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The transport of lipids across mammary gland epithelial cells (MEC) determines milk lipid content and composition. We investigated the expression of lipid transporters and their regulators in comparison to blood metabolites during lactation and dry period (DP) in dairy cows. Repeated mammary gland biopsies and blood samples were taken from 10 animals at 7 stages of the pregnancy-lactation cycle. Expression levels of the specific mRNAs were determined by quantitative reverse transcription-PCR, whereas ABCA1 was localized by immunohistochemistry. Blood serum metabolites were determined by common enzymatic chemistries. Elevated mRNA profiles of ABCA1 and ABCA7 were found during DP as compared with lactation and were inversely associated with blood cholesterol levels. Elevated levels of ABCG2, NPC1, SREBP1, SREBP2, LXRα, and PPARγ were found postpartum, whereas ABCG1 did not differ between the functional stages of the mammary gland. The ABCA1 protein was localized in MEC and showed differential activity between DP and lactation suggesting a role of ABCA1 in the removal of excess cellular cholesterol from MEC during the DP. The expression profiles of ABCA7 and NPC1 may reflect a role of these transporters in the clearance of apoptotic cells and the intracellular redistribution of cholesterol, respectively. Regulation of lipid transporters in the mammary gland is partially associated with transcription factors that control lipid homeostasis. [ABSTRACT FROM AUTHOR]

Milk yield of the dairy cow follows a pattern termed the lactation curve. We have investigated the cellular background for this pattern. Seven mammary biopsies were obtained from each of 10 cows: at the end of lactation (d 347, equal to d 77 before next parturition); during the dry period at d 48 (4 d after dry off); 16 d before parturition; and during lactation at d 14, 42, 88, and 172. The fraction of proliferating (staining positive for Ki-67) alveolar cells was higher during the dry period (8.6%) than during lactation (0.5%). The fraction of apoptotic (staining positive by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) alveolar cells was higher immediately after dry off (0.37%) and in early lactation (0.76%) than during other periods (0.15%). The enzyme activities of fatty acid synthetase, acetyl CoA-carboxylase, and galactosyl transferase were approximately 12-, 11-, and 4-fold higher, respectively, during lactation than during the dry period. In conclusion, mammary cell proliferation is substantial in a period near parturition but otherwise low, and apoptosis is elevated at dry off and in early lactation. The increase in apoptosis in early lactation may be due to discarding nonfunctional or senescent cells or to removal of a surplus of newly synthesized cells. The activity of selected enzymes central for milk synthesis is probably not limiting for milk production. [ABSTRACT FROM AUTHOR]

Chemical-specific hazard quotient (HQ) risk characterization in ecological risk assessment (ERA) can be a value-added tool for risk management decision-making at chemical release sites, when applied appropriately. However, there is little consensus regarding how HQ results can be used for risk management decision-making at the population, community, and ecosystem levels. Furthermore, stakeholders are reluctant to consider alternatives to HQ results for risk management decisions. Chemical-specific HQs risk characterization should be viewed as only one of several approaches (i.e., tools) for addressing ecological issues; and in many situations, other quantitative and qualitative approaches will likely result in superior risk management decisions. The purpose of this paper is to address fundamental issues and limitations associated with chemical-specific HQ risk characterization in ERA, to identify when it may be appropriate, to explore alternatives that are currently available, and to identify areas that could be developed for the future. Several alternatives (i.e., compensatory restoration, performance-based ecological monitoring, ecological significance criteria, net environmental benefit analysis), including their limitations, that can supplement, augment, or substitute for HQ5 in ERA are presented. In addition, areas of research (i.e., wildlife habitat assessment/landscape ecology/population biology and field validated risk-based screening levels) that could yield new tools are discussed. [ABSTRACT FROM AUTHOR]

Presents information on a study which assessed the potential effect of prolactin as a stimulator of milk production in sows. Materials and methods of the study; Results and discussion.

The impacts of a teat being suckled or not in first parity on its development, gene expression, and milk yield in the next parity were studied. Forty-seven first-parity sows (Sus scrofa) were divided into 2 groups: i) the same teats suckled in 2 subsequent lactations (controls, CTL; n = 22); and ii) different teats suckled in 2 subsequent lactations (treated, TRT; n = 25). In the first lactation, over half of the teats (Teats 1, 2, 5, 6, and 7 from 1 side of the udder, and Teats 3, 4, and 7 from the other side) were sealed with tape so that they were nonfunctional. During the next lactation, the CTL group had the same teats sealed as in the first lactation, whereas the opposite teats were sealed for the TRT group. In both parities, litters were standardized to 7 piglets around birth and to 6 piglets (1 piglet per available teat) at 48 h postpartum. During the second lactation, piglets were weighed at birth and on d 2, 4, 7, 14, 21, 35, and 56 postpartum. Weaning was at 17 ± 1 d of age. Behavioral measures were obtained (using 24-h video recording) on d 3 and d 10 of lactation on 15 sows per treatment to evaluate satiety of piglets, using aggressiveness and nursing behavior as indicators. At weaning in the second lactation, 16 sows per treatment were slaughtered and 4 functional mammary glands were collected for compositional analyses and parenchyma from 2 nonfunctional glands was collected to measure mRNA abundance for selected genes. Piglets from CTL sows weighed 1.12 kg more than piglets from TRT sows (P < 0.05) on d 56, and functional mammary glands from CTL sows contained more parenchymal tissue, more DNA, and more RNA (P < 0.01) than those from TRT sows. The relative mRNA abundance of prolactin in parenchymal tissue tended to be greater in CTL than TRT sows (P < 0.10). Behavioral measures indicated a greater hunger level for piglets using teats that were not previously suckled. Current findings clearly show that teats that were suckled in first lactation produce more milk and have a greater development in the second lactation than nonsuckled teats. [ABSTRACT FROM AUTHOR]