Absorbable deslorelin implants (Ovuplant) prolong postpartum anestrus in early ovulating dairy cows

Two experiments were conducted to investigate the use of a bioabsorbable implant of the GnRH agonist deslorelin to temporarily delay the resumption of postpartum ovulatory cycles in Holstein cows. In Experiment 1, recently calved cows were paired and received either a single implant (Ovuplant); Peptech Animal Health, Sydney, NSW, Australia) within 48 h of parturition (OVP; n=17), or remained as untreated controls (CON; n=17). Blood samples were collected for plasma progesterone assay three times weekly for 6 weeks to profile the pattern of resumption of ovulatory cycles. In Experiment 2, there were 15 CON and 15 OVP cows initially treated as for Experiment 1 as well as 15 OVP+SYNCH cows. Each cow in the CON and OVP+SYNCH groups received a progesterone vaginal insert (CIDR); Genetics Australia, Bacchus Marsh, Vic., Australia) for 7 days at 23 days postpartum (23 dpp) to synchronise estrus in cycling animals or to induce an ovulation with estrus in anestrus animals. Blood samples were collected weekly until removal of the CIDR insert, and then twice weekly until 56 dpp to monitor plasma P4 for retrospective determination of ovulation. Milk yield was monitored by twice daily electronic volume measurements and milk composition with once weekly milk composition analysis.In Experiment 1, CON cows began ovulating from 9 dpp; 15 of 17 had ovulated by the end of blood sampling at 42 dpp. None of the OVP cows ovulated until at least 24 dpp, and only 6 of 17 had ovulated by 42 dpp. The average day of first ovulation was extended from 22.4+/-2.7 dpp to 39.3+/-2.7 dpp (P<0.05). In Experiment 2, ovulation had occurred in 8 of 15 CON cows at the time of CIDR insertion (23 dpp), 0 of 15 OVP cows and 1 of 15 OVP+SYNCH cows. By 40 dpp (or 10 days following removal of the CIDR insert) every CON cow (15/15) had ovulated, but only 2 of 15 OVP+SYNCH cows and 1 of 15 OVP cows. None of these effects of treatment was associated with any changes in milk yield or composition in either experiment.In conclusion, inserting a bioabsorbable implant of deslorelin within 48 postpartum extended the interval to first ovulation to at least 24 dpp in 46 of 47 cows. Recovery periods were highly variable. This variability was not reduced by using a form of intravaginal progesterone supplementation that did produce a synchronised estrus with ovulation in anestrus animals that had not been treated with deslorelin.     

Effect of a deslorelin implant in a timed artificial insemination protocol on follicle development, luteal function and reproductive performance of lactating dairy cows

This study examined the influence of a GnRH agonist containing either 450 or 750 microg of deslorelin in an implant form or a gonadorelin injection (control) to induce ovulation in the Ovsynch protocol on pregnancy rates (PR), embryonic loss, and ovarian function in 593 lactating Holstein cows. Cows were given two injections of PGF2alpha 14 days apart, followed 14 days later by the Ovsynch protocol, and were timed artificially inseminated (TAI) at 68 +/- 3 days postpartum. Blood samples for determination of plasma progesterone concentrations were collected at 24 and 10 days prior to and 11 days after TAI. Pregnancy was diagnosed on Day 27 and reconfirmed on Day 41 after TAI. Non-pregnant, not re-inseminated cows at Day 27 had their ovaries examined by ultrasonography, and the number and size of follicles and presence of luteal tissue were determined. Simultaneously, these cows were re-synchronized with the Ovsynch protocol. Pregnancy during the re-synchronization period was determined between 35 and 41 days after insemination. On Day 27, PR were higher for control (39.0%) and deslorelin 450 microg (DESLORELIN 450) implant (41.3%) than for those receiving the deslorelin 750 microg (DESLORELIN 750) implant (27.5%; P<0.05). Pregnancy losses tended to decrease for DESLORELIN 450 compared with control (5.0% versus 12.7%; P<0.13). Plasma progesterone concentrations did not differ significantly among treatments. Deslorelin suppressed ovarian activity and decreased PR during the re-synchronization period compared with control. The percentage of non-pregnant animals that were re-inseminated by Day 27 was less for deslorelin compared with control. In conclusion, incorporation of an implant of the GnRH agonist deslorelin to induce ovulation in the Ovsynch protocol has the potential to reduce pregnancy losses, but the response was dependent upon implant concentration. Evaluation of lower doses to minimize the negative effects on subsequent fertility is warranted.     

The use of a deslorelin implant (GnRH agonist) during the late embryonic period to reduce pregnancy loss

