School of Agriculture, Food and Ecosystem Sciences - Theses
Permanent URI for this collection
Search Results
1 - 10 of 31
-
ItemDietary strategies to adapt to, and mitigate, climate change in sheep( 2023-04)Climate change and associated global warming are major menaces to the Australian sheep industry. In addition to being susceptible to the harmful effects of climate change, sheep actively contribute to it through the release of methane (CH4) into the atmosphere. The aim of this thesis was to test and identify suitable feed additives that can reduce enteric CH4 emission and improve the thermoregulatory responses, rumen and digestive functions that were impaired by heat stress in sheep. In the first experiment, sheep were exposed to 3 different durations of heat stress (1 day, 3 days and 5 days; 28 to 38oC and 40 to 60% relative humidity; RH) with thermoneutral being the control (18 to 21oC and 45 to 55% RH) and observed variations in the rumen fermentation profile and rumen microbiota. The following two studies had three different groups of sheep based on the diet; wheat based diet (WD), Bioprotect treated wheat based diet (BD) and maize based diet (MD). Sheep experienced 3 consecutive periods of varying temperature and feeding levels. Period 1 (P1) consisted of 1.7xmaintenance energy (MF) feeding level and thermoneutral conditions (18 to 21oC and 40 to 50% RH). During period 2 (P2) sheep were fed at 1.7xMF level and were exposed to heat stress (28 to 40oC and 30 to 50% RH). During period 3 (P3) sheep were held under heat stress and fed at 2.0xMF level. In the fourth experiment, sheep were supplemented with two different dosages of a sugarcane derived polyphenol (0.25PG and 1PG) and tested for their enteric CH4 mitigation potential and production responses. To explain differences in the enteric CH4 production and ascertain the influence of Polygain on rumen microbiota 16s rRNA sequencing was also explored. The final experiment reported in this thesis studied the effect of an essential oil mix, Agolin, on enteric CH4 reduction and production variables in growing lambs. Results from this thesis demonstrated that short duration heat waves particularly, 3 and 5 days of heat stress, can significantly reduce total and individual rumen volatile fatty acid (VFA) concentrations and alter the VFA profile and rumen microbial diversity indices and richness of certain microbes of second cross lambs. Treating wheat with Bioprotect can partially alleviate the effects of heat stress on the thermoregulatory responses of sheep. As Bioprotect works as a rumen bypass feed by promoting the digestion of starch and protein in the small intestine, animals experience less metabolic heat from rumen fermentation. This enables the sheep to have better body temperature control. Bioprotect can also reduce enteric CH4 from sheep without hampering diet digestibility and dry matter intake (DMI). Polygain feeding reduced CH4 emissions without compromising average daily gain (ADG) or DMI. The highest CH4 reduction (49% reduction). was achieved from the lowest dosage of Polygain (0.25% PG) used in the study. Agolin was also successful in reducing CH4 emissions from sheep. Sheep fed Agolin showed a 27% reduction in CH4 without reducing DMI or ADG. The findings from the work reported in this thesis are novel as most of the work covered in the thesis is pioneering research in the sheep industry. However, it is important to conduct follow up research over longer durations and with larger sample sizes for policymaking if these feeding strategies are to be adopted.
