Comparison of methods for the synchronization of estrous cycles in dairy cows. 2. Effects of progesterone and parity on conception.

Three experiments with 571 dairy cows indicated that significantly more primiparous cows given two prostaglandin F2 alpha injections 14 d apart conceived within 30 d of first AI than did cows given two injections 11 d apart (84 vs. 62%). Fewer multiparous cows given two injections 14 d apart and inseminated after estrus conceived than did cows given two injections and a progesterone intravaginal coil inserted 8 d after the first injection (42 vs. 66%). Fewer cows given one injection of prostaglandin and inseminated at estrus conceived than did cows given two injections 14 d apart and a progesterone coil (39 vs. 66%). Conception rates of cows given two prostaglandin injections were positively related to plasma progesterone concentrations 2 and 4 d before the second injection (r = .81 and .86). Cows with progesterone concentrations below 5 ng/ml, 2 d before the second prostaglandin injection, and synchronized by two prostaglandin injections or by two injections and a progesterone coil had conception rates of 36 and 63%, respectively. Cows with progesterone concentrations above 5 ng/ml had a conception rate of 75 and 46% in the two treatments, respectively. Conception after estrus synchronization depends on the method and on the plasma concentrations of progesterone. Progesterone coils may be used before AI to enhance fertility in cows with low progesterone concentrations.

Comparison of methods for the synchronization of estrous cycles in dairy cows. 1. Effects on plasma progesterone and manifestation of estrus.

Dairy cows (n = 571) were treated with 1) one or two injections of prostaglandin F2 alpha given 11 or 14 d apart, 2) two injections given 14 d apart and a progesterone coil inserted 8 d after the first injection for a 7-d period; or 3) a coil inserted for 7 d and prostaglandin injected 1 d before its removal. Cows given two prostaglandin injections that conceived had higher progesterone concentrations during the luteal phase preceding AI than did cows that did not conceive. Cows with progesterone coils that conceived did not have higher progesterone concentrations than did cows that did not conceive. Older cows had lower progesterone concentrations than younger ones, and they appeared in estrus earlier after treatment. In four daily observations, 75% of cows were seen in estrus within 7 d after treatment. Cows mounting two or more times had a conception rate (62%) similar to that of cows that stood to mount. Fewer cows (56%) treated with prostaglandin that had low concentrations of progesterone appeared in estrus than did cows with high progesterone (84%). Cows treated with prostaglandin differ from cows treated with progesterone coils in respect to manifestation of estrus and to the relationship between plasma progesterone and conception.

Protein secretion by mesometrial and antimesometrial rat decidual tissue: evidence for differential gene expression.

Our recent finding that decidual luteotropin, a PRL-like hormone secreted by the rat decidua, is found primarily in the antimesometrial cells suggests strongly that the synthesis of this hormone may well be an important function of the antimesometrial tissue. The objective of this investigation was, therefore, 1) to determine whether antimesometrial tissue expresses mRNA for and actively secretes a protein(s) with PRL-like activity, and 2) to examine the pattern of protein production by the antimesometrial and mesometrial zones throughout decidual development. RNA obtained from decidual tissue of day 8 pseudopregnant rats was translated in a cell-free system. The translated products were subjected to PRL receptor affinity chromatography in the presence or absence of ovine PRL to assess binding specificity. The eluted 35S-labeled proteins were analyzed by both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. A major 28K protein bound specifically to and was eluted from PRL receptor-enriched luteal membranes. This protein also cross-reacted with antibodies to human PRL. To determine where the mRNA for this 28K protein is expressed and whether this protein represents a prohormone, RNA isolated from both antimesometrial and mesometrial tissue was translated in the presence or absence of microsomal membranes. The 28K protein was synthesized specifically by RNA isolated from the antimesometrial zone. No apparent change in the relative mol wt of the 28K protein was observed when translation was performed in the presence of microsomal membranes. To determine whether this protein is a secreted product and to investigate the pattern of protein secretion by the mesometrial and antimesometrial decidua, tissue explants obtained from both zones between days 9-13 of pseudopregnancy were cultured in the presence of [35S]methionine. Antimesometrial tissue secreted one major 28K protein which was capable of binding to PRL receptors on luteal membranes and was immunoprecipitated by antibodies to human PRL, whereas the mesometrial tissue primarily secreted an approximately 180K protein. The overall pattern of protein synthesis and release not only differed between the mesometrial and antimesometrial tissues but also differed with each day of pseudopregnancy. The secretion of several proteins decreased with advancing gestational age, while the secretion of other proteins began abruptly after day 11, coincident with regression of the antimesometrial tissue. In summary, results of this investigation have established that rat decidual tissue synthesizes and selectively secretes proteins, and the specificity and rate of production of these distinct

Decidual luteotropin secretion and action: its role in pregnancy maintenance in the rat.

