Associations between milk progesterone concentration on different days and with embryo survival during the early luteal phase in dairy cows

The relationships between the concentration of milk progesterone and early embryo survival on Days 4-8 inclusive and between the concentration of progesterone on different days from Days 0-8 inclusive following ovulation and insemination were examined in dairy cows. The relationships were examined following 77 randomly chosen artificial inseminations to cows in standing oestrus. There was a significant (P < 0.05) linear and quadratic relationship between the concentration of milk progesterone on each of Days 4-6 after ovulation and the probability of embryo survival. There was no association (P > 0.05) between milk progesterone concentration and probability of embryo survival on Days 7 and 8 after ovulation. There were no associations between milk progesterone concentration on Days 0-2 and the concentrations on Days 4-7, however, progesterone concentrations on Days 4 and 5 were highly predictive of the concentration on Days 6 and 7, respectively. Overall, the results indicate that suboptimal progesterone support during the early luteal phase is likely to deleteriously affect embryo viability and in addition, that it is possible to predict milk progesterone concentrations during the early luteal phase based on earlier stage concentrations and thus identify cows at risk of early embryo loss.     

Milk progesterone levels in crossbred buffaloes (swamp x murrah) and a comparison to the original breeds

Progesterone levels in milk fat and whole milk were determined in eight crossbred buffaloes (swamp x murrah). Progesterone peaks in milk fat and whole milk during the luteal phase ranged from 44.23 to 224.50 ng/ml and 8.58 to 20.22 ng/ml, respectively. Progesterone levels were measured in two murrah cows and seven swamp cows for comparison with the levels in the crossbred buffaloes. Variation in milk progesterone levels between breeds was indicated and discussed. Radioimmunoassay for progesterone in milk fat and whole milk of buffaloes was validated.     

Use of group-specific antibodies to detect fecal progesterone metabolites during the estrous cycle of cows

Progesterone is metabolized to pregnanediones and hydroxylated pregnanes prior to its fecal excretion. Therefore, use of progesterone antibodies underestimates the actual amount of fecal metabolites. To improve the methodology of noninvasive fecal progesterone metabolite analysis, enzymeimmunoassays (EIA) using group-specific antibodies against 5-reduced 20-oxo-pregnane-C3-conjugates were developed. Fecal and milk samples were collected at 1- to 2-d intervals during the morning and evening milking throughout 1 estrous cycle in dairy cows (n = 12). Six immunoreactive metabolites were detected in the feces with high performance liquid chromatography (HPLC), eluting as 5α- and 5β-reduced pregnanes containing a 20-oxo-group (20-oxo-pregnanes). Fecal samples of 3 cows were analyzed by 3 EIAs using antibodies against 4-pregnene-6α-ol-3,20-dione 6HS:BSA (6HS-progesterone), 5α-pregnane-3β-ol-20-one 3HS:BSA and 5β-pregnane-3β-ol-20-one 3HS:BSA, respectively. The follicular and luteal phases were identifiable with each EIA. Luteal phase values and the differences between mean follicular (Days 0 to 2 and 19 to 21) and luteal phase (Days 10 to 16) values obtained with the 5-pregnane EIAs were 3- to 4-fold higher than with the 6HS-progesterone EIA. Since results with the former 2 EIAs were almost identical, the remaining samples were only analyzed by the EIA for 5β-pregnane-3α-ol-20-one. Fecal 20-oxo-pregnane concentrations were parallel to milk progesterone values, but had a lag time of about 0.5 d; the coefficient of correlation (P < 0.001) was 0.76 (y = 155.2 × + 37.2). Fecal 20-oxo-pregnane concentrations during the follicular and luteal phase were 39.5 ± 2.2 and 341 ± 15.2 ng/g feces, respectively. In conclusion, fecal 20-oxo-pregnanes are significantly correlated to milk progesterone concentrations. They consist of several metabolites and compared to a 6HS-progesterone antibody, their evaluation was improved using antibodies against 5-reduced pregnanes.     

