The neurohypophysial peptide oxytocin (OT) and OT-like hormones facilitate reproduction in all vertebrates at several levels. The major site of OT gene expression is the magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei. In response to a variety of stimuli such as suckling, parturition, or certain kinds of stress, the processed OT peptide is released from the posterior pituitary into the systemic circulation. Such stimuli also lead to an intranuclear release of OT. Moreover, oxytocinergic neurons display widespread projections throughout the central nervous system. However, OT is also synthesized in peripheral tissues, e.g., uterus, placenta, amnion, corpus luteum, testis, and heart. The OT receptor is a typical class I G protein-coupled receptor that is primarily coupled via Gq proteins to phospholipase C-β. The high-affinity receptor state requires both Mg2+ and cholesterol, which probably function as allosteric modulators. The agonist-binding region of the receptor has bee...

The Oxytocin Receptor System: Structure, Function, and Regulation

Nutrient requirements of dairy cattle , Nutrient requirements of dairy cattle , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Nutrient requirements of dairy cattle

Partitioning of Nutrients During Pregnancy and Lactation: A Review of Mechanisms Involving Homeostasis and Homeorhesis

Biology of dairy cows during the transition period : the final frontier?

Effects of heat-stress on production in dairy cattle.

The effect of embryonic death rates in cattle on the efficacy of estrus synchronization programs

Effects of presynchronization and bovine somatotropin on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows.

Influence of supplemental fats on reproductive tissues and performance of lactating cows.

Theory of maternal recognition of pregnancy in swine based on estrogen controlled endocrine versus exocrine secretion of prostaglandin F2alpha by the uterine endometrium.

Studies of ovarian follicular dynamics in cattle may lead to methods for improving fertility, for synchronizing estrus with more precision, and for enhancing superovulatory responses. Within an estrous cycle, two or three large (> 10 mm) follicles develop during consecutive waves of follicular growth. The last wave provides the ovulatory follicle, whereas preceding wave(s) provide follicles that undergo atresia. The life span of large follicles seems to depend on the pulsatile secretion of LH; decreased frequency of LH pulses results in atresia of large follicles. Aromatase activity in the walls of the largest follicles is greatest during the first 8 d of the estrous cycle and decreases by d 12. Steroidogenesis of the largest and second-largest ovarian follicles differs on d 5, 8, and 12 of the estrous cycle. Follicular dynamics are altered by negative energy balance and lactation. The number of large follicles and concentration of estradiol during the preovulatory period differs between postpartum lactating and nonlactating cows. Dietary fats stimulate follicular growth when they are fed to increase energy balance. Administration of bovine somatotropin decreases energy balance and has a differential effect on ovarian follicular responses; growth of the largest follicle does not change, but growth of the second-largest follicle is stimulated by somatotropin. Studies of follicular dynamics in lactating cows demonstrate changes in ovarian function associated with energy balance that may be related to inefficient reproductive performance of cows producing high yields of milk.

William W. Thatcher

Papers

The effect of embryonic death rates in cattle on the efficacy of estrus synchronization programs

Effects of presynchronization and bovine somatotropin on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows.

Influence of supplemental fats on reproductive tissues and performance of lactating cows.

Theory of maternal recognition of pregnancy in swine based on estrogen controlled endocrine versus exocrine secretion of prostaglandin F2alpha by the uterine endometrium.

Factors that affect ovarian follicular dynamics in cattle.