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D Bourke

Publications and source records attributed to D Bourke.

13 recordsLinked to original sources
PubMed2006

Impact of flow path length and flow rate on phosphorus loss in simulated overland flow from a humic gleysol grassland soil.

In this overland flow simulation experiment, the relationships between flow path length, flow rate and the concentration of different P fractions were investigated. Overland flow was simulated using a 3 mx0.12 m laboratory flume. To remove the impact of rainfall on P lost in overland flow, simulated rainfall was not used during these experiments. Instead overland flow was generated by pumping water into the flume at the surface of the grass sod. The experimental setup allowed for the variation in flow path length and flow rate between and during experimental runs. The results demonstrated that an increase in flow path length caused an increase in Total Dissolved P (TDP), Dissolved Reactive P (DRP) and Total Reactive P (TRP) concentration in overland flow (p<0.01) while an increase in flow rate resulted in a decrease in the concentration of these P fractions in overland flow due to dilution (p<0.01). Total P (TP), Particulate P (PP) and Dissolved Organic P were not affected by the variables tested during this study. When flow path length was increased in conjunction with flow rate, there was an increase in TDP, DRP, and TRP concentrations despite the impact of greater dilution. The results indicate that variations in flow path length during a rainfall event may play a role in determining the concentration of dissolved P fractions in overland flow at field scale.

Phosphorus↗
PubMed2001

Nutrient partitioning during adolescent pregnancy.

Human adolescent mothers have an increased risk of delivering low birth weight and premature infants with high mortality rates within the first year of life. Studies using a highly controlled adolescent sheep paradigm demonstrate that, in young growing females, the hierarchy of nutrient partitioning during pregnancy is altered to promote growth of the maternal body at the expense of the gradually evolving nutrient requirements of the gravid uterus and mammary gland. Thus, overnourishing adolescent dams throughout pregnancy results in a major restriction in placental mass, and leads to a significant decrease in birth weight relative to adolescent dams receiving a moderate nutrient intake. High maternal intakes are also associated with increased rates of spontaneous abortion in late gestation and, for ewes delivering live young, with a reduction in the duration of gestation and in the quality and quantity of colostrum accumulated prenatally. As the adolescent dams are of equivalent age at the time of conception, these studies indicate that nutritional status during pregnancy rather than biological immaturity predisposes the rapidly growing adolescents to adverse pregnancy outcome. Nutrient partitioning between the maternal body and gravid uterus is putatively orchestrated by a number of endocrine hormones and, in this review, the roles of both maternal and placental hormones in the regulation of placental and fetal growth in this intriguing adolescent paradigm are discussed. Impaired placental growth, particularly of the fetal component of the placenta, is the primary constraint to fetal growth during late gestation in the overnourished dams and nutritional switch-over studies indicate that high nutrient intakes during the second two-thirds of pregnancy are most detrimental to pregnancy outcome. In addition, it may be possible to alter the nutrient transport function of the growth-restricted placenta in that the imposition of a catabolic phase during the final third of pregnancy in previously rapidly growing dams results in a modest increase in lamb birth weight.

Adolescent↗
PubMed1997

[Pregnancy in New World camelids].

There is a growing number of llama- and alpacabreeders in Europe. Therefore veterinarians are often asked to intervene in clinical management of different problems, especially reproductive problems. In this review the authors attempt to summarize the different possibilities of pregnancy diagnosis and to give an short overview of reproduction in female llamas and alpacas. South American Camelids are induced ovulators and ovulation will occur within 12 to 24 hours following a single breeding. Llamas and alpacas develop follicular waves. The females will usually not ovulate unless a 7 mm or larger follicle exist on one of the ovaries. Corpus luteum is needed for maintenance of pregnancy.

Animals↗
PubMed1988

Cytoarchitecture of the fetal murine soleus muscle.

