Agriculture Reference
In-Depth Information
this disconnect (Rutherford
et al.,
2012; Baxter
et al.,
2013). In the farrowing house,
human behaviour and pig fear levels interact to influence piglet mortality. For example,
when sow fear levels and nervousness are high, the presence of humans may be a risk
factor for stillborn piglets (Hemsworth
et al.
, 1999), and deaths due to crushing and
savaging (Hemsworth
et al.
, 1995; Lensink
et al.
, 2009). Furthermore, Marchant-Forde
(2002), who classified gilts on a behavioural 'shy-bold' continuum on the basis of their
response in a human-approach test conducted during pregnancy, demonstrated that gilts
at the shy end of the spectrum were more likely to savage their offspring. Increased
fearfulness therefore may be a significant risk factor for piglet-directed aggression
(English
et al.
, 1977). Janczak
et al.
(2003) demonstrated that maternal anxiety can lead to
poor maternal behaviour. Indeed, they found associations between behavioural measures
of fear and anxiety of gilts at approximately two months of age and the later quality of
their maternal care, as reflected by piglet mortality.
Stressful experiences during gestation not only impact the sow's behaviour but can
have detrimental and long-term effects on the developing offspring, including trans-
generational effects. In recent work by Rutherford
et al.
(2014), primiparous sows were
subjected to the stress of social mixing during mid-gestation (a prenatal stress model
previously demonstrated by Jarvis
et al.
, 2006). Neurobiological work demonstrated that
female progeny from stressed sows were more anxiety-prone, and that those females
that went on to become mothers showed behaviours indicative of abnormal maternal
behaviour. They were also more reactive towards their piglets, and spent more time
visually attending to them compared with control sows; these differences negatively
influenced piglet survival.
11.3
Prevention of mortality
Piglet mortality can be addressed through changes in genetic selection strategies of the
animals, alterations in the farrowing environment, or changes in management. As the
challenges of hyperprolificacy increase, all of these measures need to be optimised.
11.3.1
Animal selection
Adjusting selection criteria to include traits related to neonatal survival within breeding
goals, in addition to number born, is a sustainable strategy that has achieved success
in improving piglet survival rates (Roehe
et al.
, 2009, 2010). The Danish pig industry,
renowned for its success in increasing litter size, recognized the accompanying significant
increase in mortality which initially occurred (5% increase in total pre-weaning
mortality). In 2004, it changed its selection criterion from total born to 'live piglets at
day 5' (LP5) (Su
et al.
,
2007) and mortality, although still high, was stabilised with the net
result of an increase of 2.3 pigs weaned/litter. This may partially reflect more successful
management of the surplus piglets as farmers became experienced with hyperprolific
sows, but it also indicates that selecting for LP5 may not result in as many compromised
piglets (e.g. pathologically growth-retarded individuals) as selecting for number born.
Reducing intra-litter variability, particularly with respect to birth weight, is an additional
