|Estell, Richard - Rick|
Submitted to: Applied Animal Behaviour Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2006
Publication Date: 9/7/2007
Citation: Rogosic, J., Estell, R.E., Skobic, D., Stanic, S. 2007. Influence of secondary compound complementarity and species diversity on consumption of Mediterranean shrubs by sheep. Applied Animal Behavior Science. 107:58-65.
Interpretive Summary: Sheep are important browsers of the Mediterranean maquis vegetation dominating much of the Mediterranean grazing region. This vegetation is mainly shrubs, and many of them contain toxic and/or aversive chemicals that negatively affect intake and well being of livestock. Animals may be able to increase their ability to use these shrubs by diversify their diet, because different chemicals are detoxified by different metabolic pathways. We hypothesize that sheep may be able to increase shrub consumption by increasing the number of species and/or chemical classes in their diet. We conducted four experiments to examine whether sheep offered different mixtures of shrubs containing different amounts of tannins and saponins (chemicals that reduce intake) would eat more total forage than animals fed mixtures of shrubs containing only one class of compounds (tannins). Sheep fed the mixtures containing both saponins and tannins ate more total forage than sheep consuming the same number of shrubs containing only tannins. Sheep also ate more of each individual shrub species when fed with the high-saponin shrub than when fed only high-tannin shrubs. These results suggest that complementary interactions between forages containing different classes of secondary compounds may occur in livestock browsing shrubs. Producers in Mediterranean regions may be able to capitalize on the interactions of different classes of plant chemicals to increase intake and performance of sheep.
Technical Abstract: Generalist herbivores foraging in chemically diverse grazing ecosystems like the Mediterranean maquis increase intake on mixed diets, suggesting they are more able to meet nutritional needs and avoid toxicosis. Thus, our objectives were to determine how shrub species diversity and complementary interactions between tannins and saponins influence intake of Mediterranean shrubs by sheep. We conducted four experiments comparing intake of mixtures of Mediterranean shrub mixtures varying in number of species and/or principal class of secondary compound (tannins or saponins) by sheep (n = 12). Sheep consumed more total foliage (P < 0.01) when offered a high-tannin shrub (Pistacia lentiscus; Exp. 1), two high-tannin shrubs (Pistacia lentiscus and Arbutus unedo; Exp.2), or three high-tannin shrubs (Pistacia lentiscus, Arbutus unedo, and Quercus ilex; Exp. 3) when fed in conjunction with a high-saponin shrub (Hedera helix) than with an equal number of high-tannin shrubs (20.94 vs. 16.32 g/kg BW; 28.76 vs. 20.77 g/kg BW, and 35.34 vs. 26.85 g/kg BW). Likewise, sheep ate more foliage (P < 0.01) of each individual shrub (Pistacia lentiscus, Arbutus unedo, and Quercus ilex) in the mixture when fed with Hedera helix than with an equal number of high-tannin shrubs (8.17 vs. 4.95 g/kg BW; 13.28 vs.10.68 g/kg BW, and 7.62 vs. 5.16 g/kg BW), suggesting a complementary interaction between tannins and saponins may have occurred. Sheep also appeared to increase total shrub intake as number of shrub species on offer increased, regardless of number of classes of compounds present. Our findings suggest that secondary compounds in Mediterranean shrubs (tannins and saponins) are complementary. Species diversity also plays an important role in diet selection, as plant species with different types and amounts of nutrients and phytotoxins may affect forage intake and animal production. This knowledge may be useful for livestock producers to capitalize on phytochemical interactions to improve performance of livestock foraging on Mediterranean shrublands.