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Title: The effects of growth promoters on post- mortem proteolysis in pigs
Author: Mareko, Molebeledi Horatius Dambe
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2013
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The inconsistent quality of pork meat is a major worry for the industry, and is mainly blamed on variable tenderness. Meat tenderness depends in part on the degree of alteration of the structural components of muscle and associated proteins post-mortem. Reduced activity of the calpain proteinase system is associated with tough meat. However, it is known that other proteases such caspase and proteasome proteolytic enzyme systems are involved in skeletal muscle development and remodeling, and it is their proteolytic attributes that make them possible contributors to improved meat tenderness. This research work investigated the effects of growth promoters (beta-agonist - Ractopamine ™ and growth hormone - Reporcin TM) on gilts' carcass characteristics, and longissimus muscle meat quality and proteolytic system activities (caspase 3/7, calpains and proteasome). Two experiments were carried out consisting of a short period (7 day study) of treatment aimed at assessing the immediate response of the protease systems to the two growth promoters and a time course study that aimed to assess the growth promoters' effects in a longer treatment period (13 and 27 days), simulating the commercial set up in which feed additives are used in finishing phases that can be up to 60 days. Gilts were fed a standard commercial diet ad-libitum (control) or with the same feed supplemented with beta-agonist at 10mg/kg (7days) or 20mg/kg (13 and 27days), or administered growth hormone (10mg every 2 days) in both experiments. Carcass characteristics were assessed at slaughter and longissimus muscle samples were assessed for tenderness (shear force), caspase 3/7 and proteasome (chymotrypsin-like, trypsin-like and caspase-like) activities and calpastatin protein level in the 7 day experiment, with calpains activities, MuRF, MAFbx protein levels and lipid and fatty acid content in the long treatment study of 13 and 27 days. Growth hormone increased liver weights (P < 0.001) in both experiments, but had no effect on muscle weights in both short and long treatment studies. Beta-agonist increased muscle weights over the 13 and 27 day (P < 0.05) and 7 day (P = 0.062) treatments and tended to increase shear force values (P = 0.09 and 0.107, 7day and 27day respectively) after 8 days of ageing . Caspase 3/7 and total proteasome activities decreased significantly (P < 0.001) with time during the 7 day treatment period. GH significantly increased activity of trypsin-like proteasome subunit at day 13 (P = 0.048). Beta-agonist Significantly increased activity of chymotrypsin-like proteasome subunit (P = 0.041) at 27 days, whereas GH decreased caspase-like proteasome activity (P = 0.025) at day 27. Beta-agonist decreased glycogen levels at 7 day (P = 0.015). Both growth promoters significantly decreased lipid content after 27 days of treatment (P < 0.001). v All correlations between shear force and proteases were negative for the growth hormone treated gilts and significant except for the Caspase 3/7 (P = 0.081) in the 7 day treatment period. MuRF protein level negatively and significantly correlated with shear force at slaughter day 27 (P = 0.053) for data pooled across treatments, and for gilts treated with the growth hormone (P = 0.035). These were the only negative correlations with shear force and in the expected direction, where high protease activities should translate to lower shear force to indicate a role in meat quality of improved tenderness. But the correlations between the protease systems studied and shear force were very inconsistent across this research work, indicating no role played by the systems in meat quality. No differences were observed in weights across treatments (live and carcass) in all the experiments conducted in this research work. This work indicated that caspase 3/7 and proteasome activities are not associated with meat quality (tenderness) attributes of growth promoter treated gilts, and that the slight increase observed in shear force in beta-agonist treated pigs might have been due to larger (hypertrophied) fibres that also had reduced lubrication during shearing due to low intra-muscular fat levels. vi
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available