排序方式： 共有40条查询结果，搜索用时 15 毫秒
11.
12.
13.
14.
The optimum policy of insemination and replacement of dairy cows was determined by the dynamic programming technique. The model used in the previous study was extended to allow variation in time of conception. From 2 to 7 months after calving three alternatives were considered for an open cow namely (a) inseminating the cow, with a calculated probability of success, (b) leaving her open, and (c) replacing her immediately. When it was profitable to leave a cow open, the optimum time for replacement during the lactation period was determined.The minimum production level for insemination to be the optimum choice depended on the stage of lactation and the parity of the cow. In the optimum situation the average calving interval was 371 days, while 13% of the cows had an interval of 14 months or longer.The optimum policy was greatly affected by changes in the replacement heifer price. Changes in the probability of conception and persistency of milk production had significant but smaller effects. In herds with a smaller decline in production after the peak, insemination should be continued for longer than in herds with a larger decline.The relation between production and calving interval that resulted from the optimum policy was determined. When a measure of milk production was used that was not affected by gestation, the average correlation was 0.09. The correlation increased to 0.35 when the total 305-day production was used. 相似文献
15.
The financial losses due to retained placenta in Dutch dairy cattle were estimated by using two different methods of calculation. A data-set containing the birth records of 160,188 Meuse-Rhine-Yssel cows provided data on the reproductive performance of cows with and without retained placenta. The fertility of cows after retention of the placenta appeared to be affected. An economic calculation made by adding the losses due to increased calving interval, increased culling rate, loss of milk production and the costs of veterinary treatment and drugs revealed that the total loss due to retained placenta was 471 pounds per year for a 100-cow farm with an average incidence of the condition (6.6 per cent). For a 'problem' farm with a 30 per cent rate, the loss was 2139 pounds per year. A computer farm simulation model, based on a stochastic determination of events, was used to make calculations for circumstances closely resembling those on farms. A 6.6 per cent rate of retained placenta caused a small but significant decrease in net return on labour and management; however, a 30 per cent rate caused highly significant changes. The economic effects of retained placenta were similar in magnitude in herds of high or low productivity and high or low fertility. Sensitivity analysis showed that the greatest financial losses were caused by loss of milk production, followed by the number of animals suffering from complications. The financial losses in herds with an average rate of retained placenta were thus of limited economic importance and therapeutic measures alone should be adequate.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
16.
P. B. M. Berentsen A. A. Dijkhuizen A. J. Oskam 《Preventive veterinary medicine》1992,12(3-4):229-243
An integrated model for the personal computer is presented, in which a variety of preventive and control strategies with respect to foot-and-mouth disease (FMD) in Dutch cattle and pig herds were examined economically. Special attention is given to the way in which losses due to export bans are determined. Export bans would occur as a result of an outbreak of FMD. Annual costs for the Netherlands would be reduced considerably if the yearly vaccinations were stopped. This conclusion holds even if more pessimistic values are used for some major uncertain input factors. The PC model is flexible with regard to input values, making it possible to fit different conditions. 相似文献
17.
