Abridged title: Endometrial gene expression and metabolic parameters in subfertile beef heifers. AbstractThe objective of this study was to compare the hormonal, metabolic characteristics and endometrial gene expression profiles in beef heifers yielding either a viable or a 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 CIDR-prostaglandin protocol and heifers (n=102) detected in standing oestrus (within 24-48 h post 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 post oestrus to measure progesterone (on Days 4, 5 and 7), insulin and IGF-I (on Days 4 and 6) and urea concentrations (on Day 7). All animals were slaughtered on Day 7. Uterine pH was also determined. 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 2-to 16-cell stage); n=19. The overall recovery rate was 64%. There was no significant difference in blood parameters measured or uterine pH at slaughter between the heifers with either a viable or retarded embryo. The relative abundance of 9 transcripts out of 53 tested from the endometrial tissue was different between heifers with a viable embryo or retarded embryo: MOGAT1, PFKB2, LYZ2, SVS8, UHRF1, PTGES, AGPAT4, DGKA and HGPD. Both LYZ2 and UHRF1 are associated with regulation of the immune system. PFKFB2 is a mediator in glycolysis and MOGAT, AGPAT4 and DGKA belong to the triglyceride synthesis pathway. PTGES and HGPD belong to the prostaglandin pathway.Both of these metabolic pathways are important for early embryonic development. In conclusion, retarded embryo development in this study was not related to serum progesterone, IGF-I, insulin or urea concentrations nor to uterine pH at slaughter. However, altered expression of genes involved in the prostaglandin and triglyceride pathways, as well as 2 genes that are closely associated with the regulation of immunity in the endometrium may indicate a uterine component to the retardation of the embryos in these beef heifers.

BackgroundIn contrast to studies showing gradual adaptation of melatonin (MT) rhythms to an advanced photoperiod in humans and rodents, we previously demonstrated that equine MT rhythms complete a 6-h light/dark (LD) phase advance on the first post-shift day. This suggested the possibility that melatonin secretion in the horse may be more strongly light-driven as opposed to endogenously rhythmic and light entrained. The present study investigates whether equine melatonin is endogenously rhythmic in extended darkness (DD).MethodsSix healthy, young mares were maintained in a lightproof barn under an LD cycle that mimicked the ambient natural photoperiod outside. Blood samples were collected at 2-h intervals for 48 consecutive h: 24-h in LD, followed by 24-h in extended dark (DD). Serum was harvested and stored at -20°C until melatonin and cortisol were measured by commercial RIA kits.ResultsTwo-way repeated measures ANOVA (n = 6/time point) revealed a significant circadian time (CT) x lighting condition interaction (p < .0001) for melatonin with levels non-rhythmic and consistently high during DD (CT 0-24). In contrast, cortisol displayed significant clock-time variation throughout LD and DD (p = .0009) with no CT x light treatment interaction (p = .4018). Cosinor analysis confirmed a significant 24-h temporal variation for melatonin in LD (p = .0002) that was absent in DD (p = .51), while there was an apparent circadian component in cortisol, which approached significance in LD (p = .076), and was highly significant in DD (p = .0059).ConclusionsThe present finding of no 24 h oscillation in melatonin in DD is the first evidence indicating that melatonin is not gated by a self-sustained circadian process in the horse. Melatonin is therefore not a suitable marker of circadian phase in this species. In conjunction with recent similar findings in reindeer, it appears that biosynthesis of melatonin in the pineal glands of some ungulates is strongly driven by the environmental light cycle with little input from the circadian oscillator known to reside in the SCN of the mammalian hypothalamus.