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

Effect of treatment of Bos indicus heifers with progesterone 0, 3 and 6 days after follicular aspiration on follicular dynamics and the timing of oestrus and ovulation

Synchronisation of wave emergence is used to synchronise oestrus in cattle. The aim of this study was to determine if treatment with high concentrations of progesterone in Bos indicus heifers for 3 days would synchronise new wave emergence when treatment commenced at early, mid and late stages of follicular development. Heifers were treated with a sc silicone implant containing norgestomet from Days -7 to 9 and cloprostenol (IM) on Days -7 and -2. All follicles > 4 mm in diameter were removed by transvaginal follicular aspiration either on Days 0 (Experiment 1), 3 (Experiment 2) or 6 (Experiment 3). From Days 6 to 9 every heifer was treated with two intravaginal progesterone releasing inserts that each contained either no progesterone (Control, n = 8/experiment) or 3.12 g of progesterone (n = 8/experiment). Ovarian follicular development was monitored at least once daily following aspiration until oestrus and ovulation. In each experiment, treatment with progesterone significantly increased concentrations of progesterone in plasma from Days 6 to 9 compared to Control heifers. It also significantly delayed the day of emergence of the ovulatory follicle (1.6 ± 0.6 vs 8.6 ± 0.3; 4.1 ± 0.1 vs 8.6 ± 0.2; 7.0 ± 0.0 vs 9.3 ± 0.4, for Control vs progesterone treated heifers, respectively in Experiments 1 to 3) and the interval from implant removal to oestrus and ovulation. In conclusion, treatment with high concentrations of progesterone can synchronise wave emergence in Bos indicus heifers when administered at early, mid and late stages of follicular development.

Maintenance of pregnancy in repeat breeder dairy cows by CIDR administration after breeding

The aim of this study was to assess the effect of two periods of P4 therapy by CIDR on the 1st service Conception Rate (CR) of repeat breeder dairy cows. The cows were selected on the following basis: absence of dystocia, retained placenta and endometritis after the last parturition. They were inseminated according to the AM/PM rule relative to estrus onset and randomly assigned into 3 groups: (A) CIDR on day 5 after insemination that was removed on day 9 of the cycle (n = 40); (B) CIDR on day 5 after insemination that was removed on day 19 of the cycle (n = 36) and (C) untreated controls (n = 40). Pregnancy diagnosis was conducted by rectal palpation 45-55 days after AI in cows not observed in estrus. The difference in CR among the groups was analyzed by chi square analysis. The CR in groups A, B and C was 55, 41.7 and 30%, respectively and was greater (p<0.05) in treatment (A) cows than in control cows. In conclusion, repeat breeder cows in groups A and B benefited from progesterone supplementation, but significant effects of treatment for improvement of conception rate was seen in short treatment period (4 days treatment).

