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The human population is ever increasing while the quality and quantity of natural resources used for livestock production decline. This calls for improved product efficiency and the development of improved and sustainable cattle production methods to produce higher quality products to satisfy the demands of both the modern and transient world. The goal of this review was to summarize the interactions, challenges, and opportunities in cattle production relating to their endocrine system, and how reproductive hormones and others impact economically important traits, animal welfare, and human health. A comprehensive literature search was conducted with a focus on analysis of natural hormones and the use of exogenous hormone administration for reproduction, growth, and development of beef and dairy cattle. Hormones regulate homeostasis and enhance important traits in cattle, including fertility, growth and development, health, and the production of both meat and milk products. Reproductive hormones such as testosterone, estradiol, progesterone, and related synthetics like trenbolone acetate and zeranol can be strategically utilized in both beef and dairy cattle production systems to enhance their most valuable traits, but the impact of these substances must account for the welfare of the animal as well as the health of the consumer. This scientific review provides a comprehensive analysis of the bovine endocrine system's impact on food animals and product quality which is vital for students, researchers, livestock producers, and consumers. Although important advances have been made in animal science and related technological fields, major gaps still exist in the knowledge base regarding the influence of hormones on the production and welfare of food animals as well as in the public perception of hormone use in food-producing animals. Filling these gaps through transformative and translational research will enhance both fundamental and applied animal science to feed a growing population.The animal production industry is responsible for providing products like meat, dairy, and egg products to the growing human population of the world. Within each sector, there are production practices that can improve the overall productivity of the animals and contribute to their welfare. One such avenue for enhanced production is the inclusion of hormones. Hormones are naturally produced within the body by the endocrine system which helps initiate many life processes and transition the body to different stages of production. Hormones influence many important traits such as growth and development, milk production, fertility, and health within the cattle industry. Exogenous hormone use in animals has proven to improve a number of traits and qualities of animal products, but it has also struck up controversy. There are wide deficiencies in the full understanding of roles, applications, and implications of hormones in livestock, making it of high importance for further exploration. In this review, the mechanisms of hormones and their broad uses are explored to provide more context to the conversation of hormone use in animals. Knowledge of endocrinology is powerful and can aid in the advancement of fundamental science and animal development and production.

Objectives of these two experiments were to determine if exogenous estradiol benzoate (EB) affects follicular, luteal, and uterine hemodynamics. In both experiments, 77 estrous-synchronized beef cows were assigned to one of two treatments: 1) Control (CON) or, 2) an injection of 1 mg EB the day before expected estrus (Day 0; Experiment 1) or on the day of estrus (Day 1; Experiment 2). There was transfer of an embryo (Day 7) into cows that expressed estrus. In Experiment 1, estradiol concentrations in circulation at Day 0 were greater in EB-treated cows (P = 0.003); however, concentrations of progesterone were only greater (P = 0.03) at Day 21 in cows of the EB-treated compared to those in the CON group. The follicular and luteal blood perfusion was similar, however, treatment with EB resulted in a greater uterine blood perfusion. In Experiment 2, treatment with EB did not affect size or blood perfusion of the corpus luteum (CL) on Day 7, 14, and 21. Only on Day 21, however, did pregnant cows have a larger CL than non-pregnant cows (P = 0.02). Blood perfusion to the CL was greater (P0.05) in all cows on Day 21 compared to 7 or 14 and those determined to be pregnant on Day 35 tended (P = 0.06) to have greater CL blood perfusion only on Day 21 compared to non-pregnant cows. In conclusion, EB treatment resulted in a greater blood perfusion of the uterus, and only affected the CL on Day 21 in Experiment 2.

Ovulation prompted by exogenous GnRH may cause the release of sub-mature oocytes and lead to decreased pregnancy rates. Inclusion of estradiol benzoate (EB) has improved pregnancy rates. The objective was to determine if EB affects blood perfusion of follicles, CL, or uterus, concentrations of estradiol, or incidence of standing estrus. Forty-seven suckled beef cows were synchronized (GnRH+CIDR on d -9, PGF2a+CIDR removal on d -2, expected estrus=d 0). On d -1, 24 of 47 cows received an injection of EB (1mg/2mL) while the other 23 remained as a control group. Ovaries were evaluated via Doppler ultrasonography on d -1, 0, 6, 14, and 21. A laser Doppler probe was used to measure blood perfusion of the uterus on d -1, 0, and 6. Only cows that exhibited estrus (n = 29) were evaluated on d 14 and 21. Images were analyzed via ImageJ software to determine mean area of perfusion. Blood samples were collected on d -1 and 0 and analyzed for concentrations of estradiol using RIA. Using SAS, MIXED and FREQ were used to determine the influence of treatment on blood perfusion and estradiol, and incidence of standing estrus, respectively. Treatment with EB increased (P < 0.001) the number of cows exhibiting standing estrus compared to control (21/24 vs 8/23, respectively). Treatment of EB did not (P > 0.10) alter blood perfusion of the follicles or uterus on any day or perfusion of the CL on d 6. However, EB increased (P < 0.036) the size of the CL on d 14 (25.06±1.7 vs 6.06±3.7) and tended (P < 0.097) to increase the size of the CL on d 21. Treatment of EB increased (P < 0.003) concentrations of estradiol on d 0 compared to control (21.35±4.49 vs 9.44±4.61 pg/mL). In conclusion, treatment with EB may play a role in changing the CL after ovulation.