Influence of season and reproductive status on peripheral plasma progesterone levels in the lactating bovine

Data collected monthly for one calendar year from Holstein cows lactating under Louisiana ambient climatic conditions comprised a total of 264 cowmonths. The year was divided into seasons of cool, intermediate, and hot temperatures. A highly significant (P<0.01) relationship between plasma progesterone and animal age (r=–0.57) was observed. Plasma progesterone concentrations in the hot season (4.6 ng/ ml) were significantly (P<0.01) higher than concentrations in the cool and intermediate seasons (3.4 and 3.8 ng/ ml, respectively). Plasma cortisol concentrations were lower (P<0.01) in the hot season than in the cool and intermediate seasons and suggested the adrenal cortex did not contribute to the increase in progesterone concentrations which occured in the hot season. A significant (P<0.01) positive correlation (r=0.45) between cortisol and progesterone was observed. Reproductive status did not have a statistically significant effect on progesterone levels and the affect of season on progesterone concentrations was consistant across all reproductive status. Plasma progesterone levels in the anestrus animals (3.9 ng/ ml) suggested progesterone secretion was responsible for their failure to cycle. Similar progesterone levels were observed in normal (3.5 ng/ ml) and repeat breeders (3.6 ng/ ml).Presented at the Seventh International Biometeorological Congress, 17–23 August 1976, College Park, Maryland, USA.     

Ovarian morphology,plasma progesterone concentrations and early embryo survival in the sow

Sixty-five Large White sows were used to examine relationships between ovarian morphology and embryo survival at 30 days gestation and plasma progesterone concentration before and after service.The total mass of luteal tissue was positively correlated with the number of corpora lutea on the ovaries (r = 0.68), and formed a fairly constant proportion of ovarian mass at 30 days gestation. The mean number of embryos per sow was 11.2 ± 0.76, and embryo survival rate was estimated to be 76.5%. There was a positive correlation between ovulation rate and number of embryos at 30 days of pregnancy (r = 0.39). The survival rate of embryos was inversely related (r = ?0.66) to the mean distance between embryos in the uterus. The means of plasma progesterone levels on days 11, 12 and 13 after service were positively correlated with the means of progesterone levels on days 9, 10, 11 and 12 of the cycle before service, the number of corpora lutea, the total mass of luteal tissue and the total mass of the ovaries, but not to numbers of embryos.     

Ovarian and luteal blood flow, and peripheral plasma progesterone levels, in cyclic guinea-pigs

Ovarian and luteal blood flow rates were studied using radioactive microspheres in guinea-pigs between Day 6 of the oestrous cycle and Day 1 of the following cycle. Peripheral plasma progesterone levels were measured by radioimmunoassay on the same days of the oestrous cycle. Ovarian blood flow was greatest between Days 9 and 12 and had fallen by Day 16 both in absolute (ml . min-1) and relative (ml.min-1.g-1) terms. Luteal weight and blood flow were also greatest between Days 9 and 12 and had fallen sharply by Day 16. The highest mean (+/- s.d.) luteal flows measured were 0.10 +/- 0.04 ml.min-1 per corpus luteum, and 24.26 +/- 9.3 ml.min-1.g-1 luteal tissue on Day 10 of the cycle. Mean peripheral plasma progesterone levels reached a maximum of 3.66 +/- 1.1 ng/ml at Day 12 of the cycle and fell thereafter, reaching 0.74 +/- 0.5 ng/ml by Day 1 of the following cycle. Plasma progesterone levels declined significantly between Days 12 and 14 of the cycle, whereas no significant drop in luteal blood flow was demonstrable until after Day 14. These data do not support the idea that declining luteal blood flow is an initiating mechanism in luteal regression in the guinea-pig.     

Spontaneous uterine activity and plasma progesterone and oestrogens in the ewe with live and stillborn lambs

Peripheral plasma progesterone and oestrogen concentrations were measured during late pregnancy and the parturient period in 12 ewes producing live lambs and three others producing stillborn lambs. Progesterone values started declining by 10 days before lambing but at minus 24 hours were still 6.1 +/- 3 ng/ml in the ewes bearing live lambs; during the last 24 hours progesterone was significantly lower in the ewes producing stillborn lambs. Oestrogens reached a maximum level of 550 +/- 280 pg/ml at the time of delivery and declined rapidly to basal values shortly after lambing. Oestrogens did not rise at lambing in the ewes producing stillborn lambs. In seven of the 12 ewes bearing live lambs, uterine activity, as determined by intrauterine pressure changes, was recorded throughout parturition and compared with the plasma values for progesterone and oestrogens. It was found that there was a highly significant positive correlation between uterine activity and plasma oestrogen concentrations, and a highly significant negative correlation between uterine activty and both plasma progesterone concentrations and the progesterone: oestrogen ratio.     

Post-partum oestrus in the sow in relation to the concentration of plasma oestrogens.