Resynchronization of previously timed-inseminated beef heifers with progestins

The objective was to determine the efficacy of a previously used CIDR or melengestrol acetate (MGA; 0.5mg/head/day) for resynchronization of estrus in beef heifers not pregnant to timed-AI (TAI). In three experiments and a field trial, heifers were reinseminated 6-12 h after first detection of estrus. Pregnancy diagnosis was done from approximately 25-43 days after either TAI or reinsemination. In Experiment 1, 79 heifers received a once-used CIDR from 13 to 20 days after TAI and 80 heifers were untreated controls. For these two groups, there were 34 and 35 heifers, respectively, not pregnant to TAI; median +/- S.E. intervals from TAI to onset of estrus were 22 +/- 0.2 days versus 20 +/- 0.6 days (P < 0.001); estrus rates were 70.6% versus 85.7% (P = 0.1); conception rates were 62.5% versus 76.7% (P < 0.3); and pregnancy rates were 44.1% versus 65.7% (P = 0.07), for CIDR and untreated (control) groups, respectively. In Experiment 2, heifers (n = 651) were TAI (Day 0) and 13 days later randomly assigned to one of seven groups (n = 93 per group) to receive a once-used CIDR (three groups; Days 13-20), MGA (three groups; Days 13-19), or no treatment (control group). Groups given a CIDR or MGA also received: no further treatment (CIDR or MGA alone); 1.5mg estradiol-17beta (E-17beta) and 50 mg progesterone (P4) in 2 mL canola oil on Day 13; or E-17beta and P4 on Day 13 and 0.5 mg E-17beta on Day 21 (24 h after CIDR removal or 48 h after the last feeding of MGA). Pregnancy rate to TAI was lowest (P < 0.05) for the group given a CIDR plus E-17beta and P4 on Day 13 and E-17beta on Day 21. Variability in return to estrus was greater (P < 0.001) in the control and MGA groups than in CIDR groups. Conception and pregnancy rates in heifers given a CIDR (65.1 and 61.4%) were higher (P<0.01) than those fed MGA (49.6 and 40.4%), but not different from controls (62.2 and 54.9%, respectively). In Experiment 3, 616 heifers received a once- or twice-used CIDR for 7 days, beginning 13+/-1 days after TAI, with or without a concurrent injection of 150 mg of P4 (2 x 2 factorial design). Pregnancy rate to TAI was 47.2%. In heifers that returned to estrus, there was no significant difference between a once- or twice-used CIDR for rates of estrus (68.8%, P < 0.3), conception (65.9%, P < 0.6) and pregnancy (45.3%, P < 0.8). Injecting progesterone at CIDR insertion increased the median interval from CIDR removal to onset of estrus (P < 0.05) and reduced rates of estrus (63.8% versus 73.8%, P<0.05), conception (60.5% versus 70.6%, P = 0.1) and pregnancy (38.6% versus 52.2%, P < 0.02). In a field trial, 983 heifers received a once-used CIDR for 7 days, beginning 13 +/- 1 days after TAI. Pregnancy rate to TAI was 55.2%. The median (and mode) of the interval from CIDR removal to estrus was 2.5 days. Estrus, conception and pregnancy rates were 78.2, 70.3 and 55.0% (overall pregnancy rate to TAI and rebreeding, 78.7%). In summary, a once- or twice-used CIDR for 7 days, starting 13 +/- 1 days after TAI resulted in the majority of nonpregnant heifers detected in estrus over a 4-day interval, with acceptable conception rates; however, injecting progesterone at CIDR insertion significantly reduced both estrus and pregnancy rates, and estradiol treatment after CIDR removal was associated with a decreased pregnancy rate to TAI. Fertility was higher in heifers resynchronized with a once-used CIDR than with MGA.

Induction of a new follicular wave in holstein heifers synchronized with norgestomet

Treatments with progestin to synchronize the bovine estrous cycle in the absence of the corpus luteum, induces persistence of a dominant follicle and a reduction of fertility at doses commonly utilized. The objective of the present research was to induce a new wave of ovarian follicular development in heifers in which stage of the estrous cycle was synchronized with norgestomet. Holstein heifers (n=30) were used, in which estrus was synchronized using two doses of PGF2alpha i.m. (25 mg each) 11 days apart. Six days after estrus (day 0=day of estrus) heifers received a norgestomet implant (6 mg of norgestomet). On day 12, heifers were injected with 25 mg of PGF2alpha i.m. and assigned to treatments (T1 to T4) as follows: treatment 1, heifers received a second norgestomet implant (T1: N+N, n=6), treatment 2, received 100 microg of GnRH i.m. (T2: N+GnRH, n=6), treatment 3, 200 mg of progesterone i.m. (T3: N+P4, n=6), treatment 4, control treatment with saline solution i.m. (T4: N+SS); in the four treatments (T1 to T4) implants were removed on day 14. For treatment 5, heifers received 100 microg of GnRH i.m. on day 9 and 25 mg of PGF2alpha i.m. (T5: N+GnRH+PGF2alpha) at the time of implant removal (day 16). Ovarian evaluations using ultrasonographic techniques were performed every 48 h from days 3 to 11 and every 24 h from days 11 to 21. Blood samples were collected every 48 h to analyze for progesterone concentration. A new wave of ovarian follicular development was induced in 3/6, 6/6, 3/6, 1/6 and 6/6, and onset of estrus in 6/6, 0/6, 6/6, 6/6 and 6/6 for T1, T2, T3, T4 and T5, respectively. Heifers from T1, T3 and T4 that ovulated from a persistent follicle, showed estrus 37.5 +/- 12.10 h after implant removal and heifers that developed a new wave of ovarian follicular development showed it at 120.28 +/- 22.81 h (P<0.01). Ovulation occurred at 5.92 +/- 1.72 and 2.22 +/- 1.00 days (P<0.01), respectively. Progesterone concentration was <1 ng/ml from days 7 to 15 in T1, T2 and T4; for T3 progesterone concentration was 2.25 +/- 0.50 ng/ml on day 13 and decreased on day 15 to 0.34 +/- 0.12 ng/ml (P<0.01). For T5, progesterone concentration was 1.66 +/- 0.58 ng/ml on day 15. The more desirable results were obtained with T5, in which 100% of heifers had a new wave of ovarian follicular development induced, with onset of estrus and ovulation synchronized in a short time period.

