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Equine reproductive physiology and ovarian function
The horse is a seasonally polyoestrous species in temperate locations, with onset of the breeding season occurring in spring; associated with seasonal cues which serve to synchronise an endogenous reproductive rhythm to winter and summer periods [9]. The mare’s circa-annual reproductive cycle is made up of four distinct phases. The anovulatory period of the mare can be differentiated into an autumn transitional phase, a mid- anovulatory period and a spring transitional phase, bringing the mare back into cyclic ovarian activity [10]. The physiological breeding season or ovulatory season occurs from April to September in the northern hemisphere and correspondingly from October to April in the southern hemisphere [11]. Most mares undergo an anovulatory period outside of this, the duration and occurrence of which is associated with the age and physiological status of the mare [12]. Younger mares and mares that have previously lactated undergo a long and systematic winter anoestrous but winter ovarian inactivity is observed in only about half of other mature mares [12]. In fillies, puberty occurs at 12-18 months. This is again influenced by season [10, 13]. Senescence in old mares is rarely seen and most mares continue to cycle independent of age [10]. The oestrous cycle is the period between two consecutive ovulations [9, 14, 15]. During the breeding season in spring and summer, average oestrous cycle length is about 22 days with 5-7 days of oestrus [10]. Oestrous cycle length is also affected by reproductive stage and breed [16]. During the oestrous cycle, the uterus, cervix, vagina and endometrium of the mare undergo pronounced changes related to variations in the endocrine milieu. They can easily be differentiated by clinical examination. The equine oestrous cycle is a combination of a follicular phase, or oestrus (Figure 1-1: Pro-oestrus), and a luteal phase, or dioestrus (Figure 1-2: Metoestrus).
Follicular development within the ovary involves growing, ovulating, and anovulatory haemorrhagic or regressing follicles, with approximately 40,000 primordial follicles and 100 growing follicles [15]. Developing follicles are represented by early-stage, pre-antral follicles and later-stage, antral follicles. The latter, more mature stages are of clinical importance because they are the main source of reproductive steroids (oestrogens, progestogens, and androgens). These influence follicle growth and regression, uterine and cervical structural and functional changes, oestrous behaviour, oocyte development and ovulation. In the mare, growth of antral follicles occurs in wave-like patterns, categorised as major (primary and secondary) and minor waves depending on whether the largest follicle of a wave reaches ≥30 mm in association with follicle selection (major wave) or <30 mm without selection (minor wave) [17, 18]. During the anovulatory period follicular growth is minimal, marked by few follicles of a diameter >15 mm and the maximal diameter of the largest follicle does not exceed 16 mm [19]. A dominant follicle does not develop during that time. The beginning of the spring transitional period is characterised by the development of 1-3 anovulatory follicular waves before finally ovulation occurs. The spring transitional period has a variable length that ranges from 30-90 days. Its beginning is characterised by the re-initiation of follicular deviation, i.e. the development of a dominant follicle reaching a size between 20-30 mm in diameter. In addition, an increasing number of follicles with a diameter >15 mm occur [10, 19]. In general, follicular wave emergence during the oestrous cycle is associated with the growth of a group of 5-10 antral follicles (4-6 mm) within 2-3 days of one another. During the common growth phase, most follicles increase in diameter 2-4 mm/day until the largest follicle reaches 20-25 mm near the end of the common growth phase. Afterwards, either all follicles (minor wave) or all but the largest follicle (major wave) begin to gradually regress. In general, spontaneous ovulation of a single preovulatory follicle of a major wave occurs when the dominant follicle reaches about 40 mm in diameter; maximum diameter of the preovulatory follicle is related, in part, to season, breed, type of mare and number of preovulatory follicles [20].
Chapter One: Literature review
Early work in animal population management
Equine reproductive physiology and ovarian function .
Zona pellucida proteins.
Immunocontraception
Porcine zona pellucida immunocontraception in the horse .
Recombinant zona pellucida vaccines .
Ovarian suppression subsequent to zona pellucida-based immunocontraception
Quantifying ovarian effects of zona pellucida-based immunocontraceptio
African elephant population management-Why?
Aspects of African elephant social structure, reproductive biology and interactions
Elephant management and population control using porcine zona pellucida immunocontraception
Counting elephants: Informed population management
References
Chapter Two: Scope of thesis
Chapter Three: Ovarian function following immunocontraceptive vaccination of mares using native porcine and recombinant zona pellucida vaccines formulated with a non-Freund’s adjuvant and anti-GnRH vaccines
Abstract
Introductio
Materials and methods
Mare selection, management and environment
Study design
Formulation of vaccines .
Vaccine administration
Data collection
Pasture breeding
Hormone assays
Statistical analyses
Results
Ovarian activity
Anti-Müllerian hormone
Chapter Four: Serum antibody immunoreactivity and safety of native porcine and recombinant zona pellucida vaccines formulated with a non-Freund’s adjuvant in horses
Chapter Five: A review of the current status of porcine zona pellucida immunocontraception of elephant cows in South Africa
Chapter Six: Summarising discussion