Embryonic and fetal mortality reduce reproductive performance of lactating dairy cows. The objectives of this study were to reduce pregnancy loss by administering a deslorelin implant (GnRH agonist) during the late embryonic period, to reduce follicular growth, induce accessory corpora lutea, and increase plasma progesterone concentrations. Lactating dairy cows received an implant containing 2.1 mg of deslorelin (Deslorelin group; n = 89) or no treatment (Control group; n = 92) on Day 27 of pregnancy. Pregnancy, ovarian structures and plasma progesterone concentrations were determined on Days 27 and 45, and pregnancy was re-confirmed on Day 90. On Day 45, mean +/- S.E.M. numbers of class 2 (6-9 mm; 0.72+/-0.19) and class 3 (> or = 10 mm; 0.86 +/- 0.12) follicles for cows in the Deslorelin group were lower (P < 0.01) than the numbers of class 2 (1.90 +/- 0.18) and class 3 (1.92 +/- 0.12) follicles for cows in the Control group. On Day 45, the number of accessory corpora lutea for cows in the Deslorelin group (1.80 +/- 0.07) were greater (P < 0.01) than for cows in the Control group (1.31 +/- 0.07). On Day 45, plasma progesterone concentration was increased (P < 0.01) for cows in the Deslorelin group (8.03 +/- 0.33 ng/mL) compared to cows in the Control group (6.40 +/- 0.31 ng/mL). Pregnancy losses did not differ between Days 27 and 45 and Days 45 and 90 for cows in the Control (15.2 and 11.0%, respectively) and Deslorelin groups (20.2 and 10.5%, respectively). However, in the Deslorelin group, pregnancy loss between Days 45 and 90 was lower (P < 0.05) for cows that formed an accessory CL (0%) compared to cows that did not form an accessory CL (16.1%).     

Observations on the reproductive effects of once or twice weekly injections for 6 weeks of the GnRH agonist deslorelin in the cow

This study investigated the reproductive effects in Holstein-Friesian cows of once or twice weekly intramuscular injection for 6 weeks of 100 microg of the GnRH agonist deslorelin at intervals. Oestrus was synchronized in non-lactating Holstein-Friesian cows before they were allocated randomly to receive either 100 microg deslorelin once weekly (D1; N=10) or twice weekly (D2; N=8) or acted as untreated controls (CON; N=8). The first injection was given on day 6 post-oestrus and the last injection on day 48 post-oestrus. Blood samples were collected twice weekly from each cow until day 76 after the synchronized oestrus to profile plasma P4. A single injection of prostaglandin was administered to all cows on day 20 post-oestrus to ensure luteolysis occurred. Ovaries were examined twice weekly by transrectal ultrasonography and then subsequently at weekly intervals to monitor ovarian structures. Progesterone profiles observed over two complete cycles for CON cows were typical of those expected for cows displaying regular oestrous cycles. Injection of deslorelin on day 6 post-oestrus induced ovulation in 100% (18/18; D1 and D2) of deslorelin-treated cows. Three categories of responses based on plasma P4 profiles were defined amongst the deslorelin-treated cows. Complete anoestrus was observed in 20% (2/10) of D1 and 63% (5/8) of D2 cows. A partial response characterised by intermittently low concentrations of P4 was observed in 50% (5/10) of D1 and 25% (2/8) of D2. A complete lack of response to deslorelin, with P4 profiles indistinguishable from CON cows, was seen in 30% (3/10) of D1 and 13% (1/8) of D2 cows. When results from D1 and D2 were pooled, a greater proportion of deslorelin-treated cows had abnormal ovarian cycles during the treatment period (56% versus 0%; D1 and D2 versus CON, P <0.001). In conclusion, the repeated injection of deslorelin either once or twice weekly for 6 weeks significantly altered the ovarian cycles of some cows; individual cow responses observed varied widely and ranged from complete anoestrus to a cycle indistinguishable from normal.     

Removal of deslorelin (Ovuplant) implant 48 h after administration results in normal interovulatory intervals in mares

Deslorelin implants, approved for use in inducing ovulation in mares, have been associated with prolonged interovulatory intervals in some mares. Administration of prostaglandins in the diestrous period, following a deslorelin-induced ovulation, has been reported to increase the incidence of delayed ovulations. The goals of the present study were: (1) to determine the percentage of mares given deslorelin that experience delayed ovulations with or without subsequent prostaglandin treatment, and (2) to determine if removal of the implant 48 h after administration would effect the interval to subsequent ovulation. We considered interovulatory intervals to be prolonged if they were greater than the mean +/- 2 standard deviation (S.D.) of the control group in study 1 and the hCG group in study 2. In study 1, we retrospectively reviewed reproduction records for 278 mares. We either allowed the mare to ovulate spontaneously or induced ovulation using deslorelin acetate implants or hCG. We administered prostaglandin intramuscularly, 5-9 days after ovulation in selected mares in each group. A higher percentage of mares which were induced to ovulate with deslorelin and given prostaglandins had a prolonged interovulatory interval (23.5%; n = 16), as compared to deslorelin-treated mares that did not receive prostaglandins (11.1%; n = 5). In study 2, we induced ovulation in mares with hCG (n = 47), a subcutaneous deslorelin implant via an implanting device provided by the manufacturer (n = 28), or a deslorelin implant via an incision in the neck (n = 43) and we removed the implant 48 h after administration. We administered prostaglandin to all mares 5-9 days after ovulation. In study 2, mares from which the implant was removed had a normal ovulation rate and none had a prolonged interval to ovulation. Administration of prostaglandin after deslorelin treatment was associated with a longer interval from luteolysis to ovulation than that found in mares not treated with deslorelin. Prostaglandin administration during diestrus may have exacerbated the increased interval to ovulation in deslorelin-treated mares. We hypothesize that prolonged secretion of deslorelin from the implant was responsible for the extended interovulatory intervals.     

