Bibliografías temáticas / Ovine pregnancy

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Literatura académica sobre el tema "Ovine pregnancy"

Autor: Grafiati

Publicado: 4 de junio de 2021

Última modificación: 20 de febrero de 2023

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Artículos de revistas sobre el tema "Ovine pregnancy"

Flanagan, P. G., D. Westmoreland, N. Stallard, I. M. Stokes y J. Evans. "Ovine chlamydiosis in pregnancy". BJOG: An International Journal of Obstetrics and Gynaecology 103, n.º 4 (abril de 1996): 382–85. http://dx.doi.org/10.1111/j.1471-0528.1996.tb09749.x.

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Honey, Laura. "Dealing with ovine pregnancy toxaemia". In Practice 43, n.º 2 (marzo de 2021): 59. http://dx.doi.org/10.1002/inpr.14.

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INNES, ELISABETH A., PAUL M. BARTLEY, DAVID BUXTON y FRANK KATZER. "Ovine toxoplasmosis". Parasitology 136, n.º 14 (diciembre de 2009): 1887–94. http://dx.doi.org/10.1017/s0031182009991636.

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SUMMARYCongenital infection with Toxoplasma gondii is an important cause of abortion in sheep worldwide. The cat is the definitive host of the parasite, and infected cats may shed millions of oocysts in their faeces resulting in extensive environmental contamination and an important source of infection for grazing herbivorous animals. Studies looking at development of specific antibodies in sheep, as an indicator of exposure to T. gondii, have shown that there is an increase in seroprevalence associated with age indicating that most infections in sheep occur following birth. The stage of gestation when transplacental transmission of T. gondii to the developing foetus occurs is critical in determining the clinical outcome. The importance of endogenous transplacental transmission in persistently infected ewes and its clinical importance is a subject of current debate. Ewes infected prior to mating develop immune responses that help protect against disease in a subsequent pregnancy and also against experimental challenge administered during pregnancy. Both innate and adaptive immune responses are activated following T. gondii infection and experiments involving the chronic cannulation of peripheral lymph nodes in sheep have allowed the dynamics of the immune responses to be analysed in real time. A live vaccine, Toxovax® is the only commercially available vaccine worldwide to protect against congenital toxoplasmosis.

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MacLaren, LA, GB Anderson, RH BonDurant y AJ Edmondson. "Reproductive cycles and pregnancy in interspecific sheep<==>goat chimaeras". Reproduction, Fertility and Development 5, n.º 3 (1993): 261. http://dx.doi.org/10.1071/rd9930261.

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The objectives of the current study were to determine whether interspecific sheep<==>goat chimaeras exhibited reproductive cycles of their component species and were capable of maintaining ovine and caprine pregnancies to term. All chimaeras had oestrous cycles and several exhibited characteristics of both ewes and does, including short, 6-7-day cycles. Sixteen caprine pregnancies were confirmed in eight sheep<==>goat and one hybrid<==>sheep chimaera from 21 embryo transfers; of these, six appeared normal by ultrasonographic examination during Weeks 5 or 6, but none progressed beyond Week 8. Three apparent pseudopregnancies developed in two animals. In contrast, eight of 11 pregnancies in chimaeras resulted in term ovine offspring after transfer of ovine embryos or natural matings with rams. By comparison, interspecific (caprine or hybrid) pregnancies in ewes were lost in Week 4 (n = 8) or Weeks 5-6 (n = 2). First interspecific (ovine or hybrid) pregnancies in does were maintained longer (Weeks 6-12, n = 7) than second interspecific pregnancies (Weeks 4-5, n = 5) (P < 0.05) or interspecific pregnancies in ewes (P < 0.05). The results suggest that abnormal fetomaternal interactions during the early stages of implantation are responsible for termination of caprine pregnancies in the ovine or chimaeric uterus, whereas ovine conceptuses are able to implant successfully in the chimaeric uterus. All chimaeras were fertile, since each carried at least one ovine pregnancy to term following natural matings with rams.