Fertility in beef cattle given a new or previously used CIDR insert and estradiol, with or without progesterone

The objective was to compare pregnancy rates following fixed-time AI (FTAI) in beef cattle given a new or previously used CIDR insert and injections of estradiol, with or without progesterone, to synchronize follicular wave emergence. In Experiment 1, heifers (n=616) received a new or once-used CIDR insert for 9 days and were given 1mg estradiol cypionate (ECP), with or without 100 mg of a commercial progesterone preparation (CP4), at CIDR insertion. Heifers were treated with PGF at CIDR removal and 0.5 mg ECP i.m. 24h later, with FTAI 55 to 60 h after CIDR removal. Pregnancy rate was not affected by either the number of CIDR uses (P=0.59; 48.3% versus 46.2% for new versus once-used CIDRs, respectively) or the addition of progesterone (P=0.42; 45.6% versus 48.8% for ECP+CP4 and ECP, respectively). In Experiment 2 (replicated at two locations), heifers (n=56) and lactating beef cows (n=307) received a once- or twice-used CIDR and an i.m. injection of 1mg estradiol benzoate (EB), with or without 100 mg progesterone, at CIDR insertion. Cattle received PGF in the ischiorectal fossa at CIDR removal (Day 7) and 1mg EB i.m. 24h later, with FTAI 52 to 56 h after CIDR removal. Pregnancy rate was affected by location (P<0.002; 46.0% versus 61.1% for Locations A and B, respectively), parity (P<0.04; 67.9% versus 53.1% in heifers and cows, respectively), and numbers of times the CIDR had been used (P<0.03; 62.4% versus 48.4% for once- and twice-used CIDRs, respectively). However, the addition of progesterone to the injection of EB at CIDR insertion did not affect pregnancy rate (P=0.6). In Experiment 3, heifers (n=187) received one new, one once-used, one twice-used or two twice-used CIDRs for 7 days and 2 mg EB plus 50 mg of CP4 at the time of CIDR insertion. Heifers were treated with PGF at CIDR removal and 1mg EB i.m. 24 h later, with FTAI 52-56 h after CIDR removal. Pregnancy rate was not affected by treatments (P=0.28, 57.5, 63.8, 47.9, 47.9% for one new, one once-used, one twice-used, or two twice-used CIDRs, respectively). In summary, pregnancy rate to FTAI did not differ between cattle synchronized with a new or once-used CIDR, but pregnancy rate was lower in cattle synchronized with a twice-used CIDR; however, the insertion of two twice-used CIDRs did not affect pregnancy rates. The addition of an injection of progesterone to the estradiol treatment at CIDR insertion did not enhance pregnancy rate to FTAI.

Steroid priming shortens prostaglandin-based estrus synchronization program from 14 to 7 days in cattle

Single injection of estrogen and progesterone before prostaglandin (steroid priming) was used to shorten the prostaglandin-based estrus synchronization program. Sixty-five cyclic Sistani cattle, with parity ranging from 1 to 4 and postpartum period of >80 days were selected at unknown stages of the estrous cycle and assigned to 2 groups according to their age, weight and parity. Females in the control group (n=33; 58.4 +/- 4.3 months; 277 +/- 8 kg LW) received two consecutive injections of prostaglandin F2alpha analogue (500 microg; Cloprostenol, PG) 14 days apart (Day 0 = First PG injection). On Day 7, treated females (n=32; 60 +/- 4.8 months; 292 +/- 9 kg LW) were given an intramuscular injection of 100 mg progesterone and 2 mg estradiol benzoate followed by prostaglandin 7 days later, concurrent with the second PG injection of the control group. Estrus detection was carried out every 6 hours for 7 days, commencing from 24 hours after the last PG injection. Females that allowed to be mounted were identified (standing estrus) and inseminated with frozen semen 12 hours later. Pregnancy was diagnosed on Day 50 after AI through palpation per rectum. Data were analyzed using Chi-squared and t-test. The tightness of estrus synchrony (%), the interval from the end of treatment to estrus (h) and conception rates (%) were similar (P > 0.05) between control (69.6%, 77.7 +/- 5.96 h and 56.5%) and treatment (68.2%, 82.6 +/- 7.64 h and 54.5%) groups. In conclusion, steroid priming is an efficient way to shorten the prostaglandin-based estrus synchronization program from 14 to 7 days without compromising estrous response and fertility.

Recent advances in bovine reproductive endocrinology and physiology and their impact on drug delivery system design for the control of the estrous cycle in cattle

When methods of drug intervention are being developed to control estrous cycles, a thorough understanding of the endocrine and functional changes together with the reproductive behavior of the animals are essential. This review presents our current knowledge on reproductive endocrinology, physiology and behavior, and the methods of drug intervention to control estrous cycles. It also describes current efforts to develop advanced drug delivery systems that meet the animal scientist's demands to control the estrous cycle in cattle.