This thesis was designed to investigate the problem of stimulating ovulation in mares in the vernal transition period. Previous studies found that administration of kisspeptin stimulated an LH response in mares in both breeding and non-breeding seasons, but this LH response did not result in a predictable ovulation. Work presented in this thesis investigated the effect of a 30 hour infusion of low concentrations (66.7nmol/hour and 100nmol/hour) of kisspeptin on mares in the vernal transitional period between winter and summer. Administration of kisspeptin lead to an increase in mean LH and in the area under the LH curve, however it had no effect on LH pulse amplitude or frequency. Kisspeptin administration did not stimulate ovulation, however a trend towards twin ovulations was observed. Kisspeptin does not appear to be a viable ovulating agent, but further investigations are required to see if kisspeptin can be utilised in other ways in breeding management programs. To better understand the role that kisspeptin plays in the control of LH release in mares this thesis also explores the relationships between kisspeptin, GnRH and RFRP-3 neurons in the equine hypothalamus. Using fluorescent immunohistochemistry, kisspeptin, GnRH, and RFRP-3 neurons were identified in hypothalami collected from mares in the breeding season. Cells labelled for kisspeptin were also observed in the equine pituitary gland and in the ovary. Cells labelled for kisspeptin receptor were identified in the ovary.Differences in the number of cell bodies, and interactions between the three peptides, in the hypothalamus were investigated with regard to season and oestrous cycle. The number of GnRH cells appeared lower in the vernal transition compared to animals in different stages of the breeding and non-breeding seasons. The number of kisspeptin cells appeared to be low in the non-breeding season and vernal transition period compared to all stages of the breeding season. The number of RFRP-3 cells appeared to be highest in pre-ovulatory animals compared to all other season or stages of the oestrous cycle, showing that the initial pattern of RFRP-3 cells as lower in the breeding season was incorrect; instead the difference depended on the stage of the breeding season examined. The percentage of kisspeptin appositions onto GnRH cell bodies appeared consistent in all animals regardless of season or stage of oestrous cycle. A suggested difference in the percentage of kisspeptin cell bodies with GnRH appositions was observed, with the non-breeding season and the transition period appearing to have a higher percentage compared to the pre-ovulatory phase. The percentage of kisspeptin cells receiving inputs from RFRP-3 fibres did not appear to vary with regard to both season and oestrous cycle stage. These interactions suggest the presence of an ultra-short loop feedback system between these three peptides. This thesis found no link between the expression of kisspeptin neurons and season or oestrous cycle stage in the mare. RFRP-3 was identified as a possible mechanism of reproductive control in the mare. Further investigations are required to clarify the role of RFRP-3 in the mare.
|Qualification||Doctor of Philosophy|
|Award date||01 Mar 2015|
|Place of Publication||Australia|
|Publication status||Published - 2015|