A search for biomarkers of ovine pre-partum vaginal prolapse : a thesis presented to Massey University in partial fulfilment of the requirement for the degree of Doctor of Philosophy in Biochemistry, Massey University, New Zealand
Ovine pre-partum vaginal prolapse (known as bearings in sheep) occurs within a few weeks prior to
lambing and unless treated both ewes and unborn lambs will die. Rates of prolapse in New Zealand
vary from 0.1 to 5% per annum, varying between season and farms and is a worldwide problem.
Much research has been undertaken over many years to determine the cause of this condition but
no clear etiology has emerged. In this study plasma samples were collected prior to prolapse
occurring in order to determine physiological changes leading to prolapse. 650 ewes were ear
tagged and blood sampled on one day prior to lambing, 28 of these ewes subsequently prolapsed.
The date of occurrence and tag number of prolapsing ewes was recorded to enable a comparison of
the plasma profile of prolapsing ewes and non-prolapsing ewes. An improved method for running
sheep plasma on 2D gels was developed resulting in improved protein spot resolution along with a
lower coefficient of variation for spot volume. Using this improved method samples were subjected
to 2D DIGE (two dimensional differential in gel electrophoresis) to determine if there were
differences between the two groups of ewes. One of the differences was in haptoglobin, a major
acute phase protein in ruminants, in which some isoforms were upregulated approximately 3 fold
prior to prolapse occurring. This may indicate an inflammatory response due to either infection or
injury. A good correlation was found between total haptoglobin spot volume data and quantitative
haptoglobin assay data from the same samples (r² = 0.91) validating the haptoglobin gel spot data.
Another finding was that alpha-1B-glycoprotein was down regulated close to prolapse, however the
biological significance of this is unknown. It was also found that there was a negative correlation
between cortisol and days to prolapse from sampling (r² = 0.36) i.e. ewes closest to prolapse had
higher plasma cortisol concentrations than controls. These findings in conjunction with a literature
search, field observations and an argument from logic lead the author to propose that chronic stress
or anxiety may raise intra-abdominal pressure and contribute to the development of prolapse.