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Hull, A. D., D. M. Long, L. D. Longo y W. J. Pearce. "Pregnancy-induced changes in ovine cerebral arteries". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 262, n.º 1 (1 de enero de 1992): R137—R143. http://dx.doi.org/10.1152/ajpregu.1992.262.1.r137.

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We examined the effects of pregnancy on the ovine cerebral vasculature by comparing several characteristics of isolated endothelium-intact segments of three intracranial arteries including the middle cerebral (MCA), posterior communicating (PC), and basilar (BAS) arteries taken from pregnant sheep (138-143 days gestation, term approximately 145 days) and nonpregnant controls. For comparison, segments of the extracranial common carotid (COM) artery were also studied. With pregnancy, vessel water content increased (5.4-5.8%) in all arteries except the PC. Additionally, cellular protein content increased in all arteries (4.4-50.0%). Arterial stiffness, as determined by passive stress-strain determinations, was significantly decreased during pregnancy in the MCA but not in the larger arteries. Maximum contractile responses, when normalized to vessel wall cross-sectional area, were consistently greater in arteries from pregnant than in those from nonpregnant animals (10.1-49.7%). Relaxation to the endothelium-independent guanylate cyclase stimulator S-nitroso-N-acetyl penicillamine (SNAP) increased with pregnancy only in the distal MCA (approximately 17%). Endothelium-dependent relaxation to the calcium ionophore A23187 decreased only in the larger and more proximal COM (-39%). Thus pregnancy was associated with an increase in production of contractile force, a decrease in peripheral vascular stiffness, a decrease in the relaxant response to A23187 in the COM, and an increase in the relaxant response to SNAP in the MCA. Together, these findings indicate that pregnancy has widespread and important vessel specific cerebrovascular consequences that affect not only arterial composition, but also contractility and endothelial reactivity.

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Keller-Wood, Maureen. "ACTH responses to CRF and AVP in pregnant and nonpregnant ewes". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 274, n.º 6 (1 de junio de 1998): R1762—R1768. http://dx.doi.org/10.1152/ajpregu.1998.274.6.r1762.

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During both ovine and human pregnancy plasma cortisol is increased. In human pregnancy the placenta secretes corticotropin-releasing factor (CRF), but pituitary responses to CRF are decreased. However, in ovine pregnancy there is no measurable placental secretion of CRF. This study tests for changes in pituitary responsiveness to CRF or AVP. Pregnant and nonpregnant ewes were infused with saline or CRF at three doses (3, 9, 45 μg/h), with or without coinfusion of AVP (9 μg/h). AVP infusion increased plasma AVP to ∼250 pg/ml. CRF infusions increased plasma CRF from ∼25 to 50, 150, and 850 pg/ml. ACTH was significantly increased by the infusion of AVP and by all infusions of CRF. Within-animal comparisons revealed a potentiation of the ACTH response to CRF in the presence of AVP. The ACTH responses to AVP and/or CRF were not different between pregnant and nonpregnant ewes. The results suggest that there is no change in pituitary responsiveness to CRF or AVP during ovine pregnancy.

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Simmons, Rebecca M., David W. Erikson, Jinyoung Kim, Robert C. Burghardt, Fuller W. Bazer, Greg A. Johnson y Thomas E. Spencer. "Insulin-Like Growth Factor Binding Protein-1 in the Ruminant Uterus: Potential Endometrial Marker and Regulator of Conceptus Elongation". Endocrinology 150, n.º 9 (4 de junio de 2009): 4295–305. http://dx.doi.org/10.1210/en.2009-0060.

