Nutritional factors associated with vaginal prolapse in ewes

Epidemiology of vaginal prolapse in mixed-age ewes in New Zealand

AIMS

Identify environmental, animal, and management factors associated with risk of vaginal prolapse in ewes, to enable farmers and advisors to make pragmatic decisions based on empirical observations for control of the condition.

METHODS

Two longitudinal studies conducted over 2 years to identify factors associated with incidence of prolapse in (i) cohorts of 200 individually identified mixed-age (MA) ewes, and (ii) all MA ewes, on voluntarily participating sheep-breeding farms in Hawkes Bay (HB) and Southland regions of New Zealand.

RESULTS

The overall annual incidences of prolapse on 113 farms in 2000 and 88 in 2001 were 1.21 and 0.82 per 100 MA ewes, respectively, and 1.05 for both years combined. A total of 406 prolapses were recorded among 36,695 individually identified cohort ewes. Individual farm incidences for both years varied from 0-5.9 (mean=1.56, median=1.39) on Southland and 0-3.9 (mean=0.75, median=0.54) per 100 ewes on HB farms. The crude relative risk of a prolapse occurring in a MA ewe was 5.31 times higher for ewes carrying twins and 11.3 times higher for ewes carrying triplets, than single lambs. Flocks made up of predominantly pure or crossbred Perendale ewes appeared to be at lower risk than flocks with other breeds. Shearing in the 3 months leading up to mating appeared to be protective, as was shearing in the second half of pregnancy. The risk was higher on farms with moderate to steep terrain than on farms with flat terrain. The identified risk factors in the individually identified cohorts were: access to salt and feeding of swedes in the latter part of pregnancy, moderate to steep lambing paddocks, multiple lambs detected at scanning, and weight gain between start of mating and scanning. The condition recurred in 2001 in six (35%) of 17 study ewes that had prolapsed during 2000. Culling policies for female offspring of affected ewes did not influence incidence at the farm level; nor did feeding hay or grain in late pregnancy. Furthermore, there was no association between incidence and body condition scores measured prior to and after mating, at scanning, or at time of set stocking.

CLINICAL SIGNIFICANCE

Vaginal prolapse is an inevitable consequence of sheep reproduction and its incidence is expected to increase as reproductive rates increase. This study provides some firm leads as to the relative importance of risk factors and gives guidance for risk reduction, e.g. by identification and separate management of ewes carrying twins or triplets, using flat paddocks for lambing, and guarding against gain in weight between the start of mating and scanning.

Animal models of female pelvic organ prolapse: lessons learned

Pelvic organ prolapse is a vaginal protrusion of female pelvic organs. It has high prevalence worldwide and represents a great burden to the economy. The pathophysiology of pelvic organ prolapse is multifactorial and includes genetic predisposition, aberrant connective tissue, obesity, advancing age, vaginal delivery and other risk factors. Owing to the long course prior to patients becoming symptomatic and ethical questions surrounding human studies, animal models are necessary and useful. These models can mimic different human characteristics - histological, anatomical or hormonal, but none present all of the characteristics at the same time. Major animal models include knockout mice, rats, sheep, rabbits and nonhuman primates. In this article we discuss different animal models and their utility for investigating the natural progression of pelvic organ prolapse pathophysiology and novel treatment approaches.

Morphology of the thyroid in coastal and noncoastal populations of the koala (Phascolarctos cinereus) in Queensland

The gross morphology, histology, and ultrastructure of the thyroid gland of the koala, Phascolarctos cinereus, is described. Generally, the glands were found to contain large-diameter follicles in association with an epithelium of low height. Morphometric analysis demonstrated a high relative thyroid weight (0.3 +/- 0.2 g/kg) for koalas compared with the 0.07-0.24 g/kg typical of eutherian mammals and 0.03-0.1 g/kg found in other marsupials. The relative thyroid weight of glands (0.33 +/- 0.21 g/kg) from the coastal population (less than 28 km from the coastline) was found to be significantly higher (ANOVA: P = 0.007, significant at the 1% level) than that for glands (0.21 +/- 0.11 g/kg) of noncoastal koalas (greater than 28 km from the coastline). Follicle size was positively correlated (at the 0.1% level) with relative thyroid weight in the overall koala sample. The presence of C cells, occurring singly in the epithelial layer, was demonstrated in electron micrographs. Structural features such as low epithelial height, large follicle length and width, and large intercellular spaces in association with low concentrations of free T4 (3.3 +/- 2.1 pM) and free T3 (1.4 +/- 0.9 pM) as reported previously (Lawson et al., 1996) are consistent with an unusually low level of glandular activity in the koala thyroid even though iodine concentrations in the thyroid gland [4.7 +/- 1.6 mg/g (dry weight)] as well as leaf [0.8 +/- 0.3 microg/g (dry weight)] and soil samples [3.8 microg/g (dry weight)] from the koalas' habitat appear unremarkable.