Milk progesterone profiles in crossbred Brown Swiss x Nellore cattle following natural service

Ovarian activity and estrous behaviour were monitored through milk progesterone determinations and twice daily visual observations in 70 crossbred Brown Swiss x Nellore cows following natural service. Whole milk samples were collected on the day of estrus (Day 1), Day 11, and every 5 d thereafter until the next estrus or pregnancy confirmation. Seventy percent of the cows behaved as expected, i.e. they showed a 19-to 25-d interval between estrus and the next ovulation, or they became pregnant. Estrous cycles of regular length (18 to 24 d) were found in 54% of the cases. Prolonged luteal phases (interval from estrus to next ovulation > 28 d) were found in 15.7% of cows. Short estrous cycles (interestrous interval < 18 d) were found in 7.1% of the cases. Periods of acyclicity (basal progesterone levels for periods >/= 15 d) were found in 5.8% of the cases, and one cow exhibited estrus while pregnant and had a high progesterone concentration. Cows with a prolonged luteal phase and those with a short estrous cycle had an interval between ovulations of 35.0 +/- 6.7 d (x +/- SD) and 9.6 +/- 3.1 d, respectively. Signs of estrus were not detected in 33.3% of the ovulations confirmed by progesterone determinations. Low conception rates, failures in estrus detection and a high frequency of abnormal postbreeding luteal phases were found.     

Interrelationships between progesterone, 13,14-dihydro-15-keto PGF-2 alpha (PGFM) and LH in cyclic and early pregnant cows

Plasma progesterone and LH secretion patterns were examined in 18 mature dairy cows during the oestrous cycle and after insemination. Blood samples were collected every 15 min for 8 h per day on Days 3, 5, 6, 7, 8, 9, 10, 12, 14, 16, 17, 18, 19, 20 and 21 of the oestrous cycle, then, in the same cows, at the same times during early pregnancy. PGF-2 alpha secretion rates (as determined by plasma PGFM concentrations) were also monitored on Days 14, 16 and the day of, or equivalent to, luteal regression. Mean daily plasma progesterone concentrations were similar until Day 16 in cyclic and pregnant cows, after which values in non-pregnant animals declined. Regression analysis indicated that progesterone concentrations were best described by a quadratic expression with fitted maximum values on Day 13 in non-pregnant animals but values increased linearly over the whole period to Day 21 in pregnant cows. The frequency, amplitude and area under the curve of LH episodes showed no significant differences between cyclic and pregnant animals. In pregnant cows, the amplitude and area under the curve of progesterone episodes increased linearly between Days 8 and 21, although no such increase occurred in cyclic cows. Low-level PGFM episodes were present in cyclic and pregnant cows on Days 14 and 16 after oestrus, and high amplitude episodes occurred in non-pregnant cows during luteal regression. Pregnant cows showed a significant depression of the amplitude, but not the frequency of episodes at the expected time of luteal regression. These results confirm that the corpus luteum of pregnancy secretes an increasing amount of progesterone per se and per unit of LH until at least Day 21 after mating. They further suggest that the corpus luteum of the cyclic cow may experience small episodes of PGF-2 alpha and be subjected to initial degenerative changes by Day 14 after oestrus, some time before the onset of definitive luteolysis.     

Concentrations of progesterone in milk as a monitor of early pregnancy diagnosis in dairy cows

