A significant proportion of potential lambs are lost (commonly 15-20%) between ovulation and day 30 of gestation. Moreover, little is known about factors associated with multiple birth capacity of the uterus which would be necessary to convert gains in ovulation rate to the birth of live lambs. This project has investigated the relationship between maternal uterine and hormonal environment as well as the heritability of embryonic survival (ES) in prolific ewes.
Litter size (LS) from known ovulation rate (OR) records (n=6393) collected over 16 years were analysed for heritability. ASReml analysis reported ES to be a trait of low repeatability (r� = 0.103) and heritability (h� = 0.04) which is consistent with earlier studies of this trait. However, pedigrees of outlier animals indicated a segregation pattern consistent with a single autosomal gene with a major affect on enhanced ES. From this flock, closely related high ovulation rate ewes with significantly different litter sizes (High ES; OR2.6/LS2.4 versus Low ES; OR2.9/LS1.6) were selected for further study.
The anatomy and gene expression of the uterus collected at day 14 of the oestrous cycle (n=5 High and n=5 Low ES ewes) and day 16 of gestation (n=14 high and n=10 Low ES ewes) as well as systemic concentrations of hormones indicative of uterine (activin-A, follistatin) and ovarian (inhibin-α, progesterone) function during the oestrous cycle and early gestation were compared.
Progesterone concentrations were found to rise earlier in high ES ewes with a difference in number of ewes with detectable levels of progesterone apparent by day 4 of gestation. The peak concentration and slope of progesterone increase as well as plasma profiles of oestradiol and inhibin-α were not different between groups.
A number of pathways worthy of closer investigation were implicated by microarray analysis with Ingenuity Pathway Analysis, Pubmatrix, and candidate gene approaches. In particular, the altered expression of many immune cell factors suggests that high ES ewes have maternal gene expression of the inflammatory pathways favourable to embryo implantation.
The plasma concentration of activin, but not follistatin, was found to be significantly higher in low ES ewes, a difference that remained apparent when the concentration of follistatin was corrected for individual samples. Furthermore, the concentration of activin, but not follistatin, was significantly elevated on day 16 of gestation in the uterine fluid of low ES ewes.
Further investigation of the pattern of gene expression during the oestrous cycle and early gestation (day10-16 oestrus and days10-20 gestation) revealed that a significant increase in follistatin mRNA in the luminal epithelia and interacting trophoblast cells of the embryo occurs on day 18 and 20 of gestation. It is likely the appropriate balance between activin and follistatin during the time of implantation enhances embryonic survival in this line of ewes. This may be secondary to or concomitant with the observed earlier rise in progesterone concentration. The implication that embryo survival may be positively influenced by a single autosomal gene has important implications for New Zealand's agricultural industry.
| Identifer | oai:union.ndltd.org:ADTP/266446 |
| Date | January 2009 |
| Creators | O'Connell, Anne R, n/a |
| Publisher | University of Otago. Department of Anatomy & Structural Biology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Anne R O'Connell |
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