Control of oestrus in cattle using progesterone coils

Four experiments were conducted to determine the effect of length of treatment, stage of cycle at start of treatment and administration of oestradiol benzoate or progesterone at the start of treatment with intravaginal progesterone coils on oestrous response and fertility. In Experiment 1, the number of heifers in oestrus was affected neither by injection of 5 mg oestradiol benzoate alone or with 200 mg progesterone nor by length of treatment. More heifers (P < 0.05) were in oestrus on day 2 after treatment following a 12-day treatment compared to a 9-day treatment.In Experiment 2, heifers between days 17 and 20 of the oestrous cycle received an injection of either 5 mg oestradiol benzoate alone or with 200 mg progesterone at the start of a 9-day treatment with progesterone coils. Neither the number of heifers in oestrus nor the pattern of onset were affected after treatment. In Experiment 3, heifers between days 0 and 3 of the oestrus cycle received progesterone coils for 9, 12 or 14 days. In addition, animals received (i) no further treatment, (ii) a gelatin capsule adhered to the coil containing 10 mg oestradiol benzoate (iii) a gelatin capsule adhered to the coil containing 200 mg progesterone. Following a 9- or 12-day treatment period heifers receiving the coil with the oestrogen capsule had a high oestrous response ( compared to , P < 0.05). When oestrogen was not given, there was a significant linear effect of duration of treatment on the number in oestrus (9 days, ; 12 days ; 14 days, ; P < 0.05).In Experiment 4, post-partum cows were used to compare a 9- and 12-day treatment period and half the animals in each group received either 5 mg oestradiol benzoate and 200 mg progesterone at the start of treatment or a 10 mg gelatin capsule adhered to the coil. The length of treatment affected the number of heifers in oestrus since were in oestrus after a 12-day treatment period compared with after a 9-day period (P < 0.001). There were no significant differences in the number of cows in oestrus after injection of oestrogen and progesterone ( ) or after the use of the gelatin capsule ( ).     

The application of long- and short-term progestagen treatments for oestrous cycle control in heifers.

Progestagen-impregnated pessaries were inserted into 205 heifers on eight farms. Treatments were either pessaries only for 20 days or pessaries for 10 days combined with an intramuscular injection of 250 mg progesterone+7-5 mg oestradiol benzoate on the day of insertion. Pessary retention was low (86.7%) over the 20-day period, but high (93-6%) during the 10-day period. Calving rates of heifers inseminated in oestrus following the 20-day treatment were low, while those of heifers inseminated on a fixed-time basis with the 10-day treatment were slightly higher than those of control heifers.     

Synchronization of ovulation in beef herds: improved conception rate after and interrupted course of progesterone administration

Administration of 50 mg progesterone in 6 im injections every 48 hours was used to synchronize the estrous cycles of 6 herds of cows and/or heifers. Because of a previous finding that cows in the last 3rd of their estrous cycles when progesterone treatment is begun exhibit lower fertility, such cows were excluded by presynchronization of the herd 8 days prior to the start of treatment by 4 48-hourly injections of 50 mg progesterone. 69%-86% of the animals became pregnant in 4 of the 6 herds during the synchronized estrus, which compares favorably with the average 1st insemination conception figure without synchronization (approximately 70%). Previous conception rates observed averaged approximately 47%.     

Effects of progesterone-impregnated sponge treatment on peripheral plasma hormone levels and fertility in the cyclic ewe

Cyclic ewes were treated with 500-mg progesterone-impregnated sponges for the synchronization of oestrus. In the first experiment, the sponges were removed from 79 ewes at intervals over a 17-day treatment and the residual amount of progesterone was measured in order to assess the rate of absorption of the hormone from the sponges by the animals. The residual progesterone was found to decrease linearly with the duration of sponge insertion but there was also a significant quadratic component indicative of a slowing down in the rate of progesterone absorption towards the end of the treatment period. In the second experiment, 13 cyclic ewes were treated with 500-mg progesterone sponges for 17 days and the eight ewes in oestrus following spongewithdrawal were mated. The peripheral plasma progesterone was assayed at intervals during sponge insertion and at weekly intervals after sponge withdrawal. The residual progesterone levels on the sponges and the plasma progesterone levels of the treated ewes were examined in relation to their oestrous response and fertility. There was a significantly higher residual level of hormone remaining on sponges from ewes that mated than on sponges from those that did not (P < 0.01). The 13 ewes exhibited luteal phase levels of plasma progesterone when assayed during the period of sponge insertion regardless of their response to treatment. The mated, fertile ewes had significantly higher plasma hormone levels than the non-mated and the mated infertile ewes, after sponge withdrawal.     