-
Item
-
Item
-
ItemChoosing sheep for lifetime profitability( 2004)This project investigated the selection of wool sheep for lifetime profitability by measuring the lifetime productive phenotypes of breeding ewes, their lambs and the rams to which the ewes were mated, on a commercial farm in East Gippsland. The measurements were recorded from 1992 to 2002. The seasons varied during this time, including a severe drought from 1996 to 1998. The results clearly demonstrate that the environment, its resources and demands, limit the full phenotypic expression of the genotype of the sheep. This expression varies over the lifetime of the animal. The results identify the sheep that were most suited to their environment. Phenotype interaction: It was found that enhancement of any single profitable phenotypic character resulted in changes to all other profitable phenotypic characters, usually in a negative direction. These phenotypic interactions frequently show curvilinearity and nonlinear relationships, demonstrating that to select on a linear model is frequently not appropriate for profit indicators or biological reality. Measurement of ewe body weight and the weight gain ratio of lambs A method is described for measuring the yearly and lifetime body weights of sheep from which the changing wool weights and weight due to pregnancy were removed. Birth weight, wool weight and weight gain of the suckling lamb were then expressed as a percentage of the body weight of the ewe. This resulted in a clearer understanding of how the ewe allocates metabolic resources. It also demonstrated that too high a bodyweight was itself an excessive user of resources. When the average daily weight gain of the lamb from birth to weaning was expressed as a percentage of the weight of the mother the results provided an early prediction of lifetime profitability of the lamb and indirectly of the mother. This percentage had a strong positive relation to the birth weight, weaning weight, greasy fleece weight of the lamb and to the survival rate of the progeny and the test ewes during the drought. However prediction of the fibre diameter required an independent measurement. Measuring the value of a sheep's wool: A method is described for assessing the value of wool. This eliminates the influence of monetary inflation and helps the farmer make a more accurate judgement of the wool value in the selection of his sheep. Auction prices from all districts of Victoria based on the 1987-1997 auction prices of wool were converted into a Price fibre-diameter ratio. This ratio was used to determine a commercial wool value (Ewe wool score) for each test ewe. For each of the test ewe's male and female progeny, the same ratio was used to obtain a wool score (up to two years of age). These progeny values of all her lambs were added to provide a Progeny wool score for each test ewe. A Combined wool score combined both the ewe's own woolscore and the woolscore of her progeny. The top ten test ewes were identified for each category then compared to the subjective assessments of a sheep classer, the farm manager and the wool classer. Sheep that had high Combined wool scores and were therefore the most profitable over two generations had different phenotypes from those with high individual wool scores. It should be noted that while wethers might be chosen for wool score only, ewes should be chosen for wool score and the ability to produce profitable progeny. This thesis has highlighted the fact that selection for lifetime profitability will differ for ewes and for wethers. Using the Statistica 4.1 (1994) for McIntosh program stepwise multiple regressions were carried out on the test ewes for Ewe wool score, Progeny wool score and Combined wool score. The factors with significant influence (p-level < .05) on each of the three wool scores were identified. For the Ewe wool score, the factors in order of importance are, average fibre diameter (negative), greasy fleece weight, average visual assessment of the fleece and lambs alive December 1996 (negative). Those four factors "explain" 42% of the sums of squares in the Ewe wool score. For the Progeny wool score, the factors in order of importance are, lambs alive in December 1996, which was the end of the recording of the test ewes, and the average fibre diameter (negative). These two factors "explain" 64% of sums of squares in the Progeny wool score. In the Combined wool score, the factors in order of importance are, lambs alive in December 1996, average fibre diameter 1992-6 (negative) and average greasy fleece weight 1992-6 (negative). These three factors "explain" 60% of the sums of squares in the Combined wool score. The negative partial regression for fibre diameter is explained by the position of the average fibre diameter on the Price-fibre diameter curve (finer fibres bring higher prices). The negative partial regression of the Combined wool score on greasy fleece weight suggests that there is competition between resources required for producing wool and for successful reproduction. Heritability estimates: Heritability estimates were calculated from intra-sire regressions of progeny on dams. This was done for body weight, greasy fleece weight, fibre diameter and the visual assessment of the fleece at specific ages over the years for which paired data for the test ewes and their progeny were available. Such estimates were available for hoggets and 2,3,4 and five-year olds of both the dams and progeny, with a varying numbers of pairs at different ages. The results varied between ages and between the sexes of the progeny. There were more data available (pairs of dams and progeny) from the middle age-years. 