Puberty in Beef Heifers: Endocrine Mechanisms, Reproductive Development, and Nutritional Influences on the onset of Puberty

Puberty is a physiological process in animals that results in reproductive maturity and is a crucial factor influencing fertility levels throughout their lifespan. First ovulation is an indicator that cattle have achieved puberty, which is directly controlled by endocrine processes. Reduced negative feedback from ovarian steroids stimulates the Hypothalamus-Pituitary-Ovary (HPO) gland to secrete reproductive hormones such as gonadotropin-releasing hormone (GnRH), follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol, and progesterone, which spur follicular growth and cause the first ovulation in cattle. The development of the reproductive tract accompanies follicular development in the ovary. Each organ, specifically uterine, cervical, and ovarian, shows a rapid growth process characterized by two phases: the early postnatal period and several months leading up to puberty. The reproductive tract experiences significant growth during the early gestational period, specifically between 2-20 weeks of age. Rapid growth will subsequently occur as individuals approach puberty, typically between 40-60 weeks of age. The growth occurring between these two phases tends to be constant. Various factors influence the initiation of puberty. One of the factors that has the most significant influence is nutrition. Adequate nutrition in animal feed promotes optimal body growth, leading to the secretion of growth and metabolic hormones that influence neuronal activities in the hypothalamus. This includes the release of GnRH during puberty initiation, as well as insulin-like growth factor 1 (IGF1) and leptin, which are involved in ovarian function. Keywords: Animal husbandry, cattle, fertility, luteal cycle, reproductive organs, ovulation, estrus cycle, heifer body weight