The effectiveness of steers and heifers treated with oestrogen or testosterone to detect oestrus in cattle

Two experiments were carried out to determine the effectiveness of steers and heifers, treated with oestrogen or testosterone, in the detection of oestrus in cattle.In the first experiment 17 steers castrated at birth and 16 castrated at 6 months of age were randomly allocated to three groups and received an 800 mg subcutaneous implant of testosterone, subcutaneous injections of 10 mg oestradiol benzoate per week for 16 weeks or no hormone (controls). In addition, six heifers were injected subcutaneously with 10 mg oestradiol benzoate per week for 16 weeks while six untreated heifers served as controls. Animals were observed in a standardised libido test 2, 4, 8, 16, 20 and 24 weeks after treatment commenced. The time to first mount and the number of mounts per animal responding in the presence of oestrous heifers were recorded. Both steers and heifers treated with oestradiol benzoate were superior at detection of oestrus in cattle than animals treated with testosterone or those receiving no hormone. Oestrogen-treated animals generally detected heifers in oestrus in less than 3 min after introduction and mounted these animals between 20 and 30 times in one hour. This response was consistent throughout the duration of the experiment. There was no effect of age at castration of steers on development of male behaviour.The second experiment determined the rate and degree of development of male behaviour in steers in response to weekly subcutaneous injections of 0, 2, 4, 8 or 16 mg oestradiol benzoate per 250 kg body weight, 250 mg testosterone or 150 mg dihydrotestosterone for a period of 15 weeks. Steers treated with oestradiol benzoate again proved to be more successful than untreated or testosterone-treated steers at consistently detecting and mounting oestrous heifers. The best response was obtained from steers treated with 8 mg/250 kg body weight per week. The practical application of this work is discussed.     

Effects of gonadotrophin-releasing hormone and prostaglandin F-2 alpha on corpus luteum function and timing of the subsequent ovulation in the mare

Standard bred mares that were cycling normally were treated beginning on Days 9 or 10 of the oestrous cycle with repeated pulses of GnRH (20 micrograms/h) and/or a single injection of prostaglandin (PG)F-2 alpha (alfaprostol, 3 mg), and were subsequently bled and palpated daily until the next ovulation. GnRH treatment increased serum concentrations of LH and progesterone at 4 days after the start of treatment compared to controls. The combination of PGF-2 alpha + GnRH treatment resulted in an immediate decline in serum progesterone values, and subsequently decreased the interval to next ovulation by 4.5 days compared to controls. Mean serum concentrations of FSH were not different among treatment groups 4 days after the start of treatment, and there was a consistent trend among all treatment groups for decreasing concentrations of FSH within the 6 days before ovulation. We conclude that, under our experimental conditions, pulsatile administration of GnRH provides a short-term luteotrophic stimulus, probably by the elevation in serum LH, but that this stimulus cannot indefinitely prevent the luteolytic effects of exogenously administered PGF-2 alpha. Although GnRH treatment combined with PGF-2 alpha injection hastened the impending ovulation, this regimen was no more effective than PGF-2 alpha treatment alone.     

