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Articles by V.L. Christensen
Total Records ( 12 ) for V.L. Christensen
  V.L. Christensen , M.J. Wineland , I. Yildirum , D.T. Ort and K.M. Mann
  The plateau stage in oxygen consumption of turkey embryos occurs at 25 and 26 days of incubation when many embryos die. The plateau stage creates hypoxia, hypercapnia and presents a paradox for growth and embryo metabolism. Prior to the plateau, vital tissues accumulate glycogen to ensure embryonic survival through anaerobic metabolism during the plateau. Intestinal maturation at the plateau demands great amounts of energy. Therefore, the objective of the study was to define the temperature and oxygen concentrations at the plateau that affect intestinal maturation. Three experiments were conducted to test incubator conditions during the plateau stage and their affect on intestinal maturation. In Experiment 1, turkey embryos at the plateau stage were exposed to 36, 37, 38 or 39°C. In Experiment 2, embryos at the plateau stage were exposed to 17, 19, 21 or 23% oxygen concentrations, and in Experiment 3, the extreme levels of temperature and oxygen treatments were combined to test interaction effects on intestinal maturation. Elevating temperature depressed intestinal weight but not length. The elevated temperature also depressed intestinal maltase and alkaline phosphatase activities indicating inhibited function. Increasing oxygen had little effect on intestinal weight or length, but hypoxia increased maltase and decreased alkaline phosphatase activities in hatchlings. When examined in a factorial arrangement, temperature and oxygen displayed independent effects on growth and function and did not interact. Thus, incubator temperature greater than 37°C and oxygen concentrations less than 19% during the plateau stage delay intestinal maturation.
  V.L. Christensen and G.S. Davis
  An experiment was designed to discover a mechanism for improved embryonic survival resulting from supplemental maternal dietary iodine. Commercial turkey breeder hens were fed diets containing 4 ppm supplemental iodide during a 20 wk egg production period (32 to 48 wk of age). Dietary iodide treatment depressed maternal blood thyroxine (T4) concentrations as the hens aged. Dietary iodide depressed maternal blood 3, 5, 3`- triiodothyronine (T3) levels at all times examined. The dietary iodide treatment increased embryonic blood concentrations of T4 at 25 to 28 d of incubation but depressed blood concentrations of T3 only at 27 d of incubation. In a second trial, the iodide treatment decreased embryonic T4 concentrations as well but in a time-dependent manner. When the hens were similarly fed additional iodide in Trial 2, no effects were noted in T3 concentrations. Iodide also accelerated the increase in embryo T4 concentrations and initiated earlier pipping in embryos compared with non-supplemented controls. The data indicate that embryo thyroid function during hatching is affected by the maternal dietary iodide in turkey dams even though the embryo develops outside the maternal body.
  S. Suvarna , V.L. Christensen , D.T. Ort and W.J. Croom
  Development of intestinal tissue was measured in newly hatched poults. Both anatomical and physiological measurements were made on poults produced by two half sibling sires with hens that were their full or half siblings. The poults from one sire (HBW) weighed more at hatching than those from the other sire (LBW). Survival of the heavier poults was poor indicating metabolic insufficiencies. A significant positive correlation was noted between hatchling body weights and blood glucose concentration (Christensen et al., 2000a), and this was accompanied by depressed gluconeogenesis in HBW poults. The hypothesis was proposed that the HBW poults with elevated plasma glucose concentrations might have greater glucose absorption from intestinal tissue than did the LBW poults. The data confirmed heavier weights in HBW poults than LBW, and HBW jejunum weight relative to body weight was less than that of LBW. The poults did not differ in intestinal length, glucose transport, maltase activities or plasma triiodothyronine and thyroxine or glucose concentrations. The HBW poults also utilized less yolk during development than did the LBW indicating that the HBW embryos rely more on gluconeogenesis for survival during development than do the LBW. It was concluded that the increased body weight of HBW poults compared to LBW may be due to increased absorption of all nutrients because of a greater intestinal mass relative to body weight rather than to differences in glucose digestion and uptake rates.
