ARCHIVE FILE
This article was published in 1987
See the original document
Sheep Losses From a Cold Wet Weather Change in Summer
by P.J. Ahrens, Veterinary Inspector Molong P.P. Board
Introduction
In the early hours of 2nd March, 1987, a most unseasonable cold change occurred in an area of central N.S.W. bringing with it constant rain and easterly winds that continued for several days. In Molong P.P. District, sheep losses exceeded 14,000. Adjoining P.P. Districts, namely Bathurst, Carcoar, Forbes, Condobolin and Dubbo were also affected and it would probably be no exaggeration to estimate a total mortality of at least 20,000 sheep.
Despite improved technology in weather forecasting in recent years, no warning was given of the impending disaster. Even during the event, weather reporters spoke each day of 'showers clearing'. Apparently the upper atmosphere development of a new low-pressure system such as that which occurred north of Cobar on 1st March represents a very difficult forecasting problem.
Following the mortality, various landholders and also Molong P.P. Board, wrote to the Regional Director of Meteorology and/or the Minister for Science. The inadequacy of the weather forecasting in this situation is admitted in their replies. The Minister said that more sophisticated numerical prediction models of atmospheric changes may be able to handle this type of problem in the future. For the moment some cold weather changes appear to be unpredictable.
The number of similar events that have been documented in Australia is limited. One in particular has certain features that parallel those in the Molong mortality. For instance, the fact that the weather Bureau failed to issue a warning (Buckman, 1982). In that mortality it was estimated that 100,000 sheep died in a small area of Western Australia on 21-22 January, 1982.
Methods
A week after some of the N.S.W. losses were reported, a survey questionnaire was sent by post to owners within Molong P.P. District who had reported losses and to owners quoted in 'bush telegraph' reports as having had losses.
They were asked to record each affected mob separately, to estimate the body condition of the sheep (1,2,3,4 or 5 score), whether the sheep were rising or falling in condition or holding 'steady', breed of sheep, age, sex and time since shearing. Each of the 23 owners surveyed was telephoned the following week to obtain the information.
Weather readings for Orange were obtained from records at the Agricultural Research and Veterinary Centre, Orange. Rainfall, maximum and minimum temperatures and wind run in km/24 hours were obtained from this source and tabulated (Table 2). The only other official weather records obtainable within the P.P. District were rainfall readings at Post Offices and at Orange Airport. The readings at Molong, Cumnock, Yeoval and Peak Hill are given in Table 1. Post-Offices no longer have temperature recordings as they once did. Also Monday rainfall figures (e.g. 2.3.87) now include all the weekend rainfall. In this case, the rain started gradually on Saturday 28.2.87, and the Monday reading represents the previous 40 hours or so.
Wind run does not include wind speed. The wind gusts which no doubt contributed to the stress on the wet sheep at certain times, were only recorded as part of the total wind run for the 24 hours prior to the 9 a.m. readings.
Results
Rainfall readings were as follows:
Table 1
| Rainfall in mm | 2.3.87 | 3.3.87 | 4.3.87 | 5.3.87 | Total |
|---|---|---|---|---|---|
| Molong | 64.0 | 75.0 | 15.4 | 32.0 | 186.4 |
| Orange | 12.2 + 51.2 | 51.0 | 14.0 | 21.4 | 119.0 |
| Cumnock | 43.0 | 72.5 | 26.4 | 25.0 | 166.9 |
| Yeoval | 37.0 | 43.8 | 33.0 | 7.2 | 121.0 |
| Peak Hill | 44.0 | 86.2 | 29.8 | 13.6 | 173.6 |
Table 2
Weather recordings at the Agricultural Research and Veterinary Centre, Orange.
| 28.2.87 | 1.3.87 | 2.3.87 | 3.3.87 | 4.3.87 | 5.3.87 | 6.3.87 | |
|---|---|---|---|---|---|---|---|
| Rainfall in mm | 0 | 12.2 | 51.2 | 51.0 | 14.0 | 21.4 | 0 |
| Maximum temperature °C | 29.2 | 18.6 | 11.5 | 13.0 | 14.8 | 19.8 | 22.3 |
| Minimum temperature °C | 15.1 | 16.5 | 10.2 | 8.9 | 9.7 | 11.0 | 10.5 |
| Wind Run in km/24 hrs | 147.4 | 320.3 | 170.7 | 355.3 | 376.3 | 275.7 | 191.3 |
The data recorded on the survey sheets for each owner is tabulated (Table 3). Each affected mob is numerated for each owner who is represented by a letter.
