School of Agriculture, Food and Ecosystem Sciences - Theses
Permanent URI for this collection
Search Results
1 - 10 of 20
-
ItemNutritional strategies to alleviate heat stress in pigs( 2023-07)Heat stress is a both current and increasing issue for pig production during summer in tropical and sub-tropical regions. Heat stress compromises pig production by increasing the energy cost for maintenance instead of utilising the energy for growth and reproduction. Moreover, HS increases pig’s health issues by causing oxidative stress, blood acid-base disturbance and compromises the physiological function of multiple organs. Various strategies are used to combat HS in pig production, but the use of nutritional strategies are cost-effective and once developed able to be easily incorporated into a variety of production systems. In Chapter 3, the effects of different HS duration (0, 1, 3, and 7 d) on voluntary feed intake, physiological parameters, haematological properties and gut barrier physiology were determined. The Evans blue dye (EBD) technique was also used to quantify plasma volume and tissue damage characterized by increased EBD extravasation in multiple organs. The results of Chapter 3 showed that HS resulted in respiratory alkalosis over 7 days of HS. Unlike some previous studies, HS did not compromise gastrointestinal barrier function, as evidenced by no change in intestinal integrity coupled with no differences in EBD extravasation. Plasma volume was reduced by approximately 10% on d3 and remained at this level until the end of the experiment. The reduced plasma volume, together with unchanged blood haematocrit and haemoglobin, suggest a dehydrated state of the experimental pigs despite ad libitum access to water. Increased concentrations of EBD in kidneys and pancreas may indicate extravasation in these tissues, indicating increased vascular damage and compromised function. Chapter 4 investigated the effects of betaine and isoquinoline alkaloids on the thermoregulatory response and intestinal barrier function of heat-stressed pigs. The findings from Chapter 4 demonstrated that supplementation with betaine and isoquinoline alkaloids reduced the respiration rate and rectal temperature of pigs exposed to HS, indicating improved thermoregulation. Additionally, isoquinoline alkaloids decreased the colonic permeability of pigs under HS conditions. These results suggest that betaine and isoquinoline alkaloids can mitigate the increased physiological responses and intestinal hyperpermeability induced by HS. Chapter 5 investigated the effects of recombinant superoxide dismutase (rSOD) on oxidative stress, inflammation, and intestinal barrier integrity. The results obtained from the experiment conducted in Chapter 5 demonstrated that HS triggered oxidative stress and inflammation. The administration of rSOD ameliorated the consequences of heat stress by reducing oxidative stress and inflammation. However, neither heat stress nor rSOD impacted intestinal barrier function. The findings of Chapter 5 suggest that heat stress-induced oxidative stress and inflammation can be alleviated by recombinant superoxide dismutase. Chapter 6 investigated the effects of chromium and organic acid supplementation on the blood acid-base balance and gastrointestinal integrity of heat-stressed pigs. The results of Chapter 6 indicated that heat stress increased physiological responses and triggered respiratory alkalosis, and compromised intestinal barrier function, as evidenced by reduced transepithelial electrical resistance (TER) and increased permeability. However, neither chromium nor organic acids had any beneficial effects on thermoregulation, blood acid-base balance, or intestinal barrier integrity. Hot weather in summer increases the risk of heat stress (HS) and is associated with compromised growth performance, meat quality, and economic loss in pig production. Chapter 7 investigated the effects of supranutritional levels of antioxidants (Se and VitE) and organic acids on growth performance and meat quality of finishing pigs in late summer to early autumn. The weather data indicated that the pigs were under thermoneutral conditions for most of the experimental periods and had a low risk of HS. No benefits were observed from antioxidant and organic acid supplementation on the growth performance and meat quality of the pigs, except protein oxidation was reduced with high levels of Se and VitE. These results may be attributed to the cool weather during the experiments. In summary, this thesis has shown that nutritional supplements such as betaine, isoquinoline alkaloids and recombinant superoxide dismutase can alleviate the negative impacts of HS in pigs.
