PubMed Health⌕ Search

Biomedical subjects

A De Vries

Publications and source records attributed to A De Vries.

At least 19 recordsLinked to original sources
PubMed2006

Economic value of pregnancy in dairy cattle.

The objective of this study was to estimate the value of pregnancy for dairy cows. Effects of the stage of gestation, stage of lactation, lactation number, milk yield, milk price, replacement heifer cost, probability of pregnancy, probability of involuntary culling, and breeding decisions were studied. A bioeconomic model was used, and breeding and replacement decisions were optimized. A general Holstein herd in the United States was modeled. The average value of a new pregnancy was $278. The value of a new pregnancy increased with days in milk early in lactation but typically decreased later in lactation. Relatively high-producing cows and first-lactation cows reached greater values, and their values peaked later in lactation. The average cost of a pregnancy loss (abortion) was $555. The cost of a pregnancy loss typically increased with gestation length. Sensitivity analyses showed that an increased probability of pregnancy, an increased persistency of milk yield, and a smaller replacement heifer cost greatly reduced the average value of a pregnancy. The value of a new pregnancy was negative for relatively high-producing first-lactation cows when persistency of lactation and the probability of pregnancy were increased. Breeding was delayed when the value of pregnancy was negative. Changes in milk price, absolute milk yield, and probability of involuntary culling had less effect on the value of pregnancy. The value of pregnancy and optimal breeding decisions for individual cows were greatly dependent on the predicted daily milk yield for the remaining period of lactation. An improved understanding of the value of pregnancy may support decision making in reproductive management when resources are limited.

Abortion, Veterinary↗
PubMed2006

Economic comparison of timed artificial insemination and exogenous progesterone as treatments for ovarian cysts.

The objective of this study was to compare the economic benefits of timed artificial insemination (AI) and a progesterone insert as therapeutic treatments for cows diagnosed with cystic ovarian disease (COD). A secondary objective was to illustrate the use of a stochastic dynamic simulation model to fully account for all changes in revenues and costs affected by differences in treatments. First, 4 herds of 1,000 cows each were simulated until steady state. These cows were free from COD and inseminated based on estrus only. Herds differed by probability of estrus detection (46 or 70%) and days in milk (DIM) when nonpregnant cows were culled (330 or 400 d). Second, 3 herds were created with 1,000 nonpregnant cows at 90, 170, or 250 DIM. These cows were considered diagnosed with COD at the start of the simulation (d 0); no new cases of COD developed after d 0. Cows spontaneously recovered or were treated. Treatments were either timed AI or intravaginal device containing progesterone followed by PGF(2alpha) and then AI if estrus was detected. Effects of treatments were evaluated in 48 scenarios based on compliance of timed AI (82 or 100%), probability of estrus detection (46 or 70%), and DIM when nonpregnant cows were culled (330 or 400 d). As cows became pregnant or were replaced, the herd evolved into the associated steady-state herd. Seven scenarios resulted in less than 50% of cows conceiving before they were culled. The percentage of cows diagnosed with COD that calved again ranged from 14.0 to 74.4% and was significantly reduced when COD was diagnosed later in lactation. Treatments in all cases were more valuable than waiting for spontaneous recovery. The average values of timed AI (82 or 100% compliance) and the progesterone insert were 83.29 dollars, 86.83 dollars, and 71.89 dollars, respectively, compared with waiting for spontaneous recovery. Treatments were least beneficial at 90 DIM. The benefits of timed AI (82 or 100% compliance) compared with the progesterone insert, adjusted for DIM and days to culling, were 14.98 dollars and 21.53 dollars when the probability of estrus detection was 46%. At 70% probability of estrus detection, the benefits were 7.81 dollars and 8.34 dollars, respectively. Overall benefit of treatment by timed AI was 11.39 dollars greater than by progesterone insert.

Administration, Intravaginal↗
PubMed2004

Economics of delayed replacement when cow performance is seasonal.

