Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 4 Western Australia, Series 4
Volume 6
Number 7 1965 Article 4
1-1-1965
Stocking rate and wool production at Kojonup Stocking rate and wool production at Kojonup
Davies H. Lloyd A. W. Humphries
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Recommended Citation Recommended Citation
Lloyd, Davies H. and Humphries, A. W. (1965) "Stocking rate and wool production at Kojonup," Journal of the Department of Agriculture, Western Australia, Series 4: Vol. 6: No. 7, Article 4.
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STOCKING RATE AND WOOL PRODUCTION AT KOJONUP
1 . WETHER SHEEP
By H. L L O Y D DAVIES* and A . W . H U M P H R I E S *
RESEARCH workers in several parts of the world have recognised the overriding i m - portance of stocking rate in raising animal production per acre. This article describes some o f the i n i t i a l work on the e f f e c t of stocking rate on wool production and live- weight change in medium-Peppin M e r i n o sheep. The work was carried out at the C.S.I.R.O. " G l e n Lossie" Field Station at Kojonup, Western Australia.
In 1958, when the experiment began, the average stocking rate on improved pastures in the Kojonup Shire was about 1.7 sheep per acre. Pasture production figures obtained on "Glen Lossie" over some years suggested that much of the potential of the district was going to waste, under conditions which favoured intensive wool production.
During the 1958 growing season, five paddocks were fenced oft* on an area which had carried a normal pasture for several years. The soil was typical of the district
—a sandy loam overlying a stiff clay sub- soil.
After shearing in September, groups of six Merino wethers, matched for an aver- age body weight of 105 lb. were placed on the plots. The sizes of the plots were varied so that the stocking rates over the experi- ment ranged from one sheep per acre at the lowest, to five sheep per acre at the highest.
Flock management was very simple.
The animals were kept continuously on Pasture with no supplementary feeding of any kind. The mature wethers put on the plots in September, 1958, were replaced by young sheep in September, 1959; these
remained on the plots until September, 1961, when they were replaced by young wether sheep. In both cases, the wethers were 17 months old when placed on the plots. Each time sheep were replaced, the average weight of new sheep placed on each plot was the same.
There was no drenching against inter- nal parasites.
Fertiliser applications consisted of an autumn topdressing each year with super- phosphate at 180 lb. per acre. There was no testing to determine whether this rate was the most satisfactory, but it is likely that a reduction in rate would have had little effect on the results.
This stocking rate trial was the first of its type carried out in the agricultural areas of Western Australia and had an important in- fluence on the current trend towards "set stock- i n g " of sheep at higher stocking rates.
Many other trials have followed, and some of these will be reported in coming issues of the Journal of Agriculture. These will include special progress reports on stocking rate trials being carried out by the Department of A g r i - culture in a number of important agricultural districts.
* Division of Plant Industry, C.S.I.R.O., Western Australian Regional Laboratory, Nedlands, Western Australia.
409
Information of several kinds was col- lected from the experiment:
• The body weights of the sheep were measured at intervals of three weeks.
• Fleece weights were measured at each shearing, which took place in in late August—early Septem- ber in each year.
• Pasture production was followed by cutting sample areas in each plot, over-drying the cut material,
and then weighing.
• Pasture composition (the propor- tions of sub-clover, grasses, cape- weed, etc., which were present in the pasture) was also determined by sorting cut samples into their component parts.
Wool Yields
Table 1 shows the average fleece weights of each group of six sheep for each year of the experiment, and also the average weights for the whole period.
Table 1.—Average fleece weights (lb. per sheep) of wethers stocked continuously at 1 to 5 sheep per acre.
Year 1959 I960 1961 1962 1963 Average for
5 years Stock
1
13-7 118 12-3 9 2 1 3 1 1 2 0
ing rate (Sheep per 2
131 10-5 1 1 6 8 9 I I I 1 1 0
3
12 8 10-7 I I S 8-2 I I I 10 9
4
11-4 9-6 10-7 7 1 10-1 9-8
acre) 5
10-9 9-1 10 4 7-9 9-7 9-6
Average for all stocking rates 12-4 10-3 11-4 8-3 110
Rate of stocking had fairly consistent effects on the yield of wool per sheep.
With some exceptions, the higher the rate of stocking, the lower was the fleece weight of the sheep. The difference between one sheep and two sheep an acre was a little surprising, for in both cases there was an abundance of feed on the plots throughout the year. It is possible t h a t t h e consistently better per- formance of the sheep at one per acre was due to the greater opportunity the animals had to select their diet, but this can only be surmised.
Seasonal variations had almost as much effect as stocking rate on the amount of wool produced by each animal. It will be seen in the Table t h a t the overall average fleece weight varied from 8.3 lb. per head in 1962 to 12.4 lb. in 1959. Some of these differences were due to t h e fact that young sheep were placed on the plots at shearing time in 1959 and 1961, but there is no doubt t h a t much of t h e differences were due to variations in weather from year to year. The poorest year, 1962, had a low total rainfall (17 inches) and a late
"break" (last week in May.)
