Effects of propylene glycol drenching on energy balance, plasma glucose, plasma insulin, ovarian function and conception in dairy cows

We postulated that daily drenching of propylene glycol to cows in early lactation would increase plasma glucose and insulin concentrations and improve fertility in postpartum cows. Thirty-six Holstein cows were assigned to treatment or control groups. Each treatment cow was given 500 ml of propylene glycol by drenching daily from 7 to 42 days of lactation. Blood samples for glucose, insulin, nonesterified fatty acids (NEFA), and plasma urea N were collected at 0, 30, and 90 min postdrenching once weekly during 1-6 weeks. Blood samples were collected for progesterone analysis and cows were palpated three times per week until 11 weeks to assess ovarian status. Propylene glycol did not affect dry matter intake (DMI), milk yield or energy balance in treatment cows. After drenching, propylene glycol increased (P<0.01) plasma glucose and insulin and decreased (P<0.01) NEFA; plasma urea N of the treatment group tended (P=0.07) to be higher than that of the control group through 90 min. Days to first service, days open, and services per conception were not different between groups. Conception rates to first insemination were 33% in the control group and 57% in treated cows, but these were not significantly different. First ovulation of treatment cows occurred earlier than that of control cows (32.3 versus 44.5 days, P=0.06) and the length of the first luteal phase was longer in treated cows (13.1 versus 7.3 days, P<0.05). These data are consistent with the hypothesis that insulin is important for normal ovarian function. During negative energy balance, treatment with propylene glycol, which induced small increases in plasma concentrations of insulin, prevented the short luteal phase characteristic of the first estrous cycle in control cows.     

Comparison of endocrine changes,timing of ovulations,ovarian follicular growth,and efficacy associated with Estradoublesynch and Heatsynch protocols in Murrah buffalo cows (Bubalus bubalis)

Poor estrus expression and the difficulty encountered in predicting the time of ovulation compromise the reproductive efficiency of Murrah buffalo cows. Synchronization of ovulation and timed artificial insemination are able to precisely control the time of ovulation and thus avoid the need for estrus detection. Recently, the Estradoublesynch protocol (administration of a PGF2α injection 2 days before Heatsynch protocol; GnRH 0, PGF2α 7, estradiol benzoate [EB] 8) was developed that precisely synchronized ovulation twice, i.e., after GnRH and EB injections and resulted in satisfactory pregnancy rates in Murrah buffaloes. The present study was conducted on 104 cycling and 31 anestrus buffaloes to compare (1) the endocrine changes, timing of ovulations, ovarian follicular growth, and efficacy of Estradoublesynch and Heatsynch protocols in cycling and (2) the efficacy of Estradoublesynch and Heatsynch protocols for the improvement of fertility in cycling and anestrus Murrah buffalo cows. Ovulation was confirmed after all GnRH and EB treatments by ultrasonographic examination at 2-hour intervals. Plasma progesterone and total estrogen concentrations were determined in blood samples collected at daily intervals, beginning 2 days before the onset of protocols until the day of second ovulation detection. Ovulatory follicle size was measured by ultrasonography at six time points (first PGF2α administration of Estradoublesynch protocol every 2 days before the onset of Heatsynch protocol, GnRH administration of both protocols, 2 hours before ovulation detection after GnRH administration of both protocols, second PGF2α injection of Estradoublesynch protocol, PGF2α injection of Heatsynch protocol, EB injection of both protocols and, 2 hours before ovulation detection after EB administration of both protocols). Plasma LH, total estrogen, and progesterone concentrations were determined in blood samples collected at 30-minute intervals for 8 hours, beginning GnRH and EB injections, and thereafter at 2-hour intervals until 2 hours after the detection of ovulation. The first ovulatory rate was significantly higher (P < 0.05) in the Estradoublesynch protocol (84.6%) than that in the Heatsynch protocol (36.4%). The first LH peak concentration (74.6 ± 10.4 ng/mL) in the Estradoublesynch protocol was significantly higher (P < 0.05) than that of the Heatsynch protocol (55.3 ± 7.4 ng/mL). In Estradoublesynch protocol, the total estrogen concentration gradually increased from the day of GnRH administration coinciding with LH peak, and then gradually declined to the basal level until the time of ovulation detection. However, in Heatsynch protocol, the gradual increase in total estrogen concentration after GnRH administration was observed only in those buffalo cows, which responded to treatment with ovulation. In both Estradoublesynch and Heatsynch protocols, ovulatory follicle size increased by treatment with GnRH and EB until the detection of ovulation. The pregnancy rate after the Estradoublesynch protocol (60.0%) was significantly higher (P < 0.05) than that achieved after the Heatsynch protocol (32.5%). Satisfactory success rate using the Estradoublesynch protocol was attributed to the higher release of LH after treatment with GnRH, leading to ovulation in most of the animals and hence creating the optimum follicular size at EB injection for ovulation and pregnancy to occur.     

