氯前列烯醇冷冻干燥针剂诱导母猪同期分娩研究

在急性毒性和亚急性毒性试验研究基础上，研究新研制成功的国产氯前列烯醇冷冻干燥针剂诱导母猪同期分娩的效果。结果表明，氯前列烯醇0．05，0.10，0．20mg／头均可有效诱导临产母猪在药物处理后35h内集中分娩；氯前列烯醇0．05mg组、0．10mg／头组白天分娩率分别为80．0％和73．3％，极显著（P〈0．01）和显著（P〈0．05）高于自然分娩组（30．0％）；和自然分娩对照组比较，氯前列烯醇各剂量组对仔猪出生个体重、48h成活率、死胎率等参数均未见显著影响（P〉0．05）。氯前列烯醇冷冻干燥针剂0．05～0．20mg可有效地诱导临产母猪同期分娩，但以1次肌肉注射0.05mg／头为宜。     

氯前列烯醇调控母猪分娩时间的试验

选择34头母猪随机分为试验组和对照组,试验组母猪妊娠112d时,上午9：00～9：30肌肉注射氯前列醇钠0．1～0．2mg／头;对照组不注射药物,自然分娩。试验组17头母猪。有15头白天分娩,其白天分娩率为88．2％,对照组则只有6头母猪白天分娩,其白天分娩率为43．8％,经X2检验,差异极显著（P〈0．01）,说明注射氯前列醇钠能有效诱导母猪在白天分娩。     

猪育种进展及其发展趋势

哺乳母猪日粮含消化能１４．２１ＭＪ／ｋｇ，粗蛋白１６．３～１９．２％（随猪只日增重的不同而调整），赖氨酸０．８２～１．０３％（随猪只日增重的不同而调整）。加拿大提出的最低营养标准为：中猪（２０～６０ｋｇ）（见表３）；哺乳母猪合消化能１４．０００ＭＪ／ｋｇ，粗蛋白１６％，赖氨酸０．８％，钙０．９％，磷０．７％，ＶＡ７ ５００ＩＵ／ｋｇ、ＶＤ７５０ＩＵ／ｋｇ，ＶＥ３５ＩＵ／ｋｇ，胆碱６００ｍｇ／ｋｇ；生物素０．３０ｍｇ／ｋｇ。 猪育种的进展，有赖于遗传理论的创新和育种技术的改进，国际上以遗传学为理论指…     

不同给药途径的15甲基前列腺素F_2α和乙烯雌酚注射液对奶牛持久黄体疗效的比较

本文应用不同给药途径的１５甲基前列腺素Ｆ２α（１５甲基ＰＧＦ２α）和乙烯雌酚注射液对１００例患有持久黄体的奶牛进行疗效的比较，结果表明，有黄体存在的卵巢侧的阴辱粘膜下注射１５甲基ＰＧＦ２α２ｍｇ（试验１组）效果最佳，治愈率为９０％（１８／２２），有效率为１０％（２／２０）；有黄体存在的卵巢侧的子宫角注射１５甲基ＰＧＦ２α２ｍｇ（试验２组），治愈率（１８／２０）和有效率（２／２０）同试验１组；肌注１５甲基ＰＧＦ２α４ｍｇ（试验３组）的治愈率为７０％（１４／２０），有效率为３０％（６／２０）；每日肌注１次乙烯雌酚注射液３５ｍｇ，连续注射２天（试验４组），治愈率为６０％（１２／２０），有效率为４０％（８／２０）；每日在有黄体存在的卵巢侧的阴唇粘膜下注射１次乙烯雌酚注射液３５ｍｇ（试验５组），连续注射２天，治愈率为８０％（１６／２０），有效率为２０％（４／２０）。试验１组、２组与试验３组比，差异极显著（Ｐ＜０．０１）；试验５组与试验４组比，差异亦为极显著（Ｐ＜０．０１）；试验４组与试验３组比和试验５组与试验１、２组比，差异均为不显著（Ｐ＞０．０５）。     