The objectives of the experiment were to evaluate the efficacy of using progesterone concentrations in milk and palpation per rectum on days 21 or 22 postbreeding to estimate pregnancy and evaluate management practices; and to investigate physiological occurrences leading to incorrect diagnosis of pregnancy when serial samples of milk were collected. Of particular interest were indications of early embyronic death and insemination of cows not in estrus. Milk samples were collected at the afternoon milking of days 0 or 1 (day 0 = day of estrus), 9 or 10, 21 or 22 and 27 or 28 following breeding in 200 lactating dairy cows. Tentative diagnosis of pregnancy was made based on concentrations of progesterone in milk on days 21 and 22 alone and on days 21 or 22 and 27 or 28. In addition all cows were palpated per rectum on days 21 or 22 postbreeding and a tentative pregnancy diagnosis was made. Pregnancy was confirmed by examination of the genital tract per rectum between 35 and 50 days after breeding. Values of 4 ng/ml or greater and/or the presence of a mature corpus luteum were considered positive signs of pregnancy. Progesterone in milk ranged from 0.1 to 18 ng/ml. On days 0 or 1, 9 or 10, 21 or 22 and 27 or 28 concentrations of progesterone in milk averaged 1.5 +/- 0.3, 11.1 +/- 0.5, 12.0 +/- 0.4 12.5 +/- 0.5 ng/ml for pregnant cows. Corresponding samples from nonpregnant cows averaged 1.2 +/- 0.2, 10.3 +/- 0.4, 3.0 +/- 0.4, 6.8 +/- 0.6 ng/ml, respectively. Ninety-six and 104 cows were classified as pregnant and nonpregnant on days 21 or 22 as compared to 78 and 118 cows diagnosed as pregnant and nonpregnant on days 21 or 22 and 27 or 28 combined. Pregnancy detection by progesterone in milk on days 21 or 22 with pregnancy determined via rectal palpation 35 to 50 days postbreeding was 77 and 100% accurate for positive and negative diagnosis, respectively. The percent agreement using progesterone in milk on days 21 or 22 and 27 or 28 combined was 95 and 100%, respectively, for positive and negative diagnosis. Diagnosis based on rectal palpation 21 or 22 days postbreeding was 63 92 (69%) and 76 88 (87%) for pregnant and nonpregnant cows, respectively. Ten of the 200 cows had progesterone concentratins in milk of > 4 ng/ml at the time of breeding. Six of these cows were pregnant from a previous insemination. The other four cows were nonpregnant and were inseminated during the luteal phase of the cycle. In conclusion, measurement of progesterone in milk is a useful tool in early detection of pregnant and nonpregnant cows and may be useful in detecting reproductive problems in a dairy herd. It will probably be most useful when used in combination with later pregnancy diagnosis per rectum .     

Level and distribution of progesterone in bovine milk in relation to storage in the mammary gland.

The study investigated the effect of the place of storage of milk in the mammary gland on progesterone concentrations in whole milk, skim milk and milk fat. Skim milk, milk fat and whole milk progesterone concentrations were lower (P < 0.05) in milk fractions obtained from the cisternal part of the mammary gland compared to those in the milk fractions from the alveoli. Mean milk fat concentrations did not mirror the changes in the mean skim milk, milk fat and whole milk progesterone concentrations. After administration of oxytocin, milk fat concentrations rose significantly (P < 0.01). At the same time, skim milk and milk fat progesterone concentrations remained unchanged (P > 0.05), compared to those in the milk fractions of alveolar origin, obtained before oxytocin administration. Skim milk and whole milk progesterone concentrations were higher (P < 0.01) in composite milk and in milk samples collected 1 h after milking, compared to concentrations in the milk samples collected before morning milking and at 3, 5, 7 and 9 h after milking. The results suggest that defatted milk, milk fat and whole milk progesterone concentrations were affected by the place of storage of the milk in the mammary gland, and that this effect is independent of milk fat content. Time of milk sampling, not the milk fat concentration, in relation to time of milking, was a critical factor in determining skim milk, milk fat and whole milk progesterone. The study also revealed that the concentrations of the other milk components, somatic cell count, lactose and protein were affected by the place of storage of milk in the mammary gland.     

Progesterone and follicular changes in postpartum noncyclic dairy cows after treatment with progesterone and estradiol or with progesterone, GnRH, PGF2alpha, and estradiol

