Now showing 1 - 4 of 4
  • Publication
    Evaluation of models to induce low progesterone during the early luteal phase in cattle
    Two experiments were designed to evaluate models for generation of low circulating progesterone concentrations during early pregnancy in cattle. In Experiment 1, 17 crossbred heifers (Bos taurus) were assigned to either prostaglandin F2α (PGF2α) administration on Days 3, 3.5, and 4 (PG3; n = 9) or to control (n = 8). Blood samples were collected from heifers from Days 1 to 9 for progesterone assay. Progesterone concentrations were decreased (P < 0.03) between 18 and 48 h after first PGF2α treatment in heifers assigned to PG3 compared with that of controls. In Experiment 2, 39 crossbred heifers detected in estrus were inseminated (Day 0) and assigned to either (1) PGF2α administration on Days 3, 3.5, and 4 (PG3; n = 10), (2) PGF2α administration on Days 3, 3.5, 4, and 4.5 (PG4; n = 10), (3) Progesterone Releasing Intravaginal Device (PRID) insertion on Day 4.5 with PGF2α administration on Days 5 and 6 (PRID + PGF2α; n = 10), or (4) control (n = 9). Blood samples were collected daily until Day 15, and conceptus survival rate was determined at slaughter on Day 16. Progesterone concentrations during the sampling period in the PG3 and PG4 groups did not differ but were less than that of controls (P < 0.01). After an initial peak, progesterone concentrations in the PRID + PGF2α group were similar to that of controls. More heifers in the PG4 group (6 of 10) had complete luteal regression than did those in the PG3 group (3 of 10). Conceptus survival rate on Day 16 did not differ between groups. There was a significant correlation between progesterone concentration on Days 5 and 6 and conceptus size on Day 16. In summary, treatment with PGF2α on Days 3, 3.5, and 4 postestrus appeared to provide the best model to induce reduced circulating progesterone concentrations during the early luteal phase in cattle.
      379Scopus© Citations 38
  • Publication
    Effect of progesterone supplementation in the first week post conception on embryo survival in beef heifers
    Progesterone is essential for establishment and maintenance of pregnancy in mammals. The objective of this study was to examine the effect of elevating progesterone during the different physiological stages of early embryo development on embryo survival. Estrus was synchronized in cross-bred beef heifers (n = 197, ∼2-years old) and they were inseminated 12–18 h after estrus onset (=Day 0). Inseminated heifers were randomly assigned to 1 of 3 treatments: (1) Control, n = 69; (2) progesterone supplementation using a Controlled Internal Drug Release Device (CIDR) from Day 3 to 6.5, n = 64; or (3) progesterone supplementation using a CIDR from Day 4.5 to 8, n = 64. Body condition (BCS) and locomotion scores (scale of 1–5) were recorded for all animals. Animals with a locomotion score ≥4 (very lame) were excluded. Embryo survival rate was determined at slaughter on Day 25. Conceptus length and weight were recorded and the corpus luteum (CL) of all pregnant animals was dissected and weighed. Supplementation with exogenous progesterone increased (P < 0.05) peripheral progesterone concentrations, but did not affect embryo survival rate compared with controls. Mean CL weight, conceptus length and conceptus weight were not different between treatments. There was a positive relationship (P < 0.04) between the increase in progesterone concentrations from Days 3 to 6.5 and embryo survival rate in treated heifers and a similar trend existed between the increase from Days 4.5 to 8 (P < 0.06). There was also a positive relationship (P < 0.05) between the progesterone concentration on Day 6.5 and the embryo survival rate in treated heifers. A direct correlation was seen between locomotion score and embryo survival rate, with higher (P < 0.05) early embryo survival rates in heifers with a lower locomotion score. In conclusion, supplementation with progesterone at different stages of early embryo development increased peripheral progesterone concentration and resulted in a positive association between changes in progesterone concentration during the early luteal phase and embryo survival rate. Supplementation with progesterone had no effect on either CL weight or conceptus size in pregnant animals. Lameness had a significant negative effect on early embryo survival.
