Agriculture and Food Systems - Theses

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    The nutrition of multiple-bearing ewes in late pregnancy
    Hall, David Graham ( 1989)
    The nutrition of multiple-bearing ewes in late pregnancy and relationships with lamb survival are reviewed (Chapter 1). The frequent reductions in voluntary intake in late pregnancy, the reliance on maternal reserves and the key role of glucose and protein are highlighted. The sensitivity to nutritional manipulation of traits associated with lamb survival and their variation due to litter size are discussed. The traits include lamb birth weight, lamb vigour, ewe mammary growth and colostrum production, maternal behaviour and gestation length. A hypothesis 'That short-term supplementation of multiple-bearing ewes late in pregnancy will improve responses associated with lamb survival' was developed. Supplementing prolific ewes with lupin grain for the final 10 days of pregnancy has previously significantly increased lamb survival rates (Chapter 2). Experiments were designed to test the hypothesis. Treatments included supplements of different grains, nitrogen or rumen undegradable protein and direct infusions of glucose. Responses measured included production traits associated with lamb survival, glucose, urea and fatty acid production rates, some hormone concentrations, voluntary feed intake and mobilisation of maternal reserves. The variation in responses was compared at various litter sizes. Treatments were selected so that results could be modified and then applied directly to grazing sheep in southern Australia. In the first experiment (Chapter 3) a lupin grain supplement fed to Booroola (prolific) ewes in the final 17 days of pregnancy reduced condition score losses compared to no supplement or an oat grain supplement. -Live weight gains were highest with the lupin supplement and with no supplement. There was a trend for milk production at day two post-partum to be higher with the lupin supplement. Some of the multiple-born lambs died because of low colostrum intake, as indicated by low serum immunoglobulin concentrations. The possible importance of colostrum and initial milk production was demonstrated. Colostrum production and milk production on day one and nine were similar from single and multiple-bearing ewes fed a ration containing 100 g protein/10 MJ metabolizable energy and this ration supplemented with formaldehyde-protected casein or urea (Chapter 4). The ration was fed at 90% of the average estimated requirements of all ewes in the final five weeks of pregnancy. Gestation length was two days shorter with the casein supplemented diet which resulted in twin-born lambs from this diet being about 14% lighter than lambs born to ewes fed the basal ration. Glucose production on day 121 was 32% higher with multiple than single-bearing ewes even though intakes were comparable. Many ewes had low voluntary intakes on the grain/roughage ration and this resulted in large energy deficits. On a roughage/ oat grain ration fed for the final seven weeks of gestation, single and multiple-bearing ewes had consistently low and equivalent intakes (Chapter 5). Nonesterified fatty acid production rates on day 115 and 136 averaged 65 % higher for multiple than single-bearing ewes and rates were similar on both days. Glucose production increased by 32 % between these days and was 17 % greater for multiple than single-bearing ewes. The correlation coefficient of fatty acid and glucose production rates was about 0.7 on both days of measurement. The provision of a large glucose source late in pregnancy may be beneficial to multiple-bearing ewes when their voluntary intake potential seems low. Multiple-bearing ewes were infused at the abomasum from day 119 to 145 of gestation with nil, 106 or 207 g glucose /day (Chapter 6). The glucose was estimated to provide an additional 20 or 40 % energy compared to the basal ration of lucerne chaff. The ewes which were infused with glucose gained more weight during the treatment period (90, 159 and 267 g/d for basal, +20% and +40% energy respectively). Litter weight, colostrum yield and early milk production were insensitive to additional energy, as glucose, in the last 30 days of pregnancy in the circumstances where ewes were in low condition and fed a restricted roughage ration containing a high percentage of protein. The insensitivity seemed to lie with increased insulin levels leading to peripheral tissue accretion. Again high variation occurred in colostrum yields, although amounts were higher than in previous experiments. There were significant positive correlations between litter weight and both progesterone and plasma ovine placental lactogen levels in late pregnancy. Colostrum production was negatively correlated to progesterone concentrations measured in late pregnancy. Intake declined close to parturition even with the glucose infused ewes. When ewes were fed a medium quality roughage ad libitum, a lupin supplement in the final 10 days of pregnancy increased colostrum yield by 37% and milk production on day 1 by 28% when averaged over all ewes (Chapter 9). The largest response occurred with the triplet-bearing ewes, which had much lower production than single and twin-bearing ewes. Lambs born to lupin supplemented ewes had faster growth rates to day 1 and 3 post-partum. Benefits occurred either through additional substrates and /or by changing hormonal status, specifically progesterone. Colostrum levels at birth and total milk production to 24 hours were significantly improved when multiple-bearing ewes were supplied with supplements of glucose, lupin grain or undegradable rumen protein in the final 10 days of pregnancy. The basal ration was a medium quality roughage fed at a restricted level. The results provided strong evidence that additional protein which escapes rumen degradation will increase colostrum production near birth and advance the timing of copious