An optimal dairy cow culling and replacement model was developed; it included the option to delay entering heifers into the herd after cows were culled. The objective was to investigate whether leaving a slot temporarily vacant, to enter a heifer at a more favorable time of the year, could be economically advantageous when cow performance is seasonal. The goal of the optimization was therefore to maximize net return per slot per year. The model consisted of 3 modules: 1) a bioeconomic module to enter and calculate cow performance data and prices, 2) a replacement policy module based on dynamic programming to calculate optimal culling decisions for individual cows and when to enter heifers, and 3) a herd performance module based on Markov chains to calculate summary results for the herd. Results for the optimal culling policy under typical conditions in Florida showed that immediate replacement was economically advantageous throughout the year. However, for a nonoptimal culling policy, cows culled in May, June, and July would not be replaced by heifers until August. Realistic increases in seasonality or heifer prices, or lower milk prices, showed economic advantages of delayed over immediate replacement for both culling policies. The maximum advantage of delayed replacement of 486 price scenarios was 88 US dollars per slot per year; cows that left the herd in the early summer and spring were not replaced by heifers until the late summer. Delayed replacement was economically advantageous when fixed costs and net returns per slot were low and seasonality was high, which is the case for a portion of Florida dairy producers.

Animals↗
PubMed2002

Antibodies directed against nerve growth factor inhibit the acute bronchoconstriction due to allergen challenge in guinea-pigs.

BACKGROUND: We have previously demonstrated that the administration of nerve growth factor (NGF) to guinea-pigs results in airway hyper-responsiveness within 1 h. OBJECTIVE: In the present study we document the involvement of NGF in the acute allergic airway response. METHODS: Guinea-pigs that are sensitized to ovalbumin show an acute bronchoconstriction directly after challenge with ovalbumin. RESULTS: Intratracheal application of 10 microg of antibodies directed against NGF (anti-NGF) 1 h before the challenge reduces the acute severe bronchoconstriction to approximately 40% and the sustained bronchoconstriction to approximately 20% of the reaction in controls. This shows a high potency of anti-NGF in diminishing the direct bronchoconstriction. Inhibition of the tyrosine kinases of the tyrosine kinase receptor A, the high-affinity receptor for NGF, has no effect on the bronchoconstriction. Therefore, we postulate that the p75, the low-affinity receptor for neurotrophins, is responsible for the acute bronchoconstriction. Our findings suggest a role for NGF in the induction of the acute asthmatic reaction. CONCLUSION: These findings offer a new potential therapeutic strategy for the treatment of allergic asthma.

Acute Disease↗
PubMed2001

Influence of irradiation on neutrophilic granulocyte function.

BACKGROUND: Neoadjuvant radiotherapy is a common treatment modality for patients with Stage II and III rectal carcinoma but, after surgery, often is complicated by local infections. To define a possible influence of radiotherapy on neutrophilic granulocytes in the neighborhood of tumor cells, the authors investigated their function in vitro. METHODS: Density gradient-purified granulocytes from healthy donors were used for all tests. These cells were cocultured with the colon carcinoma cell line HRT-18 and irradiated. Their function was assessed by measuring luminol-enhanced chemiluminescence and migration against the chemoattractant formyl-methionyl-leucine-phenylalanine. RESULTS: Although irradiation decreased, the addition of tumor cells increased reactive-oxygen species release in granulocytes, which was enhanced further by phorbol myristate acid (PMA), even after several hours. All contacts with tumor cells, however, caused immediate radical release that was inversely proportional to the radiation dose. Naïve and irradiated cells were stimulated further by PMA. Migration of granulocytes clearly was inhibited by tumor cells and irradiation, whereas the depth of invasion was enhanced by higher doses of radiation. CONCLUSIONS: The current data show clearly that the influence of radiotherapy on local defense against colorectal carcinoma is limited and cannot explain the increased rate of infectious complications.

Carcinoma↗
PubMed2000

Fractionated, three-dimensional, planning-assisted proton-radiation therapy for orbital rhabdomyosarcoma: a novel technique.

