Mass to height relationships in annual pastures and prediction of sheep growth rates
S. M. RobertsonDepartment of Environment and Primary Industries, Private Bag 1, Walpeup, Vic. 3507, Australia. Present address: Graham Centre for Agricultural Innovation (NSW Department of Primary Industries and Charles Sturt University), Locked Bag 588, Wagga Wagga, NSW 2678, Australia. Email: surobertson@csu.edu.au
Animal Production Science 54(9) 1305-1310 https://doi.org/10.1071/AN14072
Submitted: 5 February 2014 Accepted: 19 May 2014 Published: 10 July 2014
Abstract
The relationship between pasture height and mass influences the availability of pasture for grazing, and is important for predicting intake of pasture and liveweight change by sheep. The relationship between pasture mass and structure and sheep production is poorly defined for low-mass, clumpy pastures in low-rainfall regions. Between 2001 and 2004, 480 quadrats of pastures were measured in 23 paddocks throughout the Victorian Mallee. Pasture height was related to live mass for medic (linear; r2 = 0.70; P < 0.001) and grassy medic (asymptotic; r2 = 0.64; P < 0.001) pastures, and prediction of grassy medic pasture height was improved by inclusion of proportion live groundcover. During 2004, pasture dry matter accumulation and liveweight changes in sheep grazing annual pastures were measured and compared with predicted outputs from GrazFeed, a software model used to estimate feed intake and liveweight change in sheep. Improved predictions of liveweight gain in grazing sheep were obtained using measured height rather than the GrazFeed default height. The results show that the height to mass relationship of annual pastures in the Victorian Mallee differs between pasture types, between years, and may differ from other published relationships. This study provides information that may assist in the development of models of grazing systems.
Additional keyword: simulation.
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