milk production. The colostrum and milk yields were negatively correlated to progesterone concentrations near parturition. Prolactin and ovine placental lactogen concentrations measured before and after parturition were poorly correlated with the lactation results. Triplet bearing ewes had lower milk production than twin bearing ewes. There were no effects of the treatments on birth weight, but large effects on ewe live weight change and gestation length. The mechanisms could be due to extra fat mobilisation in late pregnancy with additional protein supplies, changes in hormone status, or possibly the supply of extra amino acids compared to the non-protein treatments. Variability in the colostrum and milk responses on the glucose treatment made it unclear what the role of glucose was for colostrum production. Milk production of multiple-bearing ewes is likely to be below that required by their litter in a cold and wet environment in the first 24 hours when the ewes are fed a medium quality roughage diet (Chapters 7 and 10). Lambs had a potential colostrum intake in the first two hours of an average 110 g and 230 g/kg birth weight during the first day (Chapter 8). This amount was usually above that available to all lambs in the litter from the dam. The potential intake was also above that required in most environments. Limited variation in intake between lambs within a litter may be crucial to survival of the complete litter. It is proposed that protein has a specific effect on the endocrinology of the ewe in late pregnancy. Thus a possible hypothesis consistent with these data is that increased amino acid supply at the tissue level results in a faster clearance of progesterone allowing lactogenic hormones and hormones involved with the initiation of parturition to act. These experiments have thus demonstrated that short-term supplementation of ewes can influence some traits associated with lamb survival, including colostrum production at birth and milk production during the following 24 hours. Multiplebearing ewes will often have lower amounts of colostrum and early milk production than single bearing ewes. Supplementing ewes on medium quality protein/energy pastures with feed sources which provide a high protein yield at the small intestine should increase the initial lactation output and possibly survival rates of multiple-born lambs.
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    Placental size and foetal growth in relation to maternal undernutrition during mid-pregnancy in sheep
    McCrabb, Graeme Jeffrey ( 1989)
    Examination of the evidence published in the literature revealed a variety of responses in birth weight of the lamb to maternal undernutrition during mid pregnancy. Explanations of the various responses are commonly made in terms of what has been named, in this thesis, as the Size Hypothesis. This hypothesis states that placental size is limiting the transfer of nutrients across the placenta during late pregnancy, and therefore determining foetal growth. The two main assumptions of this hypothesis are that (i) placental size is an index of its maximum functional capacity, and.(ii) the placenta is functioning at its maximum capacity during late pregnancy. In this thesis the validity of both of these assumptions is questioned, and, an alternative hypothesis proposed. Chapter One reviews the factors which are involved in the movement of metabolic substrate from the dam, across the placental barrier and to the site(s) of deposition in the foetus. From the limited amount of information available in the literature, it is apparent that placental size is not necessarily an accurate indicator of the maximum functional capacity of the placenta. Therefore the Size Hypothesis cannot be functionally correct. Consideration of the evidence used to support the Size Hypothesis questioned the causal relationship between placental size, and growth of the foetus during late pregnancy. Consequently experiments were designed to: (i)investigate the effect of maternal undernutrition during mid pregnancy on placental size. (ii)determine the functional relationship between placental size and foetal growth. Maternal undernutrition during mid pregnancy was chosen as the means of manipulation of placental size because of its direct relevance to the extensive grazing system of sheep management in Southern Australia. In the first experiment (Chapter Two) maternal undernutrition imposed between 75 and 100 days post coitus tended (P=0.08) to reduce both placental size, measured at 100 days post coitus, and weight of the lamb at birth. The relationship between placental size and growth of the foetus remained unresolved. Therefore a second experiment was designed. In this experiment (Chapter Three) single bearing pregnant ewes were exposed to undernutrition during one of three periods during mid pregnancy; 30 to 96 days (Group RA), 50 to 96 days (Group RB) and 75 to 96 days (Group RC) post coitus. Placental growth was retarded in ewes exposed to maternal undernutrition between 30 and 96 days post coitus, while the shorter periods of undernutrition had no significant effect on placental growth. Despite a smaller maximum placental size being achieved for group RA compared to control (well fed) ewes, and all ewes being fed on a high plane of nutrition during late pregnancy, foetal growth during late pregnancy was not significantly different between group RA and control (well fed) This evidence supports the hypothesis that placental size per se is not the prime determinant of foetal growth. The effect of altering placental size, by maternal undernutrition between the time of conception and 70 days post coitus (Chapter Four), or the number of foetuses sharing one uterus (Chapter Four, Chapter Five), on birth weight of the lamb was investigated. One experiment in Chapter Four (Experiment One) twin lambs at birth were not significantly lighter in weight, despite being associated with a smaller