Uterine involution and postpartum ovarian activity in Nili-Ravi buffaloes

Uterine involution and postpartum ovarian activity were studied in 53 Nili-Ravi buffaloes. Mean intervals to uterine involution (26 days), regression of the corpus albicans of pregnancy (22 days), resumption of follicular activity (21 days) and first postpartum estrus (56 days) were not affected by the month of calving or age. Mean interval to formation of first corpus luteum (CL) after calving as indicated by progesterone in plasma (>/= 1.5 ng/ml) was 23.8 +/- 1.7 days, but only 52% of these CL were palpable. The number of CL formed before first postpartum estrus ranged from zero to five per buffalo; mean values based upon progesterone and palpation were 1.6 +/- 1.3 and 0.8 +/- 0.2, respectively. Based upon either progesterone or palpation, length of first postpartum luteal phase (7.9 or 6.6 days) was shorter than the luteal phase immediately preceeding the first estrus (12.1 or 8.9 days). Intervals from regular cyclic ovarian activity was not established until first estrus and intervals from the end of one luteal phase to the onset of the next were as long as three weeks. High concentrations of progesterone (>/= 1.5 ng/ml) on the day of behavioral estrus were seen in 23% of the buffaloes studied.     

Evidence for a role of intrauterine infections in the pathogenesis of cystic ovaries in postpartum dairy cows

Patterns of uterine microbial recovery and serum concentrations of prostaglandin F(2alpha) metabolite (PGFM), cortisol, luteinizing hormone (LH) and progesterone (P4) were determined in normal postpartum dairy cows (n = 12) and in postpartum cows that developed cystic ovaries (n = 12). Palpation per rectum, ultrasound examinations of the reproductive tract and endometrial swab harvest were carried out once every 4 d during the first month postpartum. Daily blood samples were collected during the first 30 d postpartum and every other day until Day 60 postpartum for hormone assay. Bacterial growth densities of cultures of uterine swabs were high in cows that developed cystic ovaries. Cysts were detected between Day 8 and 16 postpartum and persisted for a period of 18.6 +/- 9.9 d (range 8 to 41 d), followed by spontaneous regression and ovulations. Serum PGFM and cortisol were elevated for several days prior to detection of cystic ovaries but not prior to first postpartum ovulations. Serum LH concentrations in cystic cows were at basal concentrations prior to discovery of cysts. The results suggest that postpartum intrauterine infections may provoke increased secretion of prostaglandin F(2alpha) and cortisol associated with the formation of cystic ovaries in dairy cows.     

Effect of days postpartum and exogenous GnRH on reproductive hormone and ovarian changes in postpartum suckled beef cows

Two experiments were conducted to determine the effect of days postpartum and exogenous gonadotropin releasing hormone (GnRH) on reproductive hormone and ovarian changes in postpartum suckled beef cows. In experiment 1, eight suckled cows were bled at .5 hour intervals for 4 hours on days 7, 14, 21 and 28 postpartum. Although mean concentrations of plasma luteinizing hormone (LH) were positively correlated with days postpartum, mean concentrations did not differ. The mean maximum change and the variance of plasma LH were low on days 7, 14, 21 and 28 postpartum. Although the number of cows with an ovarian follicle and follicular size increased with days postpartum, mean concentrations of estradiol-17beta did not change. The interval from parturition to the first detected ovarian follicle and the first postpartum estrus was 17.5 +/- 2.6 days and 36.0 +/- 2.2 days, respectively. An elevation in plasma progesterone was detected about one week prior to the first postpartum estrus in 6 of the eight cows in the absence of corpora lutea. In experiment 2, gonadotropin releasing hormone (GnRH) induced ovulation in 4 of the 8 cows treated on day 27, 28 or 29 postpartum whereas none of the 8 saline treated cows ovulated to treatment. The interval from parturition to first estrus and conception were similar for both groups (P >.10).     