Effect of continuous infusion of oxytocin on length of the oestrous cycle and luteolysis in cattle

In Exp. I oxytocin (60 micrograms/100 kg/day) was infused into the jugular vein of 3 heifers on Days 14-22, 15-18 and 16-19 of the oestrous cycle respectively. In Exp. II 5 heifers were infused with 12 micrograms oxytocin/100 kg/day from Day 15 of the oestrous cycle until clear signs of oestrus. Blood samples were taken from the contralateral jugular vein at 2-h intervals from the start of the infusion. The oestrous cycle before and after treatment served as the controls for each animal. Blood samples were taken less frequently during the control cycles. In Exp. III 3 heifers were infused with 12 micrograms oxytocin/100 kg/day for 50 h before expected oestrus and slaughtered 30-40 min after the end of infusion for determination of oxytocin receptor amounts in the endometrium. Three other heifers slaughtered at the same days of the cycle served as controls. Peripheral concentrations of oxytocin during infusion ranged between 155 and 641 pg/ml in Exp. I and 18 and 25 pg/ml in Exp. II. In 4 our of 8 heifers of Exps I and II, one high pulse of 15-keto-13,14-dihydro-prostaglandin F-2 alpha (PGFM) appeared soon after the start of oxytocin infusion followed by some irregular pulses. The first PGFM pulse was accompanied by a transient (10-14 h) decrease of blood progesterone concentration. High regular pulses of PGFM in all heifers examined were measured between Days 17 and 19 during spontaneous luteolysis. No change in length of the oestrous cycle or secretion patterns of progesterone, PGFM and LH was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reproductive performance of heifers induced to oestrous asynchrony by suprabasal plasma progesterone levels

Suprabasal progesterone concentrations around oestrus have induced disturbances in oestrous behaviour and ovulation. To determine whether fertility in such an altered oestrus can be maintained at normal levels with additional inseminations (AI) until ovulation, fertility was compared in heifers (n = 11) inseminated in normal oestrous cycles and thereafter in cycles in which the animals were treated with progesterone in order to create suprabasal concentrations after luteolysis. The treatment consisted of silicone implants containing 10.6 mg kg⁻¹ of progesterone inserted subcutaneously on Day 8 of the oestrous cycle (day of ovulation designated Day 0) and removed on Day 25. Both in control oestrous cycles and oestrous cycles under progesterone treatment, growth of the ovulatory follicle and ovulation were determined by frequent ultrasound scanning. Blood was collected frequently for further analysis of progesterone, oestradiol-17β and luteinising hormone (LH). Insemination was performed 12 h after onset of standing oestrus. if ovulation did not occur 24 h after AI, heifers were inseminated again until ovulation. Pregnancy was diagnosed by ultrasound 25 days after ovulation.In control oestrous cycles, plasma progesterone decreased to 0.3 ± 0.3 nmol 1⁻¹. Duration of oestrus was 22.9 ± 2.0 h, the interval from onset of oestrus to ovulation was 32.4 ± 2.3 h and the interval from LH peak to ovulation was 28.6 ± 1.4 h. The interovulatory interval was 20.7 ± 0.6 days. In oestrous cycles in treated heifers, progesterone decreased to 1.0 ± 0.3 nmol l⁻¹ (P > 0.10) and the interovulatory interval was prolonged to 23.5 ± 1.0 days (P < 0.05). Standing oestrus lasted 47.2 ± 12.0 h (P = 0.09, n = 7). The interval from the onset of oestrus to ovulation was 59.4 ± 13.0 h (P = 0.08) and the interval from LH peak to ovulation 25.8 ± 1.3 h (P > 0.10). The prolonged oestrus was associated with increased (P < 0.05) growth of the ovulatory follicle and higher (P < 0.05) release of oestradiol-17β. Conception rates were 90% and 46% (P < 0.05), and the numbers of AI per heifer were 1.1 ± 0.1 and 3.4 ± 0.6 (P < 0.01) for control oestrous cycles and after treatment, respectively.The induction of suprabasal concentrations of progesterone caused asynchronies similar to those observed in cases of repeat breeding. The repeated AI did not maintain fertility at normal levels. It is suggested that the extended growth of the ovulatory follicle may cause impaired oocyte maturation or it may alter the maternal milieu owing to the prolonged release of oestradiol.     