Ten sows, three entire and seven which had been ovariectomized at different stages of late gestation, were observed for post-partum oestrus. Serial blood samples were collected from six sows during the pre-and post-partum periods, and plasma oestrogen concentrations determined by radioimmunoassay. Morphological aspects of ovarian activity in the entire sows were examined at laparotomy and at autopsy. Although peak values of oestrogen concentration in the plasma varied from 3-9 to 8-0 ng/ml between individuals, the pattern of oestrogen levels was similar for control and ovariectomized sows. Peak concentrations occurred just before parturition, and the timing of ovariectomy did not affect the incidence of the oestrogen peak. Oestrus was detected in one control and one ovariectomized sow at 46 and 40 hr post partum respectively, there being no evidence of ovarian activity in the entire sows. The occurrence of post-partum oestrus in a sow ovariectomized at Day 108 of gestation indicates that this phenomenon is not directly connected with ovarian secretion of oestrogens. The post-partum oestrus is apparently a result of the peak of feto-placental oestrogens that occurs at parturition.     

Prolactin levels and the LH-response to synthetic LH-RH in the lactating sow

To determine the role of prolactin in the suppression of ovarian activity during lactation in the sow experiments were performed to investigate a possible inhibitory action of prolactin at the pituitary level. Therefore the LH-response to an intravenous injection of 25 μg synthetic LH-RH was measured in the 1st, 2nd and 3rd week of lactation. The compound was injected under high and low concentrations of prolactin in the peripheral blood, the latter achieved by removal of the piglets 6 h before administration of LH-RH. The results showed no difference in the effect of LH-RH injected at high or low prolactin levels. However, although the mean prolactin concentrations in the 1st, 2nd and 3rd week of lactation were similar, the results clearly demonstrated an increase in LH-response as lactation proceeds.The low responsiveness of the pituitary shortly post partum was also observed when the preparturient rise of prolactin was suppressed by treatment with bromoergocryptine. Injections of LH-RH in the last week of gestation given before and after the physiological increase of PRL, which occurred about 48 h before delivery, all showed low LH-response.It is obvious from the presented data that the LH-response to an intravenous injection of 25 μg LH-RH is in no way correlated with the prolactin levels at the time of treatment.     

Ovarian activity and plasma concentrations of progesterone and estradiol during pregnancy in jennies

The objectives of this study were to determine ovarian activity (with ultrasound) and plasma concentrations of progesterone and estradiol during pregnancy in jennies. There was considerable ovarian activity during the second month of pregnancy. Secondary corpora lutea (total of 2 to 7 per jenny) were formed (mainly by luteinization) starting on Day 41.8 +/- 1.0 (range Days 38 to 46; ovulation = Day 0). The echogenicity of the primary and secondary corpora lutea gradually decreased during pregnancy. Plasma progesterone concentrations increased between Days 0 and 10 (0.9 and 19.9 ng/mL, respectively), gradually decreased to Day 30 (12.1 ng/mL), increased between Days 30 and 40 (plateau, at approximately 17 ng/mL), gradually declined from Days 110 to 160 (nadir of approximately 6 ng/mL), and remained nearly constant until increasing again just before parturition. Plasma estradiol concentrations increased gradually from Day 65, peaked (1.2 ng/mL) on Day 165 (> or = 1 ng/mL on Days 150 to 210), and decreased thereafter, with very low concentrations during the last 20 d before parturition. Ovarian function and hormone profiles were generally similar to those previously reported during pregnancy in mares.     

Plasma relaxin levels during suckling and oxytocin stimulation in the lactating sow

Plasma relaxin levels were measured in animals at different stages of lactation and related to the amount of nuzzling and suckling behavior exhibited by the piglets. Only in some acute suckling episodes was relaxin secreted rapidly and episodically in spite of normal piglet and sow behavior and interaction. However, when the piglets were removed from the dams 6 h before suckling, the sows were very restless and the relaxin response to suckling was delayed. Oxytocin injection in lactating but nonsuckled sows caused an episodic secretion of relaxin similar to suckling itself. The source of relaxin in the lactating sow may be the old corpus luteum, since progesterone levels increased acutely, somewhat reflecting the profile of relaxin increase over the suckling episode.     

The relationship between plasma levels of estradiol-17beta, progesterone and the consistency of the cervix in the sow

The object of this investigation was to estimate the peripheral plasma levels of estradiol-17beta and progesterone and the consistency of the cervix by rectal palpation of sows before, during and after post-weaning estrus. The tonicity of the cervix increased from approximately 4 days before the onset of heat, became firmest during estrus, and became softer again during the post-estrual period. The levels of estradiol increased before the onset of heat and reached maximum levels on the day preceding heat, then decreased to baseline. The progesterone levels remained low until post-estrus, then increased rapidly. One sow which did not come in heat constantly had a soft cervix and low hormone levels. It is concluded that estrogen might be implicated in the increased tonicity of the cervix and that rectal examination of the cervix provides valuable information on ovarian function.     