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Abstract Establishment of pregnancy in ruminants requires conceptus elongation and production of interferon-τ (IFNT), the pregnancy recognition signal that maintains ovarian progesterone (P4) production. These studies determined temporal and spatial alterations in IGF binding protein (IGFBP)-1 and IGFBP3 in the ovine and bovine uterus; effects of P4 and IFNT on their expression in the ovine uterus; and effects of IGFBP1 on ovine trophectoderm cell proliferation, migration, and attachment. IGFBP1 and IGFBP3 were studied because they are the only IGFBPs specifically expressed by the endometrial luminal epithelia in sheep. In sheep, IGFBP1 and IGFBP3 expression was coordinate with the period of conceptus elongation, whereas only IGFBP1 expression was coordinate with conceptus elongation in cattle. IGFBP1 mRNA in the ovine endometria was between 5- and 29-fold more abundant between d 12 and 16 of pregnancy compared with the estrous cycle and greater on d 16 of pregnancy than nonpregnancy in the bovine uterus. In sheep, P4 induced and IFNT stimulated expression of IGFBP1 but not IGFBP3; however, the effect of IFNT did not mimic the abundant increase observed in pregnant ewes. Therefore, IGFBP1 expression in the endometrium is regulated by another factor from the conceptus. IGFBP1 did not affect the proliferation of ovine trophectoderm cells in vitro but did stimulate their migration and mediate their attachment. These studies reveal that IGFBP1 is a common endometrial marker of conceptus elongation in sheep and cattle and most likely regulates conceptus elongation by stimulating migration and attachment of the trophectoderm.

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Santos, A. C., G. R. Arthur, H. Pedersen, H. O. Morishima, M. Finster y B. G. Covino. "Systemic Toxicity of Ropivacaine during Ovine Pregnancy". Anesthesiology 75, n.º 1 (1 de julio de 1991): 137–41. http://dx.doi.org/10.1097/00000542-199107000-00022.

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Zoli, A. P., J. F. Beckers y F. Ectors. "Isolation of an ovine pregnancy specific protein". Theriogenology 33, n.º 1 (enero de 1990): 366. http://dx.doi.org/10.1016/0093-691x(90)90790-z.

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Magness, R. R., M. D. Mitchell y C. R. Rosenfeld. "Uteroplacental production of eicosanoids in ovine pregnancy". Prostaglandins 39, n.º 1 (enero de 1990): 75–88. http://dx.doi.org/10.1016/0090-6980(90)90096-e.

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Tesis sobre el tema "Ovine pregnancy"

Regnault, Timothy Robert Hume, of Western Sydney Hawkesbury University, Faculty of Agriculture and Horticulture y School of Agriculture and Rural Development. "Orchestrated partitioning of maternal nutrients during ovine pregnancy". THESIS_FAH_ARD_Regnault_T.xml, 1997. http://handle.uws.edu.au:8081/1959.7/15.

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Ovine placental lactogen (oPL) is postulated to be involved in the repartitioning of maternal nutrients during pregnancy, through its effect on insulin metabolism. Ovine pancreatic insulin responses to exogenous glucose are depressed during pregnancy and this depression becomes more pronounced as gestation advances. In addition, under the hormonal environment of rising oPL and growth hormone (oGH) concentrations, maternal whole body glucose irreversible loss (GIL) increases. The percentage of GIL accounted for by uterine glucose uptake also increases with advancing gestation and increasing litter size. Regression analysis of oPL concentration with glucose uterine uptake as a percentage of GIL, accounts for 39% of variation. Maternal oPL concentrations which increase with gestational age, were significantly greater in multiple bearing ewes and ewes subjected to reduced metabolisable energy (ME) intakes. It is postulated that through actions on pancreatic sensitivity, oPL plays a major role as a homeorhetic control during pregnancy. Elevated oPL concentrations were strongly associated with continually depressed pancreatic insulin secretory ability. The reduction in pancreatic sensitivity to glucose was not as a result of elevation in GH or non-esterified fatty acid (NEFA) concentrations. Muscle insulin receptor number and affinity were found to increase with increasing litter size, suggesting that pregnancy associated insulin resistance occurs predominantly in adipose tissue. During ovine pregnancy there is a specific stimulation of maternal gluconeogenesis. As gestation advances, an increasingly greater proportion of this glucose is partitioned to the gravid uterus. The development of insulin resistance, together with the suppression of pancreatic activity, ensures the preferential uptake of glucose by non-insulin dependent tissues over insulin dependent tissues. These activities favour uterine glucose uptake, decrease adipose glucose uptake, and also promote adipose mobilisation and hepatic gluconeogenesis, so as to meet the increasing energy requirement of pregnancy. It is postulated that through these effects on insulin secretion and associated adipose tissue mobilisation factors, oPL plays a major role in homeorhesis during pregnancy.
Doctor of Philosophy (PhD)

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Regnault, Timothy Robert Hume. "Orchestrated partitioning of maternal nutrients during ovine pregnancy". Thesis, View thesis View thesis, 1997. http://handle.uws.edu.au:8081/1959.7/15.

