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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ItemFactors influencing the efficacy of the boar effect( 1996)Maximizing reproductive efficiency is of high potential benefit to the pig industry. Mature boar contact has proven to be very effective in stimulating gilt puberty, although the results tend to be variable. The experimental work in this thesis was conducted in order to elucidate some of the factors which may be contributing to this variation. Three experiments have been carried out to examine the possibility of improving the efficacy of the boar effect. The first experiment investigated the effects of boar contact and transportation on the stimulation of early puberty attainment in gilts. Gilts were allocated to one of six treatments: control - no boar contact or transportation (C); daily boar contact (B1); daily transportation (T); three times daily boar contact (B3); daily boar contact and transportation (B1+T); and three times daily boar contact plus daily transportation (B3+T). Results show that transport alone has little influence on the timing of gilt puberty (P>0.05), although there was a significant positive interaction between transport and boar contact (P<0.01). Frequent boar contact (three-times daily) stimulated a higher proportion of gilts to attain puberty within 20 days of commencement of treatment (P<0.05) than did either once-daily boar contact or no boar contact. In addition, the proportion of gilts reaching puberty was significantly lower when gilts were exposed to daily boar contact, compared to three times daily boar contact. The second experiment studied the efficacy of the boar effect when conducted in a modified Detection and Mating Area (DMA), with or without full boar contact, or in a pen which was not the boar's own. Gilts were assigned to treatments of: no boar contact (C); once daily boar contact (B); DMA exposure (DMA); and boar exposure plus DMA exposure (B+DMA). Mean days taken from the start of the experiment to puberty attainment were significantly fewer (P<0.01) for gilts receiving daily boar contact than for gilts not exposed to boars (36.1 vs. 56.8 days), although boar exposure in addition to DMA exposure tended to produce the lowest mean days to puberty (20.6 days). However, neither days taken to reach puberty, gilt age at puberty, nor gilt weight at puberty was significantly affected by daily exposure to a DMA. The third experiment examined the stimulatory effect of the presence of cycling females on puberty attainment in gilts, and whether the effect was a direct one, or whether it operated via an increase in the stimulus value of the boar. The gilt treatment groups in this experiment were: control - no contact with boars or cycling females (C); contact with cycling females, but not with boars (F); contact with boars, but not with cycling females (B); contact with both boars and cycling females, where the boars were not exposed to the cycling females (BF-1); and contact with both boars and cycling females, where the boars were exposed to the cycling females (BF-2). The proportion of gilts reaching puberty was not significantly influenced by treatment in this study. However, the mean days taken from commencement of treatment until puberty attainment were significantly fewer for those boar exposed gilts not exposed to cycling females than for those gilts receiving neither boar contact nor being exposed to cycling females. Cycling females may exert a minor stimulatory effect on the timing of gilt puberty in non-boar exposed gilts, but this effect is not significant. Results from these studies confirm the efficacy of mature boar contact as a means of inducing early puberty attainment in the young gilt (i.e. the boar effect). Transport did not exert a significant effect on days taken to reach puberty, although transport may be slightly stimulatory to puberty attainment in gilts when used in combination with frequent boar contact. Full boar contact, when given in a DMA, may be a more effective form of gilt puberty stimulation than full boar contact in an isolated pen. Preliminary data also suggest a possible negative interaction between puberty stimuli from the boar and those from cycling females which, if substantiated, may have implications for the management of the replacement gilt.