山莨菪碱加微量雌激素对奶牛催情的观察研究

本研究应用盐酸山莨菪碱（１５０ｍｇ）及微量的雌激素（４ｍｇ）对１～４胎９０天以上未出现发情的不孕奶牛４５例进行催情，其有效率为７１．１１％（３２／４５），其中卵巢静止为６０％（１５／２５），持久黄体８５％（１７／２０）。同时还发现用上述两种药物处理的１０例患牛的血清孕酮含量在注射后的１２０小时以内均有程度不同的下降；当血清孕酮最低峰值＜１．０ｎｇ／ｍｌ时临床呈现发情征象的持久黄体牛为８３．３％（５／６）；卵巢静止为１００％（４／４）。５例仅用微量雌激素（４ｍｇ）注射的患牛孕酮含量虽有变化但临床上均不出现显性发情征状。初步证明：盐酸山莨菪与微量雌激素协同可对奶牛有明显的催情作用。     

前列腺素诱导母猪分娩时的内分泌状态

选用５头妊娠后期母猪,于妊娠１１１ｄ上午９∶００肌肉注射氯前列烯醇（ＰＧ）０．２０ｍｇ。５头母猪皆于次日白天分娩。从注射前至分娩结束,在整个诱导过程中多次采血,监测了血清中孕酮（Ｐ４）、硫酸雌酮（Ｅ１Ｓ）、催乳素（ＰＲＬ）和皮质醇（ｃｏｒｔｉｓｏｌ）４种激素浓度的变化。结果表明,诱导分娩过程中各种激素的变化和自然分娩基本一样。这就解释了用国产前列腺素诱导母猪分娩,只要处理时间合适（妊娠１１１ｄ或１１２ｄ）,就会有良好效果,不会产生不良副作用。     

盐酸山莨菪碱加微量雌激素对奶牛催情作用的研究

本研究应用盐酸山莨菪碱（１５０ｍｇ）及微量的雌激素（４ｍｇ）对１～４胎９０天以上未出现发情的不孕奶牛４５例进行催情，其有效率为７１．１１％（３２／４５），其中卵巢静止为６０％（１５／２５），持久黄体８５％（１７／２０）。同时还发现用上述两种药物处理的１０例患牛的血清孕酮含量在注射后的１２０小时以内均有程度不同的下降；当血清孕酮最低峰值＜１．０ｎｇ／ｍｌ时，临床呈现发情征象的持久黄体牛为８３．３％（５／６）；卵巢静止牛为１００％（４／４）。５例仅用微量雌激素（４ｍｇ）注射的患牛孕酮含量虽有变化但临床上均不出现显性发情症状。初步证明：盐酸山莨菪碱与微量雌激素协同可对奶牛有明显的催情作用，此方法迄今国内外未见报道。     

使母猪白天产仔的诀窃

在母猪临产前1～2天（即妊娠后112～113天）的上午8～9点，于母猪颈部肌肉注射氯前烯酸注射液1～2毫升，可使98．2％的母猪在次日白天分娩。此法有效率高达100％，仔猪成活率也由试验前的90％提高到98％以上。注射氯前列烯醇诱导母猪分娩，对母猪和新生仔猪均无副作用，且药物成本低，请养猪户不妨一试。使母猪白天产仔的诀窃@王超     

内蒙古白绒山羊超排及鲜胚移植技术的研究

以 １３８ＩＵ、１５０ＩＵ、１６２ＩＵ ３种剂量 ＦＳＨ，在供体羊发情的第 １５、１６、１７ｄ开始超排，３４只供体超排结果如下：排卵点平均数为１３．４１±６．７０个；胚胎回收平均数为１２．５６±６．３０枚；可用胚胎平均数为１０．２４±６．１４枚。第１６，１７ｄ起针，剂量为１５０ＩＵ组的超排效果最好，但无显著差异（Ｐ＞０．０５）。将２６９枚胚胎移植到 ２４９只受体，妊娠率为 ７０．２８％；产羔率为 ６７．０６％；共接 １７８只羔羊。受体羊与供体羊发情同期化程度、黄体质量、胚龄等因素对妊娠率影响较大，但统计学上无显著差异（Ｐ＞０．０５）。用氯前列烯醇诱导发情不影响受体妊娠率。     

乏情后备母猪药物处理试验

对８２头长大、大长９～１０个月龄一直未能发情的后备母猪进行了药物处理,以三合激素连续处理４天和以中药促情芨连喂３天后立即注射氯前列烯醇２次（上下午各１次）,处理后５天内观察发情表现。结果,三合激素组母猪发情率为４５．０％（１８／４０）,配种后４６天不返经为５．５６％（１／１８）;促情散加氯前列烯醇组发情率为９７．６２％（４１／４２）,配种后４６天不返经为９７．５６％（４０／４１）。４１头母猪平均产     

A role for the adrenal cortex in the onset of cystic ovarian follicles in the sow.