      681Scopus© Citations 49
  • Publication
    Changes in the endometrial transcriptome during the bovine estrous cycle: effect of low circulating progesterone and consequences for conceptus elongation
    In cattle, elevated concentrations of circulating progesterone (P4) in the immediate post-conception period have been associated with an advancement of conceptus elongation, an associated increase in interferon-tau production and higher pregnancy rates. Low P4 has been implicated as a causative factor in the low pregnancy rates observed in dairy cows. The aims of this study were (1) to describe the changes that occur in the bovine endometrial transcriptome during the estrous cycle, (2) to determine how elevated P4 affects the temporal pattern of gene expression in the endometrium of cyclic heifers, (3) to determine if the expression of these genes is altered in heifers with low P4 and (4) to determine the consequences of low P4 for conceptus development following embryo transfer. The main findings were that 1) relatively few differences occurred in endometrial gene expression during the early luteal phase of the estrous cycle under normal concentrations of P4 (Day 5 versus Day 7) but comparison of endometria from more distant stages of the luteal phase (Day 7 versus Day 13) revealed large transcriptional changes; 2) exogenous supplementation of P4, leading to elevated concentrations from Day 3 to Day 8, considerably altered the expression of a large number of genes at all stages of the luteal phase; 3) induction of low circulating P4 altered the normal temporal changes that occured in the expression of these genes, mainly by delaying their expression; 4) this delay in gene expression was, in part, due to delayed down regulation of the PGR from the LE and GE, and 5) the altered endometrial gene expression induced by low P4 was associated with a reduced capacity of the uterus to support conceptus development after embryo transfer on Day 7. In conclusion, the present study provides clear evidence for a temporal change in the transcriptomic signature of the bovine endometrium which is sensitive to the concentrations of circulating P4 in the first few days after estrus and which can, under conditions of low progesterone, lead to an suboptimal uterine environment and a reduced ability to support conceptus elongation.
      379Scopus© Citations 205
  • Publication
    Characterisation of endometrial gene expression and metabolic parameters in beef heifers yielding viable or non-viable embryos on Day 7 after insemination
    The aim of the present study was to compare the hormonal and metabolic characteristics and endometrial gene expression profiles in beef heifers yielding either a viable or degenerate embryo on Day 7 after insemination as a means to explain differences in embryo survival. Oestrus was synchronised in cross-bred beef heifers (n = 145) using a controlled internal drug release (CIDR)-prostaglandin protocol. Heifers (n = 102) detected in standing oestrus (within 24-48 h after CIDR removal) were inseminated 12-18 h after detection of oestrus (Day 0) with frozen-thawed semen from a single ejaculate of a bull with proven fertility. Blood samples were collected from Day 4 to Day 7 after oestrus to measure progesterone (on Days 4, 5 and 7), insulin and insulin-like growth factor (IGF)-I (on Days 4 and 6) and urea (on Day 7) concentrations. All animals were killed on Day 7. Uterine pH was determined at the time of death. Animals from which an embryo was recovered were classified as either having a viable embryo (morula/blastocyst stage; n = 32) or a retarded embryo (arrested at the two- to 16-cell stage; n = 19). In addition, 14 single-celled unfertilised oocytes were recovered, giving an overall recovery rate of 64%. There was no significant difference in the blood parameters determined or uterine pH at the time of death between heifers with either a viable or retarded embryo. The relative abundance of nine transcripts (i.e. MOGAT1, PFKB2, LYZ2, SVS8, UHRF1, PTGES, AGPAT4, DGKA and HGPD) of 53 tested in the endometrial tissue differed between heifers with a viable or retarded embryo. Both LYZ2 and UHRF1 are associated with regulation of the immune system; PFKFB2 is a mediator in glycolysis; MOGAT, AGPAT4 and DGKA belong to the triglyceride synthesis pathway; and PTGES and HGPD belong to the prostaglandin pathway. Both these metabolic pathways are important for early embryonic development. In conclusion, retarded embryo development in the present study was not related to serum progesterone, IGF-I, insulin or urea concentrations, nor to uterine pH at the time of death. However, altered expression of genes involved in the prostaglandin and triglyceride pathways, as well as two genes that are closely associated with the regulation of immunity, in the endometrium may indicate a uterine component in the retardation of embryo development in these beef heifers.
      632Scopus© Citations 52