A previous study showed that noncyclic dairy cows treated with 10 microg of GnRH and a progesterone-releasing CIDR insert on Day 0, 25 mg of PGF2alpha and CIDR removal on Day 7, followed by 1 mg estradiol benzoate on Day 9 for those cows that still had not shown estrus (CGPE program) had higher conception rate (47% vs. 29%) than cows treated only with CIDR and estradiol benzoate as above (CE program). This study was to investigate the mechanisms by which the CGPE program improved conception rate compared with the CE program. Sixteen noncyclic Holstein-Friesian cows were randomly assigned to 2 groups balanced for the size and growth pattern of the dominant follicles, which were determined by ultrasonography over a 3-d period. One group received the above CGPE treatment, and the other group received the CE treatment. Follicular and luteal development were monitored by daily ultrasonography. Blood samples were collected daily from Day -2 to Day 11, and thereafter milk samples were collected thrice weekly for a further 24 d. Blood and milk samples were analyzed for progesterone. The GnRH treatment induced ovulation in 7 of 8 cows, resulting in elevated (P<0.05) progesterone concentrations between Days 4 and 7 for cows in the CGPE group. All induced CL underwent luteolysis by 24 h after PGF2alpha treatment. Within 5 d of CIDR removal, 7 of 8 cows in both the CE and CGPE groups ovulated. The interval from emergence of the ovulatory follicle to ovulation was similar (P=0.32) but less (P<0.05) variable for the CGPE group (9.0+/-0.3 d) compared with the CE group (10.3+/-1.2 d). Progesterone concentration in milk samples was similar between the two groups up to 10 d after ovulation. In summary, the GnRH treatment induced ovulation or turnover of dominant follicles, induced a synchronized initiation of a new follicular wave, and increased the progesterone concentration from 4 d after treatment. These could be the reasons for the increased conception rate of cows treated with the CGPE program.     

Characteristics of prostaglandin F measurements in the ovarian circulation during the oestrous cycle and early pregnancy in the cow

Holstein or crossbred beef cows were anaesthetized on Days 15 to 17 after oestrus; the ovarian artery (OA), ovarian (utero-ovarian) vein (OV) and a peripheral artery (PA), were catheterized for chronic blood sampling. Beginning on the day after surgery, 6 sequential blood samples were collected every 30-40 min twice daily from 8 cyclic and 6 pregnant cows during Days 16-20: 818 blood samples (including 216 OA and PA concurrent arterial pairs) were collected. Overall least squares means for PGF concentrations (pg/ml) in the OV, OA and PA of cyclic cows were 562, 228 and 106, respectively. A significant (P less than 0.01) OA-PA difference (122 pg/ml) suggests that a local transfer system, between uterine venous effluent and ovarian arterial affluent, is functional in the cow. A transfer efficiency of about 1% was estimated. In cyclic cows differences in OA-PA concentrations of PGF were minimal on Days 16-18 and increased to about 160 pg/ml during luteal regression (Days 19-20). In pregnant cows a biphasic OA-PA pattern of difference in PGF between days was detected, with a peak on Day 18 (136 pg/ml) which was not apparent on Days 19-20. Amplitude of PGF spikes in the OA was significantly higher in cyclic (725 pg/ml) than in pregnant cows (397 pg/ml). We suggest that pregnancy suppresses PGF delivery to the ovarian circulation, resulting in maintenance of the corpus luteum in pregnant cows.     

Effects of sample handling temperatures on bovine skim milk progesterone concentrations

The effects of incubation of whole milk at various temperatures and times on the concentration of progesterone in the skim milk fraction was determined. For the study, milk samples were collected from 10 pregnant Holstein cows. The milk from each cow was transferred to culture tubes to provide 32 replicates of 3 ml volume. To begin the incubation study, all samples were placed in a 37 degrees C water bath for 4 h. The end of this incubation was designated as time 0 and a sample from each cow was centrifuged to harvest skim milk. At time 0, samples from each cow were divided among incubation temperatures of 0 degrees, 4 degrees, 20 degrees and 37 degrees C. Samples were removed from each incubation group at 30, 60, 90 and 120 min. After 120 min, all remaining samples were returned to the 37 degrees C incubation and skim milk was collected at 30, 60 and 90 min. Progesterone was measured in skim milk by radioimmunoassay. The mean +/- SE concentration of progesterone in skim milk at time 0 was 10.9 +/- 1.1 nmol/L. The mean concentration of progesterone in skim milk was higher (P < 0.05) in all samples incubated at 0 degrees and 4 degrees C, with incremental increases ranging from 34% to 67% above time 0. Progesterone in skim milk returned to time 0 concentrations in milk samples transferred from 0 degrees or 4 degrees C to 37 degrees C. There was no change in skim milk progesterone in whole milk samples incubated at 20 degrees or 37 degrees C. From this study, it can be concluded that the concentration of progesterone in skim milk is temperature dependent. Inconsistency in handling whole milk samples can have a profound effect in the concentration of progesterone on skim milk. The temperature-dependent effect was reversible and may be related to solubility of progesterone in milk fat.     

