We examined the effect of reduction in food particle size on the rate and extent of fermentation of dry matter and cell walls in ruminants using in vitro and in sacco techniques. Large particles were digested at significantly lower rates, and time to initiation of cell wall degradation by microbes was signifcantly longer for large particles. Even after 144 h, large particles were digested to a lesser extent than were small particles. These results have important implications for digestive processing in herbivores, such as reptiles, that only minimally reduce food particle size. In these herbivores, digesta must be retained for much longer periods of time to achieve digestive efficiencies similar to those of herbivores that reduce food particle size to a greater extent. Length of retention time is a function of the amount of surface area exposed to microbial attack, not total surface area. Microbial activity concentrates in areas not protected by the cuticle. Because of the complexity of plant structure, r...

Digestive fermentation in herbivores: effect of food particle size.

Diet selection and optimization may be affected by nonadditive interactions (or associative effects) among ingested diet items. Associative effects occur when one diet item affects the digestion (either positively or negatively) of another diet item. Feeding trials were conducted with an opportunistic omnivore, the yellow-bellied slider turtle (Trachemys scripta scripta), on three diets: duckweed, insect larvae, and duckweed/larvae mix. Diet had a significant effect on digestibilities and intake, but not on transit time. There was a significant associative effect in the duckweed/larvae diet. For all diet components except lipids, the digestive efficiencies measured in the duckweed/larvae diet were significantly greater than those predicted from the digestive efficiencies for duckweed and larvae diets when fed alone. The presence of larvae in the digesta significantly improved the digestive processing of duckweed, probably by supporting greater numbers or diversity of cellulolytic microbes. A given mass of duckweed provided - 70% more energy and 20% more nitrogen to the turtle when ingested with insect larvae than when ingested alone. Associative effects should be incorporated in optimal foraging models and studies of diet selection because the value of a diet item can vary with the foods with which it is ingested. The assigned value must include not only the direct nutritional gain from the item, but also the indirect nutritional gain (or loss) through positive (or negative) effects on digestion of food items with which it is ingested.

Diet mixing: nonadditive interactions of diet items in an omnivorous freshwater turtle'

The relationship between elephant damage and leaf nutrient concentration across tree species was investigated in a semi-arid savanna in western Zimbabwe with the purpose of investigating possible nutritional factors influencing elephant feeding preferences in Kalahari sand woodlands The presence of elephant damage was recorded in all trees above 1 m in height, and leaf samples were collected from all tree species encountered in 12 vegetation plots during the late dry season Elephant damage was positively correlated with leaf calcium, magnesium, potassium and protein concentration, but not with sodium, phosphorus or fibre Tree species associated with sandy soils appeared to be less preferred by elephants and to have lower nutrient concentrations than species occurring on more fertile soils, such as species associated with termite mounds Elephant damage may suppress recruitment in preferred tree species in these woodlands This notion was supported by (1) the fact that 44% of all trees surveyed had had their main stems broken by elephants, a situation that leads to a multi-stemmed growth form with limited vertical growth; and (2) the negative correlation between the height of damaged trees and elephant damage across species

Woody plant damage by African elephants in relation to leaf nutrients in western Zimbabwe

http://www.remugants.cat/2/upload/llet_efectes_pastura_vs_convencional_produccia_jdsci_2005.pdf

Performance of lactating dairy cows managed on pasture-based or in freestall barn-feeding systems.

The strangler figs, Ficus pertusa and F. trigonata, are abundant in the seasonally flooded palm savanna (llanos intermedio) near Calabozo, Venezuela. The most common host tree for the hemiepiphytic figs is the palm Copernicia tectorum; nearly half of the palms support either an epiphytic or a ground-rooted fig. During their epiphytic stage the figs are rooted behind the palms' rnarcescent leaf bases. Material trapped behind the leaf bases is higher in organic matter, nitrogen, magnesium, and potassium than soil from the ground near the palms. The suggestion that nutrient availability to epiphytes is high is supported by the observation that concentrations of several nutrients, including N, P, and K, are significantly higher in epiphytic leaves than in tree leaves. Figs retain access to the epiphytic medium by producing upwardly growing (apogeotropic) roots that remain attached in the host palm's crown long after the fig has become firmly rooted in the ground. Although upward growing roots are expected to be more important in nutrient than water uptake, there are no obvious differences in the xylem anatomy of upward and downward growing fig roots. Terrestrial roots of fig trees are generally infected with vesiculararbuscular mycorrhizae, but the epiphytic roots of the same individuals are not infected. GROWTH HABITS in the genus Ficus (Moraceae, approximately 800 species) include free-standing trees, shrubs, lianas, epiphytes, banyans, and hemiepiphytes (Schimper, 1903; Trelease, 1905; Bessey, 1908; Small, 1936; Dobzhansky and Murca-Pires, 1954; Davis, 1970; Ramirez, 1977; Putz and Holbrook, 1986). Both strangling and nonstrangling hemiepiphytes start their lives as epiphytes and later produce roots that grow down to the ground. The roots of stranglers fuse to form a cylinder around the tree on which the epiphyte started and eventually, if the host tree dies, the fused roots serve as a trunk and the strangler remains standing on its own. We use the term "host" to refer to supporting trees in full recognition of the connotation of a parasitic relationship. Strangler fig seedlings use other trees for support and later impede the growth of their host by mechanically preventing diameter growth of their host trunk, by casting shade, and by competing for water and nutrients. By starting life as epiphytes, hemiepiphytes avoid some of the con

E.J. Golding

Papers

Modification of the Neutral Detergent Fiber Procedure for Hays