Table 3
| Mob | Breed | Age | Sex | Condition Score | Condition Steady or Falling | Time off-shears | No. at Risk | No. Dead | Rainfall |
|---|---|---|---|---|---|---|---|---|---|
| A1 | Merino | Adult | C | 3 | slightly falling | 3-7 days | 901 | 728 | 176 mm |
| A2 | Merino | Adult | C | 3 | slightly falling | 8 weeks | 526 | 92 | 176 mm |
| A3 | Merino | Adult | C | 3 | slightly falling | 8 weeks | 526 | 10 | 176 mm |
| B1 | XB | 7 M | X | 4 | steady | 10 weeks | 1000 | 50 | 221 mm |
| C1 | Merino | 6 M | C | 2 | steady | 11-14 days | 3200 | 2700 | 205 mm |
| C2 | Merino | Adult | F | 2 | steady | 11-26 days | 2000 | 200 | 205 mm |
| C3 | Merino | 30 M | F | 2 | steady | 11-26 days | 1159 | 270 | 205 mm |
| C4 | Merino stud | Adult | F | 3 | steady | 11-26 days | 575 | 186 | 205 mm |
| C5 | Merino | 18 H | f | 3 | steady | 11-26 days | 1033 | 20 | 205 mm |
| D1 | Merino | Adult | X | 2 | slightly falling | 4-7 days | 567 | 137 | 190 mm |
| D2 | Merino | 12 M | X | 2.5 | moderate falling | 4-7 days | 264 | 7 | 190 mm |
| D3 | Merino | Adult | F | 4 | moderate falling | 4-7 days | 240 | 175 | 190 mm |
| D4 | Merino | Aged | F | 4 | slightly falling | 4-7 days | 130 | 85 | 190 mm |
| D5 | Merino | 10 M | X | 2.5 | moderate falling | 4-7 days | 220 | 120 | 190 mm |
| D6 | Merino | Adult | M | 3 | slightly falling | 4-7 days | 23 | 6 | 190 mm |
| E1 | Merino | 6 M | X | 2 | slightly falling | 14-17 days | 750 | 285 | 120 mm |
| E2 | Merino | 2 Y | X | 2.5 | moderate falling | 17-28 days | 1140 | 610 | 120 mm |
| E3 | Merino | 2.5 Y | F | 3 | moderate falling | 17-28 days | 1070 | 336 | 120 mm |
| E4 | Merino | 4 Y | F | 3 | moderate falling | 17-28 days | 730 | 174 | 120 mm |
| E5 | Merino | 18 M | X | 3 | moderate falling | 17-28 days | 420 | 136 | 120 mm |
| E6 | Merino | Aged | F | 2.5 | moderate falling | 17-28 days | 530 | 48 | 120 mm |
| F1 | Merino | 6 M | F | 2 | slightly falling | 30 days | 713 | 389 | 167 mm |
| F2 | Merino | 6 M | C | 2 | slightly falling | 30 days | 689 | 339 | 167 mm |
| G1 | Merino | Adult | C | 3 | slightly falling | 6-14 days | 960 | 152 | 158 mm |
| G2 | Merino | 18 M | C | 2 | steady | 6-14 days | 690 | 140 | 158 mm |
| H1 | Merino | Adult | X | 4 | steady | 24 days | 351 | 99 | 214 mm |
| I1 | Merino | 7 M | X | 3 | slightly falling | 3 weeks | 850 | 300 | 182 mm |
| J1 | Merino | 6 M | X | 3 | slightly falling | 3.5 weeks | 750 | 400 | 113 mm |
| J2 | Merino | Adult | F | 3 | slightly falling | 3.5 weeks | 500 | 50 | 113 mm |
| K1 | Corrie | 5 M | F | 3 | moderate falling | 6-7 weeks | 800 | 300 | 165 mm |
| K2 | Corrie | 5 M | C | 3.5 | moderate falling | 6-7 weeks | 812 | 60 | 165 mm |
| L1 | Merino | X | X | 2.5 | steady | 6-12 weeks | 9000 | 100 | 108 mm |
| M1 | Merino | Aged | C | 3 | slightly falling | 2 days | 570 | 40 | 225 mm |
| M2 | Merino | Adult | F | 3 | steady | 4 days | 350 | 25 | 225 mm |
| N1 | Merino | 2 Y | C | 2 | slightly falling | 3 weeks | 1380 | 178 | 150 mm |
