Rapisarda, Teresa and Mereu, Alessandro and Cannas, Antonello and Belvedere, Giovanni and Licitra, Giuseppe and Carpino, Stefania (2012) Volatile organic compounds and palatability of concentrates fed to lambs and ewes. Small Ruminant Research, Vol. 103 (2-3), p. 120-132. ISSN 0921-4488. Article.
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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 ewes, 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 (α-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 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 palatability.
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