Impacts of grazing management options on pasture and animal productivity in a Heteropogon contortus (black speargrass) pasture in central Queensland. 3. Diet composition in autumn
R. E. Hendricksen A B , D. J. Myles A B , D. J. Reid A and D. M. Orr A CA Department of Employment, Economic Development and Innovation, PO Box 6014, Rockhampton Mail Centre, Qld 4702, Australia.
B Retired.
C Corresponding author. Email: david.orr@deedi.qld.gov.au
Animal Production Science 50(4) 276-283 https://doi.org/10.1071/AN09090
Submitted: 2 June 2009 Accepted: 19 March 2010 Published: 12 May 2010
Abstract
The diet selected in autumn by steers fistulated at the oesophageous was studied in a subset of treatments in an extensive grazing study conducted in a Heteropogon contortus pasture in central Queensland between 1988 and 2001. These treatments were a factorial array of three stocking rates (4, 3 and 2 ha/steer) and three pasture types (native pasture, legume-oversown native pasture and animal diet supplement/spring-burning native pasture). Seasonal rainfall throughout this study was below the long-term mean and mean annual pasture utilisation ranged from 30 to 61%. Steers consistently selected H. contortus with levels decreasing from 47 to 18% of the diet as stocking rate increased from 4 ha/steer to 2 ha/steer. Stylosanthes scabra cv. Seca was always selected in legume-oversown pastures with diet composition varying from 35 to 66% despite its plant density increasing from 7 to 65 plants/m2 and pasture composition from 20 to 50%. Steers also selected a diet containing Chrysopogon fallax, forbs and sedges in higher proportions than they were present in the pasture. Greater availability of the intermediate grasses Chloris divaricata and Eragrostis spp. was associated with increased stocking rates. Bothriochloa bladhii was seldom selected in the diet, especially when other palatable species were present in the pasture, despite B. bladhii often being the major contributor to total pasture yield. It was concluded that a stocking rate of 4 ha/steer will maintain the availability of H. contortus in the pasture.
Additional keywords: burning, Heteropogon contortus pastures, legume oversowing, oesophageal fistula, selection indices, stocking rate.
Acknowledgements
Special acknowledgement is made to the Neill-Ballantine family (Galloway Plains Pastoral Co.) for their ready cooperation and for the long-term use of land on which the study was based. Many people contributed to the overall conduct of this grazing study during its 13-year duration and it is impossible to comprehensively list all these people here. We would especially acknowledge the large number of Department of Primary Industries and Fisheries and Department of Natural Resources and Water staff who provided major contributions to this study’s success. A Producer Advisory Group readily gave constructive advice throughout the study. Funding was provided by Meat and Livestock Australia.
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