Antiluteogenic effects of serial prostaglandin F2α administration in cycling mares

A single dose of PGF2α does not consistently induce luteolysis in the equine CL until at least 5 days after ovulation, leading to the erroneous assumption that the early CL is refractory to the luteolytic effects of PGF2α. We hypothesized that serial administration of PGF2α in early diestrus would induce a return to estrus similar to mares treated with a single injection in mid-diestrus, and fertility of the induced estrus would not differ. The objectives of the study were to evaluate the effects of the 2 approaches as reflected by: (1) concentrations of plasma progesterone; (2) interovulatory and treatment-to-ovulation intervals; (3) the proportion of mares pregnant after artificial insemination. The study consisted of a balanced crossover design in which 10 reproductively normal Quarter Horse Mares were exposed to 2 treatments on 2 consecutive reproductive cycles. At detected ovulation (Day 0), mares were randomly allotted to 1 of 2 treatment groups: I, mid-diestrus treatment, administration of a single 10-mg dose of dinoprost tromethamine (PGF2α) im on Day 10; II, early diestrus treatment, administration of 10-mg PGF2α im twice daily on Days 0, 1, and 2 and once daily on Days 3 and 4. Mares in estrus and with a follicle 35 mm or greater in diameter were artificially inseminated with at least 2 billion motile sperm from a fertile stallion. Pregnancy was defined as detection of a growing embryonic vesicle on 2 consecutive examinations approximately 14 days after ovulation. Serial plasma samples were collected throughout the study period, and concentration of plasma progesterone was determined by RIA. A mixed-model ANOVA for repeated measures was used to analyze hormonal data. Interovulatory and treatment-to-ovulation intervals were compared by a paired t test and fertility by a McNemar chi-square analysis. All mares in group I underwent luteolysis after PGF2α administration denoted by mean (±SD) concentration of plasma progesterone of 0.25 ± 0.21 ng/mL detected 2 days after treatment. In group II, mean concentration of plasma progesterone remained below 1.0 ng/mL during treatment and until the onset of the next estrus. The mean interovulatory interval in group I was 18.5 ± 2.0 days compared with 13.1 ± 3.7 days in group II (P < 0.01). Treatment-to-ovulation intervals were 8.5 ± 2.0 days and 13.1 ± 3.7 days for groups I and II, respectively (P < 0.05). In both groups, 9 of 10 mares were pregnant (P = 1.0). Serial PGF2α administration beginning at ovulation consistently prevented luteal function in 10 of 10 mares in the present study without adversely affecting pregnancy rate of post-treatment cycles.     

Ultrasound and endocrine evaluation of the ovarian response to PGF2alpha given at different stages of the luteal phase in ewes

The purpose of this study was to evaluate the ovarian response of ewes to two treatments with PGF2alpha using transrectal ovarian ultrasonography and hormone measurements. Fifteen milligrams of PGF2alpha was given to six cyclic Western White Face (WWF) ewes early in the estrous cycle (Days 4 to 7) and to six late in the cycle (Days 10 to 12 after ovulation), and a second treatment was given 9 days after the first. Ultrasound scanning and blood sampling started 7 days prior to the first PGF2alpha treatment and ended 10 days (scanning) or 19 days (blood sampling) after the second PGF2alpha treatment, for both groups of ewes. Mean ovulation rate (2.6 +/- 0.7) did not differ significantly between the ewes first treated early or late in the cycle, or after the first or second treatments with PGF2alpha. The time from treatment to ovulation was longer in ewes first treated early (4.0 +/- 0.3 days) compared to late (2.8 +/- 0.4 days) in the cycle (P < 0.05). Both the number of ovulations (range: 0-7) and time from treatment to ovulation (range: 1-9 days) were highly variable. This variability appeared to be due to the extension of the life span of ovulating follicles that emerged prior to PGF2alpha administration and also ovulation of some follicles that emerged after treatment. When results for first and second treatments were pooled, the total number of follicles > 5 mm in diameter on the day of treatment that failed to ovulate in response to PGF2alpha was higher in ewes first treated early (0.8 +/- 0.2/ewe) compared to late (0.3 +/- 0.2/ewe) in the cycle (P < 0.05). The proportion of detected luteal structures relative to the number of ovulations was lower in ewes first treated early compared to late in the cycle (60 and 86%, respectively; P < 0.05). Disruption of ovulatory follicle dynamics and normal luteogenesis, and variability in the timing of ovulation after PGF2alpha treatments could all contribute to poor or variable fertility when prostaglandins are used for estrus synchronization.     