'When the male and female progeny were considered together, the corrected body weight in years two and four gave highly significant results of 0.45 and 0.44 respectively. Year three had significant results of 0.27. Years one and five were not significantly different from zero. Fibre diameter had highly significant results of 0.89 in year one and significant results of 0.28 in year two and 0.32 in year three. Years four and five were not significant. Greasy fleece weight had significant results of 0.70 in year one. Other years were less than 0.30 and were not significant. Fleece visual assessment had highly significant results of 0.35 in year three; the other years were not significant. One wool classer classified all the fleeces subjectively at shearing over an eight-year period giving a yearly visual score to each fleece. He was unaware of the identity of the fleeces. The results showed a high degree of consistency. The above results shows that visual scores can be heritable. Fibre diameter, greasy fleece weight and their interaction: Fibre diameter was examined for lifetime variation in individual sheep and groups of sheep selected on micron. Lifetime group measurement of fibre diameter was highly predictable. This allows a fanner to get a reasonable lifetime group fibre diameter result from one year of measurement. Lifetime measurements of fibre diameter for individuals were less predictable. Fibre diameter was also examined for the effect of resources and their availability, heritability, ageing, lambing and lactation, and the health of the sheep. The two-generation realized heritability of fibre diameter for the test ewes in 1995 and the one-year old progeny in 1993 to 1995 was 0.50. Greasy fleece weight was examined for lifetime variation, in individual and group measurements, for the effect of the availability of resources, the variations of ageing and the health of the sheep. Greasy fleece weight had lower heritability estimates at hogget age than did fibre diameter. Group measurements of greasy fleece weights had more lifetime variation than did fibre diameter. Therefore a single greasy fleece group measurement would not be as reliable an indicator for lifetime results as a single measure of fibre diameter. Using 1992-6 average values, the fleeces of the Tubbut flock were examined for the relationship of the fibre diameters to greasy fleece weights, from the finest to the broadest fibre diameters. This relationship was not linear. From 25-21 microns the decrease of the greasy fleece weight for each decrease of one micron was 5.7%, from 21-18 microns the result was 9.6 %, from 17-16 microns the result was 11.4%. The limitation of the environment: The data presented in this thesis clearly demonstrate, that with limited resources available from an environment, there is an overriding and fundamental response within animals to allocate those resources to maximize their survival and that of their progeny. Any artificial selection must be carried out with the knowledge, that over time, the animals will attempt to return to the allocation of resources that maintains the best chance of survival for themselves and their progeny. Within this thesis there are many examples where, if sheep had been artificially selected for one character this would have altered all or most of the other characters usually in a negative direction. It has been shown that high artificial selection tends to have that selection reduced in value over the animal's lifetime. Important principles: Results in this thesis highlight that in selecting for lifetime profitability breeders should note that 1) The environment, its resources and demands, limit the full expression of the genotype of the sheep. The effect varies over the lifetime of the animal. 2) In the selection of animals for particular traits, due regard must be given to the effects that the selection will have on the whole of the phenotype. 3) Increased profitability resulting from the selection of one trait may result in the overall loss of profitability from the decrease in other profitable traits. 4) Where research is carried out on one particular trait to either enhance or decrease that trait, the research needs to demonstrate the effect of that selection on the whole animal over its lifetime. 5) Sheep need to be selected for an increase in lifetime profitability in their own commercial environment. Taking note of these principles will ensure true progress is made in phenotypes and genotypes suitable for any particular environment. It will also produce greater profits for Australian farmers.