Active immunization of the cow against oestradiol-17beta

Six beef heifers were immunized over a 4-month period with an oestradiol-17beta-BSA conjugate in Freund's adjuvant. There was an interference with oestrus in the treated heifers; 2 ceased to exhibit oestrus, one exhibited one oestrus and three exhibited oestrus after Day 47 of treatment. The control heifers treated with Freund's adjuvant had normal oestrous cycles. The antiserum titre rose in all treated heifers and attained its highest level in the 2 animals in which oestrus did not recur. The temporal changes in plasma LH, progesterone and oestradiol were normal during the pretreatment period, but became abnormal during the 120 days after immunization. Although plasma oestradiol-17beta rose at the expected time of oestrus after treatment, it was apparently effectively neutralized by the antiserum induced by treatment as evidenced by the absence of an LH surge. Plasma progesterone levels fell to baseline and remained low, indicating lack of formation of corpora lutea.     

Synchronization of estrus and fertility in zebu beef heifers treated with three estrus synchronization protocols

The effects on estrus and fertility of 3 estrus synchronization protocols were studied in Brahman beef heifers. In Treatment 1 (PGF protocol; n=234), heifers received 7.5 mg, i.m. prostianol on Day 0 and were inseminated after observed estrus until Day 5. Treatment 2 (10-d NOR protocol; n = 220) consisted of norgestomet (NOR; 3 mg, s.c. implant and 3 mg, i.m.) and estradiol valerate (5 mg, i.m.) treatment on Day -10, NOR implant removal and 400 IU, i.m. PMSG on Day 0, and AI after observed estrus through to Day 5. Treatment 3 (14-d NOR+PGF protocol; n = 168) constituted a NOR implant (3 mg, sc) on Day -14, NOR implant removal on Day 0, PGF on Day 16, and AI after observed estrus through to Day 21. All heifers were examined for return to estrus at the next cycle and inseminated after observed estrus. The heifers were then exposed to bulls for at least 21 d. During the period of estrus observation (5 d) after treatment, those heifers treated with the PGF protocol had a lower (P<0.01) rate of estrual response (58%) than heifers treated with the 10-d NOR (87%) or 14-d NOR+PGF (88%) protocol. Heifers treated with the 10-d NOR protocol displayed estrus earlier and had a closer synchrony of estrus than heifers treated with either the PGF or the 14-d NOR+PGF protocol. Heifers treated with the 14-d NOR+PGF protocol had higher (P<0.05) conception and calving rates (51 and 46%) to AI at the induced estrus than heifers treated with the PGF (45 and 27%) or the 10-d NOR (38 and 33%) protocol. Calving rate to 2 rounds of AI was greater (P<0.05) for heifers treated with the 14-d NOR-PGF (50%) protocol than heifers treated with the 10-d NOR (38%) but not the PGF (43%) protocol. Breeding season calving rates were similar among the 3 protocols. The results show that the 14-d NOR+PGF estrus synchronization protocol induced a high incidence of estrus with comparatively high fertility in Brahman heifers.     

Peripheral progesterone levels in pregnant and non-pregnant heifers following use of HCG.

Progesterone concentration in jugular blood of bred beef heifers was determined on days 9 and 16 in two trials. Human chorionic gonadotrophin (HCG) was administered to some of the heifers in each trial in an attempt to improve pregnancy percentage.In Trial 1, 183 heifers were divided into a control group and three groups of animals which were subjected to a 9-day estrous synchronization treatment prior to breeding. The treatment consisted of an ear implant containing 17 α acetoxy-11-beta-methyl 17 nor preg 4-ene 3, 20 dione (norgestomet) left in place for 9 days and an injection of 5 mg estradiol valerate (EV) and 3 mg of norgestomet given at the time of implantation. The heifers in one group received .25 mg estradiol-17β at time of implant removal; heifers in the 2nd group received 1500 IU of HCG in 5% beeswax and 95% sesame oil at breeding time, while heifers in the 3rd group received a placebo injection containing 5% beeswax and 95% sesame oil at breeding time. No differences in serum levels of progesterone were observed (P>0.5) between treatments or between pregnant and non-pregnant heifers on day 9 or 16 (P>.05). Pregnancy percentage in heifers receiving HCG was similar to that noted in the control heifers or the placebo injected heifers while injection of estradiol 17β decreased the proportion of heifers which became pregnant.In trial 2, 58 heifers which had been bred 1 or 2 times without becoming pregnant were divided into a control group and a group in which heifers received 1000 IU of HCG 96 hr. after observed estrus. In heifers receiving HCG, serum levels of progesterone were higher (P<.01), on day 9 and 16 post estrus than in controls but no difference in serum progesterone was noted (P>.05) between pregnant and non-pregnant heifers on day 9 or 16. The proportion pregnant did not differ (P>.05) between heifers receiving HCG and control heifers.     