Effect of estradiol-17 beta on peripheral plasma concentration of 15-keto-13,14-dihydro PGF2 alpha and luteolysis in cyclic cattle

Friesian heifers (n = 10) were assigned randomly to receive an intravenous injection of estradiol-17 beta (E2; 3 mg) or saline:ethanol vehicle solution (6 ml; 1:1) on day 13 of the estrous cycle. Blood was collected from the jugular vein by venipuncture into heparinized vacutainer tubes at 30 minute intervals for 2 hours (h) preinjection, 10.5 h postinjection and then at 3 h intervals until estrus. Repeated hormone measurements of 15-keto-13,14-dihydro-PGF2 alpha (PGFM) and progesterone (P4) were evaluated by split-plot analysis of variance. Mean concentration of PGFM for the 12.5 h acute sampling phase was 164.1 +/- .14 pg/ml. A treatment by time interaction was detected (P less than .01). After treatment with E2, PGFM concentrations began to increase at approximately 3.5 h, reached a mean peak of 330.4 +/- 44.5 pg/ml (n = 5) at 5.5 +/- .3 h, and returned to basal concentration by 9.0 +/- .6 h. Vehicle treatment did not alter concentrations of PGFM. Injection of E2 on day 13 of the estrous cycle caused luteolysis (P4 concentration less than 1 ng/ml) to occur earlier following injection (96.9 +/- 10.6 h less than 153.6 +/- 17.7 h; P less than 0.05) than did the vehicle control treatment. During the chronic sampling phase of 3 h intervals, 39 of 606 samples (6.4%) were classified as PGFM spikes (323.0 +/- 50.0 pg/ml); 21 (53%) of the spikes occurred at a mean interval of 18.9 +/- 3.86 h before the time of completed luteolysis. Exogenous E2 induced an acute increase in PGFM that may be indicative of uterine PGF2 alpha production. Peaks of PGFM in plasma were temporally associated with luteolysis on a within cow basis.     

Effects of intrauterine infection on the function of the corpora lutea formed after first postpartum ovulations in dairy cows

This study was carried out to determine the relationship between postpartum intrauterine infections, endocrine patterns and the function of corpora lutea formed following the first postpartum ovulations in dairy cows. Blood samples were collected daily starting from the day of parturition until 30 d after parturition or until the second postpartum estrus, whichever occurred first. Sera were assayed for progesterone (P(4)), prostaglandin F(2alpha) metabolite (PGFM), and luteinizing hormone (LH) concentrations. Palpations per rectum and real-time ultrasound scanning of the reproductive tracts were carried out in all cows once every 4 d for 1 mo, starting from Day 4 after parturition. In addition, endometrial swabs were collected aseptically from each cow once every 4 d during the first month postpartum. The swabs were cultured for aerobic and anaerobic bacteria. Twelve cows (60%) exhibited short estrous cycles (SC; 6 to 14 d long) following first postpartum ovulations. The mean preovulatory LH surges and LH patterns during the first postpartum cycles were similar in both groups, leading us to believe that lack of luteotrophic stimulation was not a factor in the occurrence of SC. Bacterial isolations were frequent in SC cows. The occurrence of moderate to heavy bacterial growth patterns and the repeated isolations of the similar organisms during postpartum suggests the persistence of uterine infections in SC cows. Increases in PGFM concentrations prior to luteolysis in SC cows were associated with moderate to heavy infection. Thus, postpartum uterine infections do not appear to affect ovulations, but prostaglandin (PGF(2alpha)) released in response to uterine infection may contribute to early demise of the corpus luteum formed after the first postpartum ovulation.     

Photoperiodic alteration of postpartum reproductive function in suckled cows

Three experiments were conducted using a total of 41 cows to determine if photoperiod modulates the establishment of postpartum estrous cycles and conception. Cows calving in the autumn and winter were exposed to either 18 hr light/day (18L:6D) or natural photoperiods. In Exp. 1, cows receiving 18L:6D had shorter (P<0.025) intervals from calving to estrus (61 +/- 3.8 days) than cows not receiving supplemental light (154 +/- 23.9 days). The same was true for primiparous cows in Exp. 2 (76 +/- 5.5 days vs 153 +/- 38.0 days; P<0.06) but not for the multiparous cows in Exp. 2 (56 +/- 5.2 days vs 40 +/- 7.4 days) or for all cows in Exp. 3 (60 +/- 10.1 days vs 70 +/- 13.5 days). Because conception rate was higher for cows exposed to 18L:6D for the multiparous cows in Exp. 2 and all cows in Exp. 3, interval to conception was significantly shorter for animals exposed to 18L:6D in all experiments. Generally, interval from calving to uterine involution was also reduced by exposure to 18L:6D. No effects of photoperiod were observed on body weight changes, serum levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) or estradiol or on estradiol-induced release of gonadotropins. It was concluded that in certain situations day length can hasten estrus and conception in postpartum cows. The effect of photoperiod interacts with other conditions, one of which is parity. The endocrine basis for these effects are not known.     

