. Treatment had no effect on the incidence of PE, estrous response, conception rate per AI or synchronized pregnancy rate (6- vs. 7-day interval; 8 vs. 15%; 92 vs. 93%; 77 vs. 76%; 71 vs. 70%, respectively). In Experiment 2, Angus cows (n=150) received GnRH 100 microg i.m. on Day -7 and 25 mg PGF2alpha i.m. on Day 0. Animals were randomly assigned by parity, interval postpartum, and body condition score to receive either no further treatment (Control) or 0.5 mg melengestrol acetate/hd/d from Day -7 to Day -1 (MGA). Estrous detection and AI were conducted from Day -2 to Day 7. Fewer (P < 0.05) MGA-treated cows were detected in PE (0%) compared to controls (7%). Treatment had no effect on estrous response or synchronized pregnancy rates (Control vs. MGA; 78 vs. 84%; 52 vs. 60%, respectively). Conception rate per AI of cows > or = 60 days postpartum were not affected by treatment (Control vs. MGA; 79 vs. 73%) however, control cows < 60 days postpartum tended (P < 0.10) to have lower conception rates per AI (39%) than did their MGA-treated counterparts (69%). In summary, 6- and 7-day GnRH-PGF2alpha injection intervals resulted in similar synchronized reproductive performance. Inclusion of MGA feeding between GnRH and PGF2alpha injections eliminated the occurrence of premature estrus and improved conception rate per AI of late-calving cows.     

Effectiveness of prostaglandin F2alpha in the initial treatment of bovine ovarian cysts

This study was conducted to evaluate the use of prostaglandin F2alpha (PGF2alpha) in the initial treatment of ovarian cysts in dairy cattle. Two hundred and sixty three cows diagnosed cystic on palpation per rectum were randomly assigned to one of three treatment groups (A, B or C). Cows in Groups A and B were treated with 25 mg i.m.of PGF2alpha at the time of diagnosis (Day 0), while cows in Group C received 100 mug of GnRH. Seven days following initial treatment (Day 7), cows from Group A that were not observed in estrus were treated with GnRH. Cows from Groups B and C were not treated. On Day 14, all cows that had not been inseminated received PGF2alpha. A blood sample was obtained from all cows on Days 0, 7 and 14 and was analyzed for progesterone (P4) using radioimmunoassay. Incidences of estrus were recorded and cows that were more than 60 d in milk at the time of diagnosis were bred when observed in estrus. The incidence of follicular cysts on Day 0 (as defined as P4 <0.5 ng/ml) was similar between groups and constituted about 40% of all cysts. There were significantly more cows pregnant to insemination within 7 d of initial treatment in Group B than in Groups A and C (P<0.05). After Day 14, the pregnancy rate was not statistically different between Group B and C, but Groups B and C had a statistically higher pregnancy rate than Group A from Day 21 to Day 35. At the end of the study, there was no statistical difference for the pregnancy rate between groups. We concluded that treatment of ovarian cysts diagnosed by per rectum examination with prostaglandin (at time of diagnosis and 14 d later for cows that were not inseminated) was as effective as initial treatment with GnRH followed by prostaglandins 14 d later for cows that were not inseminated previously. Cows that were initially treated with prostaglandins also tended to become pregnant sooner.     

Conception rates after artificial insemination or embryo transfer in lactating dairy cows during summer in Florida

The objective was to compare conception rates to embryo transfer relative to AI, during summer heat stress, in lactating dairy cows. Holstein cows (n = 180; 50 to 120 d postpartum) were allocated randomly to 1 of 3 groups: artificial insemination (AI, n = 84), embryo transfer using either embryos collected from superovulated donors (ET-DON, n = 48), or embryos produced in vitro (ET-IVF, n = 48). Embryos from superovulated donors were frozen in 10% glycerol and were rehydrated in a 3-step procedure, in decreasing concentrations of glycerol in a sucrose medium before transfer. Embryos produced in vitro were frozen in 1.5 M ethylene glycol, thawed and transferred without rehydration. Blood samples were collected from AI and ET recipients on Days 0, 7 and 22 for measurement of progesterone in plasma. Conception rate was estimated for the three groups at Day 22 (progesterone > 1 ng/mL) and confirmed at Day 42 by palpation per rectum. Conception rate estimates at Day 22 did not differ among groups (AI, 60.7%; ET-DON, 60.4%; ET-IVF, 54.2%), but conception rates at Day 42 differed (AI, 21.4%; ET-DON, 35.4%; ET-IVF, 18.8%; AI versus ET: P > 0.10 and ET-DON versus ET-IVF: P < 0.05). In cows considered pregnant at 22 d but diagnosed open at 42 d, the interestrous intervals were 28.8 +/- 2.2, 35.2 +/- 3.5 and 31.6 +/- 2.9 d, respectively, for AI, ET-DON and ET-IVF groups. Transfer of embryos collected from nonheat-stressed superovulated donors significantly increased conception rates in heat stressed dairy cattle. However, transfer of IVF-derived embryos had no advantage over AI. Where appropriate mechanisms are in place to attenuate the effects of heat stress, embryo transfer using frozen-thawed donor embryos increases conception rates.     