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Regnault, Timothy Robert Hume. "Orchestrated partitioning of maternal nutrients during ovine pregnancy /". View thesis View thesis, 1997. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20030513.111110/index.html.

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Thesis (Ph. D. of Philosophy)--University of Western Sydney, Hawkesbury, 1997.
"A thesis submitted to the School of Agriculture and Rural Development, Faculty of Agriculture and Horticulture, University of Western Sydney Hawkesbury, in part fulfilment of the requirements for the Degree of Doctor of Philosophy." Includes bibliographical references (p. 236-267).

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Clarkson, Alison Marie. "Maternal recognition of pregnancy and steroid receptors in ovine endometrium". Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267152.

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Smith, James Joseph. "An investigation into hormonal regulation of ovine mammary gland growth during pregnancy". Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/41561.

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Prepartum, multiparous ewes were randomly assigned to experimental groups and sacrificed at 50(n=5), SO(n=4),115(n=5), and 140(n=4) days of gestation. Serum harvested the week prior to slaughter was assayed for progesterone (PG), prolactin (PRL) and growth hormone (GH) concentrations. Mammary tissue obtained at slaughter was assayed for receptor concentrations of progesterone (PGr), prolactin (PRLr) and insulin (Ir). Quantitative biochemical, histological and autoradiographical analyses were used to measure mammary gland growth and indicated no significant glandular growth occurs prior to 8O days of gestation. However, a major phase of parenchymal growth occurred between 8O and 115 days which coincided with significant increases in PG, PGr and PRLr concentrations. Parenchymal growth continued further into late pregnancy. GH and Ir concentrations did not change significantly during pregnancy and were not strongly correlated to growth measurements. These results suggest that mammary gland growth is receptor-mediated and direct or indirect regulation of PGr and PRLr is primarily responsible for the observed growth phenomenon.
Master of Science

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Satterfield, Michael Carey. "Progesterone regulation of endometrial factors supporting conceptus growth and development in the ovine uterus". Diss., Texas A&M University, 2008. http://hdl.handle.net/1969.1/85963.

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Progesterone is unequivocally required for the establishment and maintenance of pregnancy in all mammals studied. Its known functions are complex and encompass global changes in gene expression. Therefore, studies were conducted to characterize the effects of progesterone on expression of genes for endometrial factors having roles in conceptus growth, implantation and establishment of pregnancy. The first study characterized the effect of an artificially induced early increase in circulating progesterone on conceptus growth and development and regulation of expression of galectin-15 (LGALS15), a recently identified protein secreted by the ovine uterine luminal epithelium (LE). Exogenous progesterone beginning on Day 1.5 post-mating accelerated conceptus development on Days 9 and 12. On Day 12 the conceptus was functionally and morphologically advanced to produce greater quantities of interferon tau (IFNT) than blastocysts from control ewes. Further, the endometrium responded to early progesterone and IFNT with early expression of cathepsin L (CTSL), radical S-adenosyl methionine domain containing 2 (RSAD2), and LGALS15 within the endometrium. The second study identifed structural changes within the luminal epithelium which could alter the flux of factors into and out of the uterine lumen to maintain appropriate fetal/maternal communication. In this study, progesterone reduced quantities of proteins associated with both tight and adherens junctions during the elongation period. IFNT subsequently increased these proteins after conceptus elongation. The third and fourth studies identified progesterone-regulated genes which have been implicated as having importance to implantation in sheep, mouse, and human. WNT signaling was transiently downregulated by progesterone, while members of several growth factor families are upregulated including insulin-like growth factor binding proteins (IGFBPs) 1 and 3, hepatocyte growth factor (HGF) and fibroblast growth factor 7 (FGF7), which may enhance conceptus growth. Collectively, these studies assess the role of progesterone in altering gene uterine expression to establish a favorable environment for conceptus development. The long-term goals of these studies are to establish biomarkers of receptivity to conceptus development and implantation, enhance our understanding of gene and pathway regulation in early pregnancy loss, and identify genes which may be targeted in therapeutic strategies to improve reproductive success in humans and animals.