Evaluation of timed insemination during summer heat stress in lactating dairy cattle

We wished to compare the effect of summer heat stress on pregnancy rate in cows that were inseminated at a set interval associated with a synchronized ovulation vs those inseminated upon routine estrus detection. The study was carried out on a commercial dairy farm in Florida from May to September 1995. Lactating dairy cows were given PGF2 alpha (25 mg i.m.) at 30 + 3 d postpartum and randomly assigned to be inseminated at a set time (Timed group) or when estrus was detected (Control group). Cows in the Timed group were synchronized by sequential administration of Buserelin (8 micrograms i.m.) on Day 0 at 1600 h, PGF2 alpha (25 mg i.m.) on Day 7 at 1600 h and Buserelin (8 micrograms i.m.) on Day 9 at 1600 h. They were inseminated on Day 10 between 0800 and 0900 h (Day 9 + 16 h). Cows in the Control group were given PGF2 alpha at 57 + 3 d postpartum and inseminated when detected in estrus. Estrus detection or insemination rate for control insemination cows was 18.1 +/- 2.5% versus 100% for time inseminated cows (P < 0.01). Mean interval from PGF2 alpha to insemination was shorter for time inseminated cows (3 +/- 2.1 d < 35.5 +/- 1.9 d; P < 0.01). Pregnancy rate was greater for time inseminated cows (13.9 +/- 2.6 > 4.8 +/- 2.5%; P < 0.01) as was overall pregnancy rate by 120 d postpartum (27.0 +/- 3.6 > 16.5 +/- 3.5%; P < 0.05). Number of days open for cows conceiving by 120 d postpartum was less for time inseminated cows (77.6 +/- 3.8 < 90.0 +/- 4.2 d; P < 0.05), as was interval to first service (58.7 +/- 2.1 < 91.0 +/- 1.9 d; P < 0.01). Services per conception were greater for time inseminated cows (1.63 +/- 0.10 > 1.27 +/- 0.11; P < 0.05). The timed insemination program did improve group reproductive performance. However, the timed insemination program will not protect the embryo from temperature-induced embryonic mortality, but management limitations induced by heat stress on estrus detection are eliminated. An economical evaluation of the timed insemination program indicates an increase in net revenue per cow with implementation of timed insemination for first service during the summer months.     

Seasonal variation in serum levels of steroid hormones and their relation with seminal quality and libido in buffalo bulls

Blood samples from 15 breeding male Murrah buffaloes were collected during the winter, summer and monsoon seasons. Seminal characteristics and sexual behaviour were also studied. Serum samples were analysed for testosterone, progesterone and estradiol-17beta levels by radioimmunoassay. The studies showed significantly lower values for testosterone during winter (0.53 +/- 0.06 ng/ml) than during summer (1.22 +/- 0.19 ng/ml) and monsoon (1.06 +/- 0.12 ng/ml). The progesterone level was lowest during monsoon (84 +/- 9 pg/ml), intermediate during winter (115 +/- 14 pg/ml) and highest during summer (224 +/- 24 pg/ml). The mean level of estradiol-17beta was almost double (9 +/- 0.7 pg/ml) during monsoon as compared to winter (5 +/- 0.1 pg/ml). The correlations between hormone levels, seminal characteristics and sexual behaviour were of low magnitude.     

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.     