-
ItemAttributes of pasture influencing the diet of grazing sheep( 2002)This thesis investigated how the composition, productivity and nutritive quality of Phalaris aquatica L. (phalaris) and Trifoliun: subterranean L. (subterranean clover) pasture affected diet selection and intake by sheep in temperate Australia. Field experiments were conducted at the Ginninderra Experiment Station, Canberra, (35 17' S, 149 08' E) and glasshouse experiments at the CSIRO Division of Plant Industry, Black Mountain Laboratories, Canberra, Australia. The effects of different defoliation treatments on the ability of grass and subterranean clover to compete for light were studied in a glasshouse experiment. Regular patterns of phalaris and subterranean clover were planted on a 25 mm grid to create swards with 0% clover, 25% clover, 50% clover, 75% clover and 100% clover by plant number. Swards were either defoliated regularly by clipping to 2, 4, 9 or 15 cm tall or not defoliated and harvested when they reached 2, 4, 9 or 15 cm tall. The distribution of leaf area index within the swards was measured and related to light interception and photosynthesis. Light infiltrated further into the canopy of unclipped swards than clipped swards. Regular clipping created a dense layer of planophile leaves at the top of the canopy, which intercepted most of the incident light, leaving the lower canopy in darkness. Consequently, the lower canopy contributed less to photosynthesis in clipped swards than in unclipped ones. Grass leaves were displayed more prostrate when clipped regularly such that the structure and light interception of grass was similar to clover. In the absence of defoliation, grass leaves were taller than clover, but their erect habit allowed infiltration of light to clover laminae. The relationships between herbage mass, botanical composition, intake and dietary selection by sheep grazing phalaris-subterranean clover pastures were investigated during spring. A range in pasture height (1.2 to 10.2 cm) caused a similar range in herbage mass (370 to 3030 kg DM/ha) and herbage accumulation (-18 to 52 kg/ha/day). A pasture 5 to 6 cm tall, with a leaf area index of 2.0 and an available yield of 1700 kg DM/ha was most productive. The estimated daily pasture intake by sheep ranged from 384 to 1077 g OM. On the shortest pastures, intake was limited by available yield. Intakes increased little after available pasture yield reached 1500kg DM/ha or a pasture height of 5 to 6 cm, but were restricted at pasture heights of 2-3cm or less. There was no evidence for selection in favour of either clover or phalaris, and they were consumed in the same proportion they were present in the pasture. The effect of recent diet on the selection and intake of diet by sheep grazing phalarisclover pastures was investigated. Sheep grazed phalaris, clover or phalaris-clover pasture prior to movement to either a phalaris- or clover-dominant mixture of the two species. The results were complicated by the presence of Vulpia species in the pastures. Where one species dominated the pasture, the diet was predominantly that species. Cases where pasture was a more even mixture of species could not be interpreted successfully, because the alkane concentrations of the pasture species (from which diet composition estimates were made) did not allow the pasture species in the diet to be discriminated with confidence. The daily intake of pasture was affected by previous diet, with animals tending to consume more when moved to a pasture similar to the one they were previously grazing. In an experiment on established phalaris pasture, the diurnal fluctuation in the concentration of water-soluble carbohydrates (WSC) was measured during spring. WSC increased significantly (P = 0.009) from 103 mg/g DM at 0715 hours to 160 mg/g DM at 1300 hours, and did not change further during the next two hours. The concentrations of glucose (17 mg/g DM), fructose (20 mg/g DM), fructan (14 mg/g DM) and "other carbohydrate" (predominantly the carbohydrate moiety of glycosides; 43 mg/g DM) remained relatively constant throughout the daylight period. The increase in concentration of sucrose (33 mg/g DM) was the most significant influence on the increase in WSC (57 mg/g DM). Shading to exclude light prevented the increase in WSC concentration during the day. In a subsequent experiment, a shading treatment was used to create pasture with lower WSC concentration (62 mg/g DM) than an unshaded control (126 mg/g DM). The concentration of the component carbohydrates (i.e. glucose, fructose, sucrose, fructan, "other carbohydrate" and starch) were significantly lower in shaded compared to unshaded pasture. Sheep given free choice between shaded and unshaded pasture exhibited a preference for unshaded pasture over shaded pasture and, on average, 72% of the DM in their diet was unshaded pasture. Whilst no sheep showed preference for the shaded pasture, the proportion of unshaded pasture in their diets varied between 52% and 87% (DM basis). The results are discussed in terms of their implications for grazing management and the development of strategies to improve pasture utilisation and nutritive quality. The role of WSC in diet selection and its importance as a determinant of forage nutritive quality are discussed. The potential benefits of increasing the concentration of WSC in forages by altering agronomic practices or selectively breeding for WSC are discussed.