Induction of ovulation in nonlactating dairy cows and heifers using different doses of a deslorelin implant

The objective of this study was to evaluate ovarian function after inducing ovulation with a deslorelin implant in nonlactating dairy cows and heifers. Cattle received GnRH on Day -9, and PGF2alpha on Day -2. On Day 0, in Experiment 1, cows received either 100 microg GnRH (Control), a 750 microg (DESLORELIN 750) or 1000 microg (DESLORELIN 1000) deslorelin implant. On Day 0, in Experiment 2, cows received 100 microg of GnRH or a 450 microg (DESLORELIN 450) deslorelin implant. In Experiments 1 and 2, cows received PGF2alpha on Day 16. Ultrasonography and blood sampling for plasma progesterone (P4) were used to monitor ovarian activity. On Day 0, in Experiment 3, heifers received either 100 microg of GnRH or 750 microg (DESLORELIN 750) deslorelin implant. On Day 16, all heifers received PGF2alpha. Blood samples were collected on Days 7, 13 and 16. In Experiments 1-3, deslorelin implants did not elevate plasma concentrations of P4 in a systematic manner during the late luteal phase. In Experiments 1 and 2, deslorelin implants decreased the size of the largest follicle and the number of Class II and III follicles. In Experiments 1 and 2, deslorelin-treated cows failed to ovulate by Day 28. In conclusion, deslorelin implants induced ovulation, stimulated development of a normal CL, and delayed follicular growth during the subsequent diestrus period. For future applications, the dose of the deslorelin implant will have to be adjusted, and if used for timed-inseminations, nonpregnant cows will have to be resynchronized to minimize delayed returns to estrus and ovulation.     

Effects of a new injectable short-term release deslorelin in foal-heat mares

Mares treated with subcutaneous deslorelin implants on the first postpartum estrus early in the breeding season had significant reductions in the number of large follicles at early pregnancy examinations and delayed return to estrus (in mares that failed to become pregnant); these adverse effects were attributed to a prolonged release of the drug from the implant. In 2003, an injectable short-term release (<24 h) deslorelin product became available. The objective of this study was to determine if this product would hasten ovulation in early foaling first postpartum estrus mares without reducing the number of large follicles at early pregnancy examination (14-15 days postovulation). Beginning 5-6 days postpartum, first postpartum estrus (foal-heat) mares were teased daily and examined thrice weekly (Tuesday, Thursday and Saturday) by transrectal ultrasonography. Mares in estrus with a follicle > or = 34 mm diameter on Tuesdays or Thursdays were alternately assigned to: Treatment 1, n = 17; 1.5 mg injectable short-term release deslorelin, or Treatment 2, n = 16; Control (no treatment). The schedule allowed accurate determination of the number of mares ovulating within 2 days of treatment (i.e., ovulations detected on Thursday or Saturday). Mares were mated on the day of treatment and at 2-day intervals until either ovulation was confirmed or until behavioral estrus ceased. Transrectal ultrasonography was done 14-15 days after ovulation to assess ovarian follicles and pregnancy status. Fewer covers were required and more mares ovulated within 2 days of treatment in deslorelin-treated versus Control mares (P < 0.01). Pregnancy rates were normal (69%) in deslorelin-treated mares. The number of large follicles 14-15 days after ovulation did not differ between deslorelin-treated and Control mares (P > 0.10), suggesting follicular suppression did not occur with this formulation of deslorelin.     

Reproductive responses following postpartum suppression of ovarian follicular development with a deslorelin implant during summer heat stress in lactating dairy cows

The objective was to evaluate pregnancy rate to a timed artificial insemination (TAI) protocol in the autumn for cows treated with a non-degradable GnRH agonist implant (Deslorelin [DESL], 5mg) during the summer heat stress period compared with non-treated controls (CON). Cows were randomly assigned to receive or not a DESL implant within 1-4 days postpartum (dpp) twice weekly, from 25 June through 8 August 2001. All cows in DESL implant and CON treatments were injected with PGF(2alpha) 7 days after enrollment. Ultrasonography (US) monitored numbers of ovarian follicles and corpus luteum (CL) at approximately 10, 30, 35/36, 45/44, 56/55 and 66/63dpp, while DESL implants were in situ and concurrently CON, respectively. DESL implants were removed at two specific days, 28 August and 4 September. Cows had DESL implant in situ for a range of 28-67 days, depending on date of enrollment and implant removal. Within 61-100dpp, 31 days after implant removal, DESL implant and CON cows were initiated in a Presynch-Ovsynch and TAI protocol. Pregnancy was evaluated by US and palpation per rectum at 28 and 46 days after TAI, respectively. Plasma concentrations of progesterone were analyzed for sets of blood samples collected during the Presynch-Ovsynch and at TAI day followed 8 days later. Cows in the DESL-implant treatment had more (P<0.01) Class 1 (3-5mm) follicles, less (P<0.01) Class 2 (6-9mm), Class 3 (> or =10mm) follicles and CL compared with CON cows. Proportion of cows having initiated estrous cycles after calving was less (P<0.01) in the DESL-implant treatment (52.2%, 58/111) compared with CON (93.7%, 104/111) at the beginning of Ovsynch. Pregnancy rate to TAI was less (P<0.01) in the DESL implant (27.5%, 33/120) compared with CON (53.9%, 69/128). Pregnancy rate to TAI was less (P<0.01) in DESL-implanted cows that had initiated estrous cycles after calving (30.6%, 19/62) compared with CON (53.7%, 65/121) cows having initiated estrous cycles after calving. Furthermore, pregnancy rate was less (P<0.01) for cows having ovulations that had initiated estrous cycles after TAI in the DESL implant (39.1%, 18/46) compared with CON (62.1%, 54/87) treatments. Pregnancy losses from day 28 to day 46 of pregnancy did not differ between DESL implant (15.1%, 5/33) and CON (13.0%, 9/69) treatments. The DESL implant induced a delay in initiation of a new wave of follicular development during the postpartum-heat stressed period. The lesser pregnancy rate in the DESL-implant treatment group may be due to a pool of heat stress damaged follicles that were depleted in the control group with re-occurring follicle waves.     