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Gilbert, Jeffrey Stephen. "Cardiorenal adaptations of the ovine fetus and offspring to maternal nutrient restriction". Laramie, Wyo. : University of Wyoming, 2005. http://proquest.umi.com/pqdweb?did=1044392391&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.

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Chakrabarty, Anindita. "The ovine trophoblast kunitz domain protein-1 : gene structure, evolution and transcriptional regulation /". Free to MU Campus, others may purchase, 2005. http://wwwlib.umi.com/cr/mo/fullcit?p3189904.

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Lawes, Kathryn Patricia. "The ovine cyclophilin B gene : characterisation and expression during the oestrous cycle and early pregnancy". Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391348.

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Fan, Li 1967. "Interactions of renin-angiotensin and natriuretic peptide systems in control of blood pressure during ovine pregnancy". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39904.

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This thesis focuses on the renin-angiotensin system and atrial natriuretic factors (ANF) two hormonal systems which are stimulated and which may exert important antagonizing actions on the regulation of mean arterial pressure (MAP) and body fluid homeostasis during pregnancy. All experiments were conducted in healthy nonpregnant and/or pregnant (gestational age of 105 to 140 days, term = 145 days) mixed breed ewes, using a facility designed for studies of large animals. Findings from the first study with unilateral denervated kidneys provide evidence that renal nerves are a necessary component in the control of renin secretion in both nonpregnant and pregnant ewes. The second study demonstrates that angiotensin II (AngII) and ANF do not account for the dramatic suppression of renin secretion in response to the reduction of renal perfusion pressure in sheep with bilateral renal denervation. The data from these two studies suggest that the renal baroreceptors influence renin secretion indirectly through activation of renal afferents rather than by a direct action on the juxtaglomerular apparatus. In order to study the possible effects of increased plasma AngII on ANF production during pregnancy, four doses of AngII (0.5, 5, 20, 40 ng/kg/min) and nitroprusside were simultaneously infused to separate indirect hemodynamic actions on ANF secretion from direct hormonally mediated effects on ANF secretion by AngII. The data clearly show that AngII increases plasma ANF in a dose-dependent manner but: only in the presence of the AngII pressor effect. A striking finding was the demonstration that the natriuretic and diuretic responses to intrarenal artery infusion of three doses of ANF (0.3, 1.5, 3.0 pmol/kg/min) are increased during ovine pregnancy and these responses are solely limited to actions on the distal part of the nephron without altering renal vascular or glomerular function. Finally, a study with 10 days of intrarenal artery infusion of low dose AngII (1 ng/kg/m

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Libros sobre el tema "Ovine pregnancy"

Zelinski, Mary Beth. Plasma membrane composition and luteinizing hormone receptors of ovine corpora lutea during early pregnancy. 1986.

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Capítulos de libros sobre el tema "Ovine pregnancy"

Bazer, Fuller W., J. L. Vallet, C. J. Ashworth, R. V. Anthony y R. M. Roberts. "The Role of Ovine Conceptus Secretory Proteins in the Establishment of Pregnancy". En Cell and Molecular Biology of the Uterus, 221–35. Boston, MA: Springer US, 1987. http://dx.doi.org/10.1007/978-1-4684-1297-0_13.

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Battaglia, Frederick C. "Principal Substrates of Fetal Metabolism: Fuel and Growth Requirements of the Ovine Fetus". En Ciba Foundation Symposium 63 - Pregnancy Metabolism, Diabetes and the Fetus, 57–74. Chichester, UK: John Wiley & Sons, Ltd., 2008. http://dx.doi.org/10.1002/9780470720462.ch4.