Studies of rat decidual luteotropin production and action have revealed that decidual mRNA directs the synthesis of a 28,000 MW protein in a cell-free system which binds to prolactin receptors in luteal cells and appears to represent a prohormone for decidual luteotropin. Hybridization studies indicate that although rat decidual and prolactin-like placental hormones bind to prolactin receptors, they possess little homology to other members of the prolactin family. In addition, results of this investigation have revealed a possible physiological relationship between the mesometrial and the antimesometrial cells of the decidual tissue. The large antimesometrial cells produce decidual luteotropin in which secretion and/or synthesis is inhibited by the neighboring mesometrial cells. Since mesometrial cells possess binding sites for decidual luteotropin, it is possible that decidual luteotropin acts on the mesometrial cell to affect the formation of its own inhibitor. Mesometrial cells are rich in glycogen, whose synthesis is stimulated by prolactin-like hormones in other tissues. Therefore, decidual luteotropin may also act on these cells to enhance glycogen formation. In summary, decidual luteotropin appears to have at least two sites of action--the luteal cell, where it can substitute for prolactin in maintaining progesterone production, and the mesometrial cell, where its role remains to be investigated.

Evidence for the secretion of decidual luteotropin: a prolactin-like hormone produced by rat decidual cells.

Rat decidual tissue contains a PRL-like hormone named decidual luteotropin. We have recently revealed some of its physiological and biochemical characteristics. However, because rat decidual tissue contains specific binding sites for PRL, it was important to demonstrate that the hormone found in the tissue is not locally stored and structurally transformed PRL but a hormone actively synthesized by the rat decidual tissue. Decidual explants or decidual cells obtained from day 9 pseudopregnant rats were incubated for different times under either static conditions or continuously perifused with medium at a rate of 1 ml/h. Levels of decidual luteotropin were measured by a specific radioreceptor assay using luteal membranes as source of receptors and [125I]iodo-ovine(o)PRL as a tracer. In the static incubation, no proof of hormone production was obtained; levels of decidual luteotropin in medium and tissue or cells at the end of the incubation were similar to levels found in either cells or tissue before incubation. In sharp contrast, decidual cells perifused with media secreted large amounts of hormone. This may suggest that an inhibitor of decidual luteotropin production was being removed from the culture by the perifusion. For the first 4 h of perifusion, no hormone was produced. However by the fifth hour, cells began to actively release decidual luteotropin. Secretion of the hormone increased with time and reached maximal values between 7-15 h of perifusion. During the 15 h of perifusion, decidual cells released approximately 1000 times more decidual luteotropin than the amount they originally contained. A dose-response increase in hormone secretion was obtained with increased concentrations of decidual cells. The net amount of decidual luteotropin released into the medium over an 18-h period was approximately 6.5 micrograms/30 X 10(6) cells, 3.5 micrograms/10 X 10(6) cells, and 0.5 micrograms/2 X 10(6) cells. A similar profile of decidual luteotropin release was obtained when decidual explants were perifused. However, in contrast to decidual cells which secreted no hormone for the first 4 h of culture, decidual explants immediately began to release decidual luteotropin in the medium. The secretion of decidual luteotropin in vitro was inhibited 75% by the protein synthesis inhibitor, cycloheximide. In summary, results of this investigation demonstrate for the first time that rat decidual cells secrete in vitro a PRL-like hormone, decidual luteotropin.

Acrosome reaction of bovine spermatozoa in vivo: sites and effects of stages of the estrous cycle.

Thirty-two cows were inseminated near the uterotubal junction at various stages of the estrous cycle and slaughtered 16 h later to determine the effects of stage of the estrous cycle and tubal site of sperm recovery on the frequency of acrosome-reacted bull spermatozoa. Slaughter times were 46, 70, 144, or 168 h after each cow was injected with prostaglandin (PG) F 2 alpha or during the luteal phase of the estrous cycle. Sperm were recovered from the upper uterus and the isthmus and ampulla of the oviducts and stained for both viability and acrosome reaction. The highest frequency of acrosome-reacted sperm was found in the ampulla ipsilateral to a dominant follicle (largest follicle present) or recent ovulation and primarily at 70 h after PGF2 alpha (P less than 0.05). Also, fewer sperm were acrosome reacted prior to (46 h post-PGF2 alpha) and well after (168 h post-PGF2 alpha) estrus than during or immediately postestrus (70, 90, and 144 h post-PGF2 alpha; P less than 0.05). Except for two cows, one at 46 h and one at 70 h, all cows with more than 50% acrosome-reacted sperm in the ampulla had ovulated before slaughter. These data suggest that capacitated sperm become localized in the ampulla of the oviduct of the ovulatory side around the time of ovulation.

