In-transit losses (ITLs) of market weight pigs are defined as pigs that die and (or) pigs that become nonambulatory (NA) during the process of loading and shipping from the farm to the abattoir. Annual rates of transport mortalities are low relative to the number of pigs transported to slaughter annually but are highly variable between countries and even between abattoirs within countries. In-transit losses are not fully explained by the most commonly cited risk factors, such as environmental temperature, stocking density, and journey length and other risk factors must be considered. Low numbers of ITLs compared with the large number of pigs shipped each year imply that individual pig factors should be given greater consideration. Pig health pertaining to ITLs is not well studied and post mortems are rarely completed on ITL pigs. In particular, compromised cardiac function combined with a limited ability for cardiac compensation may predispose pigs to ITLs as a result of the exertion experienced during sorting, loading, and transport. Varying stages of cardiac compromise could explain the variable nature of ITLs. Future research should focus on investigating the health conditions which could make a pig more susceptible to death or becoming NA during transport.

In-transit losses of market hogs represent a small proportion of all market-weight pigs shipped in a year. This suggests that individual pig factors may be a significant cause of in-transit losses along with more traditionally considered environmental and transport factors. An investigation was performed to determine whether cardiac pathology and heart weights were associated with pigs that did or did not die during transport to an abattoir. The hearts from 70 pigs that died in-transit to one Ontario abattoir and 388 pigs that arrived alive were collected and examined. Hearts from pigs that died during transport demonstrated greater frequencies of cardiac lesions (P < 0.05). These included hypertrophy of ventricle walls (Left: 97% vs. 64%; Right: 86% vs. 57%), dilation of ventricle chambers (Left: 79% vs. 0.5%; Right: 100% vs. 5%), and dilation of the pulmonary artery and aorta (59% vs. 1.5%). Total heart weight to body weight ratios were increased (3.6 vs. 3.3 g/kg) and left ventricle plus septum weight over right ventricle weight ratio was decreased in pigs that died during transport over non–in-transit loss pigs (2.5 vs. 2.8; P < 0.05). This may indicate reduced cardiac function in hogs that died during transport. Pigs with reduced cardiac function would have exercise intolerance and be more susceptible to death during transport due to the increased cardiac workload required during sorting, loading, and transport of the pigs to the abattoir. Further research to quantify cardiac function in pigs with cardiac lesions or abnormal heart weight ratios is warranted.