Jalvingh AW Nielen M Maurice H Stegeman AJ Elbers AR Dijkhuizen AA 《Preventive veterinary medicine》1999,42(3-4):271-295
The simulation model InterCSF was developed to simulate the Dutch Classical Swine Fever (CSF) epidemic of 1997–98 as closely as possible. InterCSF is a spatial, temporal and stochastic simulation model. The outcomes of the various replications give an estimate of the variation in size and duration of possible CSF-epidemics. InterCSF simulates disease spread from an infected farm to other farms through three contact types (animals, vehicles, persons) and through local spread up to a specified distance. The main disease-control mechanisms that influence the disease spread in InterCSF are diagnosis of the infected farms, depopulation of infected farms, movement-control areas, tracing, and pre-emptive slaughter. InterCSF was developed using InterSpread as the basis. InterSpread was developed for foot-and-mouth disease (FMD). This paper describes the process of modifying InterSpread into InterCSF. This involved changing the assumptions and mechanisms for disease spread from FMD to CSF. In addition, CSF-specific control measures based on the standard European Union (EU) regulations were included, as well as additional control measures that were applied during the Dutch epidemic. To adapt InterCSF as closely as possible to the Dutch 1997/98 epidemic, data from the real epidemic were analysed. Both disease spread and disease-control parameters were thus specifically based on the real epidemic. In general, InterSpread turned out to be a flexible tool that could be adapted to simulate another disease with relative ease. The most difficult were the modifications necessary to mimic the real epidemic as closely as possible. The model was well able to simulate an epidemic with a similar pattern over time for number of detected farms as the real outbreak; but the absolute numbers were (despite many relevant modifications) not exactly the same — but were within an acceptable range. Furthermore, the development of InterCSF provided the researchers with a better insight into the existing knowledge gaps. In part II (see the final paper in this issue), InterCSF was used to compare various control strategies as applied to this epidemic. 相似文献
18.
A. Dijkhuizen J. W. Dudley T. R. Rocheford A. E. Haken S. R. Eckhoff 《Cereal Chemistry》1998,75(2):266-270
An understanding of the genetic control of starch, protein, and oil concentrations in the corn (Zea mays L.) kernel is essential for improvement of grain quality. Because large numbers of progenies are needed for genetic studies, a rapid, accurate, analytical procedure is necessary. As part of a study to identify chromosomal regions associated with starch and protein, a rapid near-infrared reflectance (NIR) method and a more labor-intensive 100-g wet-milling procedure were compared for consistency in ranking families and identifying quantitative trait loci (QTL) using a set of 200 F2S1 families from the cross of the 70th generations of the Illinois High Protein (IHP) × Illinois Low Protein (ILP) corn strains. NIR starch and wet-milling starch values were highly correlated (r = 0.80), as were NIR protein and gluten measured by wet-milling (r = 0.72). Chromosomal regions associated with NIR starch and wet-milling starch were generally the same. Fiber concentration was significantly negatively correlated with starch and positively correlated with protein. Chromosome regions with significant associations with starch also had significant associations with fiber. The NIR method is satisfactory for measuring starch and protein in material with a wide range of variability in the early stages of a corn-breeding program. 相似文献
19.
Cows are culled at a relatively low age, which causes considerable economic loss. The annual culling rate in the Netherlands has increased from 18.8 per cent in 1951 to 25-30 per cent of the average number of cows in more recent years. The productive life is now about 3.5 years. On the thirty farms of the program group and thirty-one farms of the control group, the main reasons for culling were reproductive failure followed by mastitis and teat injuries. About 60 per cent of culling was due to health problems, the other 40 per cent to low productive capacity, old age, poor workability etc. The annual culling rate varied per farm per year but also per month. The moment of culling in the current lactation, the slaughter value and the age differed per reason. The calculated loss of forced replacement consists of reduction in both production prior to culling and slaughter value. Additionally, there is an idle production period due to lack of an immediate replacement. The biggest loss is caused by lost future income. There was a considerable difference per farm in the loss caused by culling for health problems. A low culling rate due to health problems was associated with longer longevity and a relatively lower loss. Tangible effects due to changes in the farm culling policy may not be evident for some years. The reduction in loss of culling in the program farms compared with the controls was small because the duration (2 1/2 years) of the herd health and management program was too short.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
20.
A. A. Dijkhuizen 《The Veterinary quarterly》2013,33(2):116-124
Summary The income margin in modern pig farming is generally narrow. Controlling the cost of production, therefore, is of great importance. Improving health and fertility can play a major role in this context. In this paper three interrelated issues are discussed from a farm management point of view: (1) the financial losses of common health and fertility problems, (2) the costs and benefits of disease control, and (3) the decision to replace individual sows in case of poor health and/or reduced productive performance. Priorities for further research in the field of animal health economics are also discussed. 相似文献