Restoration of LH output and 17beta-oestradiol responsiveness in acutely ovariectomised holstein dairy cows pre-treated with a GnRH agonist (deslorelin) for 10 days

The objectives of the study were firstly to identify the role of the ovary in maintaining plasma luteinising hormone (LH) concentrations in cows treated with an implant of a potent GnRH agonist (deslorelin), and secondly to characterise the changes in LH following ovariectomy (OVX) in the same animals. Oestrus was synchronised in mature Holstein dairy cows and deslorelin implants were inserted 17 days later into two-third of the cows. A further 10 days later (day 0) all cows had bilateral OVX performed. A control group (CON; n=4) received no treatment and had blood samples collected at 15-min intervals for 8h on the day prior to OVX (day -1) and similarly on days 4 and 10. One group (DES_IN; n=4) had implants in place for the duration of the study while another group had implants removed (DES_OUT; n=4) at the time of OVX. DES_IN cows were sampled hourly at each sampling session (days -1, +4 and +10), whereas DES_OUT cows were sampled similarly to CON except on day -1 when hourly samples were collected.Predictable post-operative increases in mean LH (0.61 ng/ml versus 1.79 ng/ml; P<0.01) and LH pulse amplitude (0.66 ng/ml versus 1.56 ng/ml; day -1 versus day +10; P<0.01) occurred after CON cows were ovariectomised. Smoothed LH means showed a delayed effect of time compared to arithmetic means. Pulse frequency was unchanged following OVX in CON cows. A comparison of all cows that had been treated with deslorelin from day -1 showed a significant elevation of smoothed mean LH compared to untreated cows (0.80 ng/ml versus 0.34 ng/ml; DES_IN and DES_OUT versus CON; P<0.05). DES_IN cows had a 54% reduction in mean LH from day -1 to +4 following OVX (1.05 ng/ml versus 0.48 ng/ml; P<0.01) indicating the probable involvement of the ovary in the maintenance of elevated basal LH. No further reduction was detected by day +10. The LH response to an intramuscular (IM) injection of 500 microg 17beta-oestradiol (E2) on day +11 varied significantly between treatment groups (P<0.01). CON cows showed a typical LH surge, reaching maximum concentrations (10.3 ng/ml) at 17.3h post-injection. Even though low amplitude LH pulsatility had been restored in DES_OUT cows by day +4, there was an inconsistent response to E2 on day +12; one cow had an apparently normal surge yet, others showed only attenuated responses. Pulse amplitude in DES_OUT cows was lower at days +4 and +10 compared to CON (P<0.05). DES_IN cows did not produce any surge after E2. Mean LH prior to OVX (day -1) remained unchanged following the 500 microg oestradiol injection (0.38 ng/ml versus 0.45 ng/ml pre-E2 versus post-E2 compared to 1.05 ng/ml pre-OVX).The results of this experiment implicated ovarian involvement in maintaining elevated basal LH output in cows that were chronically treated with a GnRH agonist. Individual cows varied in their LH surge response to exogenous E2 given 12 days after implant removal, even though LH pulse amplitude and frequency had been restored.     

Influence of deslorelin (GnRH-agonist) implant on plasma progesterone, first wave dominant follicle and pregnancy in dairy cattle

