Neuroendocrine Regulation of Seasonal Reproductive Activity in West African Dwarf Goats Under Tropical Photoperiodic Conditions in South South Nigeria: A Hypothalamic-Pituitary-Gonadal Axis Study

The West African Dwarf goat demonstrates a degree of seasonal reproductive variation despite the attenuated photoperiodic changes in the equatorial tropics, yet the neuroendocrine basis of this seasonality in South South Nigeria has not been characterised at the hypothalamic-pituitary-gonadal axis molecular level. This doctoral study investigated the neuroendocrine regulation of seasonal reproductive activity in West African Dwarf goats in Akwa Ibom and Cross River States, South South Nigeria. Sixty intact female goats and twenty bucks were monitored over twelve continuous months. Plasma melatonin, kisspeptin, gonadotropin-releasing hormone pulse frequency by frequent blood sampling, luteinising hormone, follicle-stimulating hormone, oestradiol, progesterone, and testosterone were quantified monthly by immunoassay. Hypothalamic kisspeptin-1 messenger RNA expression was assessed by real-time PCR in post-mortem subsets slaughtered at peak and nadir reproductive periods. A statistically significant bimodal seasonal pattern in reproductive activity was identified, correlating with rainfall-induced foraging cycles rather than photoperiod per se. Kisspeptin plasma concentrations peaked concurrently with the highest ovulation rates and were positively correlated with gonadotropin-releasing hormone pulse frequency. Melatonin did not vary significantly across seasons in this equatorial location, supporting an alternative metabolic, rather than photoperiodic, entrainment pathway. Hypothalamic kisspeptin-1 messenger RNA was upregulated twofold during the high-activity season. This doctoral study provides the first hypothalamic-pituitary-gonadal axis molecular characterisation of seasonal breeding regulation in South South Nigerian goats and proposes nutritional kisspeptin modulation as the primary seasonal trigger. Keywords: neuroendocrine, seasonal reproduction, kisspeptin, gonadotropin-releasing hormone, West African Dwarf goats.