Assessment of stocking rate and pasture management technologies on diet selection of cattle in central Queensland – An interesting case of confounding.
by
David Reid
Queensland Department of Primary Industries
Coauthors: RE Hendricksen (Queensland Department of Primary Industries)

Black speargrass (Heteropogon contortus) and forest bluegrass (Bothriochloa bladii) pastures are an important grazing resource for the beef industry of sub coastal Queensland. However, these pastures are showing evidence of deterioration with unpalatable perennial grasses, annual grasses and forbs replacing the palatable perennial tussock grasses. Management to maintain these native pastures in a healthy condition involves the judicious use of fire, stocking rate and spelling.

The effect of stocking rate and pasture management (legume over-sowing and strategic burning) on the wet season composition of the diet selected by cattle grazing these native pastures was investigated as one component of a larger long term grazing experiment in central Queensland. The general grazing experiment was a randomized complete block design consisting of 2 replicates of 11 treatments with a nested 3 x 3 factorial (3 pasture management options x 3 stocking rates). The diet selection study involved only the treatments in the nested factorial.

Oesophageal fistulated Brahman cross steers, separate to those grazing the trial paddocks, were sampled in March/April each year from 1992 to 1996 (inclusive), 1998 and 2000. Twelve steers were used in 1992 to 1995 and 9 steers in 1996, 1998 and 2000. The steers grazed similar native pastures to the main experiment except during the sampling period. At sampling each year, the steers were randomly allocated to 3 groups and each group randomly allocated to a stocking rate treatment. A group was then used to sample their allocated stocking rate treatment across replicates and pasture management treatments for that year. Although some steers were similar across years, the group and stocking rate treatment they were allocated to varied. The proportion of each species (particularly black speargrass and forest bluegrass) in the diet was measured for each of the sample steers each year.

This paper presents some of the issues related to the analysis of the diet selection data and the confounding of group and stocking rate, in particular.

Date received: September 3, 2002

Copyright © 2002 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cajn-25.