Assessment of reproductive parameters in female Dwarf goat (Capra hircus) on the basis of progesterone profiles

A study was undertaken to look into the reproductive performance of female Dwarf goats reared under traditional conditions at NIAB Farm, Faisalabad, Pakistan. The serum progesterone profile was used to monitor various reproductive parameters (length of postpartum period, resumption of cyclicity, gestation period, prepartum period, parturition) in two lots of goats. Litter size, birth weight of kids and kidding interval were also observed. Most of the animals conceived within 15-59 days of postpartum period. All the does conceived at first or second estrus. During gestation period, higher levels of progesterone were maintained with wide variations falling in the range of 3-13 ng ml(-1). However, a few days before parturition a decline was noticed at 6+/-0.9 days and it reached to the basal level of 0.1 ng ml(-1) after the completion of parturition process. The length of gestation period was found to be 145.8+/-5 days in the first lot and 145.2+/-4 days in the second lot. A very short kidding interval (203.7+/-46 days) and considerably bigger litter size (1.8+/-0.8) was observed. All the parturitions were normal and a considerable weight gain (8.2+/-0.3 kg) of mothers was recorded during pregnancy. The initial birth weight of kids was averaged as 2.1+/-0.5 kg in the first and 1.6+/-0.2 kg in the second lot. It was concluded that Dwarf goat has short gestation length, postpartum period and kidding interval along with multiple births being common. Due to these factors, its reproductive efficiency can be exploited for efficient goat meat production.     

Milk progesterone profiles in various reproductive states in dairy buffaloes under field conditions

Fifty-one dairy buffaloes in the last two months of gestation were selected at seven private peri-urban farms in the Peshawar district. Observations were recorded in buffaloes during normal (NBS, August to January) and low breeding seasons (LBS, February to July). After parturition, rectal examination of reproductive organs was carried out. Estrus detection was made through visual observation and the use of intact bull. Postpartum ovulation was confirmed by ovarian palpation per rectum and milk progesterone levels (MPL), determined through radio-immunoassay. MPL was higher (p < 0.01) at various intervals in NBS calves (1.97 +/- 0.30 ng/ml) as compared to LBS calves (0.68 +/- 0.08 ng/ml). During LBS, MPL remained < 0.30 ng/ml up to the third fortnight and started rising later, reaching a peak of 1.27 ng/ml during the sixth fortnight. During NBS, there was a sharp rise in MPL during the second fortnight, reaching 3.64 ng/ml during the sixth fortnight. MPL was significantly different on different experimental farms (p < 0.01). MPL reached the lowest levels on the day of estrus (0.10 ng/ml), reached it's peak on day 7 and started declining on day 17 of estrus. MPL showed two postpartum elevations. In true anestrus buffaloes, MPL remained consistently low. However, in the anestrus period, silent ovulations were also noted, as reflected by increasing MPL without estrus signs. In pregnant buffaloes, MPL remained > 1 ng/ml. Results of the study showed that the low postpartum reproductive performance in dairy buffaloes during LBS was primarily due to inadequate functioning of the corpus luteum in secreting optimum concentrations of progesterone. The higher incidence of silent estrus during LBS indicated improved management for the detection of estrus.     

Effect of early postpartum treatment with prostaglandin F2alpha on subsequent fertility in the dairy cow

Eighty Holstein dairy cows were treated with 25 mg of prostaglandin F2alpha (PGF2alpha) on Days 14 to 16 post calving. Eighty-four herd mates served as saline controls in the double blind study. The reproductive parameters used to measure fertility were mean days to first service on all cows and mean days open, first service conception rates and services per pregnancy on cows that became pregnant. Mean days to first service was similar in both groups (71.8 +/- 27, treated; 68.5 +/- 28.6, controls; P = 0.5352). The mean days open was 98.6 +/- 52.0 d for treated cows compared to 118.8 +/- 71.2 d for controls (P = 0.0680). First service pregnancy rates (treated, 41.3%; control, 35.7%) were not significantly different (P = 0.0630); however, the mean services per pregnancy (treated, 1.64; control, 2.33) were significantly (P = 0.0021) improved in the treated group. Ten cows in the treated group and twelve cows in the control group were diagnosed as having retained fetal membranes and/or metritis. For treated and control cows mean days to first service were 82.2 +/- 34.8 d and 82.8 +/- 58.7 d (P = 0.5652). Days open were 97.0 +/- 32.5 d and 133.4 +/-58.4 d (P = 0.3636); services per conception were 1.83 and 2.50 (P = 0.3178), respectively. In all treated cows reproductive parameters were similar whether cows had high serum progesterone ( > 1 ng/ml) or low serum progesterone ( < 1 ng/ml) on the treatment day. This study suggests that early postpartum treatment of lactating dairy cows with prostaglandin produces an improvement in fertility.     