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Actas de conferencias sobre el tema "Ovine pregnancy"

Almendros, Isaac, Paula Martínez-Ros, Nuria Farré, Mónica Rubio-Zaragoza, Marta Torres, Álvaro J. Gutiérrez-Bautista, José M. Carrillo-Poveda et al. "Late Breaking Abstract - Fetal blood hypoxia/reoxygenation swings are reduced by placental oxygen transfer in a model ovine pregnancy with sleep apnea". En ERS International Congress 2019 abstracts. European Respiratory Society, 2019. http://dx.doi.org/10.1183/13993003.congress-2019.oa4929.

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Informes sobre el tema "Ovine pregnancy"

Boisclair, Yves R., Alan W. Bell y Avi Shamay. Regulation and Action of Leptin in Pregnant and Lactating Dairy Cows. United States Department of Agriculture, julio de 2000. http://dx.doi.org/10.32747/2000.7586465.bard.

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The original project had four specific objectives: (1) To complete the development of a radioimmunoassay for bovine leptin; (2) To characterize the leptin system in lactating dairy cows during the transition from pregnancy to lactation; (3) To identify endocrine factors regulating the production of leptin by bovine adipose tissue; (4) To study the actions of leptin on bovine adipose and mammary tissues in vitro. However, BARD funded only the development of the bovine leptin RIA (Objective 1) for a single year. This report describes our work in completing this objective. Leptin, a protein hormone secreted predominantly by white adipose tissue, plays a critical role in the regulation of energy metabolism. In rodents and humans, leptin informs the central nervous system of the size of the energy reserves, coordinates adaptations to periods of nutrient insufficiency, and regulates the metabolism of key tissues involved in the storage and dissipation of energy. However, almost nothing is known on the biology of leptin in cattle, in part because of the absence of a valid assay to measure bovine leptin. To remediate this situation, we have developed a radioimmunoassay capable of measuring bovine leptin with a high degree of sensitivity, accuracy and precision. First, we produced recombinant bovine leptin and used it to immunize rabbits, and to prepare bovine leptin trace and standards. A single antiserum with sufficient affinity and titer was identified. Using this antiserum, binding of 125I bovine leptin was displaced in a dose dependent manner by the addition of bovine or ovine leptin. Serial dilution of bovine and ovine plasma gave displacement curves that were parallel to that of bovine or ovine leptin. Recoveries of external addition of bovine leptin in ewe and cow plasma ranged between 94 and 104%. Plasma leptin concentration measured by this assay was increased by the plane of nutrition in growing calves and lambs. Finally, plasma leptin concentration was linearly related to the fat content of the empty carcass in growing cattle. We conclude that circulating leptin in sheep and cattle is increased by fatness and plane of nutrition, consistent with results in humans and rodents. This assay provides an important tool to investigate mechanisms that regulate plasma leptin in cattle and sheep.

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Bazer, Fuller W., Arieh Gertler y Elisha Gootwine. Role of Placental Lactogen in Sheep. United States Department of Agriculture, enero de 2001. http://dx.doi.org/10.32747/2001.7574339.bard.

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Central problems in sheep and dairy cattle production are reproductive failure due to embryonic/fetal mortality and low birth weights, especially in prolific breeds, and reduced milk yields which adversely affect neonatal survival and economy of production. The sheep placenta expresses lactogenic (ovine placental lactogen, oPL) and somatogenic (ovine placental growth hormone, oGH) hormones. Our research has focused on the biological roles of oPL and oGH in function of the uterine endometrium during gestation and the mammary gland during pregnancy and lactation. Major conclusions were that: ( 1 ) immunization of prepubertal ewes against oPL resulted in increased birth weights of their lambs and their milk production during lactation; (2) neither oPL nor oGH had an antiluteolytic effect on uterine endometrium to affect lifespan of the corpus luteum; (3) only sequential exposure of the progesterone stimulated uterus to oIFNt and oPL or oGH increased endometrial gland proliferation and secretory protein gene expression; (4) oPL signals through a homodimer of ovine prolactin receptor (PRL-R) and heterodimer of oPRL-R and growth hormone receptor (GH-R); (5) exogenous recombinant oPL and oGH stimulated mammogenesis and milk yield during lactation; and (6) mutation of oPL and oGH was used to define specific biological effects and a rational basis for design of a specific receptor agonists or antagonists. This project was very productive in elucidating basic biological effects of oPL and oGH on intracellular signal transduction pathways, uterine development and secretory function, as well as mammogenesis and lactogenesis. We determined that immunization of prepubertal ewes against roPL increased birth weights of their lambs, especially those born as twins and triplets, as well as enhanced lactational performance. These studies significantly extended our knowledge of uterine and fetal-placental physiology and provided a foundation for new strategies to enhance reproductive and lactation efficiency. Based on these results, the major achievements were: 1) creation of a practical and cost effective management tool for producers to increase reproductive performance, neonatal survival, and milk yield of ewes in commercial flocks; and 2) define, for the first time, biological effects of oPL on endometrial functions and gene expression by uterine gland epithelium.

