Control of ovarian follicular growth in the alpaca, Lama pacos
Creators: name: Vaughan, JL
Publisher: name: CQUniversity
Year: 2023
Subjects: classificationCode: 300999
subject: Veterinary sciences not elsewhere classified

description: The aim of the studies in this thesis was to develop a treatment protocol that controlled ovarian follicular growth so that the time of optimum fertility could be predicted in female alpacas. Female alpacas exhibit growth and regression of successive large follicles and typically only ovulate in response to the mating stimulus. Non-pregnant females are sexually receptive most of the time, apparently regardless of the stage of ovarian follicular growth. Conventional breeding results in slow genetic gain because matings occur at random stages of follicular development. Because of the nature of their reproductive physiology, assisted breeding technologies are poorly developed in alpacas and the Australian alpaca industry relies on transport of males and females over relatively large distances to disseminate superior genotypes. The efficiency of this form of genetic improvement would be enhanced if conception rates to a single mating could be increased. Initial studies in this thesis aimed to clarify ovarian follicular growth characteristics in nonpregnant females. An inverse relationship between the diameter of the largest follicle and the number of follicles detected supports the hypothesis that follicular growth in camelids occurs in waves. It was established that the growth characteristics of follicular waves varied within and between females. Wide variation in the interval between successive follicular waves made the use of a mean interwave interval value inappropriate. Non-pregnant alpacas had a follicle in the size range potentially capable of ovulating, but of unknown fertility, on either ovary most of the time. A second objective was to determine the relationships between sexual receptivity, mating behaviour, ovarian follicular state and mating success. It was not possible to correlate mating behaviour or ovarian status with mating success. Matings to optimise pregnancy rates in alpacas need to occur in the presence of an oestrogenic follicle that is capable of ovulation in response to mating. Simple detection of alpacas with follicles in this state was not possible and treatments to control ovarian follicular growth were therefore investigated. Attempts to control ovarian follicular waves in alpacas were focussed on inducing regression of the existing dominant follicle of unknown age and allowing emergence of a new cohort of follicles at a known time after treatment. The induction of ovulation to remove the existing dominant follicle was not considered in these studies. Single intramuscular (i.m.) injections of 1713-oestradiol (oestradiol) or oestradiol benzoate, at different doses and with and without simultaneous injection of progesterone, were unsuccessful in controlling follicular growth to allow emergence of a new follicular wave at a known time. This finding was unexpected given that oestradiol causes the regression of follicles in cattle and sheep. It was concluded that alpacas, and perhaps camelids in general, have different intra- and/or extra-ovarian mechanisms that control follicular growth and regression compared with ruminants that are spontaneous ovulators. Subsequent studies examined the effects of different protocols of progesterone treatment on ovarian follicular growth and regression. Twice daily i.m. injection of25 mg of progesterone for 21 days was effective at inducing regression of the existing dominant follicle and suppressing emergence of a new follicular wave until treatment ceased. To make the treatment more practical and reduce the number of injections required, subcutaneous implants of norgestomet and lower frequency, higher dose progesterone treatments were examined. The most practical and effective protocol for ovarian follicular control in female alpacas was provided by 200 mg progesterone injected i.m. on Days 0, 2 and 4. The majority of females treated with this protocol had a newlyemerged follicle with a diameter capable of ovulation on Day 16, 12 days after progesterone treatment ceased. Mating trials were performed on three commercial alpaca farms to compare pregnancy rates at Day 60 in females treated with the progesterone protocol and mated on Day 16 and females mated at random. Results showed that treated females were capable of ovulation, fertilisation and pregnancy, however, there was no difference in 60-day pregnancy test percentage between females receiving the Day 0-4 progesterone synchronisation protocol and females treated with oil placebo. The oocyte contained in the first dominant follicle following progesterone treatment would need to be of normal fertility in order for the progesterone-based protocol to increase pregnancy rates to a single mating. As a first step to examining oocyte integrity, oocytes were retrieved by ultrasound-guided, transvaginal aspiration on Day 17 in females treated with the progesterone protocol described above involving injections on Days 0, 2 and 4. Half of these females had an injection ofluteinising hormone (LH) on Day 16 to simulate a mating-induced LH surge. Oocytes were examined by light and electron microscopy to observe whether the cellular ultrastructure was indicative of normal maturation. Only oocytes from those females that received LH showed changes to the cellular ultrastructure indicative of normal maturation including meiotic progression (nuclear maturation) from Prophase I to Metaphase I, an increase in the width of the perivitelline space and expansion of the cumulus cells surrounding the oocyte. This finding was interpreted to suggest that the oocyte contained in the first ovulatory follicle after progesterone treatment has a normal capacity for fertilisation and embryo development competency. This thesis presents new information on ovarian follicular wave characteristics in nonpregnant female alpacas and introduces a practical protocol based on progesterone to control ovarian follicular growth. The protocol allows for fixed-time mating. The Australian alpaca industry will benefit from more efficient utilisation of genetically superior males and females and faster dissemination of improved genotypes throughout the national herd. Potential benefits include incorporation of the progesterone protocol into other assisted breeding technologies such as artificial insemination, embryo transfer and possibly the in vivo maturation of oocytes for in vitro fertilisation.