title: Establishment of critical timing of progesterone supplementation on corpus luteum and embryo development in beef heifers.
abstract: Optimal concentrations of progesterone (P4) during early pregnancy are a major determinant of embryo survival in cattle. This study examined the effects of P4 supplementation, following a period of induced low P4, on corpus luteum (CL) development, circulating P4 concentrations and embryo development. A total of 107 beef heifers from one herd were used in the study. Following AI (Day 0) at a synchronized oestrus, heifers were randomly assigned to 1 of 5 treatment groups: (1) no subsequent treatment (control; n=15); (2) administration of a synthetic prostaglandin F2αanalogue (PG) on Days 3, 3.5 and 4 to induce low P4 and no further treatment (LP4; n=23); administration of PG as above followed by P4 supplementation via insertion of a Controlled Internal Drug Release device from (3) Day 4-7 (P4 d4-7; n=22); (4) Day 4-10 (P4 d4-10; n=23); or (5) Day 7-10 (P4 d7-10; n=24). Embryo and CL characteristics were determined following slaughter on Day 16. Embryo size was greater in heifers administered P4 d4-7 and P4 d4-10 in comparison with LP4. Corpus luteum area was significantly reduced in heifers administered P4 d4-7 and P4 d4-10 up to Day 7, and Day 10 (P4 d4-10), in comparison with LP4 heifers. Initiation of supplemental P4 on Day 7 had no effect on CL area or embryo size in comparison with LP4 heifers. Concentrations of P4 were less in P4 d4-7, P4 d7-10 and P4 d4-10 on Day 15 in comparison with LP4 heifers. The results of the study indicate an initiation and duration effect of supplemental P4 on circulating P4, embryo and CL development following induction of LP4 on Day 3 and 4.
authors.affiliation: Animal & Grassland Research and Innovation Centre, Teagasc, Mellows Campus, Athenry, Co. Galway, Ireland; School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: M H
authors.initials: MH
authors.lastname: Parr
authors.affiliation: School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: S
authors.initials: S
authors.lastname: Scully
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: P
authors.initials: P
authors.lastname: Lonergan
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: A C O
authors.initials: ACO
authors.lastname: Evans
authors.affiliation: School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: M A
authors.initials: MA
authors.lastname: Crowe
authors.affiliation: Animal & Grassland Research and Innovation Centre, Teagasc, Mellows Campus, Athenry, Co. Galway, Ireland. Electronic address: Michael.Diskin@teagasc.ie.
authors.forename: M G
authors.initials: MG
authors.lastname: Diskin
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D003008:Cloprostenol / Q000008:administration & dosage; D003338:Corpus Luteum / Q000187:drug effects* / Q000502:physiology; D004334:Drug Administration Schedule; D047108:Embryonic Development / Q000187:drug effects; D004973:Estrus Synchronization; D005260:Female; D007315:Insemination, Artificial / Q000662:veterinary; D011247:Pregnancy
chemical_list: D003008:Cloprostenol
keywords: Corpus luteum; Embryo; Progesterone supplementation