Post-insemination milk progesterone concentration and embryo survival in dairy cows

Logistic regression analysis was used to evaluate the relationship between post-insemination milk progesterone concentration and embryo survival, and between milk yield and milk progesterone concentration. Milk samples were collected on Days 1, 4, 5, 6, and 7 (insemination=Day 0) following 871 inseminations in spring-calving dairy cows. Milk progesterone concentrations were measured by enzyme-immunoassay and pregnancy diagnosis was conducted with transrectal ultrasonography at approximately Day 30. There was a negative linear relationship (P<0.01) between milk progesterone concentration on Day 4 and embryo survival while, in contrast, there was a positive linear and quadratic relationship between milk progesterone concentration on Days 5, 6 and 7 (P<0.05) and also between the rate of change in progesterone concentrations between Days 4 and 7 inclusive and embryo survival (P<0.05). There was a weak negative linear relationship between average daily milk yield at the time of insemination and milk progesterone concentrations (P<0.001). There was no association between many production parameters, including liveweight and body condition score measured at various stages between calving and insemination, and milk progesterone concentration between Days 4 and 7 inclusive (P>0.05). In conclusion, low progesterone during Days 5-7 (after insemination) was associated with low fertility in dairy cows and there were indications of a range of progesterone concentrations within which embryo survival was maximal.     

Growth and ovarian function of weanling and yearling beef heifers grazing endophyte-infected tall fescue pastures

Growth and ovarian function of crossbred beef heifers grazing low and high endophyte-infected tall fescue pastures were studied for 2 successive years. In April of each year, 20 weanling and 20 yearling heifers were included in the study. All heifers were weighed at 28-d intervals for 112 d. Blood samples were collected from each heifer on Day 0 and +7 of each of five 28-d periods and analyzed for progesterone concentration. Heifers with progesterone concentrations >/= 1.5 ng/ml on either or both Day 0 and +7 were classified as having normal cyclic ovaries. High endophyte-infected fescue pastures adversely altered the ovarian activity (P < 0.05) of weanling heifers in both years. In each trial, average weight gains were lower (P < 0.05) in yearling and weanling heifers grazing the high endophyte-infected pastures than in heifers grazing low endophyte-infected pastures. In 1992, heifers were synchronized with PGF(2alpha) administered on Days 101 and 112. Blood samples were collected on 0, 4, 8 and 12 d after the second PGF(2alpha) injection for progesterone analysis. Heifers grazing high and low endophyte-infected pastures were pastured separately with 4 bulls each and were given heatmount detectors. At 96 h, less estrus activity was observed (P < 0.10; power=0.63) in weanling heifers grazing the high vs. low endophyte pastures although pregnancy rates were similar for all groups. Progesterone concentrations suggested that weanling heifers on the high endophyte pastures had a higher incidence of luteal dysfunction after PGF(2alpha) synchronization. In summary, high endophyte-infected pastures decreased growth in both weanling and yearling heifers, ovarian activity and luteal function were adversely altered in weanling heifers with subsequent decreased estrus response to estrus synchronization.     

Change in morphology of corpora lutea, central luteal cavities and steroid secretion patterns of postpartum suckled beef cows after melengestrol acetate with or without prostaglandin F2alpha