-
ItemA study of weight-loss and compensatory gain in sheep( 1971)Two experiments of similar nature were conducted. In the first experiment 49 Corriedale wethers at approximately 8 months of age were allocated to four experimental groups and, within groups, to various slaughter weights which were spaced at 5 kg intervals. Group I animals were fed ad libitum and slaughtered - over a body weight- range of 38 - 63 kg inclusive. Groups II and III animals were fed ad libitum until 48 kg body weight hereupon intake was restricted to achieve a body weight loss of 0.9 kg/week until body weights were reduced to 38.5 kg and 34.5 kg, respectively. Ad libitum feeding was then resumed and animals were slaughtered up to 63 kg body weight at the same weight intervals as in Group I. Group IV animals were fed ad libitum until 48 kg body weight and then, food was adjusted to maintain body weight at 48 kg. Four animals were slaughtered after 60 days and a further four after 120 days of maintenance of body weight. In the second experiment, 15 wethers of similar age, breed and nutritional history as those used in Experiment 1, were allocated to four slaughter groups in a treatment similar to that of Group III in Experiment 1. Four animals were slaughtered at 33 kg body weight at the beginning of the first period of ad libitum feeding; three animals slaughtered at 45.5 kg at the end of the first period of ad libitum feeding; three animals slaughtered at 33.5 kg at the end of the weight loss phase; and five animals slaughtered at 46.5 kg at the end of the second period of ad libitum feeding. The compensatory growth rates of animals in Groups II and III were greater than those of Group I in each of the successive 5.5 kg increments in body weight. By maintaining higher growth rates over the entire weight range, the largest animals of Groups I I and III were slaughtered at a similar age to those, of Group I. Similarly, in Experiment 2, the compensatory growth rates (Group VI) were greater than continuous growth rates (Group V) over the body weight range used in this experiment. The data was transformed to logarithms in order to use Huxley's (1932) allometric growth equation in the linear form for an analysis of covariance. During continuous growth (Groups I and V), the empty body weight (EBW) increased as a proportion of full body weight (FEW) whilst during the compensatory growth which followed weight loss (Groups II, III and VI) the proportion of EBW remained constant. At the same FEW the EBW of Groups I I and III was less than that of Group I. Similarly, the EBW of animals maintained at a constant body weight (Group IV) was less, at the same FBW, than that of Group I. Carcass weight (CW) increased as a proportion of EBW as EBW increased in Groups I and V but the proportion remained constant in Groups II, III and VI. At the geometric mean FEW, treatment did not affect CW. However, the apparent dressing percentage (CW / FBW x 100) was 2% less during compensatory growth compared with that during continuous growth. The carcass length of animals in Groups II, III and IV was greater than that of animals in Group I.
-
Item
-
Item
-
ItemNutritional studies with the young ruminant( 1971)This thesis outlines a study of the calcium requirements of the young lamb (Part 1) and a comparison of the nutritional efficiency of the young lamb with the young pig (Part 2). Part 1 was carried out in co-operation with Dr. N. Palmer of the Department of. Pathology, School of Veterinary Science, University of Melbourne. The section includes a review of the methods which have been used to determine the calcium requirements of animals. The experimental work involved continuous calcium, phosphorus and magnesium balance studies of lambs from about 1 to 10 weeks of age. Dr. Palmer collected blood samples, killed the animals and prepared selected bones and liver samples for analysis. He was responsible for the calcium, phosphorus and magnesium analysis of the blood and bones and for the liver copper analysis. I was responsible for the design 'of the experiment, the collection and chemical analysis of all other material and the statistical analysis of the data. The interpretation of the results and the preparation of each section (including the review) have been my responsibility. Part 2 includes a literature review on aspects of the voluntary intake of animals and data on the comparative nutritional efficiency and body composition of the young Iambs and pigs when fed reconstituted whole cows' milk. Nutritional efficiency was expressed in terms of the voluntary intake of energy, digestibility, food conversion efficiency and the percentage retention of the nitrogen and energy contained in the milk. I was responsible for all aspects of the work appearing in this section.
