Does the Amount of Progesterone in Intravaginal Implants Used to Synchronise Oestrus Affect the Reproductive Performance of Brahman Heifers Artificially Inseminated at a Fixed Time

Abstract

The study tested the hypothesis that reduced intravaginal implant progesterone (P(4)) concentration to synchronise oestrus would increase pregnancy rates to fixed-time artificial insemination (FTAI) in Bos indicus heifers. Brahman heifers (n = 294; 2 year) were body condition scored (BCS), weighed and scanned for presence of a corpus luteum (CL). Only cyclic heifers were selected and allocated randomly within BCS and 25 kg bodyweight category to one of three P(4) treatment groups. On day 10, heifers received a P(4) implant (CueMate-1-pod, 0.78 g P(4); CueMate-2-pod, 1.56 g P(4); or CIDR-B, 1.9 g P(4)), 2 mg oestradiol benzoate (ODB) intramuscularly (i.m.) and 250 ug cloprostenol i.m.. At day 2, the implant was removed, 250 ug cloprostenol was injected i.m. and tail paint applied. The heifers received 1 mg ODB 24 h later and were FTAI 48-54 h after implant removal (day 0). Ten randomly selected heifers per group were blood sampled and scanned at days 10, 2, 0 and 6 to define the P(4) profiles pre- and post-FTAI. Heifers were heat-detected 18-20 days post-FTAI and oestrous heifers AI'd by the AM/PM rule. Bulls joined the heifers on day 27 post-FTAI. Transrectal ultrasonography estimated conception date on day 72. Statistical analysis examined the effects of treatment, technician, semen, ovarian status, BCS and liveweight, on pregnancy rate (PR) to FTAI. There was no significant difference (p = 0.362) in PR between treatment groups (CueMate 1-pod, 36.4%; CueMate 2-pod, 39.6%: CIDR-B, 28.3%), but PR was higher in those heifers with increased BCS between FTAI and pregnancy diagnosis (p = 0.005). Thirty-three per cent of monitor heifers had plasma P(4) concentrations of <1 ng/ml on day 6 after FTAI; only 20% of these conceived vs 60% of heifers with P(4) ≥ 1 ng/ml. In summary, no significant difference in PR was identified between treatments but good BCS and a rising plane of nutrition were critical to PR of these pure grade Brahman heifers in northern Australia.

Animal‐Level Factors Affecting Ovarian Function in Bos indicus Heifers Treated to Synchronize Ovulation with Intravaginal Progesterone‐Releasing Devices and Oestradiol Benzoate

“…The total LW gained between experiment induction and day 21 was significantly (p = 0.025) higher (mean difference of approximately 15 kg) for heifers with normal ovarian function after treatment to synchronize ovulation compared to those with abnormal ovarian function. These results are in agreement with the findings of field studies where BN heifers that gained more body condition or weight after synchronized ovulation had a higher likelihood of becoming pregnant to FTAI (Phillips et al. 2010; Butler et al.…”

“…2009). Using the plasma P 4 concentration 6 days after ovulation as an indicator of CL function (Phillips et al. 2010), we correlated the concentration of IGF‐I, cortisol and glucose on each day analysed.…”

“…2004, 2008). Phillips et al. (2010) reported that Brahman (BN) heifers that gained BCS from the day of FTAI to 72 days afterwards had a significantly higher (p = 0.005) pregnancy rate (PR) than heifers that failed to gain condition or lost condition.…”

“…An important factor limiting the adoption of artificial insemination (AI) in the subtropical-tropical region of northern Australia is the substantial annual variation in quality and quantity of pasture available to cattle to graze (Burns et al 2010). Measures of energy balance such as change in body condition score (BCS) and liveweight (LW) have been consistently associated with the reproductive performance of cattle grazing native or improved pastures in this region of Australia (Fordyce et al 1990).…”

“…Typical fixed-time AI (FTAI) protocols utilize combinations of progestin and progesterone (P 4 ) implants, oestradiol benzoate (ODB), prostaglandin F 2a (PGF 2a ) and equine chorionic gonadotrophin (McGowan 1999;Bo et al 2003Bo et al , 2007Baruselli et al 2004Baruselli et al , 2008. Phillips et al (2010) reported that Brahman (BN) heifers that gained BCS from the day of FTAI to 72 days afterwards had a significantly higher (p = 0.005) pregnancy rate (PR) than heifers that failed to gain condition or lost condition. Similarly, Butler et al (2011) found that heifers that were pregnant to FTAI gained 12 kg more weight (p = 0.033) from the day of FTAI to 65 days afterwards than heifers that failed to become pregnant to FTAI.…”