Reproductive characteristics of cyclic beef heifers treated with the prostaglandin analog luprostiol

One hundred and twenty crossbred Angus heifers, after exhibiting a 17- to 23-d estrous cycle, were placed into six groups of 20 heifers each and administered 2 ml i.m. propylene glycol containing either 0 (controls), 3.75, 7.5, 15.0 or 30.0 mg of luprostiol, or saline containing 0.5 mg cloprostenol (Groups 1 through 6, respectively). Heifers were observed for estrus every 6 h and all treatments were given 6.5 to 8.0 d after heifers were observed in standing estrus. Blood samples were collected after treatments from 10 heifers in each groups. Blood serum was assayed for progesterone. The synchronization period was considered to be 120 h after administration of luprostiol or cloprostenol. There were 0, 16, 17, 18, 20 and 18 heifers observed in estrus during the synchronization period in Groups 1 through 6, respectively. Progesterone concentrations in blood serum dropped below 1 ng/ml in 0, 8, 9, 10, 10 and 10 of the heifers from which blood samples had been taken in the six groups. All heifers observed in estrus were artificially inseminated. During the synchronization period, 0, 12, 14, 15, 16 and 10 heifers conceived in Groups 1 through 6, respectively. The interval from injection to estrus for the 89 heifers that exhibited estrus in the synchronization period averaged 49.0 h and was not different among the luprostiol and cloprostenol treated groups. Control heifers returned to estrus an average of 13.2 d after the treatment. The number of heifers that conceived at first insemination, regardless of when estrus occurred, was 16, 15, 16, 16, 16 and 12, and the total number that conceived at the first and second inseminations was 18, 18, 17, 19, 19 and 16 for Groups 1 through 6, respectively. Based on serum progesterone concentration and/or interval from treatment to estrus, 15 and 30 mg of luprostiol effectively regressed corpora lutea (100%) when administered between 6.5 and 8.0 d after estrus, and the estrous response and conception rate for these two groups equalled or exceeded that of the control and cloprostenol groups.     

Treating cattle with progesterone as well as a GnRH analogue affects oestrous cycle length and fertility.

Initiating the chronic administration of progesterone to cattle during metoestrus will produce shortened oestrous cycles containing one or two wave-like sequences of ovarian follicle development. Conception rates are reduced to inseminations at the oestrus preceding these shortened cycles. In contrast, a single injection of the GnRH analogue, buserelin, around mid-dioestrus can lengthen the oestrous cycle by increasing the proportion of cycles with three waves of follicular development and may also increase conception rates. A series of trials was conducted to test the hypothesis that the adverse effects of progesterone on oestrous cycle length and conception rate could be prevented with a strategic injection of GnRH. In Trial 1, progesterone was administered per vaginum to heifers for 10 days from Day 2 or 3 (Oestrus = Day 0) and with (n = 42) or without (n = 46) an injection of a GnRH analogue (10 microg buserelin) on Day 12 or 13. Other heifers (n = 44) served as an untreated control group. The average inter-oestrous interval (IOI) for those heifers treated only with progesterone was 17.0 days and was less (p<0.05) than the average intervals for those also receiving GnRH (20.2 days) or in the control group (20.0 days). In Trial 2, 45 heifers were inseminated following a synchronised oestrus. Progesterone was administered as in Trial 1 to 22 of the heifers. Their conception rate was 45.4% and this was less (p<0.05) than the 73.9% obtained with their 23 untreated contemporaries. Trial 3 was completed using 530 cows in commercial dairyherds. The 259 cows receiving progesterone and GnRH (buserelin) after their first inseminations had a conception rate of 68.3% compared to 56.1% for their 271 untreated herdmates (p<0.05%). Heifer calves born to treated cows had heavier birthweights (33.4 vs. 31.1 kg; p<0.05), but birthweights of bull calves were unaffected (35.5 vs. 35.8 kg). Gestation lengths for cows conceiving to first inseminations were similar for treated and control groups (280.9 vs. 280.5 days). The results of these trials confirmed the hypothesis that a strategic injection of the GnRH analogue, buserelin, could prevent the reductions in oestrous cycle length and conception rate associated with the chronic metoestrous administration of progesterone.     