placenta, when compared to the single lambs. This is further evidence to suggest that placental size per se was not limiting growth of the foetus during late pregnancy. The final two experimental chapters in this thesis quantify the relationship between placental size and some functional aspects of the placenta. Placental size was not closely related to either the volume of blood in the placenta (Chapter Six), or the rate of movement of calcium (Chapter Seven) across the placenta. All experiments discuss the possible sites of limitation, or regulation, to the movement of nutrients to the foetus. These include the regulation of the intake of feed, the digestion, metabolism and partition of the metabolic substrates in the dam as they influence growth of the foetus. The experiments in this thesis demonstrated that growth of the placenta can be improved, retarded or remain unaffected by maternal undernutrition being imposed at various times during the first 100 days post coitus. Explanation of the potential effect which nutritional stress has in altering placental growth, is often made in terms of the degree to which the mobilization of maternal body reserves may buffer the conceptus from any nutrient limitation on growth of the foetus. In contrast to this, the experiment described in Chapter Seven reported that growth of the placenta, in ewes fed at a restricted level of nutrition, was greater when compared with their control (well fed) counterparts. The factors causing this stimulation in placenta growth are yet to be identified. Regression analysis of data from all experiments revealed that both placental size near parturition (P<0.001), and the change in liveweight during the period of nutritional restriction (P=0.06), were related to weight of the foetus near parturition. Conversely the liveweight and/or condition score of the dam at the time of joining was not related to placental size or foetal weight near parturition. This observation suggested that the level of body reserves at the time of joining does not significantly modify the effect which maternal undernutrition has. on placental and foetal growth. Maternal undernutrition during the first 100 days post coitus had little or no effect on growth of the foetus, measured at the end of the restriction period, despite a significant depletion in the body reserves of the dam. In addition, the large differences in the patterns of placental growth caused by maternal feed restriction were not reflected in weight of the lamb at birth. Differences in voluntary food intake and the level of body reserves available for mobilization/deposition, between the previously restricted and control (well fed) ewes, were not reflected in the whole-body metabolism of either glucose or calcium (Chapter Seven). Therefore the Size Hypothesis was not confirmed by the observations made in this thesis. Evidence used to support the Size Hypothesis includes the observation that the rate of foetal growth during late pregnancy does not continue to increase at an increasing rate, even when the ewe is well fed during late pregnancy. It has been proposed by other workers (e.g. Mellor, 1983) that this indicates that the functional capacity of the placenta is limiting foetal growth. The experiment reported in Chapter Three demonstrated that, despite a retardation in placental size of as much as 23 percent by 96 days post coitus, growth of the foetus during the final 12 days of pregnancy was similar for both the control (well fed) and previously under fed (restricted) ewes. It was therefore concluded that placental size per se cannot be limiting foetal growth during late pregnancy. In another experiment (Chapter Seven) maternal undernutrition during mid pregnancy resulted in an increase in placental growth of 21 percent, despite the ewes being severely under fed between 30 and 96 days post coitus. The rate of transport of calcium across the placenta, and its lack of any relationship to placental size, indicated that placental size was not an appropriate indicator of its movement. In contrast to the prediction of the Size Hypothesis, foetal growth during late pregnancy was not improved despite the ewes being fed on a high plane of nutrition during the period between 96 days post coitus and the time of parturition. The circumstances in which a relationship between "size" and "function" were strong, and those in which no close relationship existed, were examined in an attempt to define the physiological conditions regulating foetal growth. An alternative hypothesis, termed the Functional Reserve Hypothesis was proposed. It aims to incorporate all available observations made in the experimental work reported in this thesis, and from the relevant literature reported elsewhere. The concept central to Functional Reserve Hypothesis is that the ovine placenta is not in a state of functional saturation during late pregnancy, and hence does not act as a limitation to growth of the foetus. In addition, the Functional Reserve Hypothesis proposes that placental size is not an accurate indicator of the capacity of the placenta to transfer nutrients. It is hypothesized that the ovine placenta has same level of functional reserve, even in the situations where it is retarded in its growth. Additionally it is proposed that factors regulating both (i) the partition and supply of nutrients from the dam, and (ii) the potential for growth, and the demand for nutrients by the foetus, all interact to regulate the rate of' foetal growth during late pregnancy and therefore ultimately the birth weight of the lamb. Before successful manipulation of foetal growth during late pregnancy is possible, the key metabolic substrates, and the factors regulating their movement to the foetus, need to be identified. Finally, how the above results contribute to the development of strategic feeding recommendations for the Australian sheep flock are discussed. Two specific areas for further research are identified.