PURPOSE: Most children with orbital rhabdomyosarcoma will survive their disease. However, conventional photon-radiation treatment, as part of multimodality therapy, results in varying degrees of long-term functional and cosmetic side effects. This report introduces external beam proton radiation therapy (PRT) as a conformal, three-dimensional planned radiation technique for this disease, analyzes normal tissue dosimetry, and describes the technique's application in the first 2 patients. MATERIAL AND METHODS: Between January 1995 and February 1996, 2 patients underwent PRT following biopsy and chemotherapy for orbital rhabdomyosarcoma. Fifty and 55 Cobalt Gray Equivalent (CGE) were delivered to the gross tumor volume and 40 CGE to clinical target volumes in both patients. A relative biologic effectiveness (RBE) of 1.1 was utilized to correlate proton dose calculations with CGE. To achieve dose conformity, a "patch technique" was utilized, where target regions were divided into segments, each treated by a separate proton field. Dose-volume histograms were obtained for target and nontarget regions, including lens, bony orbit, pituitary gland, optic chiasm, optic nerves, lacrimal gland, and ipsilateral frontal and temporal lobes. RESULTS: At 3.4 and 2.5 years after PRT, both patients are clinically and radiographically free of disease. Visual acuity remains excellent, without signs of cataract formation; pituitary function is normal; cosmetically, only mild enophthalmos is noticeable. Doses to 90%, 50%, and 5% of lens volume were kept at less than 1%, less than 2%, and less than 8%, respectively. Fifty percent of lacrimal gland volume received less than 36% of the prescribed dose and 50% of the volume of the optic chiasm, pituitary gland, and hypothalamus were restricted to less than 2%. Proton conformity to orbital contents resulted in between 9% and 36% of the prescribed dose reaching the ipsilateral temporal and frontal lobes immediately adjacent to bony orbit (5% volume). CONCLUSION: PRT can offer excellent sparing of lens and selected intraorbital and ocular normal structures, while maintaining conformal target-dose coverage. The steep dose gradient beyond the orbit minimizes irradiation of normal brain parenchyma, with almost complete sparing of the pituitary gland. Reduction of integral irradiation exposure of the periorbital region will, hopefully, reduce the risk of second malignancy later in life. Reduced radiation dose to specific organs in close proximity to, but not part of the target region promises improved functional outcome and better cosmesis for childhood cancer survivors.

Child↗
PubMed2000

Low prevalence of Chlamydia pneumoniae and Mycoplasma pneumoniae among patients with symptoms of respiratory tract infections in Dutch general practices.

Acute respiratory disease is one of the most common reasons to consult a general practitioner. A substantial part of these diseases cannot be explained by an infection with a virus or a common pathogenic bacterium. To study this diagnostic deficit, the prevalence of Chlamydia pneumoniae and Mycoplasma pneumoniae infections was determined in two groups of patients consulting a general practitioner. DNA of C. pneumoniae and M. pneumoniae was detected by a polymerase chain reaction (PCR) in nose/throat swabs from six (1.1%), and from seven (1.3%) patients, respectively, of 557 patients consulting a general practitioner for complaints suggestive for a virus infection during the 1994/1995 respiratory infections season. Two patients remained C. pneumoniae PCR-positive for at least 4 weeks. All others were negative within 3 weeks. Double infections of C. pneumoniae and influenza virus (3/6), and of M. pneumoniae and respiratory syncytial virus (1/7) or rhinovirus (1/7) were diagnosed. During the 1992/1993 season, attempts to isolate C. pneumoniae in cell culture or to detect C. pneumoniae DNA by PCR using throat swabs were all negative for 80 patients with a sore throat, although serological data suggested a C. pneumoniae infection in 13 (16%) patients. A specimen from another patient of this group was M. pneumoniae PCR-positive and the corresponding serum specimens showed a persistent high antibody titre. In summary, the prevalence of acute C. pneumoniae and M. pneumoniae infections was less than 2% in patients consulting a general practitioner.