Estrus synchronization in beef heifers with progestin-based protocols. I. Differences in response based on pubertal status at the initiation of treatment

Two progestin-based protocols for estrus synchronization in replacement beef heifers were compared on the basis of estrous response, interval to and synchrony of estrus, and pregnancy rate. The objective was to determine, whether addition of GnRH to a melengestrol acetate (MGA)-prostaglandin F2alpha (PGF2alpha) estrus synchronization protocol would improve synchrony of estrus without compromising fertility in yearling beef heifers. Heifers at two locations (Location 1, n = 60 and Location 2, n = 64) were assigned randomly to one of two treatments by breed and pubertal status. Heifers were defined as, pubertal when concentrations of progesterone in serum were elevated (> or = 1 ng/mL) in either one of two samples obtained 10 and 1 day prior to treatment initiation. Prior to MGA administration, 18/60 (30%) and 36/64 (56%) of the heifers at Locations 1 and 2, respectively, were pubertal. Heifers in both treatments were fed MGA (0.5 mg/head/day in 1.8 kg/head/day supplement) for 14 days followed by 25 mg of PGF2alpha i.m. (MGA-PGF2alpha) 19 days after MGA withdrawal (Day 33 of treatment). One-half of the heifers at each location received 100 microg of GnRH i.m. 12 days after MGA withdrawal (Day 26 of treatment; MGA Select). The control group received only MGA-PGF2alpha. Heifers were observed for signs of behavioral estrus continuously during daylight hours for 7 days beginning on the day PGF2alpha was administered. Heifers were inseminated 12 h after observed estrus. There was a treatment by location by pubertal status interaction (P < 0.05) for interval to estrus. Compared to the respective control treatment at each location, prepubertal heifers assigned to the MGA Select protocol at Location 1 had longer intervals to estrus, whereas at Location 2, prepubertal heifers assigned to the MGA-PGF2alpha protocol had longer intervals to estrus. The higher number of pubertal heifers at Location 2 was associated with a reduced variance in the interval to estrus among MGA Select treated heifers. Total estrous response and synchronized conception rates were similar between treatments at both locations. These data suggest that addition of GnRH to the MGA-PGF2alpha protocol may improve synchrony of estrus, however, the degree of synchrony may be influenced by pubertal status of heifers at the time treatments are imposed. Further studies are needed to define production systems in which the MGA Select protocol is warranted for use in beef heifers.     

Active immunization of post-pubertal heifers against prostaglandin F2α to suppress oestrous behaviour: effect of adjuvant and dose of immunogen

Two experiments were performed to develop an effective prostaglandin F_2α immunization protocol to suppress oestrous behaviour in beef heifers. In Experiment 1, a 3 × 2 factorial plan (n=4–5 per treatment) was used to test three doses (3.3, 10 and 30 mg) of a prostaglandin F_2α- human serum albumin (PGF-HSA) conjugate as the immunogen and two adjuvants, GNE (proprietary product; Intervet, The Netherlands) and diethylaminoethyl (DEAE)-dextran. Heifers (n=5) in a control group were untreated. Booster immunizations were given on Days 42 and 145 after the primary immunization (Day 0) and data collection for statistical purposes ended on Day 297. After Day 42 the incidence of oestrous behaviour was: (1) greater (P < 0.05) for control than immunized heifers (4.3 and 2.2, respectively), (2) greater (P < 0.05) for heifers immunized using GNE than for heifers immunized using DEAE-dextran (2.6 and 1.9, respectively), and (3) greater for heifers immunized with 30 mg of immunogen than for those immunized with either 3.3 or 10 mg (3.1, 1.7 and 1.9, respectively). Suppression of oestrous behaviour was accompanied by formation of a persistent corpus luteum (CL). Persistent CL were formed in ten of the 28 immunized heifers and the mean (± standard error of the mean) duration of persistence was 397 ± 85 days. In Experiment 2, a 2 × 2 factorial plan (n=6–7 per treatment) was used to test two doses (1 and 10 mg) of the PGF-HSA conjugate as the immunogen and two adjuvants, non-ulcerative Freund's adjuvant (NUFA) and DEAE-dextran. A control group was untreated (n=6). Booster immunization was given on Day 183 after the primary immunization (Day 0) and the experiment finished on Day 384. Antibody titres were higher (P < 0.05) in NUFA-treated heifers than in DEAE-dextran-treated (1 mg) heifers in the 183- to 283-day period. After Day 183, oestrous behaviour was suppressed in 26 out of the 27 immunized heifers. Persistent CL were maintained for longer (P < 0.05) in NUFA-treated heifers (245 days) than in DEAE-dextran-treated heifers (166 days) but there was no difference due to dose of immunogen (208 and 203 days, 1 and 10 mg, respectively). It is concluded that immunization against PGF-HSA results in suppression of oestrous behaviour in heifers due to prolongation of the life-span of the CL; however, efficacy of response is dependent on the immunization regime used.     