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    Pasture utilization for wool growth of weaner sheep in south western Victoria
    Saul, Geoffrey R (1951-) ( 1988)
    Two series of experiments are described in this thesis. The first set of experiments report on the use of young, oesophageally fistulated sheep to collect herbage samples in grazing experiments. Secondly, the biological responses of Merino and Comeback weaner sheep to changes in pasture type and season of birth are described. The experiments were conducted at the Pastoral Research Institute, Hamilton, Victoria during 1982-86, where the author is employed as a Science Officer by the Victorian Department of Agriculture and Rural Affairs. Chapters 4 and 5 report the effects of several variables on the chemical composition of oesophageal fistula samples and have been submitted for publication (see below). Mr. P.C. Flinn and Professor A.R. Egan have been included as co-authors of Chapter 4 due to their contribution to chemical analysis of samples, and to planning of the experiment respectively. Mr. P.C. Flinn and Mr. J.F. Heard have been included as co-authors due to their assistance during the experiment described in Chapter 5. Differences between the growth, composition and nutritive value of lucerne/subterranean clover and perennial ryegrass/subterranean clover pastures are reported in Chapter 6. (More detailed data on the growth and composition of the pastures is available on request to the author). The effects of these pastures on the productivity of autumn and spring born, Merino and Comeback weaner sheep are presented in Chapters 7 and 8. It. is intended to submit these three chapters for publication. Mr. R.L. Thompson and Dr. J.M. Obst will be. included as co-authors when the results reported in Chapter 7 are published. The experiments reported in this thesis make up part of a larger project (Sheep Production Systems) for which Mr. Thompson and Dr. Obst are responsible. However I accept full responsibility for the collection of all data, analysis of results and preparation of the manuscripts. In addition, I was responsible for the design of experiments reported in Chapters 4, 5, 6 and 8. Details of publications are as follows:- Chapter 4 : Saul, G.R., Flinn, P.C. and Egan, A.R. (1988). The effect of fasting, breed and sample size on the chemical composition of pasture samples from fistulated weaned lambs (submitted to Australian Journal of Experimental Agriculture). Chapter 5 : Saul, G.R., Flinn, P.C. and Heard, J.F. (1986). The nutritive value of roughages before and after mastication by oesophageally fistulated sheep. Proceedings Australian Society of Animal Production 16, 351-54.