The corticotrophin (ACTH)-adrenal cortical axis has previously been implicated in the onset of cystic ovaries in the sow. In view of the role of the ACTH-adrenal cortical axis in stress, two sows were subjected to an elevated environmental temperature of 32 degrees C for three hours daily during the follicular phase of the estrous cycle. Plasma concentrations of glucocorticosteroids and progesterone fluctuated markedly in one sow that developed cystic ovaries. Concentrations of these hormones did not vary greatly in the other sow that did not develop cystic follicles. Exposure to an environmental temperature of 32 degrees C for three hours or injection of 1 IU/kg bodyweight of ACTH for each of two ovariectomized sows resulted in an elevation in progesterone values to 5-7 ng/ml plasma from basal levels of 1-2 ng/ml and a rise in total glucocorticosteroids from basal levels of 1 or 2 microgram/100 ml plasma to 4-10 microgram/100 ml. Injection of 2 mg/kg bodyweight of progesterone and 4 mg/kg bodyweight of cortisol into the ovariectomized sows was found to approximate these elevations in plasma steroid values. When either progesterone or cortisol was injected daily during the follicular phase into two intact sows in two successive experiments at these dosage levels, similarly elevated plasma steroid concentrations were seen and cystic ovarian follicles resulted. The results suggest that glucocorticosteroids and progesterone of adrenal origin may be involved in the onset of cystic ovaries in the sow.     

氯前列醇钠、产前背膘厚及便秘对后备母猪同期分娩效果的影响

试验旨在研究氯前列醇钠、产前背膘厚、便秘对后备母猪同期分娩集中度和生产性能的影响,并进一步探讨母猪同期分娩的最优方案。选取后备母猪共295头,根据妊娠期110 d时P2点处的背膘厚,随机分为3组：对照组（CON组：0.9%生理盐水）、低剂量氯前列醇钠组（LPG组：0.1 mg氯前列醇钠）、高剂量氯前列醇钠组（HPG组：0.2 mg氯前列醇钠）,于妊娠期114 d进行阴户部注射诱导分娩。结果表明,与对照组相比,高、低剂量氯前列醇钠均可显著缩短母猪从注射到分娩的时间间隔（P<0.05）,且两试验组间差异不显著（P>0.05）。但是,LPG组后备母猪在注射氯前列醇钠后48 h内的分娩率高达95%,并且白天分娩率达75.7%。此外,LPG组后备母猪的产仔间隔也显著短于CON组（P<0.05）。同时本研究发现,背膘厚在16~20 mm范围内的后备母猪从注射到分娩的时间间隔显著短于背膘厚≤15 mm的后备母猪（P<0.05）;便秘指数0~1.0组后备母猪的产程和产仔间隔均显著大于便秘指数1.1~2.0组及2.1~3.0组的后备母猪（P<0.05）。进一步回归分析发现,母猪背膘厚分别与产程、总产仔数、活仔数存在极显著线性相关（P<0.01）,母猪便秘指数分别与产程、产仔间隔、总产仔数、活仔数存在极显著线性相关（P<0.01）。综上所述,在妊娠期114 d对后备母猪阴户部注射0.1 mg氯前列醇钠诱导分娩,不仅可显著加快母猪分娩的进程,而且还可大大节约药物成本。此外,母猪产前背膘厚和便秘均会影响母猪同期分娩的效果,应使母猪分娩前保持最佳的背膘厚（16~20 mm）,且避免母猪便秘,方可保证同期分娩的顺利实施。     

Dynamic changes of immunoglobulin concentrations in pig colostrum and serum around parturition

The aim of the study was the determination of IgA, IgM and IgG concentrations in porcine serum and colostrum, in order to evaluate their variations in the perinatal period, as well as to clarify whether there is a correlation between colostrum intake, initial level of immunoglobulins (Ig) in piglet serum and development of their own immunity. The mean IgA, IgM and IgG concentrations in sow serum 10 days before parturition were 1.58, 6.12 and 39.56 mg/ml, respectively. Seven days later only the IgG level was insignificantly lower (34.94 mg/ml, p = 0.55), while concentrations of IgA and IgM increased to 2.25 and 7.25 mg/ml, respectively (p = 0.23 and 0.62, respectively). The mean initial IgG concentration in colostrum at farrowing was 118.5 mg/ml and differed between sows. The average value of IgA in colostrum at birth was 23.8 mg/ml and decreased to 7.85 mg/ml at 6 hours (h) and to 4.59 mg/ml at 24 h after the onset of farrowing. IgM concentration at birth was 12.1 mg/ml and decreased to 4.23 mg/ml at 24 h postpartum. Positive relationships were found between concentrations of IgM and IgA in serum of piglets at 14 and 56 days of life (r = 0.41 and 0.80, respectively, p < or = 0.05) as well as for IgG concentration in the piglets serum at 7 days and 56 days of age (r = 0.48, p < or = 0.05). The above observations suggest that there is a correlation between the level of Ig in piglet serum in the first days of life and improvement of their own immunity.     