Change in morphology of the corpus luteum (CL) and patterns of progesterone and estradiol secretion after treatment with melengestrol acetate (MGA) were monitored in postpartum beef cows. Twenty Angus cows were randomly assigned to MGA or MGA + prostaglandin F(2alpha) (PGF) treatments. All cows were fed 0.5 mg of MGA per cow per day for 14 d. The MGA-treated cows (n = 10) were allowed to return to estrus spontaneously at the second estrus after withdrawal of MGA from the feed. The MGA + PGF-treated cows (n = 10) received an injection containing 25 mg of PGF(2alpha) 17 d after the last feeding of MGA. Cycle 1 was defined as the first luteal phase after MGA feeding and Cycle 2 represented the subsequent cycle or luteal phase after PGF. Blood sampling and transrectal ultrasonography of the ovaries was done daily through the completion of 2 estrous cycles upon removal of MGA from the feed. Blood samples were analyzed for plasma progesterone and estradiol concentrations. Area of CL and fluid-filled cavities within each CL were determined by ultrasonography. Concentrations of progesterone and area of CL were similar between cycles and treatments. Estradiol concentrations were higher (P < 0.05) in Cycle 2 than in Cycle 1. Fluid-filled cavities were larger (P < 0.001) in Cycle 1 than in Cycle 2 for both mid-luteal (Days 5 to 9) and late-luteal (Days 10 to 14) phases. Multiple CL (2 or more during 1 cycle) were observed in 5 cows. Progesterone concentrations and total area of luteal tissue did not change with respect to treatment or cycle, but CL morphology was altered in the first cycle after MGA treatment. Of the 19 cows that ovulated after withdrawal of MGA, 3 experienced a short luteal phase. These data characterize changes that occur among cows that are fed melengestrol acetate during the postpartum period and enhance observations from prior studies regarding MGA use.     

Conception, embryonic development and corpus luteum function in beef cattle open for two consecutive breeding seasons

High-fertility (control cows) and low-fertility (cows and heifers not pregnant after two consecutive breeding seasons — twice-open) cyclic bovine females were treated with a single injection of 1000 IU of human chrionic gonadotropin (HCG) or 100 μg of gonadotropin releasing hormone (GnRH) to enhance and/or hasten corpus luteum formation and progesterone secretion, and improve conception rate in the low-fertility females. Hormone treatments were administered to 38 parous control cows, 34 twice-open parous cows, and 27 twice-open nonparous heifers immediately after natural mating by a fertile bull. Blood samples were collected on Days 3, 6, 9, 12, and 18 after mating for determination of systemic progesterone concentrations. Pregnancy rate at necrospy approximately 33 days after mating (range 31–37) was higher in control cows (73.0%) than in twice-open cows (48.4%; P<0.05) or twice-open heifers (34.6%; P<0.01). Pregnancy rate was not affected by the HCG or GnRH treatment. The HCG treatment increased plasma progesterone concentrations in twice-open heifers but not in control or twice-open cows. Progesterone was unaffected by the GnRH treatment. Systemic progesterone concentrations were higher in control than in twice-open females but did not differ between pregnant and nonpregnant females of Days 3, 6, 9 and 12 after mating. Enhanced gonadotropin stimulation at estrus by injection of either HCG or GnRH did not increase pregnancy rate or systemic progesterone concentrations (except in HCG-treated twice-open heifers) in low- or high-fertility females. Lower pregnancy rates in twice-open females were not associated directly with the lower systemic progesterone concentrations.     

Biogenic amine regulation of bovine luteal progesterone production in vivo

Biogenic amines were administered using osmotic pumps placed subcutaneously in the neck region of regularly cycling, non-lactating dairy cows on Days 9-11 (oestrus = Day 0) of the oestrous cycle. Blood samples were collected using indwelling jugular catheters and the plasma progesterone concentrations were measured. Samples were collected at 4-h intervals for the first 12 h of treatment and thereafter at 12-h intervals for the remainder of the 72-h treatment period. After administration of various doses of noradrenaline, adrenaline and serotonin (0.5-2.0 micrograms/kg/h) significant elevation of plasma progesterone was achieved at a dosage of 2.0 micrograms/kg/h (P less than 0.01). The response to adrenaline was greater than that observed for noradrenaline and serotonin (P less than 0.05). Within-treatment comparison to pretreatment samples showed plasma progesterone concentrations to increase within 4 h after the administration of noradrenaline, adrenaline and serotonin (P less than 0.05) and this enhancement was maintained throughout the treatment period (P less than 0.05). The elevation in plasma progesterone concentrations induced by noradrenaline, adrenaline and serotonin was independent of changes in circulating concentrations of luteinizing hormone. These results support a physiological role for endogenous biogenic amines in the control of bovine luteal progesterone production.     

