Back to Search Start Over

Evaluating seasonal risk and the potential for windspeed reductions to reduce chill index at six locations using GrassGro.

Authors :
Broster, J. C.
Robertson, S. M.
Dehaan, R. L.
King, B. J.
Friend, M. A.
Source :
Animal Production Science; Oct2012, Vol. 52 Issue 10, p921-928, 7p, 1 Chart
Publication Year :
2012

Abstract

The death of newborn lambs is a major factor influencing the reproductive efficiency of sheep enterprises. Adverse weather conditions (wind, precipitation and low temperature), either alone or in combination (chill index), can increase the level of newborn lamb mortality to over 50% of births for short periods through increased heat loss. The provision of shelter to reduce wind speed and therefore chill index (heat loss) has been shown to reduce lamb mortality; however, the reduction in mortality has been variable. This study used the decision support tool GrassGro to determine the likelihood of adverse weather conditions occurring at six locations across south-eastern Australia which varied widely in climate. Data were extracted for 24 consecutive weekly periods between May and October over 39 years (1968-2006) to evaluate daily precipitation, temperature, radiation, wind speed and chill index. The minimum, maximum and median values were calculated for all climatic factors for every week and year combination. The effectiveness of reducing wind speed to reduce the occurrence of a high chill index was also evaluated. The severity of these weather events varied between locations with the median weekly chill index rarely exceeding 1000 kJ/m².h at Temora, but at both Hamilton and Orange this occurred in over two-thirds of the weeks examined. Reducing wind speed by 50% reduced the number of weeks with a median chill index exceeding 1000 kJ/m².h in twice as many weeks at Hamilton and Yass compared with Orange. These results show that the potential for shelter to reduce chill index will vary according to the location and time of year. In locations where another climatic factor, such as low temperature or rainfall, has a greater influence on the chill index, shelter which only reduces wind speed, will be less effective than at locations where wind speed is the driver of chill index. Shelter can reduce newborn lamb mortality although experimental results have been variable. The likelihood of adverse weather over the autumn to spring months and the influence that reductions in wind speed had on chill index was modelled for six locations in south-eastern Australia. Reducing wind speed was more effective in reducing chill index to below critical levels at certain locations and weeks of the year, which should be taken into account when deciding on whether to invest in shelter. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
18360939
Volume :
52
Issue :
10
Database :
Complementary Index
Journal :
Animal Production Science
Publication Type :
Academic Journal
Accession number :
79972969
Full Text :
https://doi.org/10.1071/AN12066