Use of Luprostiol and Cloprostenol for Induction of Parturition in Pregnant Goats

Pregnant goats were induced to parturition on day 145 of pregnancy, with three different protocols: group Cl (n = 19) was injected intramuscularly (IM) with 75 μg of the prostaglandin analogue R‐Cloprostenol; group L (n = 20) was treated IM with 7.5 mg of the prostaglandin analogue Luprostiol; group L₅₀ (n = 18) was injected IM with 3.75 mg of Luprostiol (IM); in addition, Group S (Control, n = 15) was injected IM with 1 ml of saline solution. Thereafter, goats were continuously observed to record the following parameters: parturition, dystocia incidence, placental delivery and kid and maternal survival. Moreover, blood sampling was performed around kidding and plasma progesterone concentrations were analyzed. The interval from injection to parturition (mean ± SEM) was not significantly different among the experimental groups: 35.1 ± 1.5 h, 33.3 ± 0.9 h and 34.1 ± 1.8 h (groups Cl, L and L₅₀, respectively). In the control group, time to parturition was 99.4 ± 12.1 h (range: 34–166 h). All the goats expelled the foetal membranes within the first 2 h after the induction. The incidence of dystocia due to foetal posture was not significantly different between induced and control goats (21.1%, 20.0%, 22.0% and 20%, for groups Cl, L, L₅₀ and S, respectively). The percentage of live kids was practically similar between induced goats (93.9%, 94.9% and 92.1%, for groups Cl, L and L₅₀, respectively); in addition, there was a case of maternal mortality in control group (6.7%; 1/15), whereas there was no mortality in induced goats (0%; 0/57). Plasma concentrations of progesterone showed an intense drop (<2 ng/ml) at 24 h after induction. This study confirms the effectiveness of the luprostiol to induce the parturition in goats, within a narrow range (30–40 h) in most of the induced females (80.0%, 7.5 mg; 77.8%, 3.75 mg).     

Incidence and Prevention of Early Parturition in Sows

A retrospective study, based on 60 990 farrowing records from 35 commercial herds, was performed to determine the incidence of early parturition (<114d) and to investigate the relationship between early parturition and total number of piglets born, number of piglets born alive and percentage of stillborn piglets per litter. The mean gestation length was 115.4 ± 1.62d, and early parturition occurred in 10% of all farrowing records. Sows with early parturition had significantly more stillborn piglets and a larger litter size compared to sows with a normal gestation length (114–117d). Sows with a gestation length <114d were 1.2 times (95% CI: 1.19–1.21; p < 0.001) more likely to have an early parturition at the subsequent parity. A second study was performed in four herds (n = 329) to investigate the efficacy of altrenogest administration on 110–112d (T112) or 111–113d (T113) of gestation for preventing early parturition and to investigate the effect of this treatment on the reproductive performance of sows. The interval between the last altrenogest treatment and the onset of parturition was 3.3 ± 1.32 (T112) or 2.0 ± 0.89 (T113) days. The gestation length of sows of the altrenogest group (T112 + T113) (115.3 ± 1.23d) was significantly longer compared to gestation length of the non‐treated sows (114.7 ± 1.69d) (p < 0.01). Altrenogest treatment had no negative effect on the reproductive performances of the sows. In conclusion, the administration of altrenogest in late gestation is an effective and safe method to prevent early parturition and can counteract the reproductive losses because of premature farrowing, which may occur in a substantial part of the farrowing events.     