-
Item
-
Item
-
ItemVariability in the intake of supplements by grazing sheep( 1979)Although the practice of feeding supplements to grazing animals is widespread through the world, its efficiency still deserves further study. Factors associated with the supplements themselves, the animals being fed, the environment, and the grazing diet being supplemented together constitute a set of variables which affects not only acceptance and intake, but also the nutritional and economic efficiencies of supplementary feeding. This study is concerned with the feeding of supplements to grazing sheep under temperate climatic conditions. Oat grain, hay and molasses-urea blocks (Barastoc, KMM Pty. Ltd., Melbourne) were used initially, but subsequent experiments were confined to the utilization of molasses-urea blocks. Only recently have researchers emphasized the importance of variability in supplement intake between individuals within a herd or flock and estimates of intake, with large ranges between animals, have now appeared in the literature. Langlands and Bowles (1976) considered that such wide variabilities in intake, limit the effectiveness of all forms of supplementation. However, little is known about the factors affecting variability in a group situation and few attempts have been made to identify the possible factors inducing such wide ranges of intakes in grazing animals. Arnold and Bush (1968) identified three types. of sheep: "shy-feeders", periodic non-feeders, and over indulgers". In some situations social dominance has been observed to affect responses to supplements (Franklin and Sutton, 1952; Wagnon, 1965; Squires and Daws, 1975) , and Arnold and taller (1974) correlated the intake of supplements with body weights of sheep. Chapter 1 of this thesis reviews the direct and indirect effects on animal performance of the main factors related to the feeding of supplements. Chapter 2 presents estimations of intake of three supplements, oats, hay, molasses-urea block, made with sheep in small paddocks. Results of behavioural observations and body measurements of the sheep are presented and discussed separately in Chapter 3. Chapter 4 provides an assessment of the acceptability of molasses-urea blocks by seven different flocks of grazing sheep on five private properties. The effects of confining sheep in yards on their acceptance of the blocks are also reported. Few studies have sought to determine whether management stratagems may improve the rate of adaptation of sheep to molasses-urea blocks and induce more uniform intakes between animals. Pilot trials described in Chapter 5 were conducted to identify possible management procedures that may be suitable for these purposes. Four such procedures were sufficiently encouraging to justify testing in a replicated experiment, which is described in Chapter 6. These treatments were imposed on sheep confined in yards and fed hay at a submaintenance levels. The investigations described in Chapter 7 utilised a different approach and are concerned with the behavioural aspects of learning, a topic which has been intensively studied with laboratory animals but only rarely with farm animals. The effects of offering molasses-urea blocks to lambs in the pre-weaning period are assessed in terms of their acceptance of blocks in later life. Inevitably only a few experimental possibilities and combinations have been assessed in the work reported in this thesis. Major attention was directed towards molasses-urea blocks because they induced wider variability in the responses by sheep than did hay or grain supplements . The blocks used were those manufactured by KMM Pty. Ltd., Melbourne, had a hard texture for protection against wet weather conditions and required animals to lick them rather than chew them. Variations in block formulation were not studied in the work described in this thesis and it remains possible that other types of block may have produced different results.