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    Intake and digestion of cereal straws by sheep
    Djajanegera, Andi ( 1986)
    This thesis reports on a series of experiments which examined the utilization of cereal straws by sheep. Cereal straws are considered low quality feeds as their intake and digestibility are low. The intake and digestibility of cereal Straws can be influenced by many characteristics of the straws themselves, by genotype/species of animal consuming the straw and by the physiological state of these animals. The effects of these factors on straw utilization are reviewed in Chapter 1. It is apparent that the intake and digestibility of straws can be increased by various pretreatments or by supplementation. The experiments conducted were intended to provide new and useful information on the effects of calcium hydroxide [Ca(OH)2] or urea pretreatments on the intake and digestion of cereal straws by sheep. The objectives of the first study were to investigate the effects of Ca(OH)2 treatment of a wheat straw on : (i) its intake and digestibility in sheep and the effect of restricting the intake of the treated material on its digestibility (Chapter 2) (ii) the effects of high calcium levels in the treated straw on the utilization of other macro-minerals (Chapter 2) and (iii) the effects of this treatment on digestive processes within the reticulo-rumen (ReRu) and on the sites of fibre digestion (Chapter 3). Pretreatment of the straw with Ca(OH)2 increased organic matter intake (WI) (685 vs 398 g/day) and digestibility (OMD) (62 vs 54%) resulting in an increase in digestible organic matter intake (DOMI) of 98%. Restricting the intake of the treated straw, which was intended to increase retention time in the ReRu, resulted in only small ( 2% units) increases in OM or neutral detergent fibre (NDF) digestibility. Although the treated straw diet contained high levels of calcium (21 g/kg DM), most of this was excreted in faeces and there were no adverse effects on phosphorus or sulphur balance. As the experiment was of 49 days duration and the ad libitum intake of the treated straw diet was maintained throughout this period, it was apparent that no serious mineral imbalances were imposed. Further, the sheep consuming the Ca(OH)2-treated straw diet lost less weight (40 vs 140 g/day) than the control animals. As regards the measurements of the amount and composition of digesta in the ReRu and the rates of digestion and passage from that organ, there was large variability between sheep within treatments. Consequently, comparisons of the dietary treatment effects were not significant due to the small number of animals used and the fact that these treatments were imposed on different animals. However, there were significant positive relationships between dry matter intake (DMI) and DM load in the ReRu and between DMI and DM flow through the abomasum. The apparent mean retention times (MELT) of DM in the ReRu for the treated straw diet fed at near ad libitum intake was 22 h and this tended to be less than that of 27 h in sheep given the untreated straw. There was also a tendency for increased fractional digestion and passage rates of the NDF of the alkali-treated compared to untreated straw. Hence, the increase in intake of the Ca(OH)2-treated straw was associated with apparent increases in ReRu DM load (40% increase) , and with non-significant increases in fractional digestion (110% increase) and passage (40% increase) rates. The amount of non-ammonia-nitrogen (NAN) apparently digested in the intestines was greater (4.8 vs 2.9 g/day) for the treated compared to untreated straw, but there were no differences when considered as the amount of crude protein apparently digested (DCPi) per 100 g DWI (7.8 vs 9.1 g DCPi/100 g DOMI). Urea pretreatment, which involves spraying straws with a urea solution followed by a period of air-tight storage, is known to increase the intake and digestibility of these feeds. However, the extent to which these improvements are due to the effects of the added nitrogen or to an alkali effect per se are not clear. An experiment was carried out in two periods in which a rice straw was fed to sheep untreated or treated with urea. In the first period both diets were supplemented with urea and sodium sulphate, while these supplements were not given in the second period. The effects of pretreatment and/or supplementation on straw intake and digestibility are reported in Chapter 4, while the processes of digestion in the ReRu and the sites at which digestion occurred in sheep given the two supplemented diets are presented in Chapter 5. Urea and sulphate supplementation of the untreated rice straw increased OMI (803 vs 576 g/day) and (MD (54 vs 48%). While the intake of urea-treated straw, which was airdried prior to feeding, was similar to that of urea-supplemented-untreated straw (779 vs 803 g/day), the OND (61 vs 54%) and NDF digestibility (60 vs 49%) were increased. The nitrogen intake on these two diets was similar and the increase in digestibility was presumably due to an alkali effect during storage. Supplementation of the treated straw with urea and sulphate further increased intake to 932 g OM/day, but had no additional effect on digestibility. Thus, while urea supplementation reduced the rate of liveweight loss of sheep from 138 to 20 g/day, sheep fed the treated and supplemented straw maintained weight (+ 38 g/day). For this particular straw, it is concluded that 50% of the improvement in nutritive value gained by pretreatment was due to the additional nitrogen added. These results are discussed in relation to the