-
ItemResponses of young sheep to supplements when fed low quality roughages( 1999)The morphological components of which cereal straw is composed vary in composition and nutritive value. In a survey of relevant literature, stem materials (ST) are usually found to be consumed by ruminant animals at a slower rate than leaf material (LF) from the same crop residues when these are fed alone as separated fractions. This is attributed to the higher content of cell wall constituents (CWCs) and often lower content of N of ST. Because ST and LF can vary in proportions in the roughage fed as a basal feed, the response of animals to supplements might also be expected to be variable particularly when the basal feed is offered in excess that permits selection. In particular the response to supplemental N sources varying in ruminai degradability may vary. The objective of this thesis program was to investigate the interactions between the basal roughage and supplement measured as effects on digestion and LW responses of young sheep. The overall hypothesis was that across diets made up of different proportions of LF and ST fractions of cereal straw, the response to N supplements is dependent on CWCs concentration. The program was completed through a series of experiments conducted at the Mt Derrimut Field Satation of the University of Melbourne. In all experiments the animals were fed on a basal feed of LF or ST fractions of barley straw, with supplements including (a) Bar+USS, barley grain (Bar) fortified with urea solution prepared at a ratio of 5:1 (urea plus Na,SO4). (b) USS, urea solution alone added to the basal roughage and (c) FM, fishmeal. With each basal feed one group of lambs did not receive any supplement and served as a control group (CONT). Experiment 1 (Chapter 3) was conducted to evaluate chemical and nutritional characteristics of straw fractions of Parwon cultivar barley. Straw was separated into 4 fractions - stem (ST), leaf blade (LB), leaf sheath (LS) and broken fractions plus weeds (OT). The separated fractions were analysed chemically ( van Soest, 1974) and in vitro digestibility (Tilley and Terry 1964 ) determined. ST was the largest fraction and contained a significantly higher concentration of neutral detergent fibre (NDF; p<0.01) than LB, LS and OT (83.1, 78.6, 76.8,and 71.5 g/100g respectively). ST contained less hemicellulose (HC) than LB but more than LS and OT (37.5, 39.6, 36.3, and 35.7 respectively). N content was lower in ST than in LB, LS and OT fractions (0.4, 0.9, 0.6, and 0.7 respectively). Digestibility in vitro was significantly lower (P<0.001) for ST than for other fractions (38.5, 72.7, 60.1, and 63.0 respectively) while energy required for grinding (Chenost 1966) was much higher (P<0.001) for ST than for other fractions (121, 54.6, 64.2, 56.6 respectivly). In Experiment 2 (Chapter 4) ST and LF fractions of the same Parwon barley straw were fed as the basal feed to lambs and DM intake of ST was 15% lower than for LF (403 vs 473 g/d). When LF feed was supplemented with USS and FM, DM intake was greater by 28% and 25% respectively, while supplementation with Bar+USS resulted in 10% lower LF intake. In contrast, with animals fed ST as the basal roughage, only FM led to an increase in DM intake of only 10%. Supplementation with Bar+US and USS and FM improved overall digestibility, estimated metabolisable energy intake and N intake. Low N intakes on the basal roughages supported low ruminai ammonia-N concentrations (mg/1) immediately before feeding (ST, 20.4 ; LF 35.8), but these were improved where supplements had been fed with each of ST Bar+USS, 263.7; USS, 186.7; and FM, 151) and LF (Bar+USS, 219.5; USS, 62.5; and FM, 150). Six hours after feeding, ammonia-N concentrations (mg/l)were higher for ST (99) still low for LF(35) when fed alone, reduced below the prefeeding levels by supplements of Bar+USS (ST,167; LF 173) but raised by USS (ST, 201; LF 148) and FM (ST, 114; LF, 192). The concentrations of total volatile fatty acids (VFA) in rumen fluid (mMoUl) were not significantly different for ST and LF before feeding except where FM was the supplement, or six hours after feeding except where Bar+USS or USS were fed with LF (before feeding: ST, 51; Bar+USS, 55.7; USS,46.5; FM, 56 ; LF, 42.6; Bar+USS, 53; USS, 55.5; FM, 63.6; 6h after feeding ST, 55.5; Bar+USS, 70.2; USS, 62.1; FM, 50.4 ; LF, 55.7; Bar+USS, 69.5; USS, 60.9; FM, 60.9). Lambs on ST and LF alone lost weight (ST, -105; LF -98 g/d ). Rate of liveweight loss was less when Bar+USS (ST, -32.3; LF -2.4g/d) and USS (ST, -79.8; LF -31.2 g/d) supplements were fed, while FM promoted LW gain (ST, 37.5; LF, 72.4g/d). N retention data was consistent with these LW gains, except where Bar+USS was the supplement, in which case the animals were in positive N balance though losing weight. Wool growth was significantly improved (P<0.001) only by FM on both ST (+47%) and LF (+57%) basal roughages. In Experiments 3 and 4 (Chapter . 