Upper critical temperatures and forced ventilation effects for high-yielding dairy cows in a subtropical climate.

Upper limit of thermal stability and subsequent rise of thermoregulatory functions as affected by forced ventilation were examined. Rectal temperature, respiratory frequency, ear skin temperature, body weight, and milk yield were recorded biweekly July to March over 2 yr for 170 Israeli-Holstein cows (305-day milk yield 9000 kg/cow) at air temperatures 10 to 36 degrees C. Cows were in an open shelter. One side was force ventilated over 2.5 m along the stanchions (air velocity 1.5 to 3 m/s) from 0500 to 2200 h. Control side mean air velocity was .5 m/s. Within the 10 to 24 degrees C range, rectal temperature was not affected by air temperature or forced ventilation but increased by .02 degrees C/kg fat-corrected milk in animals producing above 24 kg/day. Between 26 and 36 degrees C rectal temperature increased with air temperature in both groups; rate of rise was halved by forced ventilation. In this range of air temperature, rectal temperature increased with rising milk yield, as in the lower air temperature range, in both high-producing and lower-producing cows in forced ventilation. Body weight or parity did not have significant effects. Mean ear skin temperature was higher for control animals, but its rate of increase with air temperature was similar in both groups. Forced ventilation reduced mean respiratory rate. An upper critical temperature is 25 to 26 degrees C and is independent of milk yield or acclimatizational state of cows exposed to the natural sequence of climate.

Relationship between luteinizing hormone and decidual luteotropin in the maintenance of luteal steroidogenesis.

Between Days 6-11 of pregnancy or pseudopregnancy, the decidual tissue of the rat produces a prolactin-like hormone, decidual luteotropin, which can sustain luteal progesterone production when prolactin is suppressed. However, this effect is dependent upon the presence of the pituitary. The present investigation was undertaken to determine whether decidual luteotropin and luteinizing hormone (LH) act together to sustain luteal steroidogenesis and if so, to find out whether the need for LH is due to the inability of the decidual tissue to produce LH-like material and/or whether LH affects decidual luteotropin production. Pseudopregnant rats with or without decidual tissue were hypophysectomized on Day 8 and treated with either 1.5 IU human chorionic gonadotropin (hCG)/day or with vehicle. Within 24 h, serum progesterone dropped in both vehicle-treated groups and decidual luteotropin levels declined by 80% in the decidual tissue. Human CG administration had no effect on progesterone production in the control group. Yet in rats with decidual tissue, hCG stimulated progesterone production for at least 48 h and maintained the decidual tissue content of decidual luteotropin. Progesterone, but not hCG treatment, maintained decidual luteotropin concentrations in ovariectomized rats. To compare the luteotropic activity of the decidual tissue with that of the placenta, pregnant or pseudopregnant rats with decidual tissue were hypophysectomized on Day 8 and treated with 1.5 IU hCG. Control groups had decidual tissue or placentas removed and were similarly treated. Human CG stimulated progesterone production only in rats with placental or decidual tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive management of dairy cattle based on synchronization of estrous cycles.

High-yielding dairy cows (199) were allotted to a control group or one of two groups for synchronization of estrus. Synchronization of estrus was accomplished by either insertion of a progesterone-releasing intravaginal device (progesterone coil) for 7 days with .5 mg of the prostaglandin analogue cloprostenol (Estrumate) administered 1 day before removal of the progesterone coil, or by administration of .5 mg of Estrumate followed 13 days later by a progesterone coil inserted for 9 days. Following each estrous synchronization regimen, cows were inseminated during a fixed 6-day period (insemination week). Into one-half of the cows of each treatment group, a second progesterone coil was inserted 12 days following the fixed-time insemination for 9 days. Cows that calved within 21 days were included in a cluster and were treated and inseminated simultaneously at regular 3-wk intervals. Thus, insemination of synchronized cows was during only 6 out of each 21 days. The estrous synchronization regimens were applied so that the first fixed-time insemination for any cow occurred between 59 and 79 days after calving. Control cows were inseminated following estrus, commencing 59 days after calving. Conception rates for cows of groups 1, 2, and 3 were 50, 56, and 51%. Pregnancy rates at 25 days following the fixed-time insemination were 53, 78, and 69%, and at 100 days after calving, 57, 75, and 65%. A system of reproductive management is proposed in which observations for estrous behavior and inseminations are only during 6 days out of each 3 wk.

The effect of dietary and climatic factors on fertility, and on plasma progesterone and oestradiol-17 beta levels in dairy cows.

