Abstract :
The aromatic characteristics of concentrate feeds can affect feed intake in ruminants. In a
previous study, the palatability of 14 feeds, mostly concentrates, was tested in lambs and
mature dry ewes. In this study, the volatile profile of those feeds was measured by electronic
nose analysis and gas chromatography–olfactometry as well as by mass spectrometry and
the identified compounds were associated with their palatability. Another concentrate feed
(barley meal) was used in the training of the animals for the palatability tests and was also
subjected to the same instrumental analysis.
Feed palatability by the lambs ranged from 0 mg/kg BW to 1379 mg/kg BW in a preference
gradient that did not show clear cuts among types of feeds. The ewes, instead, showed clear
preferences, with higher (P < 0.05) level of intake during the 6 min palatability tests for beet
pulps, wheat grains, pea grains, and corn grains compared to the other feeds. The electronic
nose showed a good separation between the most palatable and the least palatable feeds
both in lambs and in ewes. The rank of total volatile organic compounds (VOCs) found in
the feeds was, in decreasing order: beet pulps (27 VOCs), oat grains (26 VOCs), dehydrated
alfalfa (20 VOCs), soybean hulls (19 VOCs), soybean meal 44 (18 VOCs), sunflower meal (16
VOCs), barley meal (15 VOCs), corn gluten meal and soybean meal 49 (14 VOCs), wheat brans
(13 VOCs), corn middlings (12 VOCs), canola meal (7 VOCs), wheat grains (6 VOCs), corn
grains and pea grains (5 VOCs). The aroma profile of the beet pulps, which were the most
eaten feed by ewes and had intermediate intake by lambs, was characterized by a pleasant
aroma of green and fruity notes because they were the richest of aldehydes (11 VOCs) and
poor of sulphur compounds (2 VOCs). Dehydrated alfalfa and sunflower meal, which were
commonly refused by lambs and unpleasant notes of garlic and cooked potato to the feed and probably negatively affected
its palatability. These results suggested that the aroma of several feeds might have affected
animal short-term intake responses. The gas chromatography/olfactometry analysis can
be a useful tool to identify potential candidate molecules that might explain the feeding
choices of animals in terms of sensorial perceptions. However, more research is needed
to better understand the specific compounds involved and to separate the flavour effects
from the many other factors affecting palatabilityewes, were both rich of sulphur compounds (5 VOCs),
whose unpleasant notes probably affected their palatability. Soybean meal 44, which was
refused by the ewes and the least eaten of soybean by-products by lambs, and sunflower
meal were characterized by a rich aroma profile but by a negative note due to the presence of
methanamine, which gave an off-flavour identified as rotten fish odour. Oat grains, although
characterized by pleasant flavours due to their richness of aldehydes (10 VOCs) and terpenes
(7 VOCs), were refused by lambs and ewes. This was probably due to the presence, among
the terpenes, of a unique compound ( -pinene), with a resin-pine flavour which is known
to negatively affect intake of alfalfa pellets in lambs. Corn gluten meal, which was refused by
lambs and ewes, was characterized by the presence of four sulphur compounds, which gave