Prostaglandin F2αMetabolite and Progesterone Profiles in Post-partum Cows with Retained Foetal Membranes

Post-partum prostaglandin release and resumption of cycli-cal ovarian activities were studied in 11 Swedish dairy cows with retained foetal mem-branes (RFM), leaving the RFM untreated. The main PGF2α metabolite, 15-ketodihy-dro-PGF2α, was measured in blood plasma collected twice daily during the first 50-60 days after delivery. Progesterone was monitored from all morning samples to evaluate the resumption of ovarian activity. The plasma levels of 15-ketodihydro-PGF2α were ar-bitrarily considered to be significantly elevated between 6-24 days when they exceeded the mean basal value + 2 standard deviations. Comparison between this duration in days of the post-partum PGF2α release and the time required for the completion of uterine in-volution, placental shedding and last day of post-partum clinical signs showed no sig-nificant relations. However, prior to a final decrease below a line of significance of 233-590 pmol/1, pronounced sustained and pulsatile release of PGF2α occurred in relation to the increased frequency of the bacteriological findings. These additional periods of PGF2(X release were described as the “total” duration of post-partum release, and were found to be positively correlated with the time required for uterine involution from the stand point of rectal palpation (p<0.05), while a tendency towards a positive relationship existed for the last day post-partum of clinical signs (p = 0.11). Progesterone analysis revealed resumption of ovarian activity and the first ovulation occurred between 19-29 days in 70% of the cows. The levels of the PGF2α metabolite were again high at the time of luteolysis, thus terminating the luteal phase in the ovulating animals. Thus, it is seen that non-removal of the RFM or the resultant intrauterine infection do not prolong the duration of the immediate post-partum release of PGF2α as compared to normal ani-mals. However, a second release is associated with the increased frequency of uterine infections, indicating that PGF2α may play a role for the early elimination of the infec-tions.     

Comparison of three methods of acute administration of progesterone on ovarian follicular development and the timing and synchrony of ovulation in Bos indicus heifers

The aim of this study was to induce the formation of a persistent dominant ovarian follicle and to compare the effects of 3 methods of acute administration of P4 on ovarian follicular development and on the timing and synchrony of ovulation. Stage of the estrous cycle was initially synchronized in Bos indicus heifers with a norgestomet implants (3 mg) for 10 d and with an analogue of PGF2 alpha (15 mg) on the first and last day of norgestomet treatment. Eight days after removal of the implants, heifers were randomly assigned to 4 groups. All heifers received a norgestomet implant (Day 0), which was removed 17 d later (Day 17); PGF2 alpha was administered on Days 0 and 4. Heifers in the control group (n = 5) received no other treatment. On Day 10 heifers in Group P4C (n = 5) were treated with a CIDR for 24 h; heifers in Group P4O (n = 5) were administered 100 mg i.m. of P4 in oil, while heifers in Group P4S (n = 5) were administered 100 mg i.m. of P4 in saline/alcohol. Data were analyzed using bootstrap estimates of location (mean) and spread (standard deviation; SD). Compared with the control heifers, day of emergence of the ovulatory follicle was delayed, and age and duration of dominance of the ovulatory follicle were reduced in the P4C and P4O heifers (P < 0.05) but not in the P4S heifers (P > 0.05). In all groups treated with P4 both the mean and variability (SD) in the timing of ovulation did not differ with that of the control group (P > 0.05) but there was less variability in the day of emergence, age, duration of dominance and diameter of the ovulatory follicle than in the control group (P < 0.05). Delayed timing and reduced synchrony (SD) of ovulation and greater age of the ovulatory follicle (P < 0.05) occurred in P4S heifers than in P4C heifers. We conclude that administration of 100 mg of P4 in oil is as effective as treatment with a CIDR for synchronizing emergence and ovulation of a newly recruited dominant follicle. However, reduced synchrony of ovulation, greater age of the ovulatory follicle and delayed timing of ovulation occurred following administration 100 mg of P4 in saline/alcohol compared with the CIDR device.     

Effect of early luteolysis in progesterone-based timed AI protocols in Bos indicus, Bos indicus x Bos taurus, and Bos taurus heifers

The objective of this study was to evaluate the effects of treatment with an intravaginal progesterone-releasing device (CIDR) and estradiol benzoate (EB) on follicular dynamics in Bos indicus (n=23), Bos taurus (n=25), and cross-bred (n=23) heifers. To assess the influence of reduced serum progesterone concentrations during 8 days of treatment with a progesterone-releasing device on follicular dynamics, half of the heifers received PGF at CIDR insertion (Day 0; 3 x 2 factorial design). Mean (+/-S.E.M.) serum progesterone concentrations during CIDR treatment varied (P<0.05) among genetic groups: B. indicus (5.4+/-0.1 ng/mL), B. taurus (3.3+/-0.0 ng/mL), and cross-bred (4.3+/-0.1 ng/mL). Maximum diameter of the dominant follicle (DF) was smaller (P<0.01) in B. indicus heifers (9.5+/-0.5 mm) than in cross-bred (12.3+/-0.4 mm) or B. taurus heifers (11.6+/-0.5 mm). B. indicus experienced lower (P<0.01) ovulation rate (39.1%) than did B. taurus (72.7%) and cross-bred (84.0%). Heifers treated with PGF on Day 0 had lower (P<0.05) serum progesterone concentrations during progesterone treatment. The PGF treatment on Day 0 increased (P<0.01) the diameter of the DF (11.9+/-0.4 mm vs. 10.5+/-0.4 mm). Moreover, greater (P=0.02) ovulation rates (78.8 vs. 54.0%) occurred in heifers treated with PGF on Day 0. In summary, B. indicus heifers had greater serum progesterone concentrations, smaller DF diameter, and a lower ovulation rate compared to B. taurus heifers. Prostaglandin treatment on the day of CIDR insertion reduced serum progesterone during treatment, and resulted in increased maximum DF diameter and ovulation rate.     

