Frequency distribution of sward height of kikuyu (Pennisetum clandestinum) grass pastures intensively grazed by dairy cows
R. C. Dobos A F , K. Sinclair B , G. N. Hinch C and W. J. Fulkerson D EA NSW Department of Primary Industries, Beef Industry Centre, Armidale, NSW 2351, Australia.
B NSW Department of Primary Industries, Wollongbar Agricultural Institute, Wollongbar, NSW 2477, Australia.
C School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia.
D NSW Department of Primary Industries, Wollongbar Agricultural Institute, Wollongbar, NSW 2477, Australia.
E Present address: 112 Lindendale Road, Wollongbar, NSW 2477, Australia.
F Corresponding author. Email: robin.dobos@dpi.nsw.gov.au
Animal Production Science 49(7) 574-585 https://doi.org/10.1071/EA08263
Submitted: 29 October 2008 Accepted: 5 March 2009 Published: 11 June 2009
Abstract
Swards that are grazed continuously by cattle can become heterogeneous in structure, such that frequencies of height measurements have a skewed distribution. This structure has been best described by the double-normal, gamma and Weibull distributions rather than by the more common single-normal distribution. Limited analysis of the frequency distribution of sward height under dairy cattle grazing management is available. The current paper reports the frequency distribution of sward height under intensive dairy cow grazing of kikuyu (Pennisetum clandestinum) in a subtropical environment.
Frequencies of sward height were collected during an experiment designed to investigate the effects of compressed sward height and grazing duration on grazing behaviour of dairy cows. There were two compressed sward heights (10 and 13 cm; Earle and McGowan 1979) and five grazing durations (1, 2, 4, 8 and 15 h). The frequency of height measurements taken were then fitted to four distributions – single-normal, log-normal, gamma and Weibull – to determine if treatments influenced the structure of the sward as grazing duration progressed.
The frequency of sward height measurement was best described by the log-normal distribution. However, no one distribution described the frequency of height measurements consistently as grazing duration progressed, as determined by Akaike information criteria. The present analysis did not provide unequivocal evidence for either bimodal or unimodal distributions describing the height measurements for 10- and 13-cm compressed sward height treatments as grazing duration progressed.
Additional keywords: grazing duration, log normal, single normal, Weibull.
Acknowledgements
Analysis of sward data to determine the effect due to treatments and paddocks was conducted by Mr S. Morris, Biometrician, NSW Department of Primary Industries, Wollongbar Agricultural Institute, Wollongbar. Dr E. I. Duff (Biomathematics and Statistics Scotland) assisted with the coding of the Genstat program. We also acknowledge the two anonymous referees for suggestions on improving the presentation.
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