School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemNo Preview AvailableEvaluation of dual energy x-ray absorptiometry for predicting whole body and carcass composition of pigs(University of Melbourne, 2003)This dissertation aims to evaluate the dual energy X-ray absorptiometry (DXA) technique for measuring whole body and carcass composition of pigs. Section 1 provides the appropriate calibration for quantitatively accurate DXA measurements of live body and carcass composition of pigs of varying weight, as determined by chemical analysis and manual dissection. The DXA technology provided an accurate precise measurement of composition within experiments and when measurements were compared across experiments. The precision of DXA measurements were far better than weight and P2 backfat, particularly in the prediction of fat tissue, especially when measurements were compared across experiments. The DXA measurements were highly repeatable and measurement repeatability improved as animal size increased. The placement of the regional analysis grid influenced the repeatability of all measurements except for total weight, however this influence reduced with increasing animal size. It is recommended that the scan image be positioned in the arm region of the software regional analysis grid to measure whole body composition in pigs because it provides the most repeatable measure overall and a better measure for fat tissue when compared to chemical analysis and manual dissection. The DXA regional analysis software also provided an accurate and precise measurement of dissectible composition in the primal-cuts, ie. the ham, loin, belly and shoulder. However, care needs to be taken to ensure accurate and consistent delineation of sub-regions to the true position of primal-cuts in the DXA scan image to ensure a reliable measurement. Section 2 involved a series of experiments to evaluate the ability of the DXA technology in measuring the effects of various known and innovative body composition manipulators, all directly applicable to industry. Each experiment demonstrated the use of the developed calibration equations and the efficacy of the DXA technique. Overall, corrective equations were successfully applied to DXA estimates and largely corrected differences between raw DXA outputs and chemical values. The DXA measurements confirmed that diets deficient in protein lead to sub-optimal lean tissue and bone mineral growth with no effect on fat and were substantiated by chemical analysis. Serial DXA measurements in the same animal demonstrated the lifetime differences between contemporary genotype boars and barrows under different penning conditions. These data indicated that although boars have a lower propensity to deposit fat overall, under group penned conditions there is little incentive to produce boars in terms of body composition if slaughter weights were below about 80kg. However, in the late finisher period, boars did deposit more lean tissue than barrows, but this difference was reduced when animals were group-penned. The regional analysis software successfully demonstrated the effects of pST treatment on fat distribution within the animal, and was validated using manual dissection. A dose dependent decrease in belly, loin, ham and shoulder fat was also observed, although the proportionate decrease in belly fat was more pronounced than for the whole carcass and other primal cuts. Finally, the DXA technique was sensitive enough to detect the subtle body composition changes that were induced by supplemental dietary betaine. Dietary betaine improved growth rate and protein deposition, and consequently carcass lean tissue content, in pigs fed restricted energy and the effects were additive with those of pST. Lean tissue in the loin was particularly responsive. The energy spared by betaine was not enough to increase fat deposition, carcass fat or P2 backfat regardless of energy intake. However, dietary betaine did increase fat in the more energy responsive belly region under ad libitum conditions but not under a restricted intake typical of commercial conditions. Therefore, dietary betaine did alter the distribution of lean meat and fat within the animal. These data demonstrate that the DXA technology is a "viable" replacement for the standard methodologies in animal growth and body composition research experiments and has much potential for implementation into the pork industry for carcass grading and providing data for pig growth simulation models.
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ItemAn evaluation of the role of extension in the Australian pig industry( 1978)Australian agriculture is adjusting to changes in technology, economic circumstances and markets. Extension services as much as the producers' need to change in response to changing industry needs, market trends and consumer demands. There has been much discussion on the problems that these changes present for extension, but none on the basis of empirical research or social science theories. A research program was developed to define the changes taking place in the structure and organisation of the Australian pig industry, and to identify the implications of these changes for pig producers and for extension agencies such as State Departments of Agriculture. The conclusion drawn from the review of the industry situation and from a Delphi survey of 10 experts in the pig industry was that the industry will become more technical and commercialised requiring continual adaptation by the producers to technical and economic changes in order to maintain and increase production efficiency. The survey results showed that a degree of assistance from research and extension was expected by producers to help them maintain and improve production efficiency. Based on the Theory of Personal Constructs, Kelly (1955) an interactive psychological testing procedure known as the Repertory grid was used to record producers' and extension officers' perceptions of each other and of extension services. Twenty pig industry officers, 16 non extension users, 20 extension users and 16 large commercial producers were interviewed. Separate analyses were carried out on the grids of individual subjects, providing profiles of constructs typically used by the subjects in relating to and evaluating people. The results clearly identified the constructs which farmers used in relating to extension advisers and advice. In general, all groups of subjects tended to stereotype people with whom they associated. Combination of both the results within subject groups revealed evidence of commonality within and between the groups in their perceptions. The extension officers saw themselves as progressive and useful while a large number of the producers saw them as theoretical and irrelevant. Extension users held favourable attitudes towards professional agricultural advisers, while large commercial producers and non extension users criticised them on the grounds that they were difficult to communicate with and lacking practical experience. As a group, extension officers were not aware of the questioned relevance of their advice nor of the difficulty experienced by producers in communicating with them. Owing to their practical background and shared experiences, all producers saw other producers as useful and as the most relevant source of advice. The roles they expect him to perform and the characteristics that producers expect from a professional extension adviser have been identified and their implications for the extension officer are discussed. The most obvious implications of the findings are that extension advisers fail to establish the relevance of information within the farmers' context of what is relevant. Based on the findings of the research the theory is proposed that extension programmes will be most successful when producers and extension workers share common perceptions of relevant problems. A philosophy and practice of extension is proposed to meet the farmers' own perception of needs. The interpretation of the results in terms of Personal Construct theory leads to the development of the model of human behaviour, that is, "man as an actor" instead of "man as something being acted upon". A philosophy of extension is developed based on the belief that extension can only be successful if it provides what farmers want. The philosophy states that extension should provide a helping role by facilitating, developing and supporting "man the actor" without dominating or controlling his actions. A practice of extension operating within the boundaries of the proposed new philosophy is developed from the helping relationship model of Carkhuff (1969). The goals of extension are defined as exploration, understanding and action which lead directly to the need for skills which are defined as the "interface skills" of attending, responding, personalising and initiating. The need for and the nature of extension training to provide extension officers with "interface skills" is discussed.