Effect of estrus synchronization with Syncro-Mate-B((R)) on serum luteinizing hormone, progesterone and conception rate in Brahman heifers

Twenty-two estrous cyclic, 2-yr-old Brahman heifers were randomly assigned to receive either estrus synchronization with Syncro-Mate-B((R)) (SMB; 11) or no treatment (Control; 11). Blood samples were collected via tail vessel puncture at onset of estrus and daily thereafter until Day 11 after estrus. Blood samples were also collected from five SMB and five Control heifers at 0, 4, 8 and 12 h after the onset of estrus. All samples were processed to yield serum and stored at -20 degrees C until radioimmunoassay. Heifers were inseminated by one technician using semen from a single ejaculate of a Brahman bull 12 h after the onset of estrus. All SMB heifers exhibited estrus within 72 h of implant removal. All heifers had corpora lutea (CL) detected by rectal examination 8 to 12 d following estrus. Serum luteinizing hormone (LH) was not affected by treatment, time (4 - h intervals) or an interaction of treatment by time (P > 0.10). Independent analysis with h indicated that at h 12, SMB (2.2 +/- 0.06 ng/ml) had lower LH than did control heifers (8.9 +/- 2.1 ng/ml). Serum progesterone increased from Day 1 through Day 12 in all heifers, which is indicative of functional CL. Serum progesterone was affected by treatment (P < 0.0001) and time (d intervals; P < 0.10). Progesterone elevation was lower (P < 0.05) and area under the progesterone curve was lower (P < 0.03) in SMB (5.6 +/- 0.5 ng/ml, 32.0 +/- 4.5 units, respectively) when compared with control heifers (7.0 +/- 4 ng/ml, 43.7 +/- 2.4 units, respectively). Conception rate was lower (P < 0.01) in SMB heifers (2 of 11) than in control heifers (8 of 11). The lowered conception rate in SMB treated Brahman heifers may be due to altered timing of LH release following estrus, resulting in an altered time of ovulation.     

Effects of calving-related disorders on prostaglandin, calcium, ovarian activity and uterine involution in postrartum dairy cows

Postpartum ovarian activity, uterine involution and plasma concentrations of calcium and 15-keto-13, 14 dihydro-prostaglandin F2alpha (PGFM) were assessed in dairy cows with retained fetal membranes (n=10) and milk fever (n=10) at parturition. In addition, calcium and PGFM were evaluated in dairy cows affected with uterine prolapse (n=10) and pyometra (n=14). Cows with retained fetal membrane averaged 24.2+/-3.7 d until their first postpartum ovulation, while controls averaged 29.0+/-3.7 d (P>0.10). In cows with retained fetal membranes, the difference in follicular activity between the contralateral and ipsilateral ovaries in relation to the previously gravid uterine horn was appreciably greater post partum when compared with that of the controls. Cows with milk fever had an average of 30.8+/-3.1 d until their first postpartum ovulation, while control cows had an average of 20.4+/-3.3 d (P<0.05). The mean diameter of the uterine horns in cows with milk fever was greater (P<0.05) compared with that of the controls between Days 15-32 post partum. Concentrations of plasma calcium were lower in cows with retained fetal membranes within 24 h after parturition and during the first week post partum than in the controls (6.27+/-0.18 vs 7.40+/-0.18 mg/100ml, P<0.05). Concentration of calcium was lower (P<0.05) in cows with milk fever on Day 1 prior to treatment (4.68+/-0.40 < 5.8+/-0.45 mg/100ml) than in control cows; however, the calcium (Ca) level was not different during the subsequent 7 d post partum after treatment. Cows with uterine prolapse had lower concentrations of Ca during the first 7 d post partum than the controls (6.10+/-0.15 vs 7.33+/-0.12mg/100ml; P<0.01). Cows with pyometra had higher (P<0.05) concentrations of plasma PGFM than the controls (208.+/-13.2 > 138.1+/-15.2).     

