Agriculture and Food Systems - Theses
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ItemProduction of heavy weight cryptorchid and wether lambs( 1996)Declining Iamb consumption remains a major problem facing the Australian prime Iamb industry. For Iamb to retain its market share and to remain a viable commodity in the future, leaner Iambs must be produced and marketed. Recent industry initiatives therefore focussed upon the production and marketing of Iambs to meet carcass specifications of 18-26 kg with a fat depth of 6 to 15 mm at the GR site. Emphasis was placed upon the production of lean carcasses weighing more than 22 kg, which are otherwise referred to as Elite Iambs. The development of production, management and marketing systems to produce and market Iamb carcasses of Elite Iamb specifications, both domestically and overseas, was the focus of this research program. The major objective of this experiment was to determine the potential of producing high and consistent quality meat from cryptorchid and wether Iambs meeting carcass specifications for Elite Iambs when slaughtered from six to eighteen months of age. One hundred and sixty three second cross Poll Dorset x Border Leicester/Merino cryptorchid and wether Iambs, born in May 1991 at Rutherglen Research Institute, Rutherglen, were grown and managed on annual pasture at an average liveweight of 50 kg prior to slaughter. Lambs were allocated to one of seven slaughter groups and finished every two months from 6 to 18 months of age and the influence of sex, age and nutrition on carcass composition, meat quality attributes and fat quality and consistency of cryptorchid and wether Iambs examined. Cryptorchid and wether Iambs slaughtered from 8 to 18 months of age produced carcasses meeting targeted specifications of greater than 22 kg with 6-15 mm of fat at the GR site. Lambs slaughtered at six months of age did not achieve the target liveweight of 50 kg at slaughter due to poor seasonal conditions which influenced the quality and availability of annual pasture in spring 1991. Cryptorchid Iambs had a lower dressing percentage and produced carcasses with a lower GR measurement than wethers at a cold carcass weight (CCW) of 23.5 kg. Cryptorchid Iambs exhibited growth rate advantages over wethers only when nutrition and seasonal conditions did not limit Iamb growth. When compared at the same fasted liveweight, cryptorchid Iambs deposited less internal fat than wethers. Cryptorchid carcasses also had a lower proportion of subcutaneous fat present on all primals, higher proportions of soft tissue and bone in the hindquarter and the EMA of the M. longissimus thoracis was significantly larger compared with wethers at a CCW of 23.5 kg. The proportion of CCW in the leg, chump and ribloin was not significantly influenced by Iamb sex. Nutritional management of lambs significantly influenced the proportion of subcutaneous fat on all primals. Meat quality was significantly influenced by Iamb sex however results obtained did not suggest that meat from cryptorchid Iamb carcasses was of inferior quality compared with wethers as only small differences in tenderness, intramuscular soluble collagen content, meat flavour, meat colour, intramuscular fat content and cooking loss were found. In addition, age and nutrition significantly influenced meat quality, however, consistent relationships were not found. The incidence of yellow soft subcutaneous fat was higher in cryptorchid Iamb carcasses than those from wethers with cryptorchids also producing subcutaneous fat with significantly higher levels of total unsaturated fatty acids and lower levels of stearic, palmitic and total saturated fatty acids compared with wethers. Age and nutrition also influenced the fatty acid composition of subcutaneous fat with Iambs fed lupins having significantly higher linoleic acid levels in subcutaneous fat. However, the magnitude of these differences did not explain differences found in fat quality and consistency between cryptorchid and wether carcasses slaughtered at different ages. Significant, though small, differences were found due to sex in both the triglyceride and phospholipid components of intramuscular fat. As higher levels of polyunsaturated fatty acids were found in the phospholipid component of intramuscular fat compared with cryptorchids, this may affect the keeping quality of meat from wether carcasses. Finally, although significant differences due to age were found in the fatty acid composition of intramuscular fat, these differences were not consistent with age and more likely reflected differences in nutritional management between slaughter groups. This study demonstrated that cryptorchid and wether Iambs turned off at heavy market weights on an improved plane of nutrition over a 12 month period produced carcasses meeting Elite Iamb specifications and yielded high quality, tender meat.
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ItemThe effects of post-anthesis heat stress on wheat yield and quality( 1996)Post-anthesis temperature is a major determinant of wheat yield and quality. Post-anthesis temperatures in the moderately high range (ca 25-32C) are known to reduce grain yield but increase bread wheat quality, whereas very high (>32C) temperatures are known to significantly reduce both yield and quality. In Mediterranean and continental climates, such as Australia and the US., wheat is exposed to moderately high temperatures throughout most of the grain filling period, and very high temperatures may occur for an average 8% of grain growth. This thesis is primarily concerned with examining the effects of very high temperature on wheat yield and quality. Specifically, the study was designed to: 1) quantify the effects of short (3-5 day) periods of very high temperature on wheat yield and quality; and 2) determine the extent of genotypic variation in response of wheat yield and quality to very high temperature. Two varieties of wheat differing widely in heat tolerance were selected from 75 cultivars of wheat that were screened for tolerance to very high temperature. These two varieties (Oxley and Egret, heat sensitive and heat tolerant, respectively) were exposed to a variety of heat treatments in order to determine whether varietal differences in heat tolerance were maintained for heat treatments occurring at 3) different stages of grain growth and for 4) varying durations of heat stress. The 5) interaction of moderately high and very high temperatures was examined in order to determine whether cool temperatures following severe heat stress could alleviate the deleterious effects of very high temperature on yield and quality. In order to 6) examine the importance of acclimation to heat stress and to 7) establish a repeatable selection methodology, the impact of sudden increases to a high maximum temperature was compared with more gradual (6C h-1) rises to the same high temperature (40C). For each of the experiments 3 to 7 (above) results are presented for the effects of heat stress on: a) the accumulation of grain dry matter and water during grain growth; b) the accumulation during grain growth of total protein and its functionally-important fractions (SDS-soluble and SDS-insoluble polymer [glutenin], monomer [gliadin] and albumin/globulin), as determined by size-exclusion high-performance liquid chromatography and c) dough mixing behaviour using the 2-g mixograph. It is concluded that: 1) wheat genotypes vary widely in their responses of yield and quality to short periods of very high temperature; 2) the response to heat stress varies with the timing of stress: yield was reduced more by early than late-applied stress, whereas dough strength tended to decline most markedly in response to heat stress applied towards the end of grain filling; 3) both grain yield and dough strength declined linearly with increased duration of heat stress; 4) in a heat sensitive variety, moderately high and very high temperatures during grain filling each reduced grain yield and dough strength: cool temperatures following exposure to very high temperature did not reduce the effects of very high temperature on either yield or quality; 5) some varieties of wheat appear to acclimate rapidly to heat stress: a gradual (6C h-1) increase from ca 20-40C lessened the impact of heat stress on yield and quality when compared with a sudden increase over the same temperature range. These results are discussed with special reference to their implications for: 1) selecting and breeding for heat tolerance in wheat; 2) predictive modelling of the effects of very high temperature on wheat yield and particularly quality.