Highlights of FY2005 CSREES Investments in KA305
In fiscal year 2005, CSREES invested approximately $9.595 million in KA305. Below are some of the projects that terminated in 2005. A printable, 2-page color brochure detailing these highlights may also be downloaded.
Interaction of IGF-1 and Leptin in Bovine Mammary Development: Raising dairy heifers on high energy diets that promote rapid body weight gains before puberty decreases production costs on farms but, for unknown reasons, also impairs development of the mammary gland and reduces subsequent milk production. Investigators at Michigan State University determined that leptin (a hormone produced by fat cells) inhibits mammary cell proliferation in heifers. Leptin or insulin-like growth factor (IGF-1) did not alter apoptosis. The greatest effect of leptin was to oppose cell progression. In addition, a high energy diet increases concentration of leptin protein and leptin mRNA in mammary parenchymal tissue. IGF-1 and leptin also alter expression of genes controlling cell proliferative pathways in bovine mammary tissue. Thus, leptin may mediate the inhibitory effects of high-energy intake on mammary gland development in young dairy heifers. A better understanding of these mechanisms may lead to development of methods to enhance mammogenesis in dairy cattle. (NRI)
Leptin Improves Productivity, Health, and Well-Being of Early Lactating Dairy Cows: Investigators at Cornell University showed that plasma leptin was reduced in early lactation, a time when susceptibility to metabolic and infectious diseases is greatest. In addition, leptin stimulated immune cell proliferation, suggesting that this reduction has a negative functional significance. They also showed that functional leptin receptors are sparse in most peripheral tissues, but abundant in the hypothalamic region of the brain. Studies were also conducted on the leptin allele coding for a cysteine at position 4 of the mature protein. Although a genetic test to detect this allele is being commercialized to dairy farmers, results of these studies show no detectable productive advantage for this allele and, therefore, do not support the use of this test to select superior dairy animals. (NRI)
Regulation of the Chicken Acetyl-CoA Carboxylase Gene: A correlation exists between saturated fat intake, serum lipids, and the risk of heart disease. Acetlyl-CoA carboxylase is an enzyme that catalyzes the pace-setting step of this pathway. Scientists at West Virginia University showed that expression of the acetyl-CoA carboxylase gene in chickens is strongly influenced by other proteins such as sterol regulatory element binding protein (SREBP) and the nuclear thyroid hormone receptor. They also established a new interaction between SREBP-1 and thyroid hormone receptor signaling pathways. Thus, alterations in the concentration of mature SREBP-1 play a role in mediating the effects of starvation. Factors that control the expression of the mature form of SREBP-1 provide a means to regulate fat accretion in chickens. (NRI)
In situ Adipose Tissue Metabolism in Mammals: Fat cell enlargement is the hallmark of obesity. Scientists at the University of New Hampshire studied metabolic processes in intact adipose tissue that contributes to adipose tissue accumulation in miniature Yucatan swine. Results indicate that the extracellular cyclic AMP-adenosine pathway exists in isolated adipocytes and intact adipose tissue. In addition, cyclic AMP may be metabolized extracellularly by adipose tissue. There was no correlation between adenosine level and lipolysis rate. Rather than being passive and subject strictly to external control, adipose tissue is a dynamic and metabolically active tissue that possesses inherent and sophisticated metabolic controls. These studies provide new knowledge regarding how fat cells may regulate their own size and contribute to obesity. (Hatch)
Regulation of Muscle Satellite Cell Activity in Cattle and Pigs: Scientists at Michigan State University conducted studies to generate new, fundamental information about the processes that regulate growth of skeletal muscle in meat animals. Results revealed that the proportions of proliferating and differentiating satellite cells remain relatively constant in growing cattle. Steroid implants have little apparent effect on satellite cell activity 14 days after implantation. In cattle (as in pigs) a high proportion of satellite cells are proliferating throughout the growing phase. Satellite cells contribute 70-99% of the nuclei residing in mature skeletal muscle fibers. Since each nucleus in a skeletal muscle fiber can accommodate a finite quantity of cell volume, satellite cell incorporation into muscle fibers is a critical determinant of muscle fiber size. Understanding the regulation of satellite cell proliferation, differentiation, and incorporation will enable development of strategies to increase postnatal myonuclear accretion, and thereby improve the rate and extent of muscle growth. (Hatch)