Effect of peripartum dietary energy supplementation of dairy cows on metabolites, liver function and reproductive variables

Multiparous Holstein cows (n=58) were used to study the effects of peripartum dietary supplementation on metabolic status, liver function and reproduction variables. Diets for cows were as follows: (a) no supplementation (CTL), (b) prilled fatty acids as 1.9% of DM (PrFA), (c) calcium salts of long chain n-6 fatty acids as 2.24% of DM (CaLFA) or (d) daily topdressing with 769 g of 65% propylene glycol (PGLY). Supplements were fed during the last 21 days before expected calving except for PGLY that continued until 21 days after parturition. Ovarian activity was monitored by transrectal ultrasonography and days to first ovulation were recorded. Liver biopsies were obtained on day 8 and 21 postpartum and analyzed for triglyceride content and mRNA expression of pyruvate carboxylase, cytosolic phosphoenolpyruvate carboxykinase, carnitine palmytoyltransferase 1A, and peroxisome proliferator-activated receptor-alpha. At 71 days following parturition, stage of ovarian cycles was synchronized and at day15 of the cycle oxytocin was injected i.v., blood samples were obtained at frequent intervals, and analyzed for 13,14 dihydro, 15-keto PGF(2alpha) (PGFM). Milk production and milk components were not different among treatment groups. Cows in PGLY gained body condition score (BCS) prepartum and net energy balance prepartum tended to be greater, but was not different postpartum from other groups. PGLY supplementation increased plasma insulin concentration prepartum, but not during the postpartum period. No significant differences were observed in plasma concentrations of glucose, NEFA, and insulin-like growth factor or hepatic triglyceride content, but all supplements tended to decrease beta hydroxybutyrate postpartum compared to CTL cows. Abundance of mRNA of gluconeogenic and lipid oxidation genes was not different among treatment groups. Days to first ovulation and uterine PGF(2alpha) production in response to an oxytocin treatment were not significantly different among treatment groups. Peripartum supplementation did not result in the substantial improvement of metabolic profile in early lactation nor significantly affect days to first ovulation and PGFM response to an oxytocin treatment.     

Effect of oestradiol treatment during GnRH-induced ovulation on subsequent PGF2alpha release and luteal life span in anoestrous ewes

In sheep, induction of ovulation during anoestrus is accompanied by a high incidence of short luteal phases, though pre-treatment with progesterone can overcome this problem. We have investigated the effects of supplementing oestradiol during GnRH-induced ovulation on subsequent PGF2alpha release and luteal life span. Thirty anoestrous crossbred ewes received 250 ng GnRH i.v. at 2 h intervals for 48 h to induce ovulation either alone (group 1; n=10) or in association with either an i.m. injection of 20 mg progesterone 3 days earlier (group 2; n=10) or 3 i.m. injections of 10 microg oestradiol at 8 h intervals on the second day of GnRH treatment (group 3; n=10). Laparoscopy, performed 3 days following GnRH to confirm ovulation and 8 days later, coupled with plasma progesterone analysis were used to determine luteal life span. On day 4 following GnRH, plasma samples were collected at 20 min intervals for 8 h to monitor PGF2alpha release. One ewe from group 1 failed to ovulate and was excluded from further analysis. All groups showed an increase (P<0.01) in plasma oestradiol during GnRH treatment, with group 3 showing a marked (P<0.001) increase over that seen in the other two groups. In group 1 there were 1.4+/-0.2 PGF2alpha episodes/ewe/8 h. In group 2, pre-treatment with progesterone caused the complete inhibition of PGF2alpha episodes (0 episodes/ewe/8 h) while in group 3, treatment with oestradiol resulted in a significant reduction (0.3+/-0.1 episodes/ewe/8 h) compared with group 1 (P<0.01). In group 1, 9/9 ewes exhibited short cycles compared with 2/10 ewes in group 2 (P<0.01). In group 3 the proportion of ewes showing short cycles 7/10 ewes was not significantly different from the other groups. While treatment with oestradiol caused a significant attenuation of PGF2alpha release, this was associated with only a partial reduction in the incidence of short cycles.     