Acute Disease↗
PubMed1998

Ultraviolet-B induced hyperplasia and squamous cell carcinomas in the cornea of XPA-deficient mice.

In Xeroderma Pigmentosum (XP) patients, due to a defective repair of UV-induced DNA damage, neoplastic changes occur in sunlight-exposed areas of the skin and eyes. There are seven complementation groups in XP (XP-A to XP-G). Recently, we have generated XPA-deficient mice (group-A XP) by gene targeting in embryonic stem cells. In order to evaluate UV-B sensitivity, XPA-deficient mice (n = 20), wild type (n = 7) and heterozygous mice (n = 13) were exposed to low daily doses of UV-B for 14 weeks at a cumulative dose of 22 kj m-2 (250-400 nm). For a period of 32 weeks, the mice were checked twice a week for the development of pathology. The UV-B treatment induced eye abnormalities in the XPA-deficient mice. Initially, photophobia was noticed, followed by a loss of transparency of the cornea, eventually affecting nearly all XPA-deficient mice (19 out of 20). In 12 out of 19 mice, the pathology progressed to give eye protrusion. Histology of these eyes showed hyperplasia and squamous cell carcinomas of the corneal epithelium. No eye-lesions were found in control (wild-type and heterozygous) mice that were exposed to the same UV-B dose. The corneal abnormalities found in the XPA-deficient mice appear to be similar to those found in human XP patients. These results confirm the role of the functional XPA gene in protecting the cornea from pathology by UV-B irradiation. In addition, they suggest that the XPA-deficient mouse is a suitable animal model for the study of XPA ocular disorders.

Animals↗
PubMed1998

Chlamydia pneumoniae is a risk factor for coronary heart disease in symptom-free elderly men, but Helicobacter pylori and cytomegalovirus are not.

To test the hypothesis that chronic infection with Chlamydia pneumoniae, Helicobacter pylori or cytomegalovirus is associated with coronary heart disease risk in elderly men, a nested case-control study in a cohort investigated in 1985 and 1990 in the town of Zutphen, The Netherlands, was designed. Fifty-four cases with a first diagnosed coronary event between 1985 and 1990, and 108 age-matched control subjects free of coronary heart disease during follow up were included in the study. The overall prevalence of antibodies to cytomegalovirus was 74.7%, to H. pylori 75.9% and to C. pneumoniae 84.0%. A high level of antibodies to C. pneumoniae was associated with an increased coronary heart disease risk (OR = 2.76; 95% CI = 1.31-5.81). This association was stronger in cases developing both myocardial infarction and angina pectoris, than in cases developing only one of these. This association was independent of potential confounders. Antibodies to cytomegalovirus or H. pylori were not associated with coronary heart disease risk. These results support the hypothesis of a role of chronic C. pneumoniae infections in the immunopathogenesis of atherosclerosis.

Aged↗
PubMed1984

The enigma of Darwin.

Darwin's theory of evolution by natural selection on the basis of inherited random individual variation and excessive offspring remains controversial. Arguments derive from religion (creationism)--disagreement with the Darwinian reduction of teleology to physical causation, from science--nonselective mechanism, and from logic--negation of the possibility of proof of any scientific theory allowing only for validity thusfar. Experimentation on Darwinism is beset with a practical obstacle--unattainable duration, and a logical one--nonpredictability inherent in the randomness of variation. Evolution and creationism need not be contradictive if viewed in their separate domains--rational versus miraculous.

Biological Evolution↗
PubMed1977

Effect of methoxyflurane anesthesia on serum uric acid in man.

Serum uric acid levels were significantly increased on the first and third postoperative days following methoxyflurane anesthesia in subjects undergoing various surgical procedures. The increment on each of these days was significantly correlated with the duration of the anesthesia. No such changes were found following halothane or nitrous oxide-oxygen and relaxant anesthesia.

Halothane↗