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Cardiac weights and lesions as risk factors of in-transit losses of market-weight pigs in Ontario

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Title: Cardiac weights and lesions as risk factors of in-transit losses of market-weight pigs in Ontario
Author: Zurbrigg, Kathy
Department: Department of Population Medicine
Program: Population Medicine
Advisor: O'Sullivan, Terri
Abstract: Health conditions existing prior to transport could predispose a market pig to dying or becoming non-ambulatory during transport. The objectives of this thesis were to determine if cardiac weights and gross and histological lesions were associated with in-transit loss (ITL) pigs, to determine if a heritable cardiac condition is associated with the lesions observed in pig hearts and to determine if cardiac lesions, weights and loading management risk factors on the farm were associated with higher annual rates of ITLs. Between June 2012 and April 2015, 85 ITL carcasses and the hearts from 198 ITL and 400 non-ITL (control) pigs from one Ontario abattoir were collected and examined for gross and histological lesions and differences in cardiac weights and weight ratios over several phases of the study. Post-mortem examinations of ITL pigs (N=85) from one Ontario abattoir indicated the cause of death to be heart failure because of cardiac lesions that developed prior to transport. Hearts from pigs that died during transport (N=70) demonstrated significantly greater frequencies of cardiac lesions (e.g. hypertrophy of ventricle walls), greater average heart weights and greater heart weight to body weight ratios than hearts from non-ITL pigs. Genome wide analyses were performed on a subset of the ITL and non-ITL hearts (N=536). Genes associated with hypertrophy and arrhythmias were identified, though the strength of the association was low. Examination of 300 hearts collected from the processing line and loading management data collected from 30 farms (10 hearts from each farm) classified by low, moderate and high rates of annual in-transit losses resulted in differences between cardiac weights and weight ratios and the loading management risk factors between high and low loss farms. It is plausible that pigs with cardiac lesions and increased cardiac weights are unable to respond to the increased exertion required during sorting, loading and transport to the abattoir which results in transport mortalities due to cardiac insufficiency. Further research is needed to determine what initiates cardiac remodelling in pigs and to measure cardiac function in pigs with lesions.
Date: 2018
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