Seminal oestrogens in the boar: origin and functions in the sow

The boar produces considerable amounts of oestrogens in the Leydig-cells also occurring in semen. Very high oestrogen concentrations are measurable in the fluid of the tubuli, which contribute the main part of seminal oestrogens. Additionally, the accessory sex glands add 22% of the unconjugated oestrogens and 12% of conjugated oestrogens to the ejaculate. Concentrations vary considerably according to season and individuals. So far a maximum of 15.3 micrograms was measured in one ejaculate. Infusion of oestrogens (simulation of the oestrogen content of an ejaculate) at oestrus through a catheter into the uterus lumen leads to an increase of the myometrial contraction-frequency for 3 h. Additionally "inseminations" with oestradiol-17 beta (Oe 2), oestrone (Oe 1), and oestrone-sulfate (Oe 1-S) (naturally occurring in the ejaculate) in 10-micrograms amounts at oestrus may lead to an increase of PGF2 alpha concentrations in the uterine veins within a few minutes. This increase may be found after "insemination" with each of the three steroids but not after saline. A parallel rise of the "inseminated" oestrogen is measurable in the uterine vein plasma and may reach concentrations up to several thousand pg/ml. This rise also leads to significantly increased concentrations in peripheral plasma for about 30 min after the "insemination" of Oe 2 (increase of Oe 2 and Oe 1-S) and Oe 1 (Oe 1 and Oe 1-S). Consequences of seminal oestrogens for sperm transport and the timing of ovulation are discussed.     

Social ranking and plasma progesterone levels in goats

Progesterone is essential for maintaining pregnancy in goats, and embryonic losses may be a consequence of the reduction in circulating progesterone levels close to the time of implantation. Some evidence exists regarding social dominance affecting the plasma progesterone levels in several species—where dominant females conceive earlier. The objective of this research was to determine whether serum progesterone levels differ in goats of different social status. A behavioural study was conducted for 10 days in a herd of 57 does and an individual success index (SI) was calculated according to the result of aggressive interactions. Goats were classified as high (SI: 1–0.67), medium (SI: 0.66–0.34) and low-ranking (SI: 0.33–0.0). Ovulation was synchronized using two injections of prostaglandin 11 days apart, and the plasma progesterone levels determined daily for a period of 20 days. The area under the plasma progesterone curve during the entire study was greater in the high than in the medium and low-ranking does (96.2 ± 5.8, 79.5 ± 5.3 and 81.3 ± 5.3 ng/ml, respectively, P < 0.05). During days 11–17 following prostaglandin synchronization, the plasma progesterone levels were higher in the high-ranking (P < 0.05), compared to the low-ranking does. Plasma progesterone levels were significantly correlated with SI at days 14 and 15 (r = 0.26; P < 0.05). Results suggest a relationship between social ranking of goats and the plasma progesterone production from the corpus luteum and other possible sources.     

Increasing feed intake in late gestation does not affect plasma progesterone concentration in the sow

Rate of decline in plasma progesterone concentration may influence the success of lactogenesis in the sow. The aim of this experiment was to investigate whether progesterone concentration and rate of decline of progesterone in the periparturient sow could be manipulated by changing her feeding level. Forty-two sows received either 1.15 or 2 times maintenance energy daily from day 100 of gestation up until and including the day of farrowing. Blood samples were taken on days 98 (pre-treatment baseline) and 109 of gestation, during farrowing, 6h after farrowing and at 09:00 h for the 3 days following farrowing. Plasma progesterone concentration was determined and progesterone half-life was calculated for each sow. High intake feeding had no effect on plasma progesterone concentration at any time of sampling. Progesterone half-life averaged 41.2 +/- 3.81 h and did not differ between treatments. There was no relationship between progesterone concentration, or half-life, and litter weight gain, although there was a weak correlation between decline in progesterone in the first 6h after birth and piglet growth rate from birth to 6 days of age (R(2) = 0.109, P < 0.05). It was concluded that increasing feed intake in late gestation cannot be used to increase progesterone clearance rate and hasten the onset of lactogenesis in sows.     

Control of parturition in the sow using progesterone and prostaglandin

The effect of progesterone and prostaglandin administration on the timing of farrowing was studied in three groups of 25 sows each. Progesterone treatment (100 mg/day) on days 112, 113 and 114 of gestation (group I) significantly prolonged the gestation length to 116.4 +/- 0.4 (mean +/- s.e.) days compared to the control sows (group III; 115.5 +/- 0.2; P less than 0.05). Administration of prostaglandin (200 micrograms Cloprostanol intramuscularly) on day 115 of gestation following progesterone treatment (group II) resulted in a gestation length of 116.0 +/- 0.1 days, with the sows farrowing 25.4 +/- 1.0 h after the prostaglandin injection. 80% of the sows farrowed between 0800 and 1700 h of day 116 of gestation. Plasma progesterone levels were maintained by the exogenous progesterone during treatment. At farrowing, higher levels of progesterone were observed in groups I and II compared to controls. Prostaglandin treatment did not significantly alter withdrawal of progesterone in progesterone treated sows, suggesting that the actions of exogenous prostaglandin is primarily on the myometrium and the cervix. Hormonal treatment in late pregnancy did not have any adverse effects on piglet viability and growth rate, or subsequent reproductive performances of sows. Lactation was initiated normally, and the concentrations of lactose, protein, fat, IgG, Na+, Ca2+ and K+ in colostrum and milk were similar in all groups during the first 5 days of lactation.