Reproductive performance of dairy cows following treatment with cloprostenol 26 and/or 40 days postpartum: a field trial

One hundred and seventy Holstein Friesian cows were randomly assigned to receive either 500 ug cloprostenol or saline placebo on Day 26 postpartum followed by 500 ug cloprostenol or saline on Day 40 postpartum. Four treatment groups were formed: Group 1 - saline (Day 26)/saline (Day 40); Group 2 - cloprostenol/(Day 26) saline (Day 40); Group 3 - saline (Day 26)/cloprostenol (Day 40); Group 4 - cloprostenol (Day 26)/cloprostenol (Day 40). Double blind techniques were used in administering treatments and in assessing the response to treatment. Palpation of the reproductive tract per tectum and uterine biopsies were performed on 92 cows prior to each treatment at Day 26 and Day 40 postpartum. Progesterone concentrations were determined on milk samples collected prior to treatment. There were no significant differences among treatment groups with respect to services per conception, number of heats detected before first service and culling for infertility. Cloprostenol treatment at Day 26 appeared to delay the first estrus, but it reduced the number of days to conception after the first service. Cows receiving cloprostenol at Days 26 and/or 40 had a decreased calving-to-conception interval compared to controls (P = 0.01). Sequential therapy with two doses of cloprostenol resulted in slightly better reproductive performance than either treatment on Day 26 or 40 alone. Treatment with cloprostenol resulted in a decrease in the subsequent incidence of pyometra (P < 0.05). It is concluded that in the herd studied, cloprostenol therapy at Day 26 and/or 40 postpartum was beneficial to reproductive performance. Although it was anticipated that cloprostenol would be more effective in cows with elevated progesterone levels, the opposite was observed at the Day 26 cloprostenol treatment. Uterine biopsy at Days 26 and/or 40 had a detrimental effect on subsequent reproductive performance.     

Effect of alfaprostol on postpartum reproductive efficiency in brahman cows and heifers

Brahman cows (n = 54) and heifers (n = 18) were randomly allotted by calving date, sex of calf and age to one of four treatment groups. Group 1 received no treatment (control), Group 2 received 5 mg alfaprostol (AP) i.m. on Day 21 postpartum, Group 3 received 5 mg AP i.m. on Day 32 postpartum and Group 4 received 5 mg AP i.m. on both Days 21 and 32 postpartum. Blood samples were collected via tail vessel puncture at 30 min-intervals for 8 h from half the animals in each group on Days 21 and 32 postpartum, with AP injection administered 2 h after sampling had begun. All cows were bled at weekly intervals. Samples were processed to yield serum and stored at -20 degrees C until assayed for luteinizing hormone (LH) or progesterone (P(4)). All cattle were maintained with epididymectomized marker bulls and were artificially inseminated (A.I.) at first estrus. Serum P(4) was below 1 ng/ml prior to AP treatment in all animals and did not differ (P > 0.10) between treatments. Alfaprostol treatment affected mean postpartum interval (from parturition to return to standing estrus and subsequent corpus luteum formation with serum progesterone concentrations > 1 ng/ml; P < 0.08). The control group (84.8 +/- 7.9 d) did not differ from Group 2 (86.3 +/- 11.1 d) or Group 3 (66.7 +/- 5.5 d) but did differ (P < 0.09) from Group 4 (65.1 +/- 6.4 d). Cattle injected on Day 32 had a shorter (P < 0.01) postpartum interval than those not receiving treatment on that day (65.9 +/- 4.2 vs 85.7 +/- 6.8 d). Pregnancy rate was affected (P < 0.05) by AP treatment. The control group (72.2%) did not differ (P > 0.10) from any group but, Group 2 (50.0%) was lower (P < 0.04) than Group 3 (83.3%) and (P < 0.02) Group 4 (88.9%). Cattle treated on Day 32 (Groups 3 and 4) had a higher (P < 0.02) pregnancy rate (86.1%) than those not treated on Day 32 (Groups 1 and 2; 61.1%). Serum LH was affected by day (P < 0.0003) and treatment by day (P < 0.07) but not by time (P > 0.10). Treatment Group 3 (P < 0.08) and Group 4 (P < 0.0003) mean LH concentrations differed between Days 21 and 32 postpartum. Cattle receiving AP treatment on Day 32 postpartum had a higher (P < 0.04) cumulative frequency of return to estrus by 100 days postpartum than nontreated cattle.     

