School of Agriculture, Food and Ecosystem Sciences - Theses
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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.
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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.