Sequential Hormonal Changes in the Postpartum Dairy Cow

Peripheral plasma levels of 15-keto-13,14-dihydro-PGF2α, progesterone, Cortisol, LH and prolactin were studied in 6 primiparous postpartum dairy cows. The cows were followed by hormone measurements and clinical examinations from parturition until pregnancy was established. Blood was collected 3 times per day. The cervix, uterus and ovaries were examined by rectal palpation at 6–10 days intervals. The cows were observed for signs of oestrus twice daily and were additionally teased with a bull to provoke standing heat. Four cows had a normal parturition and dropped their fetal membranes shortly afterwards. (NR group). The remaining 2 retained their fetal membranes for more than 24 h following parturition (RFM group). One out of 6 cows showed standing oestrus at the first ovulation, 4 animals were in oestrus at the second ovulation and all cows showed signs of oestrus at the third ovulation. Although the length of the first luteal phase varied from 9 to 22 days a corpus luteum was in all cases palpated. The secretion of progesterone during the first luteal phase was terminated by a PGF2α release. A significant difference in 15-keto-13,14-dihydro-PGF2α levels between the 2 groups was found on days 0–4 (2.39 vs 6.87 nmol/1 at Ρ < 0.06). Postpartum prostaglandin F2α release as reflected by the level of 15-keto-13,14-dihydro-PGF2α lasted shorter in the NR group than in the RFM group (15–17 vs 21 days). Significant positive correlations between 15-keto-13,14-dihydro-PGF2α and Cortisol as well as between prolactin and Cortisol during the first 24 days postpartum were noted only in cows having normal parturition. The most pronounced daily prolactin variations occurred during the second luteal phase (NR group), when a significant difference between the times 8.00, 12.00 and 15.00 was recorded (14.7, 31.5 and 19.7 μg/l, respectively). Moreover, a partial negative correlation between log value of prolactin and arithmetical value of LH was found in these cows only during the first luteal phase after parturition.     

Growth and regression of ovarian follicles during the follicular phase of the oestrous cycle in heifers undergoing spontaneous and PGF-2 alpha-induced luteolysis

Ultrasonography was used to monitor the growth, ovulation and regression of individual ovarian follicles greater than or equal to 5 mm during the late luteal and follicular phases of the oestrous cycle in heifers treated with injections of PGF-2 alpha to induce luteolysis and in heifers undergoing spontaneous luteolysis. Six heifers were given a single injection of PGF-2 alpha between Day 12 and 15 of the oestrous cycle and their ovaries were examined daily by transrectal ultrasonography until ovulation occurred. Another group of 5 heifers was examined daily by ultrasound from Day 14 or 15 of the cycle through spontaneous luteolysis and ovulation. Blood samples were taken twice daily from this group and analysed for progesterone to determine when luteolysis occurred. All heifers were checked for oestrous behaviour twice daily. Mean diameters of ovulatory follicles on each of the 3 days before oestrus were not different between PGF-2 alpha-treated and untreated heifers. In both groups there was large variation among heifers in the sizes and growth rates of the ovulatory follicles. At 3 days before oestrus the diameters of ovulatory follicles were between 7.5 and 11 mm in PGF-2 alpha-treated heifers and between 6 and 11.5 mm in untreated heifers. Non-ovulatory follicles decreased in size during the 3 days before oestrus and the number of non-ovulatory follicles within the size ranges of ovulatory follicles decreased. The ovulatory follicle was not consistently the largest follicle on the ovaries until the day of oestrus but was always one of the 2 largest follicles during the 3 days before oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of beta-carotene supplementation on reproductive performance of dairy heifers

Three trials were conducted to determine the effect of feeding supplemental beta-carotene on reproductive performance of Holstein heifers. In each trial, the animals were randomly assigned to either a control or treatment group. Animals in the treatment groups received 300 mg supplemental beta-carotene daily for the test periods which varied from 6 to 8 weeks in length. To facilitate sample collections and observations, estrus was synchronized with two injections of 25 mg PGF(2alpha) at 11 day intervals. The first injection was after 2 weeks of feeding supplemental beta-carotene. Blood serum beta-carotene concentrations were higher in the heifers fed supplemental beta-carotene as compared to concentrations in control heifers after 1 week of feeding and this difference increased throughout the test periods. The interval from the second injection of PGF(2alpha) to onset of estrus was shorter in the control heifers as compared to that interval in heifers supplemented with beta-carotene (trial 1,44.0 vs 56.0 hr; trial 2, 51.3 vs 70.8 hr; trial 3, 40.7 vs 62.5 hr, respectively). The intervals from PGF(2alpha) administration to the preovulatory LH peak (43.3 vs 61.5 hr) and ovulation (69.3 vs 85.9 hr) were also shorter in the control heifers in trial 3. No significant differences were found among treatments in the number of heifers that expressed estrus, the blood serum progesterone concentrations or the conception rates in any of the three trials.     

