Behavioral Genetics in Pigs and Relations to Welfare - Genetics and the Behavior of Domestic Animals - page 400

between appetite and piglet growth rate (higher appetite heavier piglets)

and between appetite and body condition at weaning (higher appetite

better body condition). Selection for high voluntary feed intake may thus
improve welfare of both piglets and lactating sows, but what would the con-
sequences of selection for larger appetite in lactating sows be for the welfare
of dry sows?
Dry sows never have ad libitum access to feed and the high-energy,
grain-based feed used for sows is quickly digested and results in long-term
periods of hunger ( EFSA, 2007 ). One way of assessing total welfare impact
is to take the number of animals, severity, and duration into account, and
sows are lactating for only a quarter of the year. The genetic correlation
between appetite during different phases of the sow's life is not known, but
it seems likely that selection for high voluntary feed intake of lactating sows
will result in more hungry dry sows. The goal conflict between high volun-
tary feed intake during lactation and restricted feed provision during preg-
nancy could be solved by giving free access to roughage or straw in addition
to selection for high appetite. Straw not only reduces hunger, it also provides
an occupation. Feed restriction and a boring environment may result in ste-
reotypies. Spoolder et al. (1995) showed that straw reduces the development
of excessive bar manipulation in sows on restricted feeding. In poultry, it has
been proposed that feather pecking is a redirected foraging behavior
( Brunberg, 2011 ) and there are genetic differences in predisposition for
feather pecking. Likewise, there may be genetic differences between sows in
how they respond to environmental enrichment such as straw, but in general
it can be assumed that straw and other edible rooting material improves the
welfare of all pigs.
There are genetic differences in eating behavior of young, growing pigs.
When fed with an automatic feeding station, the size and duration of each
meal, distribution of meals over time, etc., can be recorded ( Figure 11.2 ).
The duration of meals

and feeding frequency are heritable traits

(h 2

0.5, Labroue et al., 1997 ). Fern´ndez et al. (2011) found specific
feeding strategies for different breeds. The number of meals per day was
negatively correlated with sizes of meals and duration of meals. Large White
pigs were “nibblers and fast eaters”, Pietrain pigs were “nibblers and slow
eaters”, Duroc pigs were “meal and slow eaters” and Landrace pigs were
“meal and fast eaters”. According to Fern ´ ndez et al. (2011) , the “meal and
fast eater” strategy is related to higher growth rate. Several genes or markers
with a significant effect on feeding behavior have been found. The MC4R
gene, which codes for a melanocortin receptor, has a positive effect on daily
feed intake, probably mediated through the central control of appetite ( Kim
et al., 2000 ). Zhang et al. (2009) identified a QTL on chromosome 7 for the
number of visits of pigs to the feeder.
Aggressive interactions often occur during feeding ( Rydhmer et al.,
2006 ). In a study by Jonsson and Jørgensen (1989) where feed was a

0.4

5