Agriculture and Food Systems - Theses
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ItemThe influence of dietary lecithin and sex on growth performance, dressing percentage as well as pork texture in relation to intramuscular collagen characteristics in finisher pigs( 2012)Three experiments involving doses of lecithin ranging from 0 to 80 g/kg were fed to gilts, entire male (EM) and immunocastrated male (IC) pigs over the finishing phase to evaluate the effects of dietary lecithin and sex on the growth performance, dressing percentage as well as pork texture in relation to intramuscular collagen characteristics. Large White x Landrace pigs were used in all experiments and dietary lecithin was offered over six weeks in Experiment 1, five weeks in Experiment 2 and four weeks in Experiment 3. Pork texture was measured using Warner Bratzler shear force and compression analyses on cooked Longissimus thoracis (loin) muscle. Muscle hydroxyproline content analysis and gene expression evaluation of the genes involved in collagen synthesis were conducted to determine the mechanisms of lecithin involved in improving pork texture. The influence of dietary lecithin on pork fatty acid profile, intramuscular fat content and sensory eating quality were also investigated. In Experiment 1, dietary lecithin reduced pork chewiness (P<0.05). This may be associated with reduced hydroxyproline content (P<0.05) as well as gene expression levels of Type I (α1) procollagen, Type III (α1) procollagen and α subunit prolyl-4 hydroxylase genes in muscle from the pigs fed dietary lecithin (P<0.05, respectively). Dietary lecithin also produced pork with increased polyunsaturated to unsaturated fatty acid (PUFA: SFA) ratio of more than 0.5 and tended to decrease intramuscular fat (P=0.067) without adverse effects on eating quality. The anti-oxidant properties of dietary lecithin may play a role in delaying lipid oxidative deterioration of eating quality. Dressing percentage was increased by 2% in the gilts fed dietary lecithin (P=0.009) in Experiment 1, while feed efficiency was improved in the gilts and IC pigs fed dietary lecithin (P=0.06) in Experiment 2. These improvements may be due to a better utilisation of dietary fat (tallow), given the emulsifying properties of lecithin. Immunocastrated male pigs had the lowest shear force values (P<0.05) and the highest growth rate (P=0.001) compared with gilts and EM pigs in Experiment 3. It was possible that the improvement in shear force values may be due to increased post-mortem myofibrillar degradation and intramuscular collagen solubility during the fast growth period. However, responses of feed efficiency, dressing percentage, pork chewiness, shear force values and collagen characteristics to dietary lecithin were not consistent across experiments. This may be because of the shorter duration of treatment and lower doses of dietary lecithin used in the latter experiments than the first experiment. The variation in responses of pork chewiness and collagen characteristics to dietary lecithin may also be due to the use of loin muscle that has relatively low collagen content. In conclusion, the outcomes from the research presented in this thesis suggested that the mechanisms of lecithin involved in reducing pork chewiness may be through reduced collagen synthesis and hydroxyproline content. Dietary lecithin improved pig feed efficiency and dressing percentage in finisher gilts. Immunocastrated male pigs had the highest growth rate and the most tender meat indicated by the lowest shear force values compared with gilts and EM pigs.