To elucidate the role of estradiol feedback on GnRH pulse generation in postpartum beef cows and its implications for the resumption of estrous cyclicity. Objective 1: To quantify changes in GnRH pulse frequency and amplitude in response to varying levels of estradiol during the postpartum period. Hypothesis 1: Estradiol levels positively regulate GnRH pulse frequency and amplitude, facilitating the resumption of estrous cyclicity postpartum. Objective 2: To investigate the relationship between estradiol levels and LH surge onset in postpartum cows. Hypothesis 2: A critical threshold of estradiol is required to trigger the preovulatory LH surge, with delayed estradiol rises contributing to anovulation in early postpartum cows. Objective 3: To assess the impact of estradiol supplementation on the timing of the first postpartum ovulation. Hypothesis 3: Estradiol supplementation during the early postpartum period will advance the timing of first ovulation by enhancing GnRH and LH surge dynamics. References: Stevenson, J.S., et al. (1999). Estradiol Regulation of Gonadotropin Secretion in Postpartum Beef Cows. Journal of Animal Science, 77(5), 1320–1326. Wiltbank, M.C., et al. (2018). Regulation of Estradiol and LH Surge in Cows. Theriogenology, 112, 6–15.

To determine how varying concentrations of leptin and kisspeptin affect the onset of puberty in heifers during different developmental stages, and to evaluate how these levels are influenced by diet and environmental conditions. Objective 1: To investigate the relationship between leptin and kisspeptin expression in prepubertal and pubertal heifers fed different dietary regimens. Hypothesis 1: Heifers on a nutrient-rich diet will experience earlier puberty onset due to elevated leptin levels, which will accelerate kisspeptin expression, whereas heifers on restricted diets will show delayed puberty due to reduced leptin and kisspeptin activity. Objective 2: To assess the impact of varying leptin concentrations on GnRH release and subsequent ovarian follicular activity. Hypothesis 2: Lower leptin levels will result in decreased kisspeptin expression and GnRH release, causing delayed puberty onset, while higher leptin levels will enhance these processes. Objective 3: To evaluate the effects of environmental factors, such as temperature and photoperiod, on leptin and kisspeptin expression and their modulation of GnRH secretion in beef heifers. Hypothesis 3: Longer photoperiods and cooler temperatures will increase leptin signaling, promoting kisspeptin and GnRH secretion, leading to earlier puberty onset in beef heifers.

To investigate the regulatory relationship between kisspeptin and leptin as gatekeepers of puberty in beef heifers, evaluating their roles in hypothalamic pathways across developmental stages and production cycles. Objective 1: To elucidate the mechanisms by which leptin regulates Kiss1 expression in the hypothalamus. Hypothesis 1: Leptin acts as a Kiss1 regulator in the arcuate nucleus, influencing pulsatile GnRH frequency and subsequent reproductive processes. Objective 2: To determine if significant post-pubertal body weight fluctuations alter the neuroendocrine pathways involving NPY, POMC, and kisspeptin. Hypothesis 2: Significant weight fluctuations will impact neuroendocrine pathway function, potentially impairing reproductive efficiency in mature cows, but pathway structure will remain unaffected if fully developed prepuberty. Objective 3: To assess whether underdeveloped kisspeptin pathways can recover structurally and functionally with increased energy intake post-puberty. Hypothesis 3: Increased energy intake post-puberty can restore kisspeptin pathway efficiency, enhancing reproductive performance. References: Amstalden, M., et al. (2014). Hypothalamic Neuropeptides and Nutritional Programming of Puberty in Heifers. Journal of Animal Science, 92(8), 3211–3222. Cardoso, R.C., et al. (2018). Neuroendocrine Signaling Pathways and Nutritional Control of Puberty in Heifers. Animal Reproduction.

Which ONE of the following events indicates the start of human development?

Which ONEof the following hormones prepares the fetal lungs for respiration?

The Adam’s apple is formed by the:

Which of the following is NOT part of the uterine tube?

Chemical or environmental agents that may induce or increase the incidence of abnormalities to the physiological development of an embryo or fetus are:

From the outside in, the layers of the uterus consists of:

Most of the carbon dioxide transported in the blood is carried as: