A field investigation of a modified intravaginal progesterone releasing device and oestradiol benzoate based ovulation synchronisation protocol designed for fixed-time artificial insemination of Brahman heifers.

Pregnancy rates (PR) to fixed-time AI (FTAI) in Brahman heifers were compared after treatment with a traditional oestradiol-based protocol (OPO-8) or a modified protocol (OPO-6) where the duration of intravaginal progesterone releasing device (IPRD) was reduced from 8 to 6 days, and the interval from IPRD removal to oestradiol benzoate (ODB) was increased from 24 to 36 h. Rising 2 yo heifers on Farm A: (n = 238 and n = 215; two consecutive days AI); B (n = 271); and C (n = 393) were allocated to OPO-8 or OPO-6. An IPRD was inserted and 1mg ODB i.m. on Day 0 for OPO-8 heifers and Day 2 for OPO-6 heifers. On Day 8, the IPRD was removed and 500 µg cloprostenol i.m. At 24h, for OPO-8 heifers, and 36 h, for OPO-6 heifers, post IPRD removal all heifers received 1mg ODB i.m. FTAI was conducted at 54 and 72 h post IPRD removal for OPO-8 and OPO-6 heifers. At Farm A, OPO-6 heifers, AI on the second day, the PR was 52.4% to FTAI (P = 0.024) compared to 36.8% for OPO-8 heifers. However, no differences were found between OPO-8 and OPO-6 protocols at Farm A (first day of AI) (39.9 vs. 35.7%), or Farms B (26.2 vs. 35.4%) and C (43.2% vs. 40.3%). Presence of a corpus luteum at IPRD insertion affected PR to FTAI (43.9% vs. 28.8%; P < 0.001). This study has shown that the modified ovulation synchronisation protocol OPO-6 may be a viable alternative to the OPO-8 protocol for FTAI in B. indicus heifers.

Comparison of the pregnancy rates and costs per calf born after fixed-time artificial insemination or artificial insemination after estrus detection in Bos indicus heifers.

This study compared pregnancy rates (PRs) and costs per calf born after fixed-time artificial insemination (FTAI) or AI after estrus detection (i.e., estrus detection and AI, EDAI), before and after a single PGF2α treatment in Bos indicus (Brahman-cross) heifers. On Day 0, the body weight, body condition score, and presence of a CL (46% of heifers) were determined. The heifers were then alternately allocated to one of two FTAI groups (FTAI-1, n = 139) and (FTAI-2, n = 141) and an EDAI group (n = 273). Heifers in the FTAI groups received an intravaginal progesterone-releasing device (IPRD; 0.78 g of progesterone) and 1 mg of estradiol benzoate intramuscularly (im) on Day 0. Eight days later, the IPRD was removed and heifers received 500 µg of PGF2α and 300 IU of eCG im; 24 hours later, they received 1 mg estradiol benzoate im and were submitted to FTAI 30 to 34 hours later (54 and 58 hours after IPRD removal). Heifers in the FTAI-2 group started treatment 8 days after those in the FTAI-1 group. Heifers in the EDAI group were inseminated approximately 12 hours after the detection of estrus between Days 4 and 9 at which time the heifers that had not been detected in estrus received 500 µg of PGF2α im and EDAI continued until Day 13. Heifers in the FTAI groups had a higher overall PR (proportion pregnant as per the entire group) than the EDAI group (34.6% vs. 23.2%; P = 0.003), however, conception rate (PR of heifers submitted for AI) tended to favor the estrus detection group (34.6% vs. 44.1%; P = 0.059). The cost per AI calf born was estimated to be $267.67 and $291.37 for the FTAI and EDAI groups, respectively. It was concluded that in Brahman heifers typical of those annually mated in northern Australia FTAI compared with EDAI increases the number of heifers pregnant and reduces the cost per calf born.

Ovarian dynamics in response to two modified intravaginal progesterone releasing device and oestradiol benzoate based ovulation synchronisation protocols designed for use in Brahman heifers.

