Postprandial changes in the content and composition of nonprotein nitrogen in human milk.
The effect of a meal on human milk (HM) total nitrogen (TN) and nonprotein nitrogen (NPN) content and composition was examined. Two studies were performed in which milk and blood samples were collected 2-3 h after subjects consumed either a test breakfast or lunch. To monitor the rate of transfer of plasma urea into milk, two women were given [15N]2-urea with the meal. Milk TN concentrations were not significantly different from premeal values. However, concentrations of milk NPN, urea nitrogen, and alanine were increased by greater than or equal to 20% over premeal values. [15N]2-Urea appeared in plasma and milk within 15 min and reached maximum enrichments of 10% and 5.5% in plasma and milk, respectively. Several HM NPN components increase in concentration postprandially; however, these concentrations were not always correlated with changes in plasma concentrations, suggesting that milk NPN may also reflect metabolic activities within the mammary gland.
Marginal dietary protein restriction reduced nonprotein nitrogen, but not protein nitrogen, components of human milk.
OBJECTIVE
This study was designed to determine whether marginal dietary protein intakes of lactating women alter their milk production and composition. The study followed the observation that marginal dietary protein intakes lead to significantly negative nitrogen balances in these women.


METHODS
Twenty-four healthy, mature lactating women were divided evenly into three groups on the basis of postpartum times; 1, 5, or 12 months. Each woman was given a controlled protein diet of either 1.5 (HP) or 1.0 (MP) g/kg body weight/day for 7 to 10 days. Milk production was measured for 72 hours by test weighing the infant before and after feeding. Milk samples from alternate breasts were collected for 24 hours, pooled, and analyzed for their protein nitrogen, nonprotein nitrogen, free and protein-bound amino acid, and lactoferrin concentrations.


RESULTS
Reduced dietary protein intakes were associated with a decrease (p < 0.05) in the nonprotein nitrogen and total free amino acid fractions of milk. Although urea was unaffected, the concentrations of milk free leucine, phenylalanine, histidine, and ornithine were lower (p < 0.05) in the MP than in the HP group, while the output of leucine and histidine tended to be lower in the MP group. The amount of milk produced, as well as the amounts of protein nitrogen, protein-bound amino acid, and lactoferrin and their concentrations were unaffected by a reduction of dietary protein.


CONCLUSIONS
Maternal milk production and the protein nitrogen, but not the nonprotein nitrogen, fraction of human milk were relatively well-preserved in the presence of a short-term, marginal reduction of dietary protein.
Genetics of the phenotypic evolution in sheep: a molecular look at diversity-driving genes
Background After domestication, the evolution of phenotypically-varied sheep breeds has generated rich biodiversity. This wide phenotypic variation arises as a result of hidden genomic changes that range from a single nucleotide to several thousands of nucleotides. Thus, it is of interest and significance to reveal and understand the genomic changes underlying the phenotypic variation of sheep breeds in order to drive selection towards economically important traits. Review Various traits contribute to the emergence of variation in sheep phenotypic characteristics, including coat color, horns, tail, wool, ears, udder, vertebrae, among others. The genes that determine most of these phenotypic traits have been investigated, which has generated knowledge regarding the genetic determinism of several agriculturally-relevant traits in sheep. In this review, we discuss the genomic knowledge that has emerged in the past few decades regarding the phenotypic traits in sheep, and our ultimate aim is to encourage its practical application in sheep breeding. In addition, in order to expand the current understanding of the sheep genome, we shed light on research gaps that require further investigation. Conclusions Although significant research efforts have been conducted in the past few decades, several aspects of the sheep genome remain unexplored. For the full utilization of the current knowledge of the sheep genome, a wide practical application is still required in order to boost sheep productive performance and contribute to the generation of improved sheep breeds. The accumulated knowledge on the sheep genome will help advance and strengthen sheep breeding programs to face future challenges in the sector, such as climate change, global human population growth, and the increasing demand for products of animal origin.