Conception rates and serum progesterone concentration in dairy cattle administered gonadotropin releasing hormone 5 days after artificial insemination

The objectives of this study were to determine the effect of administration of exogenous GnRH 5days after artificial insemination (AI) on ovarian structures, serum progesterone concentration, and conception rates in lactating dairy cows. In experiment 1, 23 Holstein cows were synchronized using the Ovsynch protocol. Five days after AI (day 0) cows were assigned randomly to receive either saline (saline; n=11) or 100microg GnRH (GnRH; n=12). To examine ovarian structures, ultrasonography was performed on day 1 and every other day beginning on day 5 until day 13. On days 5 and 13 blood samples were obtained to measure serum progesterone concentrations. All cows in the GnRH-treated group developed an accessory corpus luteum (CL), whereas cows in the saline group did not. Mean serum progesterone concentrations did not differ between GnRH and saline groups on day 5 (1.64+/-0.46ng/ml versus 2.04+/-0.48ng/ml). On day 13 serum progesterone concentrations were greater (P<0.05) in the GnRH group compared with saline (5.22+/-0.46ng/ml versus 3.36+/-0.48ng/ml). In experiment 2, 542 lactating cows, at two different commercial dairies, were used to test the effect of administering GnRH 5 days after AI on conception rates. Cows were synchronized and detected for estrus according to tail chalk removal. Cows detected in estrus received AI within 1h after detection of estrus. Five days after AI, cows were assigned randomly to receive either GnRH (n=266) or saline (n=276). Pregnancy status was determined by palpation per rectum of uterine contents approximately 40 days after AI. There was no effect of farm on conception rate. There was no effect of treatment as conception rates did not differ between GnRH and saline groups (26.7% GnRH versus 24.3% saline). Regardless of treatment, days in milk, parity, milk yield, and number of services had no effect on the odds ratio of pregnancy. In summary, the results of this study indicated that GnRH administered 5 days after AI increased serum progesterone by developing an accessory CL but did not improve conception rates in dairy cattle.     

Chronic stress, hormone profiles and estrus intensity in dairy cattle

The objectives of the present study were to determine if lameness, a model for a natural chronic stressor, affects hormone concentrations in milk prior to estrus and/or the subsequent expression of estrus in the postpartum period. Dairy cows>20 days postpartum were scored for lameness and observed for estrus intensity using a weighted scoring system (>100 points=estrus=Day 0). Increasing lameness score was not associated with daily profiles of milk progesterone (throughout Days -18 to 0), estradiol (Days -6 to 2) or cortisol (Days -18 to 2) around estrus, maximum estradiol values or estradiol concentrations on Day 0. However, post hoc pair wise comparisons revealed that prior to estrus, severely lame cows had lower maximum progesterone concentrations compared to nonlame cows (1.3+/-0.1, 1.2+/-0.2, 0.7+/-0.1 ng/ml milk; P=0.042). Furthermore, severely lame cows expressed behavioral estrus with lower intensity (284+/-128 points, n=9) compared to moderately lame (662+/-310 points, n=9) or nonlame animals (583+/-275 points, n=18; P=0.05 and P=0.02, respectively). Resting concentrations of cortisol (Days 20-80 postpartum) did not vary between days postpartum or lameness score. The incidence of behavioral estrus was not affected by increasing lameness score, as 54.2%, 56.2% and 50.0% periods with low progesterone were associated with spontaneous estrus expression, respectively. Concluding, in this biological model of chronic stress, lameness did not affect the incidence of behavioral estrus but did reduce estrus intensity once ovarian cyclicity had resumed after calving. This reduced intensity of estrus was associated with lower maximum progesterone values prior to estrus but not abnormal daily cortisol or estradiol values in milk.     

Differential effects of progesterone treatment on the oxytocin-induced prostaglandin F2 alpha response and the levels of endometrial oxytocin receptors in ovariectomized ewes.

