[Influence of the number of corpora lutea on the release of luteal oxytocin, the transfer of alveolar milk to the cistern and milk production in the ewe]. / Influence du nombre de corps jaunes sur la libération d'ocytocine lutéale, le transfert du lait alvéolaire dans la citerne et la production laitière chez la brebis.

This experiment was conducted in 59 Lacaune breed ewes in order to compare milk production and milk distribution between alveolar and cisternal storage after superovulation. After a corpora lutea (CL)-free control period, the ewes were superovulated by different treatments (experimental period) and 5 classes were differentiated according to the number of corpora lutea observed (0, 1, 2, 3 to 6 and > 6 CL respectively (group A (n = 20), B (n = 7), C (n = 14), D (n = 7), E (n = 11)). Our results showed a positive correlation between the number of corpora lutea and the oxytocin and progesterone levels in plasma, total milk production and cisternal volume, and a negative correlation with alveolar volume. The milk production at the evening milking for groups A and E (388.6 and 384.8 ml respectively during the control period) respectively reached 321.7 ml (-17.2%) and 413.4 ml (+7.4%) during the experimental period; ie, a 24.6% difference between these 2 extreme groups. These results could likely be explained by oxytocin levels reaching those obtained during milking and by the effect of milk transfer from the alveolar to the cisternal lumen. Additionally, progesterone could act directly on milk synthesis at the level of the secretory cells.

[Early diagnosis of pregnancy in the cow as assessed by milk ejection induced by luteal oxytocin]. / Diagnostic précoce de gravidité chez la vache grâce à l'observation de l'éjection du lait induite par l'ocytocine lutéale.

The diagnosis of pregnancy described in this article is based on the observation of milk ejection which, in the case of corpus luteum maintenance, results from the release of luteal oxytocin induced by intravenous administration of a non luteolytic dose of PGF2 alpha. The tests were performed in 410 lactating cows, 18-22 days after insemination (mean 19.95 days, SD 0.75), 3 h prior to the evening milking. A cannula was placed in the left fore-teat; when the cisternal milk flow ceased, a small dose of a prostaglandin F2 alpha analogue (256 micrograms Dinolytic) was injected. If a corpus luteum was present, the alveolar milk flow (1,276 +/- 570 ml) started 86 +/- 35 s later and pregnancy could be presumed. If the corpus luteum was no longer functional, the milk flow did not start again and the cow was considered not pregnant. The accuracy of positive results, ie 72.3%, significantly exceeded that obtained by radioimmunoassay of plasma progesterone used as a reference method, ie 68.6% (P less than 0.05). By contrast, the accuracy of negative results was lower, ie 93.5 vs 100%, (P less than 0.05): of the 195 pregnant cows which proceeded to term, 10 did not respond to the milk ejection test. In spite of these reserves, the test has the advantage of being inexpensive, rapid (about 5 min) and easy to interpret, ie either the milk flows or it does not. In addition, it may be used early, because from day 20 after Al the reliability of prediction of non pregnant cows (67.0%) was significantly higher when compared to the use of progesterone radioimmunoassay (58.6%) (P less than 0.05). With such a test, non pregnant cows can be reinseminated immediately and not only after a 3-week period. This may contribute to reducing the length of the infertile period.

[Suppression by luteectomy of the simultaneous increase in intramammary pressure and blood oxytocin levels induced by the injection of PGF2-alpha in ewes]. / Suppression par la lutectomie de l'accroissement simultané de la pression intramammaire et de l'ocytocinémie, induit par l'injection de PGF2 alpha chez la brebis.

Seven lactating Lacaune ewes underwent either a total luteectomy on day 19 of pregnancy (D19) (compensated from that stage by a daily progesterone supplementation of 25 mg to ensure embryonic survival; group 1:4 animals) or a control laparotomy (group 2: 3 animals). Intra-jugular injection of 200 micrograms of a synthetic PGF2 alpha analogue (Dinolytic, Upjohn) caused an increase in the intramammary pressure (IMP) and a concomitant rise in oxytocinaemia only in the presence of a corpus luteum, ie in all ewes of groups 1 and 2 before D19 and only in those of group 2 after that stage. These experiments confirm that the corpus luteum, and not the other ovarian compartments, releases oxytocin when prostaglandin F2 alpha is administered.