Synchronization of estrus following 7 or 9 day treatment with chlormadinone acetate (CAP)

Synchronization of estrus and fertility were determined in a series of 8 trials. Various levels of chlormadinone acetate (CAP) were fed for either 7 or 9 days. An injection of 5 mg of estradiol valerate and CAP was given at the start of the feeding period. In some trials estradiol 17β was injected near the end of the feeding period. In trial 1, 98% of the CAP-treated heifers were in estrus in a 5-day period, but only 46% conceived at first service compared to 80% in the non-synchronized heifers (P<.01).In trials 2 through 6, 0.25 mg estradiol 17β injected either 60 or 72 hours after the last CAP feeding reduced the interval to ovulation in heifers that ovulated. However, use of estradiol 17β reduced the number of heifers ovulating in most trials.In trials 7 and 8, estrus was effectively synchronized with either 7- or 9-day feeding of 7.5 or 10 mg of CAP daily followed by .5 mg estradiol 17β, 72 hours after the last CAP feeding. Pregnancy rates at first service varied from 21 to 45% in heifers in the synchronized groups, compared to 58% in the controls in trial 7 (P<.05). In trial 8 pregnancy rates at 1st service varied from 29 to 47% in treated heifers compared to 72% in controls (P<.01).In this series of trials, fertility was reduced from 24 to 43% with the use of CAP and estradiol valerate. Conception rates at first service were not improved by varying the length of feeding (7 or 9 days), level of CAP (7.5 or 10 mg) or by attempting to reduce the variation in ovulation time with estradiol 17β. None of the combinations of these three drugs used increased fertility in these trials.     

Luteolytic effect of 13,14-dihydro-PGF-2 alpha in heifers

Holstein heifers (4/group) were injected intramuscularly with 0, 5, 10 or 25 mg 13,14-dihydro-PGF-2 alpha on Day 10 of the oestrous cycle. Complete luteolysis and precocious oestrus occurred in 3 of 4 heifers receiving 25 mg and 1 of 4 receiving 10 mg 13,14-dihydro-PGF-2 alpha injected i.m. These features were not affected in heifers injected with 0 or 5 mg 13,14-dihydro-PGF-2 alpha, although plasma progesterone concentrations were depressed in all treated heifers within 75 min. LH concentrations were elevated between 5 and 8 h after 13,14-dihydro-PGF-2 alpha in all treated heifers. The addition of 13,14-dihydro-PGF-2 alpha to dispersed bovine luteal cells did not affect progesterone accumulation during a 2-h period. These results suggest that 13,14-dihydro-PGF-2 alpha may play a role in PGF-2 alpha-induced luteolysis.     

