Neuroendocrine control of reproductive function in ruminants

Return of postpartum ovarian activity in dairy goats supplemented with different levels of energy

This study aimed to evaluate the return of post partum ovarian activity in dairy goats supplemented with different levels of energy during the dry period in the semi-arid region of Pernambuco. Twenty-four animals were allocated into four treatments of six animals each: Control, consisting of goats that had access to pasture and only received 4 kg of fresh palm, and three groups with isoproteic supplementation (20% Crude Protein), ranging in TDN content of 65%, 75% and 85%. The daily milk yield showed a linear growth behavior (P <0.05) since day 35th postpartum, when the animals recovered the weight gain and body condition score after 14 and 21 days postpartum, respectively, with slight weight gain in 75% and 85% treatments. Among the reproductive parameters, uterine involution and return to estrus activity showed a decrease in the number of days associated with the higher energy levels (P <0.05). The emergence of the 1st follicles > 2 mm occurred around 33 days postpartum and the maximum diameter of the pre-ovulatory follicle was 5,41mm. These results were not influenced by treatments (P> 0.05). We concluded that the supplementation with different levels of energy promoted a positive effect, as increased productive parameters and reduced the number of days for the reestablishment of the reproductive parameters postpartum; for instance, uterine involution, return to estrus and consequently return of ovarian activity postpartum.

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.