• Plant structure and the acceptability of different grasses to sheep

      O'Reagain, P. J. (Society for Range Management, 1993-05-01)
      Plant structure should be an important determinant of species acceptability to grazing ungulates functioning under various time-energy constraints. The acceptability of 9 grasses to sheep grazing a secondary grassland community in spring, summer, and autumn in South Africa was related to the following species attributes: plant height, leaf table height, tussock diameter, stemminess, percent leaf, leaf density, percent dry matter (DM), leaf tensile strength, and leaf crude protein (CP). Species acceptability over the grazing season was positively related to tussock diameter (P less than or equal to 0.05) but negatively related (P less than or equal to 0.01) to leaf tensile strength and DM. Discriminant function analysis successfully discriminated between species in different acceptability classes in summer (P less than or equal to 0.05) and autumn (P less than or equal to 0.01) using a combination of plant structure and leaf quality attributes. Correspondence analysis indicated that preferred species were generally short and nonstemmy and had leaves of low DM, low tensile strength, and high crude protein content. Conversely, avoided species tended to be tall and stemmy with a high leaf table height, and had leaves of high DM and tensile strength but low CP levels. It is concluded that, for sheep, acceptability is determined by a combination of plant structure and leaf quality attributes.
    • Sequence of species selection by cattle and sheep on South African sourveld

      O'Reagain, P. J.; Grau, E. A. (Society for Range Management, 1995-07-01)
      The sequence of species selection over the grazing period directly determines the effectiveness of different grazing systems. Knowledge of this sequence is also important in understanding the plant-animal interface. The sequence of tiller defoliation by cattle and sheep was compared for 7 range grasses at 4 different sites in South African sourveld. Defoliation frequency and height was monitored daily over a 6-day grazing period at each site. The sequence of species selection was the same for cattle and sheep although the acceptability of some grasses varied between animal species. Preferred species were always grazed first along with some (<20%) utilization of species of intermediate acceptability. When about 60% of the tillers of the preferred species had been defoliated, regrazing of these tillers commenced and the rate of utilization of intermediate species increased. Only after 80 to 100% of the tillers of preferred and intermediate species had been defoliated were tillers of the least-preferred species grazed. Sheep were more selective and tended to graze the least-preferred species later in the grazing period than did cattle. There was no difference between cattle and sheep in the frequency of tiller defoliation over the grazing period but tillers were defoliat- ed to a lower height (P < 0.01) and more tissue removed (P<0.01) under sheep grazing. Cattle and sheep are therefore likely to differ in their potential impact upon rangeland.