The oxytocin-induced uterine prostaglandin (PG) F2 alpha response and the levels of endometrial oxytocin receptors were measured in ovariectomized ewes after they had been given steroid pretreatment (SP) with progesterone and estrogen to induce estrus (day of expected estrus = Day 0) and had subsequently been treated with progesterone over Days 1-12 and/or PGF2 alpha over Days 10-12 postestrus. The uterine PGF2 alpha response was measured after an i.v. injection of 10 IU oxytocin on Days 13 and 14, using the PGF2 alpha metabolite, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), as an indicator for PGF2 alpha release. The levels of oxytocin receptors in the endometrium were measured on Day 14. During the treatment with progesterone, the peripheral progesterone concentrations were elevated and remained above 1.8 ng/ml until the morning of Day 14. The PGFM responses to oxytocin in untreated controls and SP controls were low on both Days 13 and 14 whereas the levels of endometrial oxytocin receptors in the same ewes were high. Treatment with progesterone either alone or in combination with PGF2 alpha significantly (p less than 0.04) increased the PGFM response on Day 14 and reduced the levels of endometrial oxytocin receptors; treatment with PGF2 alpha alone had no effect. It is concluded that progesterone promotes the PGFM response to oxytocin while simultaneously suppressing the levels of endometrial oxytocin receptors. PGF2 alpha treatment had no effect on either the uterine secretory response to oxytocin or the levels of oxytocin receptors in the endometrium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of estradiol-17beta on PGF and total protein content in bovine uterine flushings and peripheral plasma concentration of 13, 14-dihydro-15-keto-PGF(2alpha)

Two experiments were conducted to examine the effect of estradiol-17beta (E(2)-17beta) on content of immunoreactive prostagladin F(2)alpha (PGF, ng) and total protein (TUP, mg) in uterine flushings, as well as concentrations of 13, 14-dihydro-15-keto-PGF(2)alpha (PGFM) in plasma (Pg/ml). In experiment 1, Holstein heifers were utilized in a single reversal trial in which either E(2)-17beta (3 mg in 2 ml saline/ethanol 50:50; n=5) or vehicle alone (n=6) were given intravenously on day 14 or 15 of the estrous cycle (Period 1) following an induced estrus (day of estrus = day 0). Treatment (Trt) groups were reversed in Period 2 (Day 14 or 15 of the second estrous cycle). Jugular venous plasma was obtained before treatment (Oh), and at 5, 6, and 9h posttreatment (PT). Uterine flushings were collected nonsurgically in vivo , per cervix, via Foley catheter at 6h PT (20 ml of .9% saline per uterine horn). E(2)-17beta did not significantly alter (E(2)-17beta vs vehicle; x(-) +/- S.E.M.) PGF (1674 +/- .11 +/- 338.39 vs 1889.91 +/- 400.24 ng; P> .10) or TUP (33.25 +/- 2.57 vs 39.16 +/- 3.04 mg; P > .10). However, E(2)-17beta increased (P < .05) plasma PGFM (E(2)-17beta vs vehicle) after treatment (0h, 113.2 vs 163.8; 5h, 312.5 vs 203.9; 6h, 324.5 vs 198.0; 9h, 323.2 vs 246.8, pg/ml). In experiment 2, crossbred beef cattle received comparable treatments of either E(2)-17beta (n=5) or vehicle (n=5) on day 14 or 15 postestrus. Jugular venous plasma was obtained at 0h PT, and at 6h PT. Uterine flushings (1.9% saline, 20 ml per uterine horn) and peripheral plasma were collected at slaughter. Estradiol-17beta increased PGF (30.07 +/- 5.94 vs 8.46 +/- 2.01 ng; P> <.05) in uterine flushings as well as PGFM in plasma (E(2)-17beta : 55.82 +/- 19.13 pg/ml, at 0h and 89.31 +/- 14.02 pg/ml, at 6h, vs saline: 103.46 +/- 50.73 pg/ml, at 0h and 17.78 +/- 14.22, at 6h). Estradiol-17beta stimulated uterine production and release of PGF and protein as measured in flushings (experiment 2) as well as plasma PGFM responses (experiments 1 and 2). Uterine and/or cervical stimulation of experiment 1 may have masked uterine response to E(2)-17beta.