The effect of activated charcoal and number of species offered on intake of Mediterranean shrubs by sheep and goats

Maquis and garrigues are extensive shrubland vegetation types in the Mediterranean region that provide important habitat for wild and domestic herbivores. Although the majority of these shrubs are nutritious, virtually all contain secondary compounds that reduce their forage value. Understanding how animals cope with ingesting secondary compounds is vital for increasing consumption of shrubs and for enhancing and maintaining biodiversity of these shrublands. Ingesting compounds such as activated charcoal can ameliorate the negative effects of secondary compounds and enable animals to eat more shrubs, but offering a variety of shrubs may have a similar effect on increasing intake. Thus, our objectives were to determine if supplemental charcoal and numbers of shrub species offered influenced intake of shrubs by sheep and goats. We conducted two trials each with 12 sheep and 12 goats (six activated charcoal versus six controls). In Trial 1, we offered six shrubs. In Trial 2, we initially offered three shrubs (Period 1: Juniperus phoenicea, Helichrysum italicum and Juniperus oxicedrus), then two shrubs (Period 2: J. phoenicea and H. italicum), and finally one shrub (Period 3: J. phoenicea). In Trial 1, goats ate more total shrub biomass than did sheep (45.7 +/- 1.0 g/kg b.w. versus 27.2 +/- 0.7 g/kg body weight (b.w.), respectively), and there was no difference in shrub intake (P = 0.39) between charcoal-treated animals and controls (mean 37.5 +/- 0.8 g/kg b.w.). In Trial 2, supplemental charcoal had a positive effect on total shrub intake for both sheep and goats in all three periods (Period 1, P < 0.001; Period 2, P < 0.001 and Period 3, P < 0.03), and goats ate more shrubs than did sheep in all three periods (P < 0.01). Regardless of period, both species of animals showed a numerical decrease in total shrub intake, with or without supplemental charcoal, as the number of shrub species on offer decreased. Our findings support the hypothesis that plant biochemical diversity plays an important role in diet selection, thus enabling animals to better meet their nutritional needs and avoid toxicity. In addition, as the number of shrubs in the diet decreased, and supplemental energy was reduced, activated charcoal had a greater impact on shrub intake. Finally, activated charcoal had the same influence on sheep and goats throughout the trials, even though goats always ate more shrubs than did sheep.