The effects of different photoperiods on reproduction in the sow

Three groups of Yorkshire sows (total of 106) were exposed to photoperiods of light:dark (LD) 24:0, 12:12 and 0:24, respectively, from d 1 postweaning to 24 h postestrus. The onset and duration of estrus, conception rate, farrowing rate and litter size were recorded. Serum concentrations of luteinizing hormone (LH), estrogen and progesterone were measured. Sows in the LD 24:0 exhibited behavioral estrus for a longer period (P less than .0001) than those in LD 12:12 (4.0 vs 2.7 d). The number of days to estrus from d 1 postweaning (5.4, 4.5 and 4.7 d, respectively), conception rate (60, 67 and 73%, respectively), farrowing rate (60, 67 and 73%, respectively) and litter size (10.6, 10.2 and 10.8, respectively) were not different (P greater than .05) for the three light regimens of 24:0, 12:12 and 0:24. Maximum serum levels of LH (5.4, 5.0 and 4.5 ng/ml, respectively) and estrogen (71.8, 63.3 and 60.4 pg/ml, respectively) were not different, nor were progesterone profile means (P greater than .05) for the sows in LD 24:0, 12:12 and 0:24. These data suggest that long photoperiods prolong manifestations of behavioral estrus in the sow.     

Serum Progesterone Concentrations and Blood Neutrophil Alkaline Phosphatase Activity in Cows Following Normal and Abnormal Parturition

Serum progesterone concentrations and alkaline phosphatase (ALP) activity of blood neutrophils were determined in 3 groups of cows (n = 5 each) on days 1 and 2 and then at 3-day intervals up to 32 days post-partum. Group I cows had a normal delivery, Group II cows had dexamethasone-induced parturition and Group III cows were subjected to a caesarian section. All cows in Group III and 2 cows in Group II retained their fetal membranes. Mean serum progesterone concentrations declined the second day after calving (to < 0.67 ng/ml) and remained at low levels (< 0.54 ng/ml) throughout the observation period, except for the values in Group III, which were elevated on day 16 (0.94 ng/ml), declined again on day 26 (0.46 ng/ml) and peaked (1.05 ng/ml) on day 32 portpartum. Significant (P < 0.01) differences were found between serum progesterone concentrations on day 1 and on each of the other sampling days in Groups I and III. Day X parturition group interaction was significant (P < 0.05) for the progesterone concentrations. No significant differences were found between the overall means of ALP activity of blood neutrophils in the 3 parturition groups nor between days of the experiment. No significant correlation was found between serum progesterone concentrations and ALP activity values of blood PMN during the first 32 days post-partum. Inhalt: Serum Progesteron Konzentrat und Aktivität der alkalischen Phosphatase in neutrophilen Blutzellen bei Küken mit normalem und abnormalen Geburtsverlauf Serum-Progesteronkonzentrationen und alkalische Phosphatase- (ALP) Aktivität von neutrophilen Granulozysten, nach der Abkalbung am Tag 1 und 2 und dann im Abstand von 3 Tagen bis zum 32. Tag p.p. bei Kühen untersucht, die in drei Untersuchungsgruppen (n = 5) eingeteilt waren. Gruppe I kalbte normal ab, in Gruppe II wurde die Geburt durch Dexamethason eingeleitet, und Kälber der Gruppe III wurden via Kaiserschnitt gewonnen. Alle Tiere der Gruppe III und 2 Kühe der Gruppe II wiesen Nachgeburtsverhaltungen auf Der mittlere Serum-Progesterongehalt sank am 2. Tag p.p. auf < 0,67 ng/ml ab und blieb auf niederigem Niveau (< 0,54 ng/ml) während der gesamten Untersuchungs-periode. Lediglich in Gruppe III, mit erhöhten Werten (0,94 ng/ml) an Tag 16 p.p., sanken die Werte wieder an Tag 26 p.p. (0,46 ng/ml) und erreichten einen Maximalwert an Tag 32 p.p. mit 1,05 ng/ml. Signifikante (P 0,01) Unterschiede in der Serum-Progesteronkonrentration wurden zwischen Tag 1 p.p. und allen anderen Untersuchungstagen in den Gruppen I und III gefunden. Interaktionen zwischen den Gruppen für Tag X waren signifikant (P 0,05). Keine signifikanten Unterschiede wurden für den Gesamtmittelwert der ALP-Aktivität in den neutrophilen Granulorysten zwischen den Gruppen und im Vergleich der Untersuchungstage gefunden. Es wurden auch keine signifikanten Korrelationen zwischen den Serum-Progesteronkonzentrationen und der ALP-Aktivität der PMN während der ersten 32 Tage p.p. nachgewiesen.     