| O1 | Merino | X | F | 3 | steady | 2-5 days | 1082 | 599 | 150 mm |
| P1 | Merino | 6 M | X | 3 | moderate falling | 2.5 - 6 weeks | 414 | 114 | 137 mm |
| P2 | Merino | X | 3 | moderate falling | 2.5 - 6 weeks | 352 | 72 | 137 mm | |
| P3 | Merino | 18 M | X | 3 | moderate falling | 2.5 - 6 weeks | 525 | 74 | 137 mm |
| P4 | Merino | Adult | F | 4 | moderate falling | 2.5 - 6 weeks | 310 | 20 | 137 mm |
| P5 | Merino | Adult | F | 3 | moderate falling | 2.5 - 6 weeks | 515 | 30 | 137 mm |
| Q1 | Merino | Adult | C | 4 | steady | 10 days | 430 | 101 | 150 mm |
| R1 | Merino | Adult | F | 2-3 | steady | 3-5 weeks | 480 | 160 | 190 mm |
| R2 | Merino | Adult | C | 2-3 | steady | 3-5 weeks | 424 | 70 | 190 mm |
| R3 | Merino | 18 M | X | 2-3 | steady | 4 weeks | 342 | 190 | 190 mm |
| R4 | Merino | 6 M | X | 2-3 | steady | 3 weeks | 502 | 38 | 190 mm |
| R5 | Merino | Aged | F | 2-3 | steady | 2 weeks | 974 | 317 | 200 mm |
| R6 | XB | 5 M | X | 2-3 | steady | 11-12 days | 904 | 283 | 200 mm |
| S1 | Merino | Adult | F | 3 | steady | 2-4 weeks | 2000 | 300 | 170 mm |
| S2 | Merino | 6 M | X | 3 | steady | 2-4 weeks | 550 | 96 | 130 mm |
| S3 | Merino | Adult | C | 2 | steady | 2-4 weeks | 1100 | 100 | 170 mm |
| T1 | Merino | Aged | F | 3 | steady | 5 days | 184 | 94 | 193 mm |
| T2 | Merino | Adult | F | 3 | steady | 4 days | 611 | 270 | 193 mm |
| T3 | Merino | 18 M | F | 4 | steady | 3 days | 259 | 49 | 193 mm |
| T4 | Merino | 5 M | X | 3 | steady | 2 days | 589 | 384 | 193 mm |
| U1 | Merino | Adult | C | 4 | slightly falling | 3 days | 725 | 410 | 200 mm |
| V1 | Merino | 18 M | C | 3 | steady | 5 days | 573 | 83 | 191 mm |
| V2 | Merino | Adult | C | 3-4 | steady | 4 days | 230 | 60 | 191 mm |
| V3 | Merino | Adult | C | 2-3 | slightly falling | 2 days | 360 | 207 | 191 mm |
| W1 | Merino | 7 M | X | 3-4 | slightly falling | 3 weeks | 450 | 300 | 225 mm |
| W2 | Merino | Adult | F | 3-4 | slightly falling | 3 weeks | 300 | 162 | 225 mm |
| W3 | Merino | Adult | X | 3-4 | slightly falling | 3 weeks | 350 | 89 | 225 |
On the morning of 2nd March, 1987, recorded temperatures fell to 10.2°C and during the day rose no higher than 11.5°C. These temperatures were much lower than the normal summer temperatures to which the sheep were acclimatised.
However, of even more importance was the 'wind-chill' on the sheep whose fleeces were thoroughly saturated with incessant rain. The wind-chill factor would be difficult to quantify but the circumstances of the mortality suggest it was very severe.
No real relationship could be determined between the death rate in various mobs and the condition of the sheep or whether the owner thought their condition was steady or falling. Because of the deteriorating pasture conditions in the preceding weeks it was widely believed that nutrition played a major role in the mortality. However, this was not borne out in the survey.