likely effects of treating or supplementing straws of higher or lower nutritive value than the one used in the present work. There were no differences in the quantity or composition of digesta in the ReRu of sheep fed untreated straw supplemented with urea and sulphate or urea-treated straw given with similar supplements (Chapter 5). The MRT of DM in the ReRu was less (18 vs 21 h) in sheep given the treated rice straw. In addition, treatment increased fractional digestion rate (3.4 vs 1.9 %/h), but did not affect fractional passage rate (2.7 vs 2.9 %/h) of NDF. While the higher intake of the treated and supplemented straw was associated with increased amounts of NAN reaching (17.6 vs 12.6 g/day) the small intestines, there were no differences in the amounts of NAN apparently digested in the intestines (9.3 vs 8.0 g/day or 9.8 vs 11.2 g DCPi/100 d DCtII). These results are discussed in relation to current theories on the regulation of intake in sheep. In the final experiment (Chapter 6), the effect of body condition of sheep on the intake and digestion of the urea-treated rice straw used in the previous experiments was examined. The sheep used were those involved in previous experiments and they were allocated to two groups. Prior to the experiment, one group was fed a forage (grass hay + urea-treated rice straw in the proportion 0.75 : 0.25) and lupin grain diet (0.84 forage : 0.16 grain, DM basis) ad libitum, while the other group was given the same diet at a restricted level. At the commencement of the experiment the sheep weighed 57.7 versus 42.6 kg fleece-free liveweight and had 15.8 versus 9.7 kg total body fat. At this point the sheep in both groups wire offered the treated straw ad libitum and were given infusions of urea and sodium sulphate into the rumen. Feed intake was measured continously for 51 days, while the quantity and composition of digesta in the ReRu and flowing through the abomasum were measured on four occasions (about days 10, 18, 32 and 50). The thin sheep consumed consistently more (1170 vs 1040 g/day) feed throughout the experiment, but there were no differences in digestibility. Associated with the increased intake were larger ReRu fills (8.59 vs 7.67 kg) and DM loads (1040 vs 960 g) in the thin animals. However, the fractional digestion (3.3 vs 3.4 %/h) and passage (2.0 vs 2.0 %/h) rates of NDF were not different in the two groups of sheep. These results are discussed in relation to the likely effects of body condition on the intake of less digestible straws where nutrient limitations might exist. In the concluding chapter (Chapter 7) the implications of these findings are discussed in relation to other information on the utilization of cereal straws.
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    Flystrike in sheep : producers' knowledge, opinions, and management methods
    Lottkowitz, S. N ( 1986)
    Blowfly strike was recorded as a serious problem of Australian sheep during the first decade this century, and has remained a problem ever since. The cost of control was estimated at $44 million in 1975-76, and rising each year (Brideoake 1979). Much of the present knowledge of blowfly biology and strike aetiology was gained in the 1920's and '30's, and by the end of the 1940's simple, cheap and effective procedures were recommended which reduced flystrike by about 90 per cent. In the early 1970's, flystrike still caused major problems. The pest species had not changed, and the original recommendations had not been universally adopted (Graham 1979). This two stage survey assessed awareness of flystrike management among sheep producers, identified some commonly used communication channels for strike control information, and identified and assessed the importance of some socio-psychological and communication factors inhibiting access to or use of strike control information. Communication strategies were suggested for overcoming ineffective use of strike control information. Producers had poor knowledge of theoretical aspects of strike aetiology and the blowfly life cycle, but were well aware of readily observable aspects. Thirty percent of producers used three-joint tails, and the remainder used sub-optimal lengths. The advantages of using three-joint tails were not obvious to producers using other tail lengths, or manifested in practice. There was no association between three-joint tails and expressions of easier or more flexible management, or indications that flystrike was less important in management decisions. Low awareness, and poor capitalisation of the established advantages of three-joint tails probably are barriers which impede extension efforts. Evidence suggested that managers of flocks smaller than 1500 (more than 60 per cent of Australian enterprises) did not aim to maximise net flock revenue. This would be an important and profound barrier to current. extension practice. Mulesing was much more common among larger flocks, and was paradoxically used as an adjunct of other preventative management. Consequently, the majority of Australian flocks were relatively unprepared for strike control, and mulesed flocks were disproportionately well prepared. Producers' assessment of information and its sources varied according to the type of information sought. Popular sources for tail length, mulesing and jetting equipment information included the Department of Agriculture. There is an opportunity for state extension services to work together with other identified sources to stimulate the process of information transfer, and to improve producers' understanding of the practical advantages of strike management recommendations.