ROLE OF SPECIES DIVERSITY AND SECONDARY COMPOUND COMPLEMENTARITY ON DIET SELECTION OF MEDITERRANEAN SHRUBS BY GOATS.

Authors: ROGOSIC, J. - UNIV SPLIT, CROATIA; Estell, Richard - Rick; SKOBIC, D. - UNIV MOSTAR, BOSNIA; MARTINOVIC, A. - UNIV MOSTAR, BOSNIA; MARAIC, S. - UNIV MOSTAR, BOSNIA

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2006
Publication Date: 5/31/2006
Citation: Rogosic, J., Estell, R.E., Skobic, D., Martinovic, A., Maric, S. 2006. Role of species diversity and secondary compound complementarity on diet selection of Mediterranean shrubs by goats. Journal Chemical Ecology. 32:1279-1287.

Interpretive Summary: Goats are primary consumers of the Mediterranean maquis vegetation that predominates much of the Mediterranean grazing region. This vegetation is mainly shrubs, many of which contain toxic and/or aversive chemicals that have negative consequences for intake and well being of the animals consuming them. One strategy that animals may use to increase their ability to use these shrubs is to diversify their diet, because different chemicals are detoxified by different mechanisms in the body. We hypothesize that goats may be able to increase shrub consumption by increasing number of species and/or chemical classes consumed. We conducted a series of experiments to examine whether goats offered different mixtures of shrubs containing different amounts of tannins and saponins (chemicals that cause goats to eat less) would eat more total forage than animals eating a single shrub species or class of compound. We found that goats fed a mixture of three tannin-rich shrubs ate more foliage than goats offered only one of these shrubs. However, goats fed a mixture of the same three tannin-rich shrubs ate less foliage than goats offered a mixture of only two shrubs, one of which contained tannins, but one containing saponins. Within a class of compounds (tannins), increasing number of species consumed (increasing diet diversity) increased total intake. However, feeding two shrub species (one each containing tannins or saponins) resulted in greater intake than feeding three shrub species all containing the same class of compounds (tannins). Goats may be able to increase shrub intake by selecting from a large number of species containing a wide variety of plant toxins, possibly because the chemicals interact to reduce their negative effects.

Technical Abstract: Goats foraging on Mediterranean shrubs containing secondary compounds (toxins) may consume a variety of shrubs that contain different phytotoxins to increase shrub intake and avoid toxicosis. We conducted eight experiments to examine whether goats offered different mixtures of shrubs containing different phytotoxins (tannins and saponins) would consume more shrub biomass than goats offered one shrub with a single phytotoxin (tannin or saponin). In the first three experiments, goats fed a mixture of three tannin-rich shrubs (Quercus ilex, Arbutus unedo, and Pistacia lentiscus) ate more foliage (P < 0.01) than goats offered only one shrub (23.2 vs.10.7 g/kg BW; 25.2 vs.13.4 g/kg BW, and 27.9 vs. 7.9 g/kg BW), regardless of tannin concentration in individual shrub species. Goats also consumed more foliage (P < 0.01) when offered the same three tannin-rich shrubs than when offered the saponin-rich shrub Hedera helix in Exp. 4 (25.4 vs. 8.0 g/kg BW). However, goats offered a mixture of the same three tannin-rich shrubs consumed less foliage (P < 0.01) than goats offered a mixture of two shrubs containing tannins and saponins (Exp. 5 – 7): Quercus and Hedera (21.6 vs. 27.1 g/kg BW), Arbutus and Hedera (21.8 vs. 27.1 g/kg BW), and Pistacia and Hedera (19.7 vs. 22.0 g/kg BW). Comparison of intake of shrubs containing only tannins (Exp. 1, 2, and 3) or saponins (Exp. 4) to intake of shrubs containing both tannins and saponins (Exp. 5, 6, and 7) indicated goats consumed more total biomass (P < 0.01) when fed shrubs with both classes of compounds than with either tannins or saponins alone. Our results suggest goats can increase intake of Mediterranean shrubs high in secondary compounds by selecting those with different classes of phytotoxins. Simultaneous ingestion of shrubs containing tannins and saponins may promote chemical interactions that inhibit toxic effects of these phytotoxins in the intestinal tract. In addition to complementary interactions between tannins and saponins, biological diversity within Mediterranean maquis vegetation also plays a positive role in increasing shrub intake by goats.