Increase in progesterone and luteal blood flow without a luteolytic response after prostaglandin F2α treatment in early luteal-phase heifers

Acute changes in circulating progesterone concentration and luteal blood flow in heifers after a conventional dose of prostaglandin F(2α) (PGF; 25mg dinoprost, i.m.) were compared between the early luteal phase (Day 3) and midluteal phase (Day 10; Day 0=ovulation), using four groups (Day-3 control, Day-3 PGF, Day-10 control, and Day-10 PGF; n=6 heifers/group). Blood samples were collected at 0, 2, 5, 10, 15, 30, 60, and 120 min (0 min=treatment). Percentage of luteal area with color-Doppler blood-flow signals was estimated at 0, 10, and 30 min. In the Day-3 and Day-10 PGF groups, progesterone increased to a peak at 15 min. In the Day-3 PGF group, progesterone decreased to the pretreatment concentration by 60 min but did not decrease to below the pretreatment concentration during the 2-h experimental period. In the Day-10 PGF group, progesterone decreased to below pretreatment concentration by 30 min, indicating a luteolytic response. In the Day-3 and Day-10 PGF groups, luteal blood flow increased within 10 min and remained elevated until the last examination at 30 min. The absence of a decrease in progesterone to below pretreatment concentrations in the Day-3 PGF group indicated that luteolysis does not necessarily follow a transient increase in progesterone and a concomitant increase in luteal blood flow. The immediate transient increase in progesterone and an increase in luteal blood flow without a subsequent decrease in progesterone to below pretreatment concentrations after PGF treatment in early luteal-phase heifers are novel findings.     

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.     

Ovarian consequences of low dose peroral Fusarium (T-2) toxin in a ewe and heifer model

The effect of low dose peroral Fusarium produced T-2 toxin intake upon the ovarian function was evaluated in ewes (n = 30; Trial 1) and heifers (n = 7; Trial 2). Half of the ewes and all of the heifers were fed rich, acidosis-inducing concentrate. The 30 ewes were divided into 6 groups of 5 animals each. They were given 0, 0.3 or 0.9 mg/day (0, 5 or 15 ug/kg) purified T-2 toxin per os for 21 days (3x2 factorial design). Four of the 7 heifers were fed 9 mg/day (25 ug/kg) of the same purified T-2 toxin for 20 days while 3 remained untreated. The estrus cycles in all animals were synchronized prior to the trials and the T-2 exposure was started in the mid-luteal phase. The acidic condition in the rumen was estimated by the determination of urinary net acid-base excretion. The ovarian activity was followed with blood sampling for progesterone on alternate days (Trial 1) or with ultrasonography and sampling for progesterone daily (Trial 2). All of the heifers and concentrate-fed ewes showed a compensated acidosis, during first two thirds of T-2 exposure. In Trial 1, ovarian malfunction manifested as lower P4 peak concentration in the midluteal phase, shortening of the CL lifespan and prolonged follicular phases. These malfunctions were detected in 3 and 3 ewes fed concentrate and 0.3 mg and 0.9 mg T-2 toxin. Lower P4 peak concentration was observed in 1 ewe fed regular diet and 0.9 mg T-2 toxin. None of the control and acidotic groups (0 mg T-2), or ewes fed regular diet with 0.3 mg T-2 showed any ovarian malfunction. In Trial 2, after PGF2, administration the ovulation occured later and the plasma progesterone level remained low (< 3 nmol/l) for a longer period in T-2 treated heifers, than their untreated control mates (5.0+/-0.7 vs 3.7+/-0.5 d, P<0.05 and 8.3+/-0.4 vs 6.3+/-0.9 d, P<0.01, respectively). These results show that the peroral T-2 intake can significantly retard the folliculus maturation and ovulation and perhaps the subsequent luteinisation also in ruminants kept on concentrate-rich diet.     

Intermittent nutritional stimulus by short-term treatment of high-energy diet promotes ovarian performance together with increases in blood levels of glucose and insulin in cycling goats

The aim of this study was to determine if short-term intermittent treatments of high-energy diet have any stimulatory effects on ovarian function and metabolic status in goat. Cycling Shiba goats were divided into treatment (TG; n=6) and control (CG; n=6) groups. After the detection of ovulation (1st ovulation, Day 0) by ultrasonography, a high-energy diet (250% of maintenance) was fed to the TG from Day 12 to Day 15 (4 days) and from Day 18 to Day 21 (4 days). The high-energy diet comprised 1000 g hay-cubes and 300 g of concentrated feed/head/day (approximately 15 MJ of digestible energy/day). The CG was offered maintenance diet throughout the experiment. Transrectal ultrasound examinations were conducted every other day during the luteal phase and were conducted daily during the follicular phase. Blood samples were collected daily from Day -2 to 7 days after ovulation (2nd ovulation) following the nutritional treatment for analysis of follicle stimulating hormone (FSH), progesterone, oestradiol, glucose and insulin in plasma. Two wave-like rises in the concentrations of glucose and insulin appeared in response to the intermittent nutritional stimulus. Mean plasma concentrations of glucose and insulin were significantly (P<0.05) higher in the TG than in the CG on almost all days during each treatment period. For ovarian performance, the total number of follicles that developed on the day prior to the 2nd ovulation in the TG (7.5 ± 2.7) was significantly higher than that of the CG (4.5 ± 2.6). Ovulation rate of the 2nd ovulation (4.5 ± 1.0) in the TG was significantly higher than that of the 1st ovulation (3.0 ± 0.6) of the TG and than both 1st (2.5 ± 0.5) and 2nd (2.7 ± 0.5) ovulations of the CG. No significant difference was detected in the concentrations of FSH, progesterone and oestradiol throughout the experiment between TG and CG. The present experiment demonstrated that short-term intermittent nutritional stimulus from the luteal phase increased the total number of ovulatory follicles and the ovulation rate in association with increasing plasma concentrations of glucose and insulin in goats.     

