Conditioned feeding responses of sheep towards flavoured foods associated with the administration of ruminally degradable and/or undegradable proteinsources
G. Arsenos et al., Conditioned feeding responses of sheep towards flavoured foods associated with the administration of ruminally degradable and/or undegradable proteinsources, ANIM SCI, 71, 2000, pp. 597-606
The main objective of the experiment was to investigate the conditioned res
ponses of sheep towards food flavours associated with the administration of
ruminally degradable protein (RDP) and ruminally undegradable, but readily
digestible protein (DUP) sources given either alone or in combination. The
experiment consisted of three consecutive periods during which sheep were
conditioned to associate a flavoured food with a nutritive stimulus (or wat
er, W). Two foods (basal and novel test) with different crude protein (CP;
92 and 64 g/kg dry matter (DM) respectively) and similar metabolizable ener
gy (congruent to9 MJ/kg DM) contents were used on a total of 48 Texel x Gre
yface female sheep. The basal food was offered during non-experimental (res
t) days whereas the test food was used in combination with two flavours, or
ange and aniseed, during experimental days. Food was presented for 8 h (09:
00 to 17:00 h) daily throughout the experiment. Two nutritive stimuli (case
in, C, and formaldehyde treated casein, FC) were chosen such as to provide
major contrasts in their RDP and DUP contents, on an isonitrogenous basis.
Each dose (50 g) of a particular nutritive stimulus was administered by gav
age through a stomach tube twice daily (at 10:00 and 14:00 h). Sheep were r
andomly assigned to one of four (C v. W, FC v. W, C v. FC, C v. FC + C) tre
atments (no. = 12 per treatment). For the first 2 days (days I + 2) of each
conditioning period half of the sheep within each treatment were offered o
ne flavoured food paired with the administration of C (treatments C v. W, C
v. FC and C v. FC + C) or FC (treatment FC v. W). The other half were offe
red the opposite flavoured food paired with the administration of water (tr
eatments C v. W and FC v. W), FC (treatment C v. FC) or C + FC (treatment C
v. FC + C). There followed 2 days (days 3 + 4) of rest and for the 2 days
subsequently (days 5 and 6) received the opposite flavoured food and the op
posite stimuli to that received earlier. In the morning of day 7 sheep were
offered a choice between the two flavoured foods for 20 min. After the com
pletion of the preference test sheep were offered the basal food. The same
procedure was followed for each of three conditioning periods (i.e. each an
imal followed the same flavour/stimulus association throughout the experime
nt). The design was balanced for order of flavour and stimulus presentation
. Sheep preferred the flavoured food associated with C (P < 0.05) or FC (P
< 0.01) over the opposite flavoured food associated with water in C v. W an
d FC v. W treatments respectively. In the C v. FC treatment sheep showed a
strong preference for food flavours associated with the administration of F
C to those associated with C (P < 0.05). In the C v. FC + C treatment sheep
showed equal preference towards the food flavours associated with either s
timuli. These results: (i) support the view that sheep are able to form lea
rned preferences for food flavours associated with the administration of pr
otein, and (ii) suggest that sheep are able to distinguish between food fla
vours associated with the administration of both RDP and DUP sources. Sheep
preferred flavours associated with DUP administration only over flavours a
ssociated with RDP administration only; however such preferences did not de
velop when DUP was administered concurrently with RDP. Given the learned re
sponses of sheep towards flavours associated with RDP and DUP the expectati
on is that they may be able to select their diet on the basis of these qual
ities when they are offered a choice.