Biology Reference
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FIGURE 11.2
Pigs often eat together, but when individual feed intake should be recorded,
they have to eat one by one in an automatic feeding station. Photograph: Nils Lundeheim
restricted resource, social rank was correlated to growth rate (high rank
high growth rate). Growth rate is included in the genetic evaluation of all
pigs and in many breeding programs young pigs are tested in systems with
automatic feeders where only one pig at a time can eat. The genetic correla-
tion between feeding behavior in this system and feeding behavior when the
pigs are group fed in a trough is not known.
Residual feed intake (RFI) is a measure of feed efficiency that accounts
for the animal's energy requirements for production and maintenance. It is
calculated as the difference between observed and predicted feed intake. The
RFI concept was proposed as a selection trait for several species in the
1990s. With today's increasing awareness of the climate impact of animal
production, breeders' interest in RFI has increased. Low RFI in the growing
pig is genetically correlated to high leanness and low feed intake. Selection
for decreased RFI is, however controversial from a welfare standpoint, given
that the genetic variation in RFI reflects the genetic variation in activity and
response to stress (
Luiting and Urff, 1991
). In fact, RFI indirectly measures
the quantity of buffer resource available for activity, immune system, some
metabolic processes and stress response.
Sadler et al. (2011)
found a genetic
correlation between activity and RFI (high RFI
high activity level).
Reduction of RFI by selection increases feed efficiency at the expense of
reduced feeding activity, owing to a positive genetic correlation between RFI
and feeding duration (
von Felde et al., 1996
).
Young and Dekkers (2011)
compared a line selected for reduced RFI with a control line in pens where
pigs from both lines were mixed, and fed with a single-space electronic
feeder from 3 months until slaughter. Pigs selected for low RFI had less
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