The organogenesis of the soleus muscle of the 129 ReJ mouse (a mixed muscle, which in the adult contains approximately equal numbers of slow-twitch oxidative and fast-twitch oxidative-glycolytic myofibers) was studied in spaced, serial transverse, and longitudinal sections of muscles of 14-, 16-, and 18-day in utero and 1- and 5-day postnatal mice. A discrete soleus muscle was distinguished by 14 days in utero. It consisted of groups of closely apposed primary myotubes displaying junctional complexes and a pleomorphic population of mononucleated cells. Between 14 and 16 days in utero there was little de novo myotube formation. At 16 days in utero, basal lamina surrounded groups of primary myotubes; and primitive motor endplates were found on these myotubes. At 18 days in utero, the basal-lamina-enclosed groups of primary myotubes were no longer present. At this stage, basal lamina surrounded clusters (consisting of one primary myotube and one or more secondary myotubes) or independent myotubes (single myotubes surrounded by their own basal lamina). Cluster formation and cluster dispersal occurred concurrently, beginning at 18 days in utero and extending until birth. At birth, there was still a substantial population of immature, secondary myotubes that interdigitated with larger, more mature primary myofibers. At this stage, intermuscular axons had begun to myelinate, and postsynaptic specialization of the motor endplates had begun. Cluster dispersal and myonuclear migration was completed during the first 5 days postnatally with the muscle taking on adult characteristics. Beginning at 16 days in utero and extending into the neonatal period, there was evidence of myotube death in the soleus muscle.

Actin Cytoskeleton↗
PubMed1988

Morphometric analysis of the developing mouse soleus muscle.

The pattern of organogenesis of the soleus muscle of the 129 ReJ mouse was evaluated quantitatively using spaced, serial, ultrathin sections and computer-assisted morphometric analysis. Muscles from 14-, 16-, and 18-day in utero mice and muscles of 1- and 5-day-old mice were analyzed to determine age-related alterations in the maximal girth and length of the muscle, number of myotubes, cluster frequency, and the lengths and diameters of myotubes. Primary myotubes are found in the muscle at 14 days in utero. There is little de novo myotube formation between 14 and 16 days in utero, this interval being principally one of primary myotube growth and maturation. The interval between 16 and 18 days in utero is marked by extensive secondary myotube formation, with more myotubes being formed during this period than in any period studied. Morphometric data support the hypothesis that secondary generation myotubes use primary myotubes as a scaffold on which they are formed. Morphometric data also confirm the hypothesis that cluster formation and cluster dispersal occur concurrently during the prenatal period. Secondary myotubes continue to form until birth. At birth, the soleus muscle contains the adult number of myofibers. The first 5 days postnatally are marked by myofiber growth and maturation.

Actin Cytoskeleton↗
PubMed1982

Secondary myogenesis of normal muscle produces abnormal myotubes.

The extensor digitorum longus muscles of 2-, 4-, and 12-week-old 129-ReJ mice were subjected to homotopic, whole-muscle transplantation. Subsequent to myofiber necrosis and phagocytosis, a new population of myotubes was produced. The three-dimensional cytoarchitecture of these newly formed myotubes was determined in spaced, serial, ultrathin sections. Myotubes, which for long distances along their length appeared to be separate and discrete, were found to branch and recombine, forming a complex syncytium.

Aging↗
PubMedDate not supplied

The size of the myofibers in mature grafts of the mouse extensor digitorum longus muscle.

The histochemical profile of stabilized orthotopically grafted mouse extensor digitorum longus muscles (EDL) and fiber type diameter distribution in the graft was compared with control muscles. Histochemical fiber typing, based on myofibrillar ATPase reactions, indicated that type 1 fiber accounted for less than 1%, type 2a fibers for 30%, and type 2b fibers for 69% of the total fiber population of the graft. In control muscles of 56-day-old and 156-day-old mice, type 1 fibers accounted for less than 1%, type 2a fibers for 36%, and type 2b fibers for 63% of the total fiber population of normal muscles. The regenerating myofibers in stabilized grafts failed to achieve the normal fiber diameter. The type 2b fibers exhibited greater growth inhibition than did type 2a fibers.

Animals↗