School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemAcute prenatal androgen treatment in sheep( 1994)The steroid environment of the cell nucleus in differentiating mammals is a major determinant of subsequent cellular function. The exogenous manipulation of this environment has resulted in permanent changes in metabolism, behaviour, reproduction, endocrinology and growth. The experiments described in this thesis suggest that an acute exposure to exogenous androgen, established as an intramuscular depot in the gravid ewe, can effect these changes. The growth responses resulting from acute prenatal androgen treatment (APAT) are similar to those reported for chronic androgenization.The undesirable side effects of androgenization, e.g. reduced birthweight, deformed external female genitalia and masculine urination posture, can be avoided with APAT. The literature and the experimental data indicate that mammalian development is strongly influenced by tissue steroid status. Furthermore, the literature and the experimental data suggest that both the timing and duration of the modification of mammalian developmental steroid status (MDSS) affect the response of ovine tissues to androgens. Some of the observed responses appear refractory in nature. The periods of sensitivity to MDSS manipulation differ between tissues and between species. MDSS manipulation via APAT is capable of effecting changes to tissues not normally considered sexually dimorphic, including the ovine pancreas, liver, brain, kidney, bone and wool follicle.
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ItemCytogenetic sex determination of embryos( 1990)The purpose of the research presented in this thesis was to establish a rapid method to allow the cytogenetic determination of sex in sheep embryos. A simplified air-drying technique to allow cytogenetic sex determination initially established in mouse embryos. These techniques were then applied to sheep embryos. The techniques involved treating embryos with three types of fixatives :- fixing solution, softening solution and drying solution. Methanol : glacial acetic acid
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ItemIntake and utilization of a barley supplement treated with virginiamycin by gestating and lactating ewes( 1991)A pen feeding study was conducted to evaluate the influence of virginiamycin (40 g virginiamycin/tonne barley ) on the production of pregnant and lactating ewes fed barley supplement. Twelve single and sixteen twin-bearing ewes were randomly allocated to one . of 3 groups to receive either lupins, barley or barley plus virginiamycin (BVM), fed for 3 weeks before and 3 weeks after lambing. During late pregnancy, feed intakes in ewes carrying twins were not altered by treatments. Mean liveweights at parturition of the barley-supplemented 'ewes. were below than those of the other groups (p=0.14). Feed conversion efficiency was significantly improved (p=0.05) in the lupin and BVM groups as compared to the barley supplemented ewes. The condition score of the ewes was not improved by supplementation and type of supplement had no effects on body condition score loss. Mean retention time of Cr-hay in the GI tract was increased (p<0.05) by supplementation with virginiamycin treated grain. However the dry matter digestibility on the BVM diet was not improved (p<0.05) as compared to the lupin supplemented ewes. The performance of ewes carrying singles was generally unaffected by treatment (p>0.1). The. exception occurred during lactation, where the barley-supplemented ewes lost more weight than the other groups (p<0.05). Differences in the mean birth weight of twin lambs were significant (p=0.05) while those of lambs born as singles was not significant. Twin lambs from ewes fed barley showed significantly higher mortality (p<0.01) than lambs born to ewes in lupin and BVM groups. However , no single born lambs in any group died from birth to 42 days of age. No significant differences were found between total milk yields of ewes nursing either twin or single lambs. The yield of milk fat from ewes nursing twins in lupin group was significantly higher (p<0.05) at day 20 of lactation than the other groups. The results suggest that lupin grain was not superior to barley grain plus virginiamycin as a supplement for gestating and lactating ewes carrying twin lambs fed hay as a basal diet. However, on the basis of cost, barley plus virginiamycin would generally be prefered.
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ItemThe nutrition of multiple-bearing ewes in late pregnancy( 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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ItemPlacental size and foetal growth in relation to maternal undernutrition during mid-pregnancy in sheep( 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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