School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemLactation in mice as a model to study genetic improvement of dairy cattle in the tropics( 1989)In chapter one of this thesis aspects of reproduction and production, mainly milk production were reviewed. Components of reproductive efficiency such as the fertility components: age at calving, service periods, days open, calving interval and non return rate; were also investigated. The physiological relationship between those traits and milk production and persistency, in both temperate and tropical environments, was also considered, as well as longevity or stayability as other alternatives for evaluating reproduction. Attention was put on first and second lactation performance. With a view towards understanding physiological aspects of reproduction and production in dairy cows, the nature of lactation in mice was reviewed from the relatively few works that have been done. The papers reviewed included the role of pre-natal and post-natal maternal effects and the relationship between littersize and milk-yield. Daily yield and lactation from a number of studies were compared. Theories of genotype-environment interaction (GM) and adaptation, as well as their implications, were reviewed in the subsequent part of. chapter 1. Evidence of GEE in dairy cattle (Friesian, Holstein or Friesian-Holstein, crossbred with Friesian, and native) in both reproductive characters and milk production throughout the tropic regions were examined particularly closely. Mating systems and selection responses in genetic improvement programmes also were reviewed. Constraints and shortcomings for the achievement of genetic progress through natural mating, AI and progeny-testing in the tropics were examined in conjunction with attainment of high milk production in the temperate countries. The use of new technology (MOET) for manipulating reproductive efficiency was also introduced in the hope that it can be used to increase breeding efficiency in the tropics. The milk-yield and reproductive . characters, of two genotypes of mice (one genotype had been selected for high early reproductive and milking performance and the other was a random bred control) were measured in the normal and a hot environment to check if GEI were present. Both genotypes had been developed in the normal temperature. Evidence of interaction was found in the second parity and only in reproductive traits, e.g. fecundity, interval between mating and birth of second parity. These results are supported by many studies of GEI for both milk-yield and reproductive characters in dairy cattle in the tropics. Milk production does not show GEI, if the environment is defined merely as temperature. The previous selection of the improved genotype had resulted in positive correlated responses in: litter size and litter weight at birth in the first parity, production characters (growth characters and preweaning weight of the litters) in both parities, and on milk production but not on persistency. The selected line did maintain its superiority across environments. However females from the improved genotype performed worse in almost all characters in the hot environment compared to the normal environment. In an analogy with dairy cattle, the high production capacity of the selected line was not exhibited in the adverse environment. Problems of genetic improvement in the tropics were discussed. They included the use of appropriate selection criteria based on . more knowledge of both physiological and genetical relationships between milk-yield and other-characters, with the aim of increasing adaptability and productivity in the target environment. Other possibilities for genetic improvement of dairy cattle in the tropics and the use of synthetic breeds for overcoming the problems in the long term were also discussed.
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ItemStepwise adoption of a complex agricultural technology( 1989)Previous studies of technology transfer have frequently treated the process as being controlled by the providers of the technology, with minimal involvement of the potential users. However, technology transfer is likely to be more effective and beneficial when based on a model with gives more thought to the needs and demands of the potential adopter. Complex technologies have been regarded previously as monolithic: adopted as a whole, but more slowly than simpler technologies. A complex technology is redefined as one which can be broken up into separate technological components, each of which may be adopted separately. It is proposed that adoption of a complex technology, as defined, occurs in a stepwise manner. Components are adopted in some order, which reflects the adopter's perception of their value to his operation. Not all components are taken up by all adopters. The theory was tested using, as a case study, the Tatura Permanent Beds system, a complex technology for irrigation cropping, in Northern Victoria and Southern New South Hales. The first three years of use of the technology by the 43 identifiable adopters was examined. It was found that adoption of the components of Tatura Permanent Beds occurred in a stepwise manner, but more components were adopted in the first year of use than in later years. It was also found that different farmers adopted different numbers of components, and adopted them . in different orders. Attempts were made to discover demographic, attitudinal and cognitive reasons for these differences. Possible refinements of the theory are suggested, and implications for extension discussed.