A number of owners reported that losses were heaviest in paddocks with an easterly aspect. Sheep in relatively 'sheltered' paddocks with westerly aspect were much less affected, and this was due to the wind and rain coming predominantly from the east. By contrast, most adverse weather changes in this part of the world come from the south-west.
Because of difficulties in this type of survey, little attempt was made to evaluate shelter. Where sheep could be given total shelter, such as in a shearing shed, losses were minimal, but few of the surveyed owners were able to do this. In one goat mortality, freshly shorn Angora females were successfully shedded whereas of 85 wether goats left in a paddock with tree shelter, only 3 survived. One sheep owner described how sheep running before the wind, found an open door in an abandoned farmhouse and successfully sheltered inside. Other sheep on his property ran to a rough cave but many sheep smothered there or against the fence. Another grazier told of large numbers of dead sheep in the lee of a 4 metre earth bank. Yet others described sheep sheltering in erosion gullies, sometimes slipping down the banks in the mud to be smothered or drowned. There were also sheep that preferred sitting in dam water instead of being exposed to the unrelenting cold wind. Drownings were common. Generally it seemed that paddock shelter had little effect on losses and this is in support of the findings in Western Australia by Buckman (1982).
One factor that did have a strong relationship with mortality was wool cover. The mobs of sheep were grouped according to the number of weeks since shearing had taken place (weeks 'off-shears'), the mortality figures given by the survey respondents were converted to percentages and an average percentage determined for each group. A graph of these results is presented opposite.
Discussion
It is interesting to compare these survey findings with those of Buckman (1982) and Geytenbeek (1982). In the Western Australia disaster of January 1982, it was estimated that approximately 100,000 sheep died in two days. Buckman's survey involved 53,300 sheep on 17 properties which had a total mortality of 27 per cent. Rainfall figures were similar but rain fell on virtually only two days. Mortality figures showed that flocks which were 12 days or less off-shears suffered losses between 30 and 56 per cent whereas flocks 2 weeks or 3 weeks off-shears had generally low mortalities. There were one or two exceptions where in one case nearly 16% of sheep over 30 days off-shears died and another where 9% of sheep died with 37-40 days wool cover.
In the South Australian episode detailed by Geytenbeek (1982) about 5,000 shorn sheep died. On the surveyed properties which held 21,102 sheep 'at risk', mortality figures totalled 2,055. Nearly all deaths occurred in those sheep which were within 12 days off-shears.
While rainfall during the Molong mortality continued for several days, the bulk of the losses occurred in the first day or two. The death rate in sheep which were 1-2 months off-shears was quite substantial as shown in the graph. The reason for the difference between the death rate in this group of sheep at Molong and those with a similar wool cover in the Western Australia and the South Australian episodes is unclear.
Conclusion
A survey was conducted following reports of a heavy death toll among sheep exposed to a sudden cold wet weather change in March, 1987. A total of 13,620 sheep died out of 50,954 sheep comprising 62 mobs on 23 surveyed properties. Percentage mortality in each mob ranged from 1.1% to 80.8% with an average of 30.0% overall. Some factors which may have affected the death rate were discussed. The percentage of sheep which died in flocks of sheep which were several weeks off-shears was greater than recorded in previous off-shears mortalities.
Acknowledgements
I wish to thank Dr. R.L. Colman, Director of Research, Department of Agriculture, Orange for the Orange weather readings, Miss Maree Graham, typist, for the preparation of tables and graph, and the 23 land holders in Molong P.P. District who responded, all of them poorer but wiser men, to the survey questionnaire.
References
Anon (1961) Rural Research in CSIRO 36:21
Buckman, P.G. (1982) in 'Proceedings of a Seminar on Losses of Sheep after Shearing due to Adverse Weather', The Australian Society of Animal Production (W.A. Branch), p 11
Geytenbeek, P.E. (1982) ibid p8
Hutchinson, J.C.D. (1968) Australian Journal of Experimental Agriculture Anim. Husb. 8:393
Hutchinson, J.C.D, Bennett, J.W. and Wodzicka-Tomaszewska, M (1960) Proceedings of the Australian Society of Animal Production 3:199
Panaretto, B.A. (1967) Wool Technology and Sheep Breeding 14:27