Fibroblast Growth Factor and the Extracellular Matrix Interact to Regulate Myogenic Satellite Cell Activity in Turkeys: To develop procedures to augment muscle growth and increase production efficiency, scientists at South Dakota State University and Ohio State University studied the factors that influence turkey satellite cell activity in culture under controlled conditions. Myogenic satellite cells isolated from a single muscle differed in their responsiveness to both stimulatory and inhibitory growth factors. Satellite cell clones that are more responsive to mitogenic effects of fibroblast growth factor (FGF) express greater levels of heparin sulfate proteoglycan (a key extracellular matrix component that interacts with growth factors). Slower growing clones increased their expression of FGF receptor 1 during proliferation and differentiation while faster growing clones decreased expression of FGF1 receptor during differentiation. Studies on heparin sulfate proteoglycan expression (which is associated with FGF receptor regulation) show heparin sulfate proteoglycan expression to be linked to growth rate and gender. These data are suggestive of heparin sulfate proteoglycans having a role in muscle growth. (Hatch)
Effects of Progesterone on Skeletal Muscle Growth and Differentiation in Beef Cattle: An increased understanding of the mode of action of growth promotants on lean muscle deposition will improve our ability to continue to enhance the efficiency of meat-animal production and also provide a safe, wholesome product to consumers. Researchers at Kansas State University demonstrated that progestins increase carcass fatness and reduce muscle deposition. The mechanisms responsible for these changes may involve inducing early cell cycle withdrawal in bovine satellite cells, which then causes early terminal cell differentiation through up-regulation of IGF-1 and myogenin. A better understanding of the fundamental mechanisms of muscle growth will aid in the implementation of alternatives to exogenous growth promotants and will aid in increasing global markets for red meat produced in the United States. (Hatch)
Segregated Early Weaning Improves Gut Immune Status in Neonatal Pigs: Pigs produced in conventional, intensively managed swine production systems are routinely weaned as early as 19-21 days of age. Weaning pigs at an early age results in a less immunologically-developed pig which may lead to increased mortality rates. Researchers at the University of Arkansas demonstrated that raising weanling pigs in an off-site facility can improve growth performance. During the nursery period, performance may be dependent on the immune status of the pig. Supplementation with microbials (such as Lactobacillus brevis) during the weaning phase resulted in improved average daily gain, feed intake, and body weight, which resulted in potentially beneficial alterations in gastrointestinal microflora, morphology, monocyte/macrophage activity, and immune cell populations. A better understanding of the impact of management system on immune function is essential to understanding the growth performance enhancement associated with off-site production systems and direct-fed microbials. (Animal Health)
Endothelin-1 and Equine Laminitis: Laminitis is a debilitating, excruciatingly painful, and often life-threatening disease of the soft tissues of the equine digit. Scientists at Louisiana State University studied the role of endothelin-1 (a potent vasoconstrictor peptide synthesized by the endothelium) in the pathophysiology of acute laminitis. The equine endothelin-1 gene was cloned and sequenced. Expression of endothelin-1 mRNA was increased in laminar samples of laminitic horses. Studies were also conducted to determine if a novel endothelin-1 antagonist prevents vascular and clinical signs of acute laminitis. Administration of the endothelin-1 antagonist prevented alterations in digital hemodynamics that promote laminar edema formation. In addition, the return to soundness occurred in half the amount of time compared to controls. Thus, by decreasing the vascular contractile effects of endogenous endothelin-1, improvements in hemodynamics and clinical signs of laminitis were observed. (Animal Health)
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