  V.L. Christensen , M.J. Wineland , I. Yildirum , B.D. Fairchild , D.T. Ort and K.M. Mann
  Avian embryo thyroid responses to incubator temperature and oxygen concentrations during the plateau stage in oxygen consumption were measured. It was hypothesized that turkey embryo thyroid responds in a limited way at this critical time to environmental conditions to modulate basal metabolism. Turkey embryos were exposed to one of four incubator temperatures (36, 37, 38 or 39oC) beginning on the 25th day of incubation at the onset of the plateau, a time when plasma thyroxine (T4) and triiodothyronine (T3) concentrations normally increase. Blood was collected and thyroid hormone concentrations were measured at pipping (27th day) and hatching (28th day). Elevated temperatures depressed T3 and T4 concentrations and increased the T3 to T4 ratios. In a second experiment four oxygen concentrations (17, 19, 21 or 23% oxygen) were provided to the embryos using identical procedures. The 21% treatment significantly reduced T3 and T4 at pipping compared to all other treatments, but 23% oxygen increased plasma T3 and the T3 to T4 ratio compared to all other treatments. The 17% oxygen treatment elevated T3 compared to all other treatments. At hatching, 23% oxygen elevated T3 and T3 to T4 ratios compared to all other treatments. When temperature and oxygen treatments were applied together in a factorial arrangement, temperature and oxygen affected T3 and T4 hormone concentrations independently but did not interact. Therefore, we conclude that temperature and oxygen are independent stimuli of the avian embryonic thyroid gland during the plateau stage, and that incubator temperature and oxygen concentrations can modulate development of turkey embryos by changing plasma T3 and T4 concentrations.
  V.L. Christensen , M.J. Wineland , D.T. Ort and K.M. Mann
  Eggshell conductance (G) and incubator ventilation (VENT) were hypothesized to affect embryo viability and growth of poults following hatching. Nearly 6,000 eggs were weighed on the day of oviposition to determine eggs of like weight but of different G. From the 6,000 eggs, 4,000 were selected that were within 2 standard deviations of the mean. The eggs were randomly divided equally between two incubator cabinets. One cabinet operated with a closed VENT and a second operated with it open. At the completion of the 24th day of development, all eggs were weighed a second time to determine eggshell G. Three groups were formed at that time exhibiting high (Hi), average (Avg) or low (Low) G. The eggs within each group were placed into hatching trays of 100 eggs each and placed into he same incubation cabinet for hatching. Weights were recorded for cardiac, hepatic and intestinal tissues, and blood was collected from each treatment. The tissues were subsequently assayed for energy substrates. Embryo viability was noted and growth was observed up to 6 wk of age. More embryos in eggs of Hi or Avg G survived than did those in Low G eggs, but neonates at 6 wk from Hi G eggs weighed less than those from Avg or Low G eggs. Low G embryos had reduced heart, liver and intestinal weight and function. Embryo thyroid hormone concentrations were elevated in Hi G eggs but suppressed by Low G and Closed VENT. Thus, in the developmental process of the embryonic turkey, G may determine energy balance and maturity of each hatchling and may affect its survival and growth rates following hatching.
  W.J. Croom , Jr. , J. Decubellis , B.A. Coles , L.R. Daniel and V.L. Christensen
  Previous studies in this laboratory have demonstrated that peptide YY (PYY) administration to turkey poults at d25 of incubation enhances intestinal Na-dependent active glucose uptake. This study was designed to further characterize the ontogeny of glucose transport in embryonic and hatchling poults and to investigate the effects of PYY on this process during development. In Trial 1, 20 turkey eggs were randomly selected at days 20, 23, and 26 of incubation, as well as the day of hatch. Hatchlings were cervically dislocated and the body weight, jejunal length and jejunal weight were recorded. Jejunal glucose uptake was estimated by measuring 3H-3-O-methyl-D-glucose accumulation in 2 mm jejunal rings in vitro. Jejunal O2 consumption was measured in vitro on jejunal rings using an O2 probe. In Trial 2, 40 turkey eggs were randomly selected at days 20, 23 and 25 of incubation and injected, via the air sac, with either 0.9% saline or 0.9 % saline plus 400 μg PYY/kg egg weight. Embryos from each treatment were harvested on days 23, 26 and day of hatch. Measurements and analyses on jejunal tissue were conducted as in Trial 1. In Trial 2, embryonic weight and jejunal weight adjusted for body weight increased (p< 0.05) with stage of incubation, while adjusted jejunal length decreased (p< 0.01). Active and total glucose uptake and jejunal O2 consumption increased with age (p< 0.05). The energetic efficiency of glucose uptake increased (p< 0.05) between d26 and hatch. In Trial 2, PYY failed to significantly affect body or jejunal weight, glucose absorption, and O2 consumption at any stage of development. PYY did however, decrease the efficiency of glucose uptake at d26 and at hatch (p< 0.05). In contrast to earlier investigations using higher dosages of PYY, this study demonstrated that in ovo PYY administration at 400 μg/kg egg weight has little effect of jejunal function in turkeys.