The effects of high dietary protein concentrations, high ambient temperatures and low dietary beta-carotene levels on fertility and on plasma progesterone and oestradiol-17 beta levels in high-yielding dairy cows, are described. High-yielding dairy cows were fed diets containing 15 or 20% crude protein. Cows fed the higher level of protein were less fertile and had a lower plasma progesterone concentration during the oestrous cycle preceding the first insemination. This phenomenon was especially pronounced in cows fed a diet containing 85% concentrates and 15% hay, where plasma progesterone levels during days 9-17 of the oestrous cycle were 2.5-3.7 ng/ml in cows fed the high level of protein and 4.0-5.5 ng/ml in cows fed the low level of protein (P less than or equal to 0.05). In cows fed 50% more energy before parturition, plasma progesterone levels did not differ between animals fed the low and high protein diets. Heat stress, which caused a rise in body temperature, decreased fertility and plasma progesterone levels during the luteal phase of the oestrous cycle but increased plasma oestradiol-17 beta levels during the 36 h preceding the onset of oestrus from 5 to 7 pg/ml (P less than or equal to 0.005). The effect on fertility of supplementing the diet of dairy heifers and cows with beta-carotene is reviewed. In some of the experiments where the basal plasma beta-carotene levels were lower than 50 micrograms/100 ml, beta-carotene supplementation significantly increased fertility. However, in no case was fertility affected when plasma beta-carotene levels exceeded 150 micrograms/100 ml. The possible relationships among body weight changes, energy balance, plasma progesterone levels and fertility of dairy cows are discussed.

Effect of climatic conditions on peripheral concentrations of LH, progesterone and oestradiol-17 beta in high milk-yielding cows.

In a subtropical climate, high milk-yielding dairy cows were kept during the summer under ventilated conditions or untreated; during the winter, cows were kept untreated. The afternoon mean rectal temperature for multiparous cows in the three groups was 39.3, 39.8 and 38.9 degrees C, respectively. Each group was significantly different from the other two (P less than 0.05). Plasma LH concentrations measured every 6 h during the oestrous period in 38 'summer' cows were not significantly different for untreated and ventilated animals. Conception rate was higher (P less than 0.05) in cows that showed oestrous behaviour before the LH surge reached its peak than in cows in which oestrus coincided with or occurred later than the LH surge. Plasma progesterone levels measured in 62 cows during the oestrous cycle before the first insemination were higher in the winter than in the summer in multiparous, but not in primiparous, cows. Ventilation increased progesterone levels in multiparous and primiparous cows. Plasma oestradiol-17 beta levels did not differ between groups until 36 h before the onset of oestrus, when they remained at 4.75 pg/ml in winter and summer-ventilated cows but increased to 6.75 pg/ml in summer untreated cows (P less than 0.01). Significant negative correlations were found between oestradiol levels observed 12 h before to 12 h after the onset of oestrus and plasma progesterone concentration during both the preceding and the subsequent oestrous cycles.

Fertility of dairy heifers given a commercial diet free of beta-carotene.

1. Dairy heifers given concentrates including vitamin A and wheat straw from 7 to 17 months of age had an average plasma beta-carotene concentration of 20--60 micrograms/l. Control heifers given the same diet but supplemented with beta-carotene had a beta-carotene plasma concentration of 630--2190 micrograms/l. 2. In contrast to previous findings no differences in duration of standing oestrus, length of oestrous cycle, plasma progesterone and luteinizing hormone (LH) concentrations and interval between LH peak and ovulation were observed between the groups. All the heifers conceived after one or two inseminations; conception rate being 69% for heifers given a diet free of beta-carotene and 78% for the controls. 3. Average rate of growth of heifers not supplemented with beta-carotene was 0.75+/-0.02 kg/d v. 0.81+/-0.02 kg/d for the controls (P less than or equal to 0.02). 4. The possible reasons for the discrepancy between present and previous findings are discussed.

Seasonal variations in post-partum plasma progesterone levels and conception in primiparous and multiparous dairy cows.

Progesterone concentrations in peripheral plasma of 18 primiparous and 34 multiparous dairy cows were determined by radioimmunoassay every 4 days, from 10 days post partum until the next conception. The interval from parturition to the first progesterone peak (greater than 4 ng/ml plasma) was significantly longer (P less than 4 ng/ml plasma) was significantly longer (P less than 0.01) in primiparous than in multiparous cows. The progesterone concentrations on Days 4-15 of the oestrous cycle were significantly lower (P less than 0.025) during the summer than in cycles occurring in winter. The conception rate during the summer was lower than in winter. In cows inseminated in summer, conception was related to the shape of the progesterone curve in the cycle preceding insemination.