Milk fat progesterone concentrations in goats and early pregnancy diagnosis

Blood and milk samples from foremilk during afternoon milking, were simultaneously collected from 285 dairy goats. In experiment 1, fiva cyclic goats were sampled daily for 21 days. In experiment 2, 280 females from 9 flocks were submitted to sampling 21 days after insemination. In addition, some milk samples were divided in two parts, after which one was frozen and the other kept at +4 degrees C until assay. Progesterone concentrations were measured in blood, whole milk and milk fat by radioimmunoassay. No difference in whole milk or fat progesterone levels was found between frozen and refrigerated milk samples. Milk butterfat progesterone concentrations paralleled those in plasma or whole milk throughout the estrous cycle and ranged from about 20 ng/ml at estrus to about 400 ng/ml in mid-luteal phase. The ratio of mid-luteal phase progesterone levels to those seen in the estrous period was over 20 in fat and in blood. This ratio was very much lower in whole milk. Consequently the determination of pregnant and non-pregnant goats from the samples collected 21 days after service was very much easier and accuracy was better when the progesterone content was assayed from milk fat than from whole milk. It was concluded that early pregnancy diagnosis in goats can be done routinely by determination of progesterone levels in milk fat.     

Luteal function and conception in lactating cows and some factors influencing luteal function after first insemination

The objective of this study was to investigate the types and incidence of luteal sub-function in lactating cows after artificial insemination (AI) and their relationship with pregnancy, and to clarify the relationship between luteal function and parity, body condition score (BCS), milk yield, and dietary intake. In 19 cows, milk samples were collected daily from AI to confirmation of pregnancy. Milk progesterone concentrations were determined by EIA. Based on peak progesterone concentration and the day of onset of luteal phase, 15 of 30 progesterone profiles (50%) were normal, with progesterone concentration reaching 1.0 ng/ml within 5 days after insemination and > or =2.0 ng/ml thereafter. In addition, 6 (20%) were insufficient, (progesterone concentration remained < 2.0 ng/ml), 5 (17%) were delayed (progesterone reached 1.0 ng/ml after 5 days), 2 (7%) were both delayed and insufficient, one (3%) was short (progesterone >1.0 ng/ml for only 7 days), and one (3%) remained basal. Cows with a normal profile had a higher (P < 0.05) pregnancy rate than those with an abnormal profile (87% versus 33%, respectively). The amount of progesterone secreted in milk after first AI, as indicated by progesterone area under curve (AUC), was negatively correlated with milk yield (r = -0.83, P < 0.01), dry matter intake (r = -0.81, P < 0.05), total digestible nutrients (r = -0.82, P< 0.05), and digestible crude protein (r = -0.79, P <0.05). Cows that produced more milk and consumed more dry matter had less progesterone during the luteal phase. In conclusion, abnormal luteal function was associated with reduced pregnancy rates and high milk production and increased dietary intake during breeding were associated with reduced progesterone concentrations.     

Oviductal progesterone concentration and its spatial distribution in cyclic and early pregnant cows

Changes and local distribution of oviductal progesterone (P(4)) concentration during the estrous cycle and early pregnancy in cows were investigated. Intact reproductive tracts were collected from 16 Holstein cows at an abattoir. Samples were classified in to 4 stages (follicular, postovulatory, luteal and early pregnant,< 20 d) based on visual observation of corpus luteum (CL), uterine characteristics and luteal P(4) concentrations. Oviducts were separated from the uterus at the utero-tubal junction and divided into 4 parts: fimbriae, proximal, medial and distal parts. Luteal tissue samples were also collected. Progesterone levels in oviductal and luteal tissues were determined by radioimmunoassay (RIA). Comparatively higher (P < 0.001) P(4) levels were found in stages with a functioning CL ( luteal phase and early pregnancy) than in those with a regressing CL (follicular phase and post ovulation). The oviduct ipsilateral to the CL bearing ovary during the luteal phase and early pregnancy showed higher ( P < 0.001) P(4) concentrations than the contralateral side. Such a difference was not observed during the follicular phase or post ovulation. The ipsilateral oviduct to the functioning CL at early pregnancy showed higher (P <0.05) P(4) levels than at the luteal phase, while no significant difference in luteal P(4) levels between these 2 stages was observed. Neither were any differences in P(4) concentration within the oviduct observed during any phase of the estrous cycle or during early pregnancy. A positive relationship between luteal and oviductal P(4) concentrations was noted. In conclusion, changes in P(4) levels in the oviduct depend on the location and functional stage of the CL. Localized levels of P(4) in the oviduct may be due to local delivery of P(4) from the CL.     