5 and 6) the objective was to investigate the factors responsible for low feed intake and poor performance of lambs fed ST compred to those on LF. The DMI (g/d) of lambs fed ST and LF were similar to those achieved in experiment 2; and were significantly greater for LF (P<0.001). Likewise supplements of Bar+USS, USS and FM had similar effects to those reported for experiment 2_ Changes in DMI, MEI ruminai environment before feeding or 6 and:12 hours after feeding were consistent with those recorded during experiment 2. However concentration of total VFA was significantly elevated at 12 hours after feeding. Differences in ruminal environment were evident in terms of VFA concentrations and the distribution of rumen digesta particulate material in different size fractions; both variables were affected both by the basal diet and the supplement. For LF, the proportions of particles >2mm and of very fine particles (0.125 mm) were greater and for particles between 0.5 and 1 mm less those for ST in all cases. Further, the proportion of particles >2mm was less where FM was fed than for any other feeding regime. The mean retention times of rumen fluid, measured from CoEDTA dilution rate, and calculated for rumen particulate material was longer (24%, P<0.01) for ST than for LF but there was no significant effect of supplement on this (Experiment 4, Chapter 6). The mean percentage of very fine particles in the faeces of lambs fed on LF was higher than for lambs fed ST alone or with supplements. Rate of ruminai degradation of OM of ST and LF as measured by nylon bag technique ( Experiment 3, Chapter 5) was similar at 12 and 24 hours but greater for LF than for ST at 48 and 96 hours of incubation. Bar (cracked whole grain) was degraded more rapidly and extensiveley than FM; in LF fed sheep this difference was more marked. Rate of degradation of acid detergent fibre (ADF) was influenced by the kind of supplement and was greatest in lambs given FM , and least in lambs given ST with no supplement. Only the FM supplement resulted in LW gains, though rates of LW loss were least and LW gains with FM were greatest with LF as the basal roughage. The responses are interpreted as flowing from the greater proportion of ADF and lignin in the CWCs content and the greater digestibility of ADF in the LF fraction. The ST feed fraction with higher concentrations of cell wall constituents (CWCs) as NDF was eaten at a slower rate (Experiment 5, Chapter 7) and digesta particulate material and, in these experiments, the fluid phase are retained longer in the rumen. LF showed not only an advantage over ST in these respects but also in terms of a number of important digestion parameters supported a greater response to supplements, particularly N supplements of low degradability. Thus FM is these experiments interacted with the roughage component of the diet. It provided more consistent ruminai ammonia concentrations supporting a better environment for microbial activity and growth. Microbial protein together with undegraded dietary protein together provide a balance of nutrients that allows LW gains on otherwise submaintenance basal feeds. The greater enhancement of performance with LF compared to ST and the particle size measurements suggest that greater fragmentability of LF may be a major contributor . In terms of technical improvement of livestock feeding systems, providing the animal with opportunity for selection of more leaf and less stem may improve the likelihood of responses to supplements but this was not demonstrated in Experiment 5. FM was used as the experimental supplement to provide slowly degraded and undegraded dietary protein of high biological value to the animal. FM is expensive and other crop byproducts and local feed materials with properties of slow degradability of protein and good amino acid balance need to be identified. An alternative strategy would be to provide a maximum opportunity for the selection of most digestible parts. If refusals are then collected, quality could be further improved with alkali treatment and necessary supplementation. This would provide a strategy for the use of morphological fractions which could be an economical approach for the efficient utilization of roughages.