-
ItemEffects of resistance to prehension and structure of pastures on grazing behaviour and intake of dairy cows( 2000)Pasture intake by dairy cows is affected by plant and sward structural characteristics of the pasture. In the meantime, grazing animals are constrained to gather their food bite by bite removing only a portion of the herbage present at the location which they bite. The extent to which grazing animals overcome the constraints imposed by the plant and structural characteristics of the pasture is the major determinant of herbage intake. The experiments which form the basis of this thesis concentrated on determining the role of sward resistance to prehension, measured in situ, as an integrating sward characteristic that determines foraging decisions of cows and the extent to which they defoliate pasture swards. Under rotational grazing systems, a cow is offered an area of pasture that is often smaller than the area from which the cow harvests its bites (defoliated area, DA). The cow therefore faces changing sward conditions during the process of grazing down into the sward and removing bites at successive lower defoliation planes. The defoliation pattern in grazing down the sward profile and the consequent herbage intake and diet composition, are examined in this thesis. A novel apparatus was designed to measure the BFF in situ at different sward profile heights. In the initial experiment, changes in BFF down the sward profile of six pasture species were examined in order to evaluate the mechanical efficiency of defoliating bites at different depths, in terms of bite weight:BFF ratio. The hypothesis tested was that cows remove 30 - 40% of the sward height at each bite due to a mechanical advantage in terms of BW:BFF. The BFF varied more between defoliation strata than between pasture species. The bite weight and BFF increased with the depth of defoliation. The mechanical efficiency of defoliating bites estimated as the BW:BFF ratio declined slightly with bite depth until a depth of about 30 - 40% of the sward height is reached, when the ratio declined more rapidly. Based on these results and those of Wade (1991), four theoretical defoliation planes (DPI, DP2, DP3 & DP4) were set each at 35% of the pre-grazing sward heights to estimate the total area defoliated by grazing cows under different sward conditions. DP2 is the plane of removal of a second bite after a first bite has removed DPI. Three spring grazing experiments were conducted to explore relationships between pasture allowance and/or sward structure and intake dynamics. In the first experiment, cows were offered a herbage allowance (HA) of 50 kg DM/cow/day either as one block with continuous access for 24 hours, or as six equal break rations opened at intervals during a 24 hour period. In the two subsequent experiments, different sward types were created in order to alter the BFF. In the second experiment swards were created with two different surface heights (USH) and in a 2 x 2 factorial, cows were offered two HA (35 and 70 kgDM/cow/day). In the third experiment, swards with three different tiller densities were created and cows were offered a similar HA of 8 kg DM/cow/3 hours. The defoliation pattern, BFF at 30, 50 and 70% of USH, DM intake, grazing behaviour and the energetics of grazing were measured. The major conclusions derived from these experiments are as follows. The average depth of defoliation (DD) increased with sward height and fell between DP2 and DP4. However, the proportion of area defoliated at each defoliation plane declined down the profile, at rates that varied with HA and tiller density but was unaffected by sward height. At a HA of 70 kg, cows barely reached DP4. The area defoliated at DP4 increased with decreasing herbage allowance and decreasing tiller density. The initial bulk density and post-grazed bulk density declined with USH, but the grazed-stratum bulk density was not significantly affected by USH. Therefore, it was concluded that the volume of canopy defoliated was the major determinant of intake. With increasing HA, the average bite weight (BW) increased, prehension bite rate declined but the overall intake rate increased. The time cost of a bite increased with BW. However, the energy expenditure on prehending a bite did not show a consistent relationship with BW. The BFF increased with sward height and tiller density. However, BFF in the leafy layer of 70% of the sward height was not affected by initial sward height or tiller density. The increase in BFF with initial sward height and tiller density was greater in the lower stemmy layer of 30% sward height. The average bite area (BA) and BW increased with HA. Intake was positively correlated with HA (R = 0.49), HM (R = 0.65) and tiller density (R = 0.51). Multiple regression analysis with herbage intake as the dependent variable indicated that, in addition to HM and HA (R2 = 0.887) , inclusion of the difference in BFF between that at 30% USH and that at 70% USH (BFFdif) as a sward characteristic provided an equation with a substantially better fit (R2 = 0.956). DMI = -3.47 + 1.80 HM + 0.225 HA R2 = 0.887 DMI = -2.73 I + 2.76 HM + 0.732 HA - 0.0416 BFFdif R2 = 0.956 It is concluded that the BFFdif has a significant value in integrating the changes in sward characteristics down the profile and is useful in improving the intake model.
-
ItemThe diet and helminth parasites of foxes, dingoes and feral dogs in Victoria( 1973)This thesis was prepared while the author was employed with the Victorian Department of Crown Lands and Survey at the Keith Turnbull Research Station, Frankston. It is in the form of three papers which describe the experimental work and a review of pertinent literature. The literature review outlines the extent of previous knowledge on the subjects of fox diet and fox parasites (helminth) in Australia. A short review of selected overseas studies is included. The experimental work deals with the incidence of various food items and helminth parasites in the gastro-intestinal tracts of foxes, dingoes and feral dogs collected in Victoria during the period from 1968 to 1970. The paper dealing with dingoes and feral dogs has been published (Aust. vet. J., 1972, 48 : 456-461) and the remaining papers have been submitted for publication. All funds for this research project were supplied by the Australian Meat Research Committee.