Breeding for trypanotolerance in African cattle

Trypanosomosis, or sleeping sickness, is one of the most important livestock diseases in Africa. Some West African cattle breeds show a degree of resistance to a trypanosome infection: they are trypanotolerant. At the International Livestock Research Institute (ILRI) in Nairobi, Kenya, an F2 experiment has been established to unravel the genetic background of trypanotolerance. This thesis had two main aims: First to determine the genetic background of trypanotolerance, and second to investigate opportunities to incorporate this information in a breeding scheme to increase performance of cattle in tsetse-infested areas. Based on the results from the F2 experiment, several traits were defined, which reflected features of trypanotolerant cattle. Subsequently, based on preliminary results from an analysis to determine chromosome fractions containing genes (QTL) involved in trypanotolerance performed at ILRI, the mode of expression of these QTL was investigated and one of the QTL was found to be maternally imprinted. These QTL could be utilised in an introgression scheme, but also for within breed selection. Both options were investigated. When introgressing QTL for disease resistance the optimal number of backcross generations from genetic or economic point of view was found to be different. The number of animals required is increasing very rapidly with increasing number of QTL to be introgressed. Within breed selection to increase production under constant infection pressure can be applied with or without aid of QTL for disease resistance. Mass selection on production under infection can be applied if no QTL information is available. A non-linear selection response is achieved in both potential production and disease resistance. Important advantage of QTL information for disease resistance is that animals can be selected outside the infected environment. In implementing a breeding scheme it is important to take into account that social-economic values and environments are very different in large parts of Africa as compared to Western countries. This thesis has demonstrated that there are good opportunities for using selection to improve the results of local farming systems.</p

Using genetic markers for disease resistance to improve production under constant infection pressure

Animals will show reduced production when exposed to a constant infection pressure unless they are fully resistant, the size of the reduction depending on the degree of resistance and the severity of infection. In this article, the use of QTL for disease resistance for improving productivity under constant infection pressure is investigated using stochastic simulation. A previously published model was used with two thresholds for resistance: a threshold below which production is not possible and a threshold above which production is not affected by the infection. Between thresholds, observed production under constant infection is a multiplicative function of underlying potential production and level of resistance. Some simplifications of reality were adopted in the model, such as no genetic correlation between potential production and resistance, the absence of influence of lack of resistance on reproductive capacity, and the availability of phenotypes in both sexes. Marker-assisted selection was incorporated by assuming a proportion of the genetic variance to be explained by the QTL, which thus is defined as a continuous trait. Phenotypes were available for production, not for resistance. The infection pressure may vary across time. Results were compared to mass selection on production under constant as well as intermittent infection pressure, where the infection pressure varied between but not within years. Selection started in a population with a very poor level of resistance. Incorporation of QTL information is valuable (i.e., the increase in observed production relative to mass selection) when a large proportion of the additive genetic variance is explained by the QTL (50% genetic variance explained) and when the heritability for resistance is low (h2R = 0.1). Under constant infection pressure, incorporating QTL information does not increase selection responses in observed production when the QTL effect explains less than 25% of the genetic variance. Under intermittent selection pressure, the use of QTL information gives a slightly greater increase in observed production in early generations, relative to mass selection on observed production, but still only when the QTL effect is large or the heritability for resistance is low. The additional advantage of incorporating QTL information is that use of (preventive) medical treatment is possible, or animals may be evaluated in uninfected environments

Results of the SURFnet4 management project 1997

This technical report bundles the five reports that were written for two SURFnet4 projects in 1997. Each report discusses a different research aspect of the SURFnet4 ATM network. The topics are 1) the Architecture of a ATM PVC Management Tool, 2) Reporting on the Use of the ATM Network, 3) SVCs in a Production Environment, 4) Quality of Service Measures, 5) Operation and Maintenance (OAM)

Morphological features of indigenous chicken populations of Ethiopia

This study describes the variations in the physical features and the useful attributes of different populations of indigenous chickens. Five populations of chickens in different regions of Ethiopia were studied based on 13 qualitative traits recorded for a total of 1 125 chickens. Additional measurements on quantitative traits (shank length and body weight) were also included. Descriptive statistics (nonparametric and F tests) were used to analyze the data. Each of the study populations possessed multiple variants of plumage colours and other physical features. However, white body plumage is one of the prominent features of Farta chickens and red is predominant in the other populations. Pea comb is the dominant comb type in all regions. Most of the chickens in the high altitude regions have yellow skin. The geographic distribution and frequency of naked neck chickens are generally small, and the available small proportion is found mainly in the low altitude regions. Males in all populations are heavier and taller than the females. Body weights range from 1 411 g (Konso) to 1 700 g (Horro) in adult males and from 1 011 g (Konso) to 1 517 g (Sheka) in females. Most of the morphological traits that were studied showed a very low level of associations with each other

Management of networks that provide QoS guarantees

This paper presents the results of a case study to the feasibility of introducing ATM SVCs into the Dutch SURFnet research ATM network. The key issue that is examined are the implications of the Quality of Service support of ATM. QoS guarantees for a connection require a portion of the finite ATM network resource. Once all network resource is allocated to connections no new connections will be accepted, and users will start experiencing denial of service. The key research question here is if and how this denial of service probability can be kept to a minimum