Plasma progesterone profiles and fertility status of anestrus Zebu cattle treated with norgestomet-estradiol-eCG regimen

Zebu cattle are notorious for poor fertility characterized by late maturity and long intercalving intervals attributed to a variety of factors, including genetic, nutritional and climatic. The aim of the present investigation, therefore, was to induce fertile estrus in acyclic pubertal heifers and postpartum anestrous Zebu cows by hormonal intervention. Pubertal Hariana and Sahiwal anestrous heifers (n=51) and postpartum cows (n=55) were either assigned a placebo (controls, N=6 for each breed and parity) or treated with 10-d norgestomet (3 mg) subcutaneous ear implants, with an initial injection of 3 mg, im norgestomet + 5 mg estradiol valerate, followed by 500 IU eCG at implant withdrawal (NOR-treated groups). Jugular venous plasma samples were obtained from a total of 28 animals (controls : 4 heifers and 4 cows; NOR-treated : 12 heifers and 8 cows) on Days 0 (implant insertion), 3, 7, 9 and Day 10 (implant withdrawal), every 12 h on Days 11 and 12, and then once daily on Days 17, 24 and 31. All the samples were assayed for progesterone. Almost all (97%) heifers and 81% cows were induced to estrus, the majority (92% heifers and 79% cows) within 120 h of implant removal. Synchrony of the induced estrus was better in cows, but interval to estrus and estrus duration were significantly longer in heifers (P<0.05). Post-treatment fertility, based on Day 28 nonretum rate, first service, and overall conception rates, was better in heifers (78.9, 60.5 and 73.7%, respectively) than cows (77.1, 48.6 and 62.9%, respectively), but the differences were significant only for the overall pregnancy rate (71.8% for heifers and 51.2% for cows; P<0.05). Low pre-treatment plasma progesterone values (<0.5ng/mL) were consistent with ovarian inactivity, confirming the true anestrus status of experimental animals. Controls failed to exhibit estrus and maintained low progesterone concentrations throughout the study. In treated animals, high progesterone values from Day 17 onwards suggested ovulatory estrus. These early luteal phase progesterone concentrations in nonpregnant (P=0.06) and nonpregnant, nonretum (P<0.05) animals were low in comparison with those of pregnant animals. Good fertility resulting from breeding according to estrus, inspite of variable intervals to estrus and estrus duration, advocates its advantage over fixed-time insemination in norgestomet-treated anestrous Zebu cattle.     

Ultrasonography and hormone profiles of adrenocorticotrophic hormone (ACTH)-induced persistent ovarian follicles (cysts) in cattle

The objective of this study was to develop a model for the study of abnormal ovarian follicles in cattle by treating heifers with adrenocorticotrophic hormone (ACTH) (100 iu at 12 h intervals for 7 days, beginning on day 15 of the oestrous cycle). Cortisol concentrations increased (P < 0.05) within 24 h after beginning ACTH treatment and cortisol and progesterone concentrations remained elevated after cessation of ACTH treatment for 8 and 4 days, respectively. The pulses and surges of LH decreased during ACTH treatment, but FSH profiles were similar to those in controls and persistent or prolonged follicles were eventually observed in all heifers. In five heifers, prolonged dominant follicles ovulated after 10 days, whereas in six heifers, persistent follicular structures were present for 20 days, but ceased to secrete oestradiol after approximately 12 days. In the heifers with persistent follicular structures, new follicles emerged when the persistent follicle became non-oestrogenic. During the last 2 days of normal follicular growth, the concentration of oestradiol was greater than it was during prolonged or persistent follicle development (P < 0.05). There were no differences in the growth rates or maximum diameters of abnormal follicles that had different outcomes, but oestradiol concentrations were greater in prolonged follicles that ovulated compared with those follicles that persisted (P = 0.06). In conclusion, stimulation with ACTH resulted in a marked deviance from normal follicular activity. The aberrations were probably caused by the interruption of pulsatile secretion of LH (but not FSH) leading to decreased but prolonged oestradiol secretion.     

Synchronisation of oestrus in cattle using a potent progestin (SC21009) and PGF2a

Two experiments are described in which the time relationships of oestrus and ovulation and fertility to artificial insemination in sexually mature Friesian heifers are compared with similar animals treated with PGF₂a alone or in combination with SC21009. It is concluded that neither treatment adversely affects the parameters studied but that the combined treatment will lead to an enhanced oestrous response; and offers a practical method of oestrous synchronisation at farm level.