Fixed-time insemination in peripuberal,lightweight replacement beef heifers after estrus synchronization with PGF2alpha and GnRH

Estrus synchronization contributes to optimizing the use of time, labor, and financial resources by shortening the calving season, in addition to increasing the uniformity of the calf crop. We determined whether acceptable pregnancy rates could be achieved after synchronization of ovulation and fixed-time artificial insemination (AI) in peripuberal replacement beef heifers using gonadotropin-releasing hormone (GnRH) and PGF2alpha. Crossbred heifers from two herds (MH, n=239; SS, n=330) were wintered at a single location. After a prebreeding examination revealed that 55 heifers had a reproductive tract score (RTS) of 1 (infantile reproductive tracts), they were culled and the remaining heifers were assigned randomly to one of three treatment groups: administration of 25mg PGF2alpha i.m. on Days -12 and 0 followed by estrus detection and insemination between 10 and 14 h after an observed estrus (Control; n=173); administration of 100 microg GnRH i.m. on Day -6, followed by 25 mg PGF2alpha i.m. on Day 0, then fixed-time AI and administration of 100 microg GnRH i.m. on Day +2 (GPG; n=172); and, treatment as for group GPG in addition to administration of 100 microg GnRH i.m. on Day -12 (GGPG; n=169). Bulls were introduced 10 days after AI for 60 days to breed heifers which did not conceive after AI (clean-up bulls). On Days -12, -6, and 0 transrectal ultrasonography was used to monitor ovarian structures in a subset of heifers (30 per treatment). At 30-35 days after AI, ultrasound was used to determine the presence of a viable fetus. Presence of a fetus and stage of pregnancy were determined via palpation per rectum 61-63 days after the conclusion of the breeding season. Heifers in the MH herd (309+/-1.9 kg) were heavier (P<0.001) than those in the SS herd (283+/-1.7 kg) at initiation of the breeding season. Synchronized pregnancy rates were greater (P<0.05) in GGPG (25.4%) and GPG (22.1%) than Control (12.7%) heifers. Pregnancy rates were 9, 21, 32, or 31% for heifers with RTS of 2, 3, 4, or 5, respectively. The average diameter of 22 follicles induced to ovulate in heifers treated with GnRH (GPG and GGPG treatments) was 14.2+/-0.8 mm (range=10.0-23.6 mm). In conclusion, a fixed-time ovulation synchronization program using GnRH and PGF2alpha improved pregnancy rates in peripuberal, lightweight replacement beef heifers.     

Effect of prostaglandin F2alpha dosage and stage of estrous cycle on the estrous response and corpus luteum function in beef heifers

Ninety-five normal cyclic crossbred beef heifers were used to determine if the proportions of heifers showing estrus, intervals to estrus and corpus luteum (CL) function were influenced by PGF(2alpha) dosage and (or) the stage of luteal phase when PGF(2alpha) was administered. Heifers were assigned randomly to treatments in a 4 x 3 factorial arrangement. Treatments were 5, 10, 25 or 30 mg PGF(2alpha) injected either in early (5 to 9 d), mid (10 to 14 d) or late (15 to 19 d) stages of the luteal phase. Jugular samples were taken at 0 h and at 8 h-intervals for 48 h and again at 60 h after PGF(2alpha) treatment for progesterone assay. Heifers were observed for estrus continuously for 120 h PGF(2alpha) treatment. The proportion of heifers showing estrus was dependent upon (P<0.05) both dosage of PGF(2alpha) and stage of luteal phase. Heifers given 5 mg of PGF(2alpha) showed estrus only if treated during the late stage, while those given 10 mg of PGF(2alpha) showed a progressive increase of heifers in estrus as stage of luteal phase advanced. The proportion of heifers showing estrus after 25 and 30 mg of PGF(2alpha) increased from 56% for the early stage to 100% for the mid and late stages. Interval to estrus in heifers showing estrus within 120 h after PGF(2alpha) treatment did not differ (P>0.05) among dosages but tended (P=0.10) to be longer in heifers treated during the mid luteal stage (67 h) than in heifers treated in the two other stages (56 h). A greater proportion of heifers (P<0.05) showed estrus by 60 h after PGF(2alpha) when treated during the early and late luteal stages (75.5%) than for heifers treated during the mid luteal stage (30.4%). Patterns of progesterone concentrations were influenced (P=0.08) by the three way interaction of dosage, stage and time. In heifers that showed estrus, rate of decline in progesterone tended (P=0.07) to be slower during the mid luteal stage than during the early and late stages. Progesterone did not drop below 1 ng/ml until 32 h in heifers treated during the mid luteal stage; whereas progesterone dropped below 1 ng/ml by 24 h in heifers treated during the early and late stages. These data may be useful in designing more efficient systems for using PGF(2alpha) or its analogues in estrus synchronization of beef cattle.     