The objectives of this study were to investigate the effect of a synthetic GnRH-agonist (Deslorelin) implant on CL function and follicle dynamics when administered 48 h after PGF2 alpha, in a timed-insemination protocol, and to determine if the incorporation of a Deslorelin implant into a timed-insemination protocol to synchronize ovulation would be beneficial to the establishment of pregnancy. In Experiment 1, 15 non lactating cyclic Holstein cows received Buserelin (8 micrograms, i.m.) on Day-9, Lutalyse (25 mg, i.m.) on Day-2, and then on Day 0 received either a Deslorelin implant (700 micrograms, s.c.; n = 5), Buserelin (8 micrograms, i.m.; n = 5), or no treatment (control; n = 5). Blood samples were collected on Days-9, -2, 0 and thereafter daily until the next ovulation. Ovaries were scanned by ultrasound on Days-9, -2, 0, 1 (day of ovulation) and 3 times a week thereafter until a subsequent ovulation. From Days 0 to 15, the rate of increase of plasma progesterone (P4) was greater (P < 0.01) for Deslorelin than for control and Buserelin. Establishment of the first-wave dominant follicle (FWDF) as a Class 3 (> 9 mm) follicle was delayed (P < 0.01) with Deslorelin (14.2 +/- 1.3 d) compared with the control (4.6 +/- 1.3 d) and Buserelin (5.0 +/- 1.5 d) treatments. The FWDF resumed growth after Day 13 in all 5 Deslorelin-treated cows, and 2 cows ovulated spontaneously. In 1 Deslorelin-treated cow, the FWDF regressed, and a second-wave dominant follicle ovulated, while 2 other Deslorelin cows failed to ovulate until after Day 36. The cumulative numbers of Class 2 and 3 follicles was lowest in the Deslorelin group (P < 0.01), while the cumulative number of Class 1 follicles was highest (Deslorelin > Buserelin > Control; P < 0.01). The number of days to CL-regression and days to subsequent estrus did not differ (P > 0.05) among treatments. In Experiment II, 16 lactating potentially subfertile (body condition score 2.25) cows received Cystorelin (100 micrograms, i.m.; Day-9), Lutalyse (25 mg, i.m.; Day-2), and either a Cystorelin injection (100 micrograms, i.m.; n = 8) or Deslorelin implant (700 micrograms, s.c.; n = 8) on Day 0 and inseminated 16 h later. Deslorelin-treated cows had a higher plasma P4 concentration between Days 0 and 16 (P < 0.05) than the 2 other groups, and 5 of the 8 cows in this group were pregnant (Day 45, palpation) compared with 1 of 8 cows in the Cystorelin group (P < 0.05). Incorporation of a Deslorelin implant into a timed-insemination protocol enhanced the pregnancy rate in cows of poor body condition. The results support the hypothesis that enhanced CL function and delayed establishment of the first-wave dominant follicle may enhance embryo survival.     

Effects of abnormal ovarian cycles during pre-service period postpartum on subsequent reproductive performance of high-producing Holstein cows

The primary objective of this study was to investigate the effects of abnormal ovarian cycles during the pre-service postpartum period on subsequent reproductive performance of high-producing Holstein cows. The study was conducted in a commercial dairy farm with approximately 150 lactating cows, in a subtropical region of Japan. Animals were kept in free-stall barn, and fed a total mixed ration. Cows that calved from June 2001 to July 2002 were included in the study. Milk samples were collected twice weekly from 2 to 11 weeks postpartum, and progesterone concentrations in skim milk were determined by ELISA. After a voluntary waiting period of 40 days, cows detected in estrus were bred by artificial insemination (AI). Pregnancy was confirmed by palpation per rectum 40-70 days after AI. Out of a total of 91 cases, 39 (42.9%) had normal ovarian cycles (ovulation within 45 days after calving, followed by normal ovarian cycles), 32 (35.2%) had prolonged luteal phase (i.e. luteal activity for >20 days), and 12 (13.2%) had anovulation or delayed first ovulation (i.e. first ovulation did not occur until >45 days after calving). The remaining (8.8%) had other types of abnormalities. When compared with cows with a normal ovarian cycle, prolonged luteal phase cows had a lower 100 days AI submission rate, conception rate and pregnancy rate (84.2% versus 56.3%; P<0.05, 50% versus 16.7%; P<0.05 and 42.1% versus 9.4%; P<0.01, respectively), and longer intervals to first AI and to conception ( 67+/-6 days versus 98+/-7 days and 95+/-9 days versus 136+/-11 days; P<0.01 for each). Similarly, when compared with cows with normal ovarian cycles, those with anovulation had lower 100 days conception rate and pregnancy rate (50% versus 0%; P<0.05 and 42.1% versus 0%; P<0.01, respectively), and longer intervals to first AI and to conception ( 67+/-6 days versus 93+/-12 days; P<0.05 and 95+/-9 days versus 155+/-14 days; P<0.01, respectively). Survival analysis of the data for calving to conception interval showed that cows with prolonged luteal phase or anovulation were getting pregnant at a slower rate, and took longer to get pregnant than the cows with normal resumption of ovarian cyclicity postpartum. In conclusion, abnormal ovarian cycles during the pre-service period postpartum adversely affected reproductive performance, including AI submission rate, pregnancy rate, interval to first AI, and calving to conception interval in high-producing Holstein cows.     

Reproductive hormone secretions and first service conception rate subsequent to ovulation control with Synchro-Mate B

Two groups of beef females receiving suboptimal energy diets were treated with Synchro-Mate B to control ovulation. The first group consisted of 30 suckled cows and 16 heifers. These females were bled 10 days and immediately prior to the implantation of norgestomet implants, at implant removal, 24, 27, 30, 33 and 36 hours and 9 and 16 days post-implant removal. The second group which consisted of 40 cows and 8 heifers was handled in the same manner except no blood samples were collected from 24 to 36 hours following implant removal. Calves were removed from all the cows for 48 hours, beginning at implant removal. All animals were artifically inseminated 48 hours following implant removal. Blood plasma was assayed for concentrations of progesterone and LH. The first service conception rate was 21% and 40% for groups 1 and 2. Several factors were identified that reduced the first service conception rate. In summary, Snychro-Mate B is an effective method to synchronize estrus in cattle. However, stress subsequent to implant removal should be avoided in order to obtain a higher first service conception rate.     

