Agriculture Reference
In-Depth Information
emptying (Guerin
et al.
, 2001), attenuated glucose and insulin peaks and increased SCFA
production can also channel the feeding pattern by promoting satiety and thus postponing
the onset of a new feeding bout (De Leeuw
et al.
, 2008; Meunier-Salaün
et al.
, 2001;
Philippe
et al.
, 2008). These metabolic changes, however, seem to be partly transient over
time, which was attributed to an increased volume of gastrointestinal organs (stomach,
caecum, colon) due to the supply of high water-binding and fermentable dietary fibres
that promote a higher ingestive capacity (Jorgensen
et al.
, 1996; Whittaker
et al.
, 2000).
Investigations on feeding motivation in sows fed fibrous diets used various paradigms
including the observation of spontaneous behaviour, preference tests or operant
conditioning apparatuses. Data on the spontaneous feed intake of sows when fibrous diets
are offered
ad libitum
remain limited and concern mainly studies using mixed sources
of dietary fibres (Meunier-Salaün
et al.
, 2008; Philippe
et al.
, 2008). Nevertheless, the
comparative study of Brouns
et al.
(1997) on isoenergetic diets formulated with inclusion
of either sugar beet pulp, barley straw, oat husks, malt cums, or rice brain, showed a
lower voluntary feed intake of a diet with a high level of unmolassed sugar beet pulp
suggesting a self-restriction by animals, feed intake decreasing from 5.0 to 3.0 kg/d when
the inclusion level increased from 400 to 650 g/kg of feed. Such a reduction in feed
intake could be attributed to the specific properties of that fibre source, such as low
palatability and high water binding and fermentation characteristics. This could also be
interpreted as resulting from a reduced feeding motivation, which has been tested using
operant conditioning procedures at different time points after the meal. The apparatuses
used were either an electronic operant feeder or a food dispenser equipped with a wheel
where pigs had to press a button or turn the wheel to obtain a food reward. The number
of presses reflected the level of feeding motivation, thereby assessing hunger and satiety
levels (Bergeron
et al.
, 2002; Lawrence and Illius, 1989; Ramonet
et al.
, 2000b; Robert
et
al.
, 1997; Souza da Silva
et al.
, 2012).The appetitive phase of feeding behaviour, related
to food-searching, has also been tested in a runway where sows had to individually walk
a fixed U-shaped track to obtain a food reward at its end (Souza da Silva
et al.
, 2012).
Whatever the paradigm, sows fed fibrous diets tend to have lower numbers of rewards
when tested short-term after a meal, and Souza da Silva
et al.
(2012) reported stronger
effects of bulky (lignocellulose) or fermentable (resistant starch) fibres compared with
viscous fibres (pectin). Moreover, a comparative study on fermentable fibres by the
same authors also showed a reduced feeding motivation with increasing levels of dietary
fermentable fibres, with most pronounced effects of a retrograded tapioca starch (resistant
starch) compared with guar gum and inulin (Souza da Silva
et al.
, 2013). Nevertheless,
there is a high variation in the responses, linked to differences in procedures, including
the task to perform (fixed or progressive ratio in the operant test), nature of the reward
supplied (control diet, palatable or fibrous diet), and time point relative to the previous
meal. Indeed, sows fed a bulky diet could express physical difficulty for further ingestion
while still being 'metabolically hungry' or motivated to eat with a full stomach. This
suggests that the supply of a bulky diet could increase the feeling of satiation in the short
term but may not solve the sustained feeding motivation over a medium and a long-
term period after a meal. This was reported in multiparous sows tested with operant
conditioning 4.5 and 23 h after the meal and fed fibrous diets based on sugar beet pulp
or wheat bran (Ramonet
et al.
, 2000b), or tested 1.5 and 5.75 h after the meal and fed
