Forage Intake and Free-ranging Ruminants: a Tropical Perspective

نویسنده

  • M. B. Hardy
چکیده

Grasslands in tropical environments are characterized by greater diversity than is found in temperate areas. In South Africa, greater diversity is found with the seasonally limited production which occurs on dystrophic soils under humid conditions in the sourveld, as opposed to the year round production that occurs on eutrophic soils under warm and drier conditions in the sweetveld. Most of the animal and plant characteristics that affect the intake of pasture plants in the temperate regions and in the sweetveld are involved in tropical areas and in the sourveld as well. However, some of these characteristics assume much greater significance in the tropics compared to temperate grasslands. In tropical areas, the grazing cutoff, or the amount of total herbage that must be present for any intake to occur, takes place with herbage yields below 500 kg dry matter (DM) ha for immature forage whereas it occurs with yields of over 1500 kg DM ha-1, when the forage is mature. Quality factors reducing intake of tropical pastures may be attributed to their relatively high content of fibre and to the unique plant anatomy of tropical forages, which combine to reduce the degradation rate, particularly of grass species, in the rumen. Sward greenness is also an important characteristic affecting intake. Gross modelling of performance of ruminants on tropical pastures demonstrated that stocking rate was negatively related to daily gain of cattle and plant species composition had very little effect on animal performance under conditions of overstocking. Analysis of results from mixed grazing studies, with sheep and cattle, found that systems with sheep only or ratios of cattle to sheep of less than 3:1, were less productive in terms of pasture output than systems where the cattle to sheep proportion was 3:1 or greater.

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تاریخ انتشار 1999