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Spencer, Thomas E., Elisha Gootwine, Arieh Gertler y Fuller W. Bazer. Placental lactogen enhances production efficiency in sheep. United States Department of Agriculture, diciembre de 2005. http://dx.doi.org/10.32747/2005.7586543.bard.

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The key objectives of this BARD project were to: (1) study long-term effects of immunization of prepubertal ewes against recombinant ovine placental lactogen (roPL) on subsequent birth weights of their lambs and their milk production; (2) optimize the anti-roPL immunization protocol using adjuvant preparations acceptable to producers and regulatory agencies; and (3) determine the physiological mechanism(s) whereby immunization against oPL increases fetal growth and development and mammogenesis. These objectives were based on key findings from a previous BARD project that: (a) immunization of ewes against roPL increased lamb birth weight and ewe milk production during lactation; (b) roPL and recombinant ovine growth hormone (roGH) increased the proliferation and differentiated function of endometrial glands that, in turn, would enhance uterine secretions necessary for fetal and placental growth; and (c) exogenous roPL and roGH stimulated mammogenesis and milk production during lactation. The BARD projects address central problems in sheep production, including reproductive failure due to embryonic/fetal mortality, low birth weight of lambs especially in prolific breeds, and reduced milk yields which affect neonatal survival. The sheep placenta secretes both lactogenic (oPL) and somatogenic (oGH) hormones. The receptors for those hormones are present in the fetus and placenta as well as maternal uterus, and mammary gland. Our research has focused on determining the biological role of these placental hormones in development and differentiation of the uterus during gestation and the mammary gland during pregnancy and lactation. Studies conducted in the current BARD project indicated that the effects of anti-roPL immunization were variable in ewes and that commercially available and widely acceptable adjuvant preparations were not effective to produce high anti-roPL titers in pre-pubertal ewes. In the non-prolific Rambouillet ewe in Texas and in the Awassi and the Assaf in Israel, anti-roPL immunization increased lamb birth weight; however, the magnitude of this effect and the inherent variability precluded our ability to determine the physiological mechanism of how the immunization increases fetal growth. Collectively, our findings suggest that anti-roPL immunization is not currently feasible as an easy and efficacious tool for the producer to increase flock reproductive and production efficiency. The variability in response of individual ewes to anti-roPL immunization likely includes modifying the recombinant hormone and the type of adjuvant used for the immunization. In particular, the oPL may need to be modified to ensure maximum antigenicity in a broad range of breed types. Nonetheless, the investigators continue to collaborate on identifying fundamental mechanisms that can be improved by genetics or management to enhance the efficiency of uteroplacental function and, in turn, fetal growth and development. High prolificacy is a desirable trait in intensive sheep production systems. One of the main limitations of using prolific breeds of sheep is that increased litter size is associated with low birth weights and increased mortality of lambs. Further, low birth weight is associated with an increased propensity for adult diseases and decreased production efficiency. Indeed, our recent studies find that the birth weights of lambs born in large litters can be improved by both genetics and management. Future cooperative research will continue to focus on reproductive efficiency of sheep that have broader implications for improving production efficiency in all types of ruminant livestock.

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