-
ItemFinishing prime lambs using pulse stubbles, and pulse and cereal grains in the Wimmera region of Victoria( 1998)Three trials were conducted as part of this study. The first trial evaluated faba bean and chick pea stubble as feed source for the finishing of lambs. The second trial evaluated the use of barley and field peas in feed lot rations for lambs, and the final trial evaluated narbon beans and vetch as substitute grains for field peas in feed lot rations for lambs. In the first experiment one hundred and twenty six Poll Dorset x (Border Leicester x Merino) mixed sex lambs with a mean liveweight of 40.0 kg � 0.3 kg were grazed on faba bean (FB) or chick pea (CP) stubble at a stocking rate of 6.5/ha and received a supplement of 300 g/hd/day of barley (+B) or were unsupplemented (-B). There was no significant difference (P>0.05) in average daily gain (ADG) over the duration of the trial between lambs grazing faba bean and chick pea stubble, supplemented with barley or unsupplemented. Lambs supplemented with barley tended (P- 4.06) to have a lower ADG in the first fortnightly period, and had significantly lower (P<0.05) ADG in the second period. This result is supported by the observation of supplemented lambs not grazing the stubble but waiting to be fed the barley supplement. This result was reversed in the third period when supplemented lambs tended (P~.06) to have a higher ADG, and in the final period when the ADG was significantly higher (P<0.05) than the unsupplemented lambs. There was a significant correlation (P<0.01 for faba bean stubble and P<0.05 for chick pea stubble) between ADG of unsupplemented lambs and the quantity of grain residue in the stubble. In the second experiment eighty Border Leicester x Merino mixed sex lambs with a mean liveweight of 27.3 kg � 0.2 kg were fed barley (B) or barley + field peas (B+FP) (60:40) either daily at 800 g/hd/day or ad libitum for 56 days following a 14 day introductory period. Hay was provided ad libitum. There was no significant difference (P>0.05) in ADG between lambs fed the treatment rations. Lambs fed B+FP were significantly different to lambs fed barley in the following: higher carcass weight (P<0.05); fatter (P<0.05); higher dressing percentage (P<0.01); higher estimated carcass weight gain (P<0.05) and lower dry matter intake to estimated carcass weight gain ratio (P<0.05). There was no significant difference (P>0.05) in any of the measured characteristics between lambs fed restricted or lambs fed ad libitum. In the third experiment twenty four Poll Dorset x (Border Leicester x Merino) lambs with a mean liveweight of 28.8 kg � 0.45 kg were individually penned and fed ad libitum a ration of narbon beans (NB), vetch (V) or field peas (FP) mixed with wheat and formulated to 16% crude protein. Milled hay was provided separately ad libitum. There was no significant difference (P>0.05) in growth rate, carcass weight, dressing percentage, feed intake, or dry matter intake to liveweight gain ratio between lambs fed the three rations. The growth rate and feed intake of lambs fed FP was more consistent than lambs fed NB or V. Scouring was observed in lambs fed V. There was highly significant (P<0.001) separation and selection of wheat in the NB and FP based rations. Further research needs to be carried out to evaluate meat quality of lambs fed narbon beans and vetch, in particular to determine if there is any effect on flavour of the meat. The use of pulse stubbles, combined with lot feeding can form a feeding system to enable lambs to be finished in the autumn-winter period in the Wimmera region. The growth rate of lambs grazing pulse stubbles is dependent on the quantity of grain residue on the ground. The growth rate can be maintained as grain level declines by the introduction of a barley supplement. Lot feeding can be used to finish lambs when pulse stubbles have been grazed out. A combination of a cereal grain and a pulse grain formulated to 16% crude protein can be fed ad libitum. Hay can be provided separately ad libitum, or a more controlled intake of hay can be achieved by feeding a calculated amount daily.
-
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.
-
Item
-
Item