Use of deslorelin short-term implants to induce ovulation in cycling mares during three consecutive estrous cycles

Alternatives to human chorionic gonadotropin (hCG) for inducing ovulation in cycling mares over several consecutive cycles were explored. Placebo, one, three or five short-term implants each containing 2.2 mg of gonadotropin-releasing hormone (GnRH) analogue (deslorelin) were administered to cycling mares after identification of a follicle over 30 mm. Mares were treated over three consecutive cycles, and artificially inseminated during the third cycle only. Serum was assayed for concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and progesterone during each cycle. All deslorelin doses decreased the interval to ovulation (4.0 days, 2.6 days, 2.4 days and 2.0 days), increased the proportion of mares ovulating within 48 h (20.0%, 83.3%, 73.3% and 85.7%), and decreased the diameter of the largest follicle at ovulation (45.8 mm, 38.0 mm, 41.0 mm and 37.2 mm) for the placebo, 2.2 mg, 6.6 mg and 11.0 mg groups, respectively (P < 0.05). The interovulatory interval was lengthened in the 11.0 mg group compared with all other groups (21.2 days, 21.8 days, 26.4 days and 32.7 days for the placebo, 2.2 mg, 6.6 mg and 11.0 mg groups, respectively, P < 0.05). No differences (P > 0.05) were detected in serum concentrations of progesterone or pregnancy rate among the groups. Cycle number had no effect (P > 0.05) on the reproductive parameters or serum concentrations of progesterone. Concentrations of LH were higher in Cycle 3 in the 6.6 mg and 11.0 mg groups, and FSH concentrations were decreased in Cycles 2 and 3 in treated mares. Deslorelin was efficacious for inducing ovulation in cycling mares with no diminished activity over three consecutive cycles. However, ovarian suppression and changes in serum concentrations of gonadotropins were noted at higher doses.     

Effects of buserelin injection and deslorelin (GnRH-agonist) implants on plasma progesterone, LH, accessory CL formation, follicle and corpus luteum dynamics in Holstein cows

The influence of Buserelin injection and Deslorelin (a GnRH analogue) implants administered on Day 5 of the estrous cycle on plasma concentrations of LH and progesterone (P4), accessory CL formation, and follicle and CL dynamics was examined in nonlactating Holstein cows. On Day 5 (Day 1 = ovulation) following a synchronized estrus, 24 cows were assigned randomly (n = 4 per group) to receive 2 mL saline, i.m. (control), 8 micrograms, i.m. Buserelin or a subcutaneous Deslorelin (DES) implant in concentrations of 75 micrograms, 150 micrograms, 700 micrograms or 2100 micrograms. Blood samples were collected (for LH assay) at 30-min intervals for 2 h before and 12 h after GnRH-treatment from cows assigned to Buserelin, DES-700 micrograms and DES-2100 micrograms treatments and thereafter at 4-h intervals for 48 h. Beginning 24 h after treatment, ovaries were examined by ultrasound at 2-h intervals until ovulation was confirmed. Thereafter, ultrasonography and blood sampling (for P4 assay) was performed daily until a spontaneous ovulation before Day 45. A greater release of LH occurred in response to Deslorelin implants than to Buserelin injection (P < 0.01). Basal levels of LH between 12 and 48 h were higher in DES-700 micrograms group than in DES-2100 micrograms and Buserelin (P < 0.05). The first wave dominant follicle ovulated in all cows following GnRH treatment. Days to CL regression did not differ between treatments, but return to estrus was delayed (44.2 vs 27.2 d; P < 0.01) in cows of DES-2100 micrograms group. All GnRH treatments elevated plasma P4 concentrations, and the highest P4 responses were observed in the DES-700 micrograms and DES-2100 micrograms groups. The second follicular wave emerged earlier in GnRH-treated than in control cows (9.9 vs 12.8 d; P < 0.01). However, emergence of the third dominant follicle was delayed in cows of DES-2100 micrograms treatment (37.0 d) compared with DES-700 micrograms (22.2 d), Buserelin (17.8 d) or control (19.0 d). In conclusion, Deslorelin implants of 700 micrograms increased plasma P4 and LH concentrations and slightly delayed the emergence of the third dominant follicle. On the contrary, Deslorelin implants of 2100 micrograms drastically altered the P4 profiles and follicle dynamics.     

Induction of fertile oestrus in the bitch using Deslorelin, a GnRH agonist

Oestrus induction in various canine breeds was attempted in 32 bitches. A group of 8 bitches were treated 80–160 d following their previous oestrus (G1) whereas a second group of 24 bitches (G2) were implanted 200–590 d following their previous oestrus. The treatment for each bitch consisted in one Deslorelin implant (Suprelorin®4,7mg, Virbac, France), inserted subcutaneously in the post-umbilical region. Ovulation, pregnancy rate and litter size were recorded. All bitches came in heat 4.3 ± 1.4 d after implantation (2–7 d). Ovulation was reported in 62.5% in G1 and 87.5% in G2. One bitch refused mating and since no AI was performed, she was not considered for further analysis. Pregnancy was obtained in 25% in G1 versus 78.3% in G2. Mean litter size was 6.7 ± 3.5 puppies (1–14). Luteal failure was suspected in 3 bitches, two that remained non-pregnant and one which aborted 58 d post-ovulation since the owner refused progesterone supplementation. Deslorelin implants can therefore be considered as a valuable alternative to induce fertile oestrus in bitches in anoestrus. Follow-up of the luteal phase is recommended, since some bitches might encounter luteal failure.     

