Effect of dietary intake on steroid feedback on release of luteinizing hormone in ovariectomized cows

Effect of short-term fasting on hepatic steroid hormone metabolism in cows

In the present study, the effect of 4-day fasting on steroid hormone metabolism in the liver and secretion of LH was examined in cows. Six non pregnant, dry Holstein cows were used. The estrous cycle was synchronized in all cows using CIDR-Ovsynch. Cows were allocated to a control group (n=3) and a fasting group (n=3). In the fasting group, cows were fasted for four days from day -4 to day -1 (day 0=day of 2nd GnRH injection) but otherwise were fed ad libitum. The experiment was repeated in a crossover design after an interval of about one month. The peripheral progesterone (P(4)) concentration in the fasting group was significantly higher than in the control group on day -1 and 0. The peripheral estradiol-17β concentration in the fasting group was also significantly higher than in the control group on day -1 and 0. The portal vein P(4) concentration in the fasting group was significantly higher than in the control group. On day 0, there was no difference in LH secretion between groups. The mean percentages of lipid droplets in liver cells in the fasting group were significantly higher than in the control group on day 0. These results suggest that short-term fasting leads to reduced hepatic steroid hormone metabolism by accumulation of fat in the liver, which causes high peripheral steroid hormone concentrations.

Invited review: New perspectives on the roles of nutrition and metabolic priorities in the subfertility of high-producing dairy cows

Management, nutrition, production, and genetics are the main reasons for the decline in fertility in the modern dairy cow. Selection for the single trait of milk production with little consideration for traits associated with reproduction in the modern dairy cow has produced an antagonistic relationship between milk yield and reproductive performance. The outcome is a multi-factorial syndrome of subfertility during lactation; thus, to achieve a better understanding and derive a solution, it is necessary to integrate a range of disciplines, including genetics, nutrition, immunology, molecular biology, endocrinology, metabolic and reproductive physiology, and animal welfare. The common theme underlying the process is a link between nutritional and metabolic inputs that support complex interactions between the gonadotropic and somatotropic axes. Multiple hormonal and metabolic signals from the liver, pancreas, muscle, and adipose tissues act on brain centers regulating feed intake, energy balance, and metabolism. Among these signals, glucose, fatty acids, insulin-like growth factor-I, insulin, growth hormone, ghrelin, leptin, and perhaps myostatin appear to play key roles. Many of these factors are affected by changes in the somatotropic axis that are a consequence of, or are needed to support, high milk production. Ovarian tissues also respond directly to metabolic inputs, with consequences for folliculogenesis, steroidogenesis, and the development of the oocyte and embryo. Little doubt exists that appropriate nutritional management before and after calving is essential for successful reproduction. Changes in body composition are related to the processes that lead to ovulation, estrus, and conception. However, better indicators of body composition and measures of critical metabolites are required to form precise nutritional management guidelines to optimize reproductive outcomes. The eventual solution to the reduction in fertility will be a new strategic direction for genetic selection that includes fertility-related traits. However, this will take time to be effective, so, in the short term, we need to gain a greater understanding of the interactions between nutrition and fertility to better manage the issue. A greater understanding of the phenomenon will also provide markers for more targeted genetic selection. This review highlights many fruitful directions for research, aimed at the development of strategies for nutritional management of reproduction in the high-producing subfertile dairy cow.

Influence of estradiol on adrenal activity in ovariectomized cows during acute stress

Stress-dependent activation of the hypothalamo-pituitary-adrenal axis (HPA) can compromise reproductive function in animals and humans. In addition, it has been shown that estrogens are also capable of influencing the activity of the adrenal cortex. The objective of this study was to evaluate the effect of estradiol (E2) on adrenocortical secretion of cortisol and progesterone as well as on pituitary LH-release in cows during stress. Five ovariectomized Brown Swiss cows were exposed to acute restraint stress (2-h immobilization in a trimming chute), either with or without E2 treatment. Blood samples were taken every 15 min during a 5-h period for determination of cortisol progesterone and LH. Our results demonstrate that during the 2-h stress period mean cortisol concentrations significantly (P < 0.05) increased in all cows independent of E2 treatment. Mean progesterone concentrations also increased during stress, but the effect was only significant in E2-untreated cows. In contrast to cortisol and progesterone, mean LH values decreased in all animals during stress, but the decline was not significant. However, significantly lower mean LH values were seen at the end of the stress period comparing to values before stress. In cows without stress, E2 treatment had no significant effect on mean values of all three hormones analyzed. From our results it can be concluded that in ovariectomized cows (a) acute stress increases cortisol and progesterone secretion but decreases LH release and (b) the stress induced adrenocortical and pituitary responses were clearly attenuated under the influence of estradiol.