  M.W. Wineland , V.L. Christensen , I. Yildrum , B.D. Fairchild , K.M. Mann and D.T. Ort
  Incubator temperature and oxygen concentrations were tested as factors determining the intestinal maturation of two lines of broiler chickens. One line was a Low G line selected because its eggs display low eggshell conductance. The second line was a High G line that grew at a reduced rate and its eggs show high eggshell conductance values. All eggs were incubated normally until the 18th day of development or the beginning of the plateau stage in oxygen consumption. At that time the eggs were divided randomly and placed into experimental cabinets operating at 36, 37 38 or 39oC in experiment 1 or with 17, 19, 21 or 23% oxygen in experiment 2. In experiment 3, the best and worst conditions observed in experiments 1 and 2 were combined in a factorial arrangement. Body weight and intestinal maturation were measured by assaying for maltase and alkaline phosphatase activities in intestinal tissues. Increasing temperatures suppressed intestinal maturation whereas increasing oxygen concentrations enhanced intestinal maturation. When examined together in a factorial arrangement, it was clear that the effects of temperature and oxygen on the embryos were independent because they did not interact. The effects of temperature and oxygen were greater on Low G broiler embryos than they were on High G type embryos. It is concluded that incubator temperatures greater than 37oC, and oxygen concentrations less than 21% are detrimental to intestinal maturation in broiler chicks.
  M.J. Wineland , V.L. Christensen , I. Yildrum , B.D. Fairchild , D.T. Ort and K.M. Mann
  We hypothesize that temperature and oxygen in conjunction with genetic lines of broilers regulate embryo thyroid function. Thyroid response of broiler embryos of the two lines was measured at different incubator temperature and oxygen concentrations at the plateau stage in oxygen consumption (days 17 to 20 of embryo development). Each of the lines showed different eggshell conductance (G) values. Eggs of the same weight from the lines of broilers were incubated identically until the 17th day of development. On the 17th day (plateau stage in oxygen consumption), eggs were randomly distributed by line into four incubators operating at 36, 37, 38 or 39oC in trial 1 or at 17, 19, 21 or 23% oxygen in trial 2. At external pipping (the end of the plateau stage in oxygen consumption) as well as at hatching ten embryos or chicks per treatment were sampled for blood plasma. Plasma was analyzed for thyroxine and triiodothyronine concentrations. In trial 3, temperature line of broiler and oxygen treatments were arranged factorially. Increasing temperatures suppressed hormone concentrations in embryos, and the suppression was greater with low G. Increasing oxygen increased hormone concentrations in low G embryos to a greater degree than high G. It can be concluded that incubation temperature suppresses plasma thyroid hormone concentrations in low G lines whereas oxygen increases it.
  V.L. Christensen , L.G. Bagley , T. Olson , J.L. Grimes , R.D. Rowland and D.T. Ort
  Supplementing 500 ppm of a chelated calcium proteinate (CCP) to a commercial breeder diet resulted in thicker shells and improved embryo livability. The CCP diet was fed to one half of a flock of breeders on a commercial farm that was suffering shell problems, and a standard commercial diet was fed to the remaining half. Egg production, eggshell thickness, fertility and hatchability of eggs were all monitored over an 18 wk laying period. Feeding CCP increased shell thickness and reduced numbers of cull eggs after 8 wk of lay compared to the controls. When differences in eggshell thickness were seen after 10 weeks of egg production, embryo survival and cardiac physiology were examined in three trials comparing the thicker shells to thin. Thick shells (0.44 versus 0.39 mm) improved embryo survival 2% by decreasing numbers of embryos dying late in development compared to controls and affected cardiac physiology. Thus, thick shells may improve embryo viability by affecting cardiac health during the plateau stage in oxygen consumption.