[Milk ejection induced by PGF2 alpha during the first two months following insemination of cows. Application to pregnancy diagnosis]. / Ejection du lait induite par PGF2 alpha pendant les deux premiers mois qui suivent l'insémination des vaches. Applications à un diagnostic de gravidité.

Milk ejection after intrajugular injection of 256 micrograms of a synthetic PGF2 alpha analogue (Dinolytic, Upjohn) was measured every 2 days until D60 in 7 pregnant cows and until D25 in 5 non pregnant inseminated cows (trial 1). There was a very close correlation (r around + 0.98) between the values of the 3 parameters used to characterize milk ejection, i.e. amplitude of intramammary pressure deflection, surface area under the pressure curve, alveolar milk volume collected by a teat probe. In the two groups of animals, these values behaved similarly until D15 with a sudden increase between D2 and D7. From D15 they decreased abruptly in females where insemination had failed while they still remained at a high level until D25 (then decreasing until D60) in those presumed to be pregnant (fig. 2). These responses were assumed to result from the release of luteal oxytocin and it is suggested that a single injection of 256 micrograms of Dinolytic on D20, together with milk ejection control using a teat probe, would be a rapid, little expensive method for the farmer (without risks of luteolysis) (trial 2 and fig. 3) to distinguish between pregnant and non pregnant cows.

PGF2 alpha-induced milk ejection in ewes having cyclic or pregnant corpora lutea.

The production of luteal oxytocin in ewes, resulting from the intrajugular injection of 200 micrograms of PGF2 alpha, could be determined by the increase in intramammary pressure. This simple indirect method of measuring the activity of the corpus luteum enabled easy detection of renewed post-partum ovulation or the onset of pregnancy. The response was monitored every two days between Days 0 and 25, then every 4 days between Days 25 and 59 in: 9 cyclic ewes (group B); 9 cyclic ewes treated with three daily intramuscular injections of 25 mg of Trilostane, a steroid synthesis inhibitor, between Days 7 and 25 (group A); 11 pregnant ewes (group C). Progesterone levels were determined each day from blood sampled in the jugular vein. Trilostane produced a decrease in plasma progesterone, not a total suppression (fig. 3), but did not significantly modify the intramammary pressure variations resulting from PGF2 alpha injections. These were identical in both cyclic and pregnant ewes during the first 15 days: they increased from D0 to D7 and decreased between D12 and D15 (fig. 4). After D15, the increase in intramammary pressure progressively weakened and became 0 at D17 in the cyclic ewes, whereas in the pregnant animals there was a renewed increase in intramammary pressure until D20; this regressed progressively afterwards and disappeared towards D45. This transitory, renewed activity between D15 and D20 might be an indirect or direct result of the message delivered by the embryo to maintain the corpus luteum. Several hypotheses are discussed with a view to explaining this phenomenon.

[Effects of PGF2 alpha prostaglandins on milk ejection in the ewe. Consequences of ovariectomy with or without estroprogestative complementation]. / Effets des prostaglandines PGF2 alpha sur l'éjection du lait de la brebis. Conséquences de l'ovariectomie accompagnée ou non d'une complémentation oestroprogestative.

The intrajugular administration of 200 micrograms of Dinolytic (tromethamine salt of PGF2 alpha) to lactating ewes caused an intramammary pressure (IMP) increase only during the luteal phase of the sexual cycle (group A). The increase in progesteronemia, induced by three daily injections of 2.5 micrograms of LH-RH, did not modify response amplitude (group B). On the other hand, bilateral ovariectomy (groupe C) led to the suppression of those responses, but supplementary oestroprogestative (table 1) did not re-establish them. It is probable that the milk ejection caused by PGF2 alpha resulted from a release of oxytocin by the corpus luteum. The ineffectiveness of the exogenous and endogenous reinforcement of progesterone therefore suggests that this hormone plays no part in the putative control of hypothalamic receptivity to prostaglandins.