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ItemSocial and sexual factors affecting reproduction of the domestic boar( 1978)This thesis describes the results of work in three general areas; (i) the influence 0f the social environment during rearing and after puberty on the sexual behaviour of the boar, (ii) the role of the courting behaviour of the boar in his reproductive performance, and (iii) the influence of sexual stimulation on the spermatozoan output of the boar. The major portion of the work relates to the importance of the social environment. Boars reared from three weeks of age in the absence of visual and physical contact with pigs had markedly lower copulatory performance and level of courting activity compared with those reared from three weeks in either an all-male or mixed-sex group. Lack of physical contact with pigs during rearing was responsible for approximately 70% of this depression in copulatory performance. The copulatory performance of boars reared from 12 weeks of age in the absence of visual and physical contact with pigs was considerably less than that of boars reared in an all-male group, but the difference was not significant. Boars reared from three or 12 weeks- of age individually in adjacent wire-mesh pens had similar copulatory performance to that of group-reared boars. However, an apparently important feature of courting behaviour, 'nosing activity', was significantly reduced for those boars reared from three weeks individually in adjacent wire-mesh pens. These data were interpreted as evidence of the importance of social contact, particularly physical contact with boars or gilts, during rearing on the level of sexual behaviour of the boar. In addition to the social environment during rearing, the social environment after puberty was demonstrated to have a dramatic influence on the level of sexual behaviour of the boar. Isolation of post-pubertal boars from female pigs for six weeks significantly reduced their copulatory performance and level of courting activity. The stimuli received from the presence of sexually receptive or sexually non-receptive female pigs were equally capable of maintaining the level of sexual behaviour of the boar. Two experiments conducted at a commercial piggery revealed the importance of the courting behaviour of the boar on reproductive performance. A significant positive correlation was found between the observed level of nosing activity during courting and the conception rate record of the boar. The proposal that the nosing activity of the boar may stimulate one or more physiological mechanisms leading to fertilisation in the sow is supported by the results of the second experiment. Brief courting of sows by a boar prior to artificial insemination significantly increased the farrowing rate and litter size of group-housed sows. Finally, sexual stimulation of boars prior to semen collection significantly increased the number of spermatozoa . in the sperm-rich fraction of the ejaculate. The technique of sexual stimulation of the boar involved either allowing the boar a false mount and then briefly restraining him or allowing the boar to observe a semen collection. The former technique failed to maintain a significant increase in the yield of spermatozoa from the sperm-rich fraction over a six-week collection period. Prostaglandin F2a, which may be involved in the mechanism by which sexual stimulation increases the number of spermatozoa in the short term, was also studied. Administration of 20 mg of PGF2a 30 minutes before collection significantly increased the number of spermatozoa in the sperm-rich fraction of the ejaculate. The experiments of this thesis demonstrate that sexual and social factors have a major influence on the reproduction of the domestic boar.
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ItemInvestigation of infertility in mated sows under intensive conditions( 1978)This thesis details a series of experiments investigating infertility in mated sows. The particular problem of delayed return to oestrus in sows following a normal mating to a fertile boar, was studied. The vaginal biopsy and ultrasonic methods of pregnancy diagnosis were tested for use in diagnosis of pregnancy in herds where a large proportion of sows showed a delayed return to oestrus. These methods were found unsuitable in this instance and so plasma progesterone and oestrogen levels were examined in sows,18 days after mating, in an attempt to identify affected sows. Facilities for hormone analysis were established and workable assays for progesterone, oestrogen and corticoid levels developed. Two laboratory experiments accompanied these field trials. The first was to study the temporal relationships between progesterone, oestrogen, and corticoid levels during the oestrous cycle and early pregnancy in sows. The second was to look at the effects of ACTH administration on plasma progesterone, oestrogen, corticoid, and LH levels and upon oestrus and ovulation. These experiments are described and the results discussed in this thesis. An integrating discussion and summary is included to link each section and to combine the conclusions of this thesis.