  V.L. Christensen , M.J. Wineland , D.T. Ort , K.M. Mann and E.R. Neely
  Eggshell conductance (G) and incubator humidity (RH) were hypothesized to affect poult embryo survival and hatchling growth. Nearly 4,000 fertilized eggs of the same weight were selected (within 2 standard deviations of the mean). Selected eggs were divided randomly between two incubators. One cabinet operated at 65% RH whereas the second operated at 50% RH, and both cabinets had the same temperature (37.2oC). At the completion of the 24th day of development, all eggs were weighed a second time to determine eggshell G. Three groups were formed at this time by calculating eggshell conductance and sorting into groups of eggs exhibiting high (Hi), average (Avg) or low (Low) G. The eggs were then placed in the same incubation cabinet for hatching. Measurements were made of embryo cardiac and intestinal physiology. Samples were collected at external pipping and hatching from each of the groups. Tissues were assayed for plasma glucose and lactate, cardiac and hepatic glycogen and lactate. The RH and G effects on survival were noted, and poult weights were recorded for the first 6 weeks of age. More embryos from eggs of Hi or Avg G survived than Low G eggs, but poults from Hi G eggs did not grow as well as those from Avg or Low G eggs. Low G poults showed depressed cardiac glycogen and elevated lactate and had less mature intestines. Thus, in the developmental process of turkey embryos, G and RH may determine organ maturity at hatching thereby influencing survival and growth.
  V.L. Christensen , L.G. Bagley , T. Olson , J.L. Grimes and D.T. Ort
  Embryo heart rates were measured on 400 fertilized turkey eggs (399 viable embryos) at 4 day intervals beginning at day 12 of development. Heart rates varied directly with eggshell porosity and were significantly and positively correlated with eggshell conductance (G) and conductance constants (k) but not with initial egg weight. When only eggs with embryos that died were analyzed the significant correlation coefficients increased. In a second experiment, eggshell pores were occluded to reduce G then heart rates were measured. Heart rates decreased concomitantly with decreases in G. In the final experiment, approximately 15,912 eggs were weighed individually to calculate G for each egg and were then incubated. Embryo survival was noted in High and Low G groups. Embryo heart rate and cardiac physiology in each group was measured. Low G reduced heart rates and improved embryo survival and cardiac physiology compared to High G. Thus, cardiomyopathy due to High G and its consequent lack of energy for myocardial function may contribute to turkey embryo mortality late in development.
  V.L. Christensen , L.G. Bagley , J. Prestwich , T. Olson , M.J. Wineland and D.T. Ort
  The relationship describing eggshell conductance constants (k) suggests that eggshell conductance (G) is directly related to the length of the incubation period, but inversely with the weight of the egg. Prior studies showed clearly that G is a factor in cardiac health. We tested the hypothesis in the current study that the length of the incubation period may be a factor along with G that affects cardiac physiology and embryo survival. Incubation temperatures were reduced stepwise by 0.2oC in three treatments (37.5, 37.3 and 37.1oC) to prolong embryo developmental periods. The length of the developmental period was increased concomitantly in preliminary trials by 6 and 12 h, respectively by the 37.3 and 37.1oC treatments compared to 37.5oC. Fertilized eggs were incubated using the three temperatures in each of three independent trials. The time of hatching was closely noted and embryo survival was compared among treatments. Embryo heart rates and cardiac physiology in each group were observed. Long developmental periods reduced heart rates in a stepwise fashion and improved embryo survival and cardiac physiology. Thus, cardiomyopathy may be influenced by the length of the developmental period of turkey embryos because longer periods facilitated energy metabolism for myocardial function. Longer developmental periods would be easier to manage than G and may contribute to better turkey embryo viability late in development
 
 
 
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