Agriculture Reference
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and Swierstra, 1987; Edwards, 2002; Edwards et al. , 1994; English and Edwards, 1996;
English and Morrison, 1984; English and Smith, 1975; Lay et al. , 2002; Marchant et al. ,
2000; Mellor and Stafford, 2004; Svendsen, 1992). Amongst these reviews there is a great
deal of consistency, particularly regarding the main causes of death and in implicating
the first 72 h of postnatal life as the critical period. Dyck and Swierstra (1987) identified
eight specific causes of death, but the main three are stillbirths, crushing by the sow
and starvation. However, when analysing the causes of mortality single attributions
are hard to find. The multifaceted nature of piglet mortality means the sow, piglets and
their environment all contribute interacting causal factors. Unravelling these complex
interactions to determine an accurate primary cause of death requires longitudinal
study of individual piglets and careful post-mortem examination. It has been shown
that misdiagnosis is common in farmer-reported causes of death, which form the data
source for many surveys. For example, stillbirths typically account for 4-8% of all pigs
born (English and Edwards, 1996), or approximately 30-40% of the total mortality, and
crushing is by far the major reported cause of live-born death (Easicare, 1995). However
crushing and starvation are not mutually exclusive conditions; it is likely that one follows
another and that both are influenced by the incidence of hypothermia (Curtis, 1970).
Hypothermia is considered, directly or indirectly, to be responsible as a primary cause
for more deaths than crushing, starvation, disease or low viability (Curtis, 1970). Since
it cannot be perceived without continuous monitoring of rectal temperatures, the most
easily discernible cause of death, crushing by the sow, is over recorded instead. Farmer-
recorded causes of death therefore often mis-represent why piglets die (Christensen and
Svensmark, 1997; Vaillancourt et al. , 1990) and underestimate the real predisposing risk
factors. It is these predisposing factors and their complex interactions (represented in
Figure 11.1) that need to be addressed in order to reduce piglet mortality.
11.2.1
Maternal influences
The sow plays a crucial role in fetal and postnatal survival through provision of vital
resources in utero and during lactation, and by displaying good maternal behaviour.
The sow's genotype and parity, as well as her physical condition during gestation and
lactation, all influence piglet survival.
Intrauterine effects on piglet quality
Fetal survival depends upon blood flow to the uterus, adequate partitioning of maternal
nutrients, and the effectiveness of placental transfer. Mortality in utero during the
embryo elongation phase can be followed by post implantation losses in crowded
uterine conditions (Foxcroft et al. , 2006). Placental development is compromised by
uterine crowding and placental insufficiency is a major cause of intrauterine growth
restriction/retardation (IUGR). Such prenatal insults can result in a stillborn piglet or
a live-born piglet with low viability and compromised postnatal survival. There are
breed differences that highlight the importance of an optimal prenatal environment;
Meishan sows are better adapted to meet fetal demands and are more successful than
their occidental counterparts in producing greater litter sizes of viable piglets, as well as
producing significantly fewer stillborn piglets (Canario et al. , 2006). Their success arises
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