Pattern and manipulation of follicular development in Bos indicus cattle

Bos indicus cattle are widespread in tropical regions due to their adaptation to these environments. Although data on reproductive performance have indicated both inferior and superior results for B. indicus cattle, there is little doubt that B. indicus cattle are superior than Bos taurus cattle when they are both kept in tropical or subtropical environments, where stressors like hot temperatures, humidity, ectoparasites and low quality forages are greater. Reproductive endocrinology and oestrus behaviour of the B. indicus cattle have been studied for over 30 years; however, the application of technologies such as real time ultrasonography and Heat-Watch systems has expanded our knowledge on the ovarian follicular-wave dynamics during the oestrous cycle and the time of ovulation. Ovarian follicular dynamics in B. indicus cattle is characterised by the occurrence of two, three or sometimes four waves of follicular development. While dominance is similar to that in B. taurus cattle, maximum diameters of the dominant follicle and CL are smaller than those reported in B. taurus and are probably due to a lower capacity for LH secretion than in B. taurus. Duration of oestrus is approximately 10 h and the interval from oestrus to ovulation is about 27 h. However, the variability in response to prostaglandin F2alpha (PGF) treatments and the difficulty for oestrus detection in B. indicus cattle have limited the widespread application of artificial insemination (AI) and emphasizes the need for treatments that control follicular development and ovulation. Follicular-wave development in B. indicus cattle can be controlled mechanically by ultrasound-guided follicle ablation, or hormonally by treatments with GnRH or oestradiol and progestogen/progesterone in combination. Treatments with GnRH plus PGF and a second GnRH (synchronization protocol known as Ovsynch) or oestradiol benzoate (known as GPE) have resulted in acceptable pregnancy rates after fixed-time AI (FTAI) in cycling cows, but results were lower in heifers and cows in postpartum anoestrus. Alternatively, treatments with oestradiol and progestogen/progesterone releasing devices resulted in synchronous emergence of a new follicular wave, and a second oestradiol or GnRH treatment after device removal resulted in synchronous ovulation and acceptable pregnancy rates to FTAI. Furthermore, oestradiol and progesterone treatments combined with eCG (given at the time of device removal) increased pregnancy rates in suckled B. indicus cows and may be useful for the treatment of cows in postpartum anoestrus. In summary, exogenous control of luteal and follicular development facilitates the application of assisted reproductive technologies in B. indicus cattle by offering the possibility of planning AI programs without the necessity of oestrus detection and without sacrificing the overall results.     

Ovarian follicular development in Holstein cows following synchronisation of oestrus with oestradiol benzoate and an intravaginal progesterone releasing insert for 5-9 days and duration of the oestrous cycle and concentrations of progesterone following ovulation

The aim of this study was to determine if the duration of treatment with an intravaginal progesterone releasing insert (IVP(4)) after treatment with oestradiol benzoate (ODB) at the time of insertion and 24 h after removal would affect selected variables including: size of ovarian follicles at the time of removal of inserts, diameter of ovulatory follicles, plasma concentrations of progesterone following ovulation, and duration of the following oestrous cycle. Characteristics of oestrus at a synchronised and spontaneous oestrus were also monitored. Non-lactating Holstein cows were synchronised with an IVP(4) for 5 (n = 10), 7 (n = 10), 8 (n = 9) or 9 (n = 9) days together with injections of ODB at device insertion (2 mg) and 24 h after removal (1 mg). Ultrasonography showed no significant effect of treatment on the day of emergence of preovulatory follicles relative to the day of removal of inserts (overall mean = -4.22 +/- 0.58; P = 0.15) for cows that ovulated within 120 h insert removal (n = 36). Treatment with ODB and an IVP(4) for 5 days reduced the diameter of preovulatory follicles at the time of removal of inserts and for the following 2 days compared to cows treated for 7-9 days (mean difference 2.56 +/- 1.15 mm; P = 0.033) but did not reduce the diameter of the ovulatory follicle (P = 0.21). Day of emergence relative to removal of inserts was associated with the diameter of the ovulatory follicle (R2 = 0.69; P < 0.001). Concentrations of progesterone and the diameter of the corpus luteum following ovulation were not affected by treatment (P > 0.20), but were affected by the diameter of the ovulatory follicle (P < 0.01). Diameter of the ovulatory follicle did not affect interoestrous and interovulatory intervals (P > 0.40). We conclude that treatment with an IVP(4) for 5 compared to 7-9 days with ODB administered at device insertion, and 24 h after removal reduced the diameter of preovulatory follicles at the time of removal of the insert but did not reduce the diameter of the ovulatory follicle or concentrations of progesterone in plasma. Emergence of preovulatory follicles closer to the time of removal of inserts reduced the diameter of the ovulatory follicle when oestrus was induced with ODB. Ovulation of smaller follicles reduced concentrations of progesterone in plasma following ovulation but did not affect oestrous cycle duration.     

