Agriculture Reference
In-Depth Information
Large litter size
Sub-optimal
ambient temperature
Maternal e
ects
(e.g. weight, parity,
condition, history)
Farrowing kinetics: prolonged
farrowing, born later in birth
order, longer birth intervals
Lowering of body
temperature
Fatigue
Low birth
weight/viability
Placental quality (e.g.
poor placental
e
ciency, su
ciency
and vascularisation)
Stressed sows
Restrictive environment
High environmental
temperature
Chilling
Lethargy
Reduced colostrum
intake
Mis-use of
oxytocin
Poor maternal
behaviour
Asphyxiation
Starvation
Piglet death
Overlying/crushing
Disease
Figure 11.1. Predisposing factors of piglet mortality.
from overcoming the limitation of uterine capacity by markedly increasing the ratio
of the fetal size to placental size through increased placental efficiency (Biensen
et al.
,
1998). This includes increasing the density of blood vessels at the placental: endometrial
interface in response to increasing fetal demands (Biensen
et al.
, 1998; Wilson
et al.
,
1998). Despite their smaller size, Meishan piglets are more physiologically mature at birth
than piglets from modern occidental prolific lines, having a higher percentage of carcass
fat and larger adipose tissue adipocytes (Herpin
et al.
, 1993). In contrast, selection for
increased litter size in modern prolific lines has achieved the intended production of large
numbers of offspring, but at the expense of reduced viability. Coupled with the increase
in prevalence of smaller piglets is a greater within-litter weight variation; both are known
risk factors for piglet mortality (Foxcroft
et al.
, 2006). The piglet's degree of development,
as well as its size, has a major impact on survival. Recent studies involving morphological
measures indicative of growth retardation have emphasised the importance of piglet
shape as a predictor of survival (Baxter
et al.
, 2008), predisposing neonates of the same
weight to different survival outcomes. Baxter
et al.
(2008) found that stillborn piglets
were disproportionately long and thin, with lower ponderal index (PI) and body mass
index (BMI) (indicative of IUGR) compared with surviving littermates; PI and BMI
were more predictive of whether or not a piglet would be stillborn than birth weight
alone. They also associated their gross measures of IUGR (i.e. BMI and PI) with lower
total placental areolae number and areolae density, placental traits that are key in the
transfer of nutrients between mother and fetus and determinants of piglet vitality at
birth. Rootwelt
et al.
(2012) not only replicated the results linking gross measurements
of IUGR with piglet survival, but also associated placental area with piglet vitality, thus
