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How much progesterone do we really need? An investigation for fixed-time artificial insemination of Angus yearling heifers.

AUTHOR:

27 March 2017

PROCEEDING FROM ACV/ARV Annual Conference, Sydney, 2017

How much progesterone do you really need? An investigation for fixed-time artificial insemination of Angus yearling heifers.

Dr Sophia Edwards^1,2 and Michael Chambers³

¹Vetoquinol Australia, Unit 302.2, 6 – 12 Boronia Rd, Brisbane Airport, QLD 4008

²School of Veterinary Science, The University of Queensland, Gatton, QLD 4343

³Invetus, Locked Bag 6865, Armidale West, NSW 2350

Abstract

The study compared the use of an intravaginal progesterone (P₄) releasing device (IPRD) that contained half the standard dose of P₄ to an IPRD that contained the standard dose of P₄. The IPRDs were compared in an ovulation synchronisation protocol for fixed-time artificial insemination (FTAI) of yearling Angus heifers (n = 176). Heifers originating from two herds were allocated to one of two treatment groups: 1) 1-Pod (0.78 g P₄; 1-Pod Cue-Mate^®) and; 2) 2-Pod (1.56 g P₄; Cue-Mate^®). Heifers were allocated randomly according to herd, bodyweight and presence of a corpus luteum (CL) that was recorded five days prior to commencement of synchronisation treatments (Day -5). Post analysis of allocation procedures confirmed heifers allocated to the 1-Pod and 2-Pod treatment groups to have an average bodyweight of 309.1 ± 2.4 kg and 307.4 ± 2.4 kg, respectively, and 31.4% and 32.6% with a CL present, respectively. On Day 0, every heifer received an IPRD (Cue-Mate^®) either 1-Pod or 2-Pod depending on allocated treatment group, and 1 ml oestradiol benzoate (ODB; Bomerol^®) i.m. On Day 8, the IPRD was removed from all heifers and every heifer received 2 ml cloprostenol (PGF_2α; Ovuprost^TM), i.m. and 1.5 ml equine chorionic gonadotrophin (eCG; Pregnecol^®). On Day 10, at 54 h after IPRD removal, all heifers received 1 ml gonadotrophin releasing hormone (GnRH; Ovurelin^®) and were FTAI. Foetal ageing was performed on Day 96. Heifers in the 1-Pod group resulted in a pregnancy rate to FTAI of 54.1% vs. 47.1% (p = 0.357) for the 2-Pod group. The overall pregnancy rate, after being exposed to bulls post FTAI was 89.4% vs. 83.5% (p = 0.262), for the 1-Pod and 2-Pod group, respectively. The results suggest that a new cost effective approach to synchronisation of yearling Angus heifers should be considered.