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ItemEvaluation of the concepts and methods of response farming using crop growth simulation models( 1989)This thesis considers aspects of the application of the CERES-Maize simulation model of the growth and yield of the maize crop to the analysis of "response farming" in the semi-arid region of East Kenya. Response farming comprises a set of management tactics by which sowing density and nitrogen application can be targeted to the yield potential of the season based upon the timing and nature of the opening rains. Sowing density and nitrogen application are set by the timing of the opening rains and then further adjustments are made four to five weeks after sowing. The in-season adjustments involve additional nitrogen fertilizer in seasons that promise high yield potential and crop thinning when yield promises to be low. These combinations have the purpose of maximizing yield in seasons of high potential and minimizing fertilizer and seed input in seasons in which the rainfall is too low for it to have any advantage. The scheme is possible, it is proposed, because the timing and nature of the opening rains are closely correlated with total seasonal rainfall and hence yield potential. The thesis discusses the potential that simulation models hold in the analysis of alternative cropping strategies (Chapter 2). It presents a validation study of the model with experimental data collected in the region (Chapter 3) and discusses the relationships between maize agronomy in the region and the components of response farming (Chapter 4). The tuned model is shown to provide a good explanation of the response of the common cultivar of maize to a range of combinations of water and nitrogen supply and a reasonable capacity to describe the response of the crop to thinning (Chapter 5). The model is then used (Chapter 6) to compare response farming with conventional practices at various levels of inputs. It shows that the common practice of the region by which-crops are sown at low density without fertilizer has the least risk of failure but low expected yields. Fertilizer is required to increase yields, but its use incurs a greater chance of crop failure. Compared to alternative strategies using fixed or variable sowing dates at comparable levels of crop density and nitrogen fertilizer, it is shown that response farming does provide higher mean yield with less chance of failure. It is proposed that continuing experimentation with the current and improved versions of the model have an important role to play in the identification of better management strategies for East Kenyan farmers.
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ItemA study of some aspects of adaptation and yield of Serradella (Ornithopus Spp.) in Victoria( 1989)Serradella (Ornithopus sp.) is potentially useful on deep acid sandy soils in the > 350mm average annual rainfall areas of southern Australia, where many other pasture legumes fail to persist. Subterranean clover (Trifolium sp.) is one of the most important annual pasture legumes usually sown on non-alkaline soils within this climatic region, but it often fails to establish and persist on deep acid sandy soils. In these situations serradella may be a more productive alternative and may become the dominant pasture legume. One of the main limitations to the widespread use of serradella has been the limited amount of genetic variation in Australia, with there being only very few naturalised and commercial strains. In its area of origin, serradella covers the full area of origin of subterranean clover in the Mediterranean region and extends farther into north-western Europe and onto acid sandy soils on which subterranean clover is absent. Yellow serradella (Ornithopus compressus) appears to have the greatest potential for commercial development in Australia, but only one relatively late flowering cultivar, derived from a chance introduction, was available. This was the cultivar Pitman which was suited to an average annual rainfall of 500mm and thus did not leave enough seed for survival of the species in the large areas of grazing land in drier (350-500mm average annual rainfall) areas. In the period from 1970-1980, mainly in an effort to extend the use of serradella to the drier areas, artificially induced mutants of the cultivar Pitman were produced and a wide range of serradella seed was collected from the Mediterranean region. This new variation available to Australian scientists and farmers has been, and is still being, assessed for characters considered to be important for the success of serradella as a pasture legume in Australia. In 1982 seed of 26 of the new accessions, the cultivar Pitman and the Pitman derived mutant, Uniserra, became available to the University of Melbourne for testing under Victorian conditions. These accessions were grown, in single rows and pots, in Gippsland and growth assessments and flowering times were recorded. There was considerable variation in growth response and flowering times and at the end of this trial six lines with good growth were chosen, so that the full range from early to late lines were represented. In the following season, also in Gippsland, the six chosen lines were each sown at five different dates, in single rows with two cultivars of subterranean clover. The flowering and growth responses were recorded allowing direct comparisons to be made. To clarify the comparative vernalization responses of serradella and subterranean clover, a range of accessions of serradella and two cultivars of subterranean clover were grown in the field and in pots in northern Victoria and southern N.S.W., in summer. A similar range of serradella and subterranean clover lines/cultivars was also subjected to artificial vernalization and the resultant flowering responses were recorded. Some of the new accessions flowered earlier than the cultivars Pitman and Uniserra, and the general flowering responses to climate appeared to be similar in both serradella and subterranean clover, with there being similar individual responses between early and late lines of both species. It has been widely reported that on deep acid sandy soils serradella has a more efficient root system, compared with other annual pasture legumes. The cultivar Pitman was grown alongside the subterranean clover cultivar Mt. Barker in an acid sandy loam, treated with varying lime application rates to achieve a range of pH levels (pH 4.3-6.3). The plants were grown in shallow (20cm deep) pots, deep (lm deep) pots and in the field. The application of lime had significant effects on root nodulation, root morphology and root growth of both species. The results generally support the findings of others that serradella's comparative advantage on deep acid sandy soils is due to a finely divided deep root system. A marked feature of serradella appears to be the extensive development of highly branched fine lateral root systems, which can also reach depths of lm.