Postpartum anoestrus is reduced by increasing the within-day milking to suckling interval in dual purpose cows

In the dual purpose milk/beef production system practised in Mexico, the cows are milked once a day in the presence of the calf and then the calf suckles for the next 1-8 h. It was hypothesised that the imposition of milking and suckling in close succession contributes to the long postpartum anoestrous periods experienced by cows in this system. Therefore, separating these two inhibiting factors, by delaying the start of suckling after milking would lower the impact on the hypothalamus-hypophysial axis and allow it to recover more readily. This hypothesis was tested in two experiments using Bostaurus x Bosindicus cows which weighed 541.3 +/- 12.7 kg (mean +/- S.E.M.; experiment 1) and 537.8 +/- 10.6 kg (experiment 2) and had a body condition score of 5-6 (scale 1-9) at calving. The cows and calves were maintained on separate pastures and the cows were offered concentrate supplements. Experiment 1 was conducted in the dry season and cows were offered a daily supplement of 3 kg of 17% crude protein (CP) concentrates plus 1 kg molasses per cow. Experiment 2 was conducted during the wet season and the nutritional supplement consisted of only 1 kg of 17% CP plus 1 kg molasses per cow per day. Each experiment lasted for the first 100 days postpartum and the cows were not mated during this time. Cows were hand-milked once a day in the presence of the calf to stimulate milk let-down. In experiment 1, 30 multiparous cows were assigned at random by date of calving, to one of three treatments: controlled suckling (CS; n = 10), delayed suckling (DS; n = 10) and prolonged delayed suckling (PDS; n = 10). The suckling period on all treatments lasted for 2 h and started at 0 h (CS), 4 h (DS) or 8 h (PDS) after milking. In experiment, 34 multiparous cows were assigned at random to three treatments: CS (n = 11), PDS (n = 11) or prolonged delayed short suckling (PDSS; n = 12), in this last treatment the suckling period was reduced to only 30 min. In both experiments, one quarter of the udder of cows on treatment CS was not milked but all the udder was milked on the other treatments. Body weights of cows and calves and cow milk yields were recorded. Weekly blood samples were collected for plasma progesterone assay to detect the first postpartum corpus luteum. Data were analysed by ANOVA and chi-square test. Cows in experiment 1 had similar weight changes during the first 100 days postpartum. Milk production was higher for DS (8.0 +/- 0.7 kg per day) and PDS (7.0 +/- 0.5 kg per day) cows than for CS (5.2 +/- 0.7 kg per day) cows (P < 0.01). Calf daily gain was greater (P < 0.05) for PDS (827 +/- 35 g per day), than CS (702 +/- 26 g per day) or DS (715 +/- 29 g per day). The proportion of cows ovulating during the first 100 days postpartum were 50.0, 70.0 and 100.0%, for CS, DS and PDS, respectively (P < 0.05). The intervals from calving to first significant rise in progesterone were 70.4 +/- 1.6, 72.1 +/- 1.3 and 64.6 +/- 1.5 days for CS, DS and PDS (P > 0.05), respectively. In experiment 2, cow body weight during the first 100 days postpartum did not differ between treatments. Milk production was not significantly different between CS (7.3 +/- 1.0 kg per day) and PDSS (6.8 +/- 1.0 kg per day), but was higher (P < 0.05) for CS than PDS (5.2 +/- 1.0 kg per day). Calf daily gain was lower for CS (576 +/- 31 g per day; P < 0.05) than PDS (779 +/- 38 g per day) and PDSS (780 +/- 20 g per day). The proportion of cows ovulating was higher (P < 0.05) for treatments PDS (100%) and CS (81.8%) than PDSS (50%). Calving to first ovulation interval was shorter (P < 0.05) for PDS (57.3 +/- 4.5 days) and PDSS (49.7 +/- 3.0 days) cows than CS (72.1 +/- 3.5 days) cows. It is concluded that delaying suckling for 8 h after milking, increases the proportion of cows ovulating within 100 days of calving, shortened the calving to first ovulation interval and improved calf performance without adversely affecting cow milk yield or body weight change.     

Ovarian and endocrine responses and reproductive performance following GnRH treatment in early postpartum dairy cows

At calving forty-eight Holstein and Guernsey cows were assigned according to age and breed to one of six postpartum periods (1 or 2, 3 or 4, 5 or 6, 7 or 8, 12 or 13 and 18 or 19 days postpartum). Thirty-six of the cows (6 cows per postpartum period) received a single intramuscular injection of 100 μg GnRH. The other twelve cows (2 cows per postpartum period) served as controls and received a single intramuscular injection of the carrier vehicle for GnRH.Four of 36 cows administered GnRH and three of the 12 control cows ovulated by the day following treatment. Four of the cows were 12 or 13 days postpartum (1 control and 3 GnRH treated) and three were 18 or 19 days postpartum (2 controls and 1 GnRH treated). Six of the seven cows that ovulated the day following treatment had a follicle > 1.0 cm the day prior to treatment. Follicular growth was detected in the earlier postpartum periods but ovulation the following day was not detected for either control or GnRH treated cows. Following estrus or silent estrus, plasma progesterone concentrations increased to about 4 ng/ml on day 13. However, in cows ovulating the day following GnRH treatment, plasma progesterone declined from about 3 ng/ml on day 9 to approximately 1 ng/ml on day 13 postestrus. In addition, LH in plasma was higher (P < .01) ? through 13 days following estrus or silent estrus in cows ovulating the day after GnRH treatment in comparison to cows during the first or subsequent postpartum estrous cycles.In summary, in addition to days postpartum other factors including follicular development and maturity are probably involved in GnRH induced ovulation.