[Efficacy of PGF2 alpha on milk ejection during the sexual cycle of the cow]. / Etude de l'efficacité de PGF2 alpha sur l'éjection du lait au cours du cycle sexuel de la vache.

After 30 days of lactation, 15 non-pregnant French Friesian cows were divided into groups A and B, balanced by the milk yield and lactation number of the cows. The 7 cows of group A were given a series of intrajugular prostaglandin F2 alpha (Upjohn Dinolytic) injections every morning, administered in increasing logarithmic doses (1, 4, 16, 64, 256, 1 024 micrograms). The aim of the experiment was to determine the minimal dose that would induce an increase in intramammary pressure (IMP) during the sexual cycle and milk let-down through a cannula in the teat cup. The 8 cows of group B were given a single injection of 256 micrograms of PGF2 alpha every morning to determine the changes during the sexual cycle in the response parameters of IMP (latency and amplitude) or of milk let-down (latency and collected volume) through a cannula. The following results were obtained: 1. The minimal dose of prostaglandin inducing milk let-down varied during the cycle; it was lower (1 to 16 micrograms) during the luteal phase (D4 to D12) than during the perioestral phase (256 to greater than 1 024 micrograms from D - 2 to D + 3) (figs. 2, 3). 2. During daily administration of the same dose (256 micrograms) of PGF2 alpha no response was obtained during the perioestral phase, while during the luteal phase; - maximal IMP deflection reached 12 to 14 mmHg (figs. 5, 6); - the volume of milk ejected was on an average higher than 3 liters per quarter (figs. 5, 6); - the latency time between injection and let down response was about 1.8 times shorter between D10 and D12 than between D4 and D5 (fig. 7). 3. The cyclic changes in the milk ejection parameters caused by PGF2 alpha were closely related to the plasma progesterone level (figs. 2, 3, 5, 6). The coefficients of correlation between the progesterone level and the - threshold dose: r = - 0.809** (group A), - volume of ejected milk: r = + 0.872*** (group B), - deflection amplitude: r = + 0.805*** (group B) were always significantly higher than the threshold of 0.001. Various hypotheses concerning the endocrine control of cyclic variations in milk let-down under the effect of PGF2 alpha are discussed.

[Attempted interpretation of water injected into the inguinal artery on the augmentation of intramammary pressure of the sheep]. / Essai d'interprétation de l'action de l'eau injectée dans l'artère inguinale sur l'augmentation de pression intramammaire de la brebis.

The increase in intramammary pressure caused by injecting small amounts of water into the udder artery of anesthetized ewes does not seem to be a nervous reaction induced by the stimulation of sensitive mammary receptors: the deflections remain unchanged after complete denervation of the gland (fig. 4) and after the injection of water at different temperatures (4 to 37 degrees C; fig. 1) or pH's (4.6 to 9.8; fig. 2). Since injecting the same volumes of blood (fig. 3), isotonic NaCl (fig. 5) or glucose (fig. 6) solutions does not cause the intramammary pressure to increase, water effect would appear to result from a change in blood osmotic pressure. Among the substances released when the blood corpuscles or platelets are destroyed, kallikrein and histamine do not seem to play a role. These products induce intramammary pressure to rise (fig. 7, 9) but latency and duration are longer than with water Also, their respective inhibitors, aprotinin and phenergan, always block their effect on intramammary pressure but not that of water. On the other hand, water and bradykinin (fig. 8) produce similar responses, indicating that the latter substance may play a role. We must consider also the possible action of extra-capillary water transfer, modifying ion flux and myoepithelial cell membrane potential or simply inducing the alveolar cells to swell and the acini to flatten. This last hypothesis permits a better interpretation of the pressure decreases noted after injection of hypertonic solutions (figs. 5, 6) since reverse water movements would have the opposite effect.