Superovulatory responses in dairy cows following ovulation of the dominant follicle of the first wave

In the present study we investigated the effect of hCG administration on Day 7 (Day 0 = day of standing estrus) to ovulate the dominant follicle of the first wave and the associated increase in progesterone concentration on subsequent superovulatory response in dairy cows. Twenty cyclic lactating cows were allocated at random to 2 groups: control (n = 10) and hCG-treated (n = 10). The ovaries of each cow were scanned using an ultrasound scanner on Day 7, to confirm the presence of the dominant follicle and thereafter every other day until embryo recovery. All cows received a total dose of 400 mg Folltropin-V in decreasing amounts for 5 days (Days 9 to 13) and 35 mg PGF(2alpha) on Day 12. In addition, the treated cows received 1000 IU hCG on Day 7. All cows were inseminated twice during estrus, and the embryos were collected 7 days later by a nonsurgical procedure. Blood smaples were taken at different times of the treatment period for progesterone determination. All cows possessed a dominant follicle at Day 7, and all but one of the hCG-treated cows ovulated the dominant follicle and formed an accessory corpus luteum. Plasma progesterone concentrations were significantly higher (P<0.01) in hCG-treated cows than control cows on the first day of Folltropin treatment and on the day of PGF(2alpha) injection. The mean number of follicles at estrus, the number of ovulations, the total number of embryos and the number of transferable embryos were not different (P>0.05) between control and hCG-treated cows.     

Spontaneous reduction of advanced twin embryos: its occurrence and clinical relevance in dairy cattle

Twin pregnancies represent a management problem in dairy cattle since the risk of pregnancy loss increases, and the profitability of the herd diminishes drastically as the frequency of twin births increases. The aim of this study was to monitor the development of 211 twin pregnancies in high producing dairy cows in order to determine the best time for an embryo reduction approach. Pregnancy was diagnosed by transrectal ultrasonography between 36 and 42 days after insemination. Animals were then subjected to weekly ultrasound examination until Day 90 of gestation or until pregnancy loss. Viability was determined by monitoring the embryonic/fetal heartbeat until Day 50 of pregnancy, and then by heartbeat or fetal movement detection. Eighty-six cows (40.8%) bore bilateral and 125 (59.2%) unilateral twin pregnancies. Embryo death was registered in one of the two embryos in 35 cows (16.6%), 33 of them at pregnancy diagnosis. Pregnancy loss occurred in 22 of these cows between 1 and 4 weeks later. Thus, 13 (6.2% of the total animals) cows, carrying one dead of the two embryos, maintained gestation. Total pregnancy loss before Day 90 of pregnancy (mean 69 +/- 14 days) was registered in 51 (24.2%) cows: 7 (8%) of bilateral pregnancies and 44 (35.2%) of unilateral pregnancies, and it was higher (P = 0.0001) for both right (32.4%, 24/74) and left (39.2%, 20/51) unilateral than for bilateral (8.1%, 7/86) twin pregnancies. The single embryo death rate was significantly (P = 0.02) lower for cows with bilateral twins (9.3%, 8/86) than for total cows with unilateral twins (21.6%, 27/125). By way of overall conclusion, embryo reduction can occur in dairy cattle, and the practical perspective remains that most embryonic mortality in twins (one of the two embryos) occurs around Days 35-40 of gestation, the period when pregnancy diagnosis is generally performed and when embryo reduction could be tried.     

Comparative fertility of normal and repeat-breeding cows as embryo recipients

Morphologically normal embryos were transferred surgically into uteri of normal and repeat-breeder cows at seven days post-estrus to compare embryo survival rates in the two kinds of cows. All cows were less than ten years of age and had no abnormal genital discharges, cystic ovarian follicles, or anatomical abnormalities of the reproductive tract. Normal cows had not been inseminated after last calving. Repeat-breeders had at least four infertile services within the past six months (average of 6.2 services after calving). To test fertility of repeat-breeders at synchronized estrus, 22 anatomically-normal repeat-breeders were treated by intramuscular (i.m.) injection with prostaglandin F(2)alpha (PGF(2)alpha) on day 11 of an estrous cycle (estrus = day 0) and inseminated at induced estrus; 11 cows (50%) had a normal fetus at necropsy on day 60. Twenty-three repeat-breeders and 23 normal cows were assigned as embryo recipients and treated i.m. with PGF(2)alpha to synchronize estrus. All embryo donors were normal cows. Donors were treated with FSH and PGF(2)alpha and inseminated at estrus. On day 7 after estrus, embryos were recovered nonsurgically from donors and one embryo was transferred through a flank incision to the anterior end of the uterine horn adjacent to the corpus luteum of each recipient. Recipients that did not return to estrus were necropsied at day 60. Of 28 normal and 23 repeat-breeder recipients, 23 normal cows (82%) and 16 repeat breeders (70%) were pregnant at day 60 (P=0.235). Thus, at seven days post-estrus, the maternal environment of most of these repeat-breeders was satisfactory for maintaining pregnancy.