To study the effects of dietary crude protein (CP) and energy on milk urea N concentrations in dairy sheep, eight pelleted total mixed rations were prepared to obtain two levels of energy density (1.65 and 1.55 Mcal of net energy for lactation per kilogram of dry matter for high energy and low energy rations, respectively) and four concentrations of CP within each energy level (mean CP concentrations, 14.0, 16.4, 18.7, and 21.2% of dry matter). The experimental design consisted of two 4 x 4 Latin squares (one per energy level) with two replications per treatment within each 3-wk period. Milk urea N concentrations were similar between dietary energy levels. Within each energy level, milk urea N was linearly and positively associated with dietary CP content and intake (range of milk urea N concentrations, 12.2 to 25.8 mg/dl for ewes fed high energy rations and 12.9 to 26.7 mg/dl for ewes fed low energy rations). The comparison of these results with those from other trials suggested that milk and blood urea N concentrations are closely correlated with dietary CP concentrations and less closely correlated with dietary CP intake. Our results suggest that milk or blood urea N concentrations can be used as indicators of protein metabolism and intake of lactating ewes.

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Hematopoietic stem cells (HSC) are responsible for the production of blood and immune cells during life. HSC fate decisions are dependent on signals from specialized microenvironments in the bone marrow, termed niches. The HSC niche is a tridimensional environment that comprises cellular, chemical, and physical elements. Introductorily, we will revise the current knowledge of some relevant elements of the niche. Despite the importance of the niche in HSC function, most experimental approaches to study human HSCs use bidimensional models. Probably, this contributes to the failure in translating many in vitro findings into a clinical setting. Recreating the complexity of the bone marrow microenvironment in vitro would provide a powerful tool to achieve in vitro production of HSCs for transplantation, develop more effective therapies for hematologic malignancies and provide deeper insight into the HSC niche. We previously demonstrated that an optimized decellularization method can preserve with striking detail the ECM architecture of the bone marrow niche and support HSC culture. We will discuss the potential of this decellularized scaffold as HSC niche model. Besides decellularized scaffolds, several other methods have been reported to mimic some characteristics of the HSC niche. In this review, we will examine these models and their applications, advantages, and limitations.

We conclude that out-of-phase feeding during pregnancy and lactation can lead to glucose intolerance in male offspring, which is caused by a disruption in insulin secretion capacity. This metabolic programming is possibly caused by mechanisms dependent on miRNA modulation of syntaxin 1a.

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