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Publication Date
1981
Description
Diet selection by steers in northern Australia on a continuously grazed pasture of Setaria sphacelata var. sericea (Kazungula), Macroptilium atropurpureum (siratro), and Stylosanthes guianensis var. guianensis (Schofield) was studied. The pasture treatment that supported the highest annual weight gains (254 kg/steer) in a stocking-rate experiment had 1.7 steers/ha. Mean annual rain-fall was 1,490 mm, with 70 % falling from December to March. Monthly average temperatures are highest in December (30 .1 °C) and lowest in July (11. 9°C). Pastures were sampled in 1973 (seven 3-day periods) and 1975-1976 (six 3-day periods) with three esophageal fistulated steers. Extrusa samples were analyzed for nitrogen (N), in-vitro digestibility (IVD), and botanical composition. Pasture yield and composition were determined and herbage samples were analyzed for Nin 1973 and N and IVD in 1975-1976. In 1973 the proportion of legume (mostly siratro) in the cattle's diets was lower than the proportion of legume in the pasture (8 .2 % ), except in March, when it was 12 .3 % . The N content of the diet was always higher than the derived value of diet components. The IVD of extrusa samples exceeded 70% in five periods and was lowest (66.5 % ) in August 1973. Except for December 1975, the cattle selected a higher proportion of legume (again mostly siratro) in their diets than the proportion oflegume in the pasture, particularly in June (38.0% compared with 7.1 % ). Except for October 1975, the N content of the extrusa samples was greater than the derived values. The IVD of the diet was highest (67. 7 % ) in April and lowest ( 52.3 % ) in October 1975. Seasonal variations in pasture quality were apparent. Nitrogen and IVD values illustrated the relatively low quality of tropical pastures and the need for a high degree of diet selection to satisfy nutritional requirements. This degree of selection can be achieved only under lenient stocking pressures. On pastures continuously grazed at low stocking rates, preference for setaria over legumes during the early growing season is of practical importance in maintaining legumes. Higher legume yields can be obtained by resting pastures at critical times. In 1973, preference for setaria was associated with higher cool-season temperatures giving continued pasture growth.
Citation
Walker, B; Rutherford, M T.; and Whiteman, P C., "Diet Selection by Cattle on Tropical Pastures in Northern Australia" (1981). IGC Proceedings (1977-2023). 7.
(URL: https://uknowledge.uky.edu/igc/1981/section11/7)
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Diet Selection by Cattle on Tropical Pastures in Northern Australia
Diet selection by steers in northern Australia on a continuously grazed pasture of Setaria sphacelata var. sericea (Kazungula), Macroptilium atropurpureum (siratro), and Stylosanthes guianensis var. guianensis (Schofield) was studied. The pasture treatment that supported the highest annual weight gains (254 kg/steer) in a stocking-rate experiment had 1.7 steers/ha. Mean annual rain-fall was 1,490 mm, with 70 % falling from December to March. Monthly average temperatures are highest in December (30 .1 °C) and lowest in July (11. 9°C). Pastures were sampled in 1973 (seven 3-day periods) and 1975-1976 (six 3-day periods) with three esophageal fistulated steers. Extrusa samples were analyzed for nitrogen (N), in-vitro digestibility (IVD), and botanical composition. Pasture yield and composition were determined and herbage samples were analyzed for Nin 1973 and N and IVD in 1975-1976. In 1973 the proportion of legume (mostly siratro) in the cattle's diets was lower than the proportion of legume in the pasture (8 .2 % ), except in March, when it was 12 .3 % . The N content of the diet was always higher than the derived value of diet components. The IVD of extrusa samples exceeded 70% in five periods and was lowest (66.5 % ) in August 1973. Except for December 1975, the cattle selected a higher proportion of legume (again mostly siratro) in their diets than the proportion oflegume in the pasture, particularly in June (38.0% compared with 7.1 % ). Except for October 1975, the N content of the extrusa samples was greater than the derived values. The IVD of the diet was highest (67. 7 % ) in April and lowest ( 52.3 % ) in October 1975. Seasonal variations in pasture quality were apparent. Nitrogen and IVD values illustrated the relatively low quality of tropical pastures and the need for a high degree of diet selection to satisfy nutritional requirements. This degree of selection can be achieved only under lenient stocking pressures. On pastures continuously grazed at low stocking rates, preference for setaria over legumes during the early growing season is of practical importance in maintaining legumes. Higher legume yields can be obtained by resting pastures at critical times. In 1973, preference for setaria was associated with higher cool-season temperatures giving continued pasture growth.