Effects of a 6-day treatment with medroxyprogesterone acetate after prostaglandin F2 alpha-induced luteolysis at midcycle on antral follicular development and ovulation rate in nonprolific Western white-faced ewes

Medroxyprogesterone acetate (MAP) from intravaginal sponges prolongs the lifespan of large ovarian follicles when administered after prostaglandin F2alpha (PGF2alpha)-induced luteolysis early in the luteal phase of ewes. The present study was designed to determine whether a PGF2alpha/MAP treatment applied at midcycle would alter the pattern of antral follicle growth and increase ovulation rate in nonprolific ewes. A single injection of PGF2alpha (15 mg, i.m.) was given, and an intravaginal MAP (60 mg) sponge was inserted for 6 days, on approximately Day 8 after ovulation, in 7 (experiment 1), 8 (experiment 2) or 11 (experiment 3) ultrasonographically monitored, cycling Western white-faced ewes; seven ewes (experiment 1) served as untreated controls. Blood samples were collected each day and also every 12 min for 6 h, halfway through the period of treatment with MAP (experiment 1), or every 4 h, from 1 day before to 1 day after sponging (experiment 2). Seventeen of 26 treated ewes (experiment 1, n = 6; experiment 2, n = 5; experiment 3, n = 6) ovulated 1 to 6 days after PGF2alpha, but this did not affect the emergence of ensuing follicular waves (experiments 1 and 2). These ovulations, confirmed by laparotomy and histological examinations of the ovaries (experiment 3), were not preceded by an increase in LH/FSH secretion and did not result in corpora lutea, as evidenced by transrectal ultrasonography and RIA of serum progesterone (experiments 1 and 2). Following the removal of MAP sponges, the mean ovulation rate was 3.1 +/- 0.4 in treated ewes and 2.0 +/- 0.3 in control ewes (experiment 1; P < 0.05). In experiments 1 and 2, the ovulation rate after treatment (3.1 +/- 0.4 and 2.8 +/- 0.4) was also greater than the pretreatment rate (1.9 +/- 0.3 and 1.9 +/- 0.1, respectively). Ovulations of follicles from two consecutive waves before ovulation were seen in five treated but only in two control ewes (experiment 1), and in seven ewes in experiment 2. There were no significant differences between the MAP-treated and control ewes in mean daily serum concentrations of FSH and estradiol, and no differences in the parameters of LH/FSH secretion, based on frequent blood sampling. Treatment of nonprolific Western white-faced ewes with PGF2alpha and MAP at midcycle changed follicular dynamics and increased ovulation rate by approximately 50%. These effects of MAP, in the absence of luteal progesterone, may not be mediated by changes in gonadotropin secretion.     

Ultrasonic morphology of corpora lutea and central luteal cavities during the estrous cycle and early pregnancy in heifers

Ultrasonography was used once daily to quantify corpora lutea, central luteal cavities, and luteinized tissue during interovulatory intervals (n = 66) and during Days 0 to 60 of pregnancy (n = 14) in nulliparous Holstein heifers (ovulation = Day 0). The corpus luteum of the estrous cycle was detectable by ultrasonography in most heifers from the day of ovulation (mean, Day 0.5) and extending into the regressive phase beyond the next ovulation (mean, Day 1.4 +/-0.2 after the next ovulation). During pregnancy, the corpus luteum was detected until Day 60 (end of study). Maximal central luteal cavity area detected on Days 0 to 20 was used retrospectively to group luteal glands into four cavity categories: no, small, medium, and large. These categories corresponded to approximate cavity diameters of <2 mm, 2 to 5 mm, 6 to 10 mm, and >10 mm, respectively. The incidence of each cavity category was similar between interovulatory intervals and pregnancies (combined incidence, 17 80 , 8 80 , 33 80 , and 22 80 for no, small, medium, and large cavities, respectively; total with cavities, 63 80 , 79%). Mean day of first detection of a central cavity was earliest for large cavities during interovulatory intervals (means, Days 4.7, 4.4, and 3.0 for small, medium, and large cavities, respectively; P<0.04) and during pregnancies (means, Days 5.5, 4.2, and 3.3, respectively; NS). However, the day that the cavities reached maximum size (range of means, Days 5.5 to 7.0) did not differ among categories. Mean day of last detection of the central cavity was significantly different among cavity categories during interovulatory intervals (means, Days 9.3, 11.1, and 17.4 for small, medium, and large cavities, respectively) and pregnancies (means, Days 7.0, 8.8, and 20.2, respectively). Time of loss of central cavities was similar between nonbred and pregnant heifers, and there was no significant difference among cavity categories in the length of the interovulatory interval (mean, 20.1 d). Luteal tissue area was not significantly different among cavity categories during interovulatory intervals. There were no indications that cavities were functionally important. Luteal tissue area increased linearly in pregnant heifers on Days 21 to 60 (mean slope, 2.6 mm(2)/day).