氯前列烯醇诱导母猪同步分娩的效果

选择 2～ 4胎龄施格母猪 1 32头 ,分为 2组。对照组 ( 6 5头 )不做任何处理 ,试验组 ( 6 7头 )又分妊娠 1 1 2d组 ( 34头 )、1 1 3d组 ( 33头 )。用氯前列烯醇 ( 0 .1 g/L)分 0 .5m L/头、1 m L/头 2个剂量组分别处理上述各试验组母猪 ,观察母猪的分娩情况。结果 ,处理至分娩开始的间隔 ,1 1 2 d组为 2 8.72 h,1 1 3d组为 2 3.34 h,2组差异极显著 ( P<0 .0 1 ) ;分娩产程 ,1 1 2 d组为 3.0 8h比对照组长 4 .2 min,1 1 3d组为 2 .31 h比对照组短4 2 min,无显著性差异 ( P>0 .0 5) ;而白天分娩率经χ2 检验有显著性差异 ,1 1 2 d、1 1 3d组分别有 6 1 .76 %和78.78%的母猪在白天分娩 ,而对照组仅为 4 6 .1 5% ( P<0 .0 5)。1 1 2 d组、1 1 3d组母猪的生产成绩 ,死胎率分别为 2 .2 7%和 2 .0 8%比对照组低 1 .82 %、2 .0 1 % ( P<0 .0 5) ;初生窝重分别为 1 1 .56、1 0 .55kg,分别比对照组高 0 .0 8kg和低 0 .0 7kg( P>0 .0 5) ;2 0日龄窝重 ,1 1 2 d组平均为 33.56 kg比对照组低 1 .9kg,1 1 3d组为2 9.30 kg比对照组高 1 .77kg( P>0 .0 5) ;断奶个体重 ,1 1 2 d组平均为 8.1 4 kg比对照组低 0 .2 7kg,1 1 3d组平均为 9.2 7kg比对照组高 0 .85kg( P>0 .0 5)。结果表明 ,氯前列烯醇能有效控制母猪分娩时间集     

Induced Parturition in Swine Herds

Intramuscular injections of various levels of prostaglandin F(2alpha) were administered to 116 pregnant swine in three commercial herds and the University research unit on Day 111, 112 or 113 of gestation. Sixty-three percent of the treated animals farrowed during the working day immediately following treatment. The parturition time, birth weight, litter size, number of piglets weaned, growth of the piglets to weaning and subsequent rebreeding of the dams were comparable with the expected performance in the herds. The results indicated that prostaglandin F(2alpha) in doses ranging from 5 to 12.5 mg per animal were effective for induction of parturition in a substantial proportion of the treated animals. Successful induction of parturition could reduce the farrowing interval for batches, allow more supervision of farrowing, facilitate transfer of piglets from large to small litters and generally increase efficiency in the farrowing unit. This technique could have practical application in intensive swine production units.     

Aspects on Hormonal Control of Normal and Induced Parturition in the Dog

Average length of gestation on the dog is 63 ± 2 days but may vary between 57-71 days due to the long period of receptivity at oestrus and the extended period of sperm survival in the female genital tract. In contrast to other domestic animals progesterone- and oestrogen concentrations are almost identical in pregnant and non pregnant bitches, except for their rapid decline immediately prior to parturition. Control of luteolysis still poorly understood. Experiments with indomethacin leading to a blockade of the prepartal PgF_2α increase, which commences with the decrease of progesterone, point toward a role of PgF_2α at this stage of pregnancy, which was extended for several days. At physiological conditions first visible signs of parturition were observed at peak-PgF_2α levels, 33.6 ± 17.6 hours after onset of luteolysis, which lasted over 16.8 ± 3.4 hours. Pulse-type releases of oxytocin were only observed after this point of time. To test for the effect of progesterone-withdrawal, four 51-57 days pregnant bitches were treated with the antiprogestin RU 38486 which inhibits the activity of progesterone at the receptor level. In all dogs first visible signs of parturition were observed 33.5 ± 7.5 hours after onset of treatment. However, the process of parturition came to an end after cervical opening and totally only one puppy was born. Different to a normal parturition no increase of PgF_2α was observed. Relaxin levels were not influenced by treatment. These observations suggested that treatment with antiprogestin followed by PgF_2α might be an adequate method to induce parturition in the dog; first experiences seem to confirm this conclusion.