The objective was to investigate the ovarian response of Brahman heifers to two modified ovulation synchronisation protocols developed to increase the proportion of normal synchronous ovulations. Experiment 1 characterised the growth of the ovulatory follicle in heifers (n=19) treated with an intravaginal progesterone releasing device (IPRD) and oestradiol benzoate (ODB), to determine the optimal time to induce ovulation. Using the findings from Experiment 1, Experiment 2 investigated the effect of reducing the duration of IPRD insertion and increasing the interval from IPRD removal to ODB treatment (modified protocol 1 - OPO-6; n=20), and omitting ODB treatment at the time of IPRD insertion (modified protocol 2 - PO-6; n=20). An IPRD (0.78 g progesterone) was inserted at Day 0 (OPO-8) or Day 2 (OPO-6 and PO-6) and all heifers also received 1 mg ODB i.m. Day 8: IPRD removed + 500 µg cloprostenol i.m. At 24 h (OPO-8) and 36 h (OPO-6 and PO-6) post IPRD removal: 1 mg ODB i.m. Fixed-time AI (FTAI) occurred at 54 h for OPO-8 and 72 h for OPO-6 and PO-6, post IPRD removal. After IPRD treatment all OPO-6 and OPO-8 heifers initiated a new follicular wave whereas 25% of PO-6 heifers failed. Diameter of the dominant follicle was larger at FTAI in the PO-6 (11.34 ± 0.50 mm) compared to the OPO-8 protocol (9.74 ± 0.51 mm; P<0.05), but similar to the OPO-6 protocol (10.52 ± 0.51 mm). Proportion of ovulations occurring 12 h prior and 24 h post FTAI was similar for the PO-6 (80%) and OPO-6 (75%) protocols but numerically lower in the OPO-8 heifers (60%). The apparent improvement in ovarian response in heifers treated with the modified protocols needs to be confirmed in larger field studies.

Follicle stimulating hormone secretion and dominant follicle growth during treatment of Bos indicus heifers with intra-vaginal progesterone releasing devices, oestradiol benzoate, equine chorionic gonadotrophin and prostaglandin F(2α).

The aim of this study was to investigate the effects on follicle stimulating hormone (FSH) secretion and dominant follicle (DF) growth, of treatment of Bos indicus heifers with different combinations of intra-vaginal progesterone releasing devices (IPRD), oestradiol benzoate (ODB), PGF2α and eCG. Two-year-old Brahman (BN; n=30) and Brahman-cross (BNX; n=34) heifers were randomly allocated to three IPRD-treatments: (i) standard-dose IPRD [CM 1.56g; 1.56g progesterone (P4); n=17]; (ii) half-dose IPRD (CM 0.78g; 0.78g P4; n=15); (iii) half-dose IPRD+300IU eCG at IPRD removal (CM 0.78g+G; n=14); and, (iv) non-IPRD control (2×PGF2α; n=18) 500µg cloprostenol on Days -16 and -2. IPRD-treated heifers received 250µg PGF2α at IPRD insertion (Day -10) and IPRD removal (Day -2) and 1mg ODB on Day -10 and Day -1. Follicular dynamics were monitored daily by trans-rectal ultrasonography from Day -10 to Day 1. Blood samples for determination of P4 were collected daily and samples for FSH determination were collected at 12h intervals from Day -9 to Day -2. A significant surge in concentrations of FSH was observed in the 2×PGF2α treatment 12h prior and 48h after follicular wave emergence, but not in the IPRD-treated heifers. Estimated mean concentrations of total plasma P4 during the 8 days of IPRD insertion was greater (P<0.001) in the CM 1.56g P4 treated heifers compared to the CM 0.78g P4 treated heifers (18.38ng/ml compared with 11.09ng/ml, respectively). A treatment by genotype interaction (P=0.036) was observed in the mean plasma P4 concentration in heifers with no CL during IPRD insertion, whereby BN heifers in the CM 1.56g treatment had greater plasma P4 than the BNX heifers on Days-9, -7, -6, -5, and -4. However, there was no genotype effect in the CM 0.78g±G or the 2×PGF2α treatment. Treatment had no effect on the DF growth from either day of wave emergence (P=0.378) or day of IPRD removal (P=0.780) to ovulation. This study demonstrates that FSH secretion in B. indicus heifers treated with a combination of IPRD's and ODB to synchronise ovulation was suppressed during the period of IPRD insertion but no significant effect on growth of the DF was observed.