Evaluation of models to induce low progesterone during the early luteal phase in cattle

Two experiments were designed to evaluate models for generation of low circulating progesterone concentrations during early pregnancy in cattle. In Experiment 1, 17 crossbred heifers (Bos taurus) were assigned to either prostaglandin F_2α (PGF_2α) administration on Days 3, 3.5, and 4 (PG3; n = 9) or to control (n = 8). Blood samples were collected from heifers from Days 1 to 9 for progesterone assay. Progesterone concentrations were decreased (P < 0.03) between 18 and 48 h after first PGF_2α treatment in heifers assigned to PG3 compared with that of controls. In Experiment 2, 39 crossbred heifers detected in estrus were inseminated (Day 0) and assigned to either (1) PGF_2α administration on Days 3, 3.5, and 4 (PG3; n = 10), (2) PGF_2α administration on Days 3, 3.5, 4, and 4.5 (PG4; n = 10), (3) Progesterone Releasing Intravaginal Device (PRID) insertion on Day 4.5 with PGF_2α administration on Days 5 and 6 (PRID + PGF_2α; n = 10), or (4) control (n = 9). Blood samples were collected daily until Day 15, and conceptus survival rate was determined at slaughter on Day 16. Progesterone concentrations during the sampling period in the PG3 and PG4 groups did not differ but were less than that of controls (P < 0.01). After an initial peak, progesterone concentrations in the PRID + PGF_2α group were similar to that of controls. More heifers in the PG4 group (6 of 10) had complete luteal regression than did those in the PG3 group (3 of 10). Conceptus survival rate on Day 16 did not differ between groups. There was a significant correlation between progesterone concentration on Days 5 and 6 and conceptus size on Day 16. In summary, treatment with PGF_2α on Days 3, 3.5, and 4 postestrus appeared to provide the best model to induce reduced circulating progesterone concentrations during the early luteal phase in cattle.     

Effect of short-term treatment with bovine somatotropin at estrus on conception rate and luteal function of repeat-breeding dairy cows.

We studied the effect of recombinant bovine somatotropin (rbST) at the time of estrus on progesterone concentrations and conception rates of repeat-breeding Holstein cows. We used repeat-breeding cows of varied parity (n = 510). All the animals were clinically healthy and had had at least three unsuccessful services before entering the study. After detection of estrus, the cows were randomly assigned to either a treated (n = 201) or a control (n = 309) group. The animals in the treated group were given rbST (500 mg s.c.) at the time of estrus and again 10 d later. Artificial insemination was performed 12 h after the first detection of estrus. In order to evaluate the effect of rbST on luteal function, blood samples were taken from 10 cows in each group every 3 d for 18 d, starting on the day of insemination (Day 0) to determine progesterone concentrations. Conception rates were significantly higher (P < 0.05) in the cows treated with rbST (29.3%) than in the control cows (16.9%). The effects of rbST were maximal in cows with 8 or more previous unsuccessful services and in cows with 2 to 4 calvings. Progesterone concentrations tended to be higher in nonpregnant cows that were treated with rbST than in those that were not treated. The difference between groups was significant (p < 0.05) on Day 18 after insemination. In pregnant cows there were no significant differences in progesterone concentrations between treated and nontreated animals at any time. Treatment with rbST at estrus improved the conception rate of repeat-breeding Holstein cows. This effect was associated with an increase in circulating progesterone concentrations on Day 18.