These variations are of some import- ance, especially because they were meas- sured in a district usually regarded as
"reliable." In areas of lower average rainfall even bigger variations are pos- sible, and the hazards of stocking at high rates would be correspondingly greater.
Careful and conservative management would be more necessary in that case.
Although wool yields per sheep declined as the rate of stocking was increased, wool yields per acre of pasture climbed steadily. This is illustrated in Figure 1, in which the average production per acre over the five year period is given.
The economic importance of this result needs no emphasis. Even though higher stocking rates are likely to increase costs per acre in several ways, there can be no
Fig. 1.
SHECP PE# ACXE -Average wool production per acre per year over five
years at five rates of stocking
410
question that increasing stocking rate will increase net returns. Not necessarily, of course, will the highest rate be the best economic rate, nor the best in terms of animal and pasture husbandry. This problem will be discussed further later in this article.
Wool Quality
Independent reports on the quality of the wool produced were obtained from a wool store, and from the flock-testing unit of the Department of Agriculture, in 1963.
The sale report showed little effect of stocking rate on quality, or on the price received at auction. Tender wool was found in all lots, but there was a little more in the fleeces from the higher stock- ing rates. All lots were rated "Good" or
"Average-Good," except for two fleeces from the five sheep per acre flock.
The Department of Agriculture report also disclosed only minor differences.
Staple length was shorter for the five sheep per acre group, and quality ratings were also a little lower for that group.
There were no apparent differences over the range for one to four sheep per acre.
Liveweight Changes
Measurement of liveweight of each animal at three-weekly intervals was
carried out, to assess the effects of rate of stocking on the condition of the sheep.
The general seasonal trends were con- sistent from year to year.
From the break of the growing season, liveweights increased slowly through the winter, then rapidly in the spring. By about January, a slow loss of weight began, and continued until the next growing season. The effects of rate of stocking on liveweights showed trends generally similar to fleece weights. For most of the five-year period, the flocks at one sheep per acre maintained the highest body weight and those at five per acre the lowest. This was not invariably the case, for in the spring period especially, the animals at the highest stocking rate gained weight very rapidly, and, in two of the years, had the highest average body weight for a short period. The graphs of bodyweight changes for 1960-61, a "good" year for wool production, and 1961-62, a "poor" year, are shown in Figure 2 (a and b).
Deaths
Stock losses did take place on the experiment, as is almost inevitable in a total of 90 animals over a five-year period. The total number of deaths, how- ever, was quite insignificant, and showed no relationship to rate of stocking.
Fig. 2a.—Liveweight changes of wether sheep a t five rates of stocking, 1960-61 (a " g o o d " year for wool production}
411
Sheep set-stocked at five sheep an acre in one paddock of the "Glen Lossie" experiment.
and volunteer grasses
The pasture was mainly capeweed
Pasture Composition
The intensive production of wool achieved at the higher stocking rates was obtained from pastures containing little clover. In the 1960 winter, the proportion
(by weight) of sub-clover in the pastures ranged from 22 to 38 per cent. In most pastures, the proportion of clover usually falls as spring advances; by October of
1960, the measured proportions of clover had declined to a minimum of 3 and a maximum of 14 per cent. For the remain- ing years, no plot contained more than 16 per cent, clover, and most values ranged from 1 to 4 per cent.
Pasture production depended mainly on capeweed and volunteer grasses (mainly ripgut brome grass and barley grass).
SHEEP PER ACRE
Fig. 2 b — L i v e w e i g h t changes of wether sheep at five rates of stocking, 1 9 6 1 - 6 2 (a "poor" year for wool production)
412
There was no evidence, in this experiment, that clover was encouraged by heavy grazing. With most of the pastures con- taining only 1 to 4 per cent, of clover, it is likely that some other factor was responsible for the virtual absence of the legume. It would be misleading to assume that the lack of any effect of higher stocking rates on clover content of the pastures in this experiment would apply generally.
Application to the Farm
The general conditions chosen for the experiment—pasture type, soil type, fer- tiliser applications, type of sheep—are those which are typical for many farms.
However, it is clear t h a t the results cannot be applied directly to farms, without further consideration. The sizes of the experimental paddocks were very small by farm standards, and this may affect the carrying capacity of the pasture.
For experimental purposes, the risk was deliberately taken that the highest rates of stocking might be too high, perhaps causing serious losses in the poorer seasons. This did not happen, but there were periods of up to three to four months when the average body weight of the sheep stocked at five per acre dropped to 80 to 90 lb. per head, and the amount of pasture available was very small. On the farm, risks perhaps should be taken, but not to the extent that can be taken for experimental purposes.
Another serious limitation encountered on the five sheep per acre plot was the loss by erosion of some surface soil. This was caused by heavy rain falling in the late summer—early autumn when the ground cover was very thin. Although in this case the damage was not great, and was confined to one year, erosion of that kind is clear evidence of one risk of over- stocking.
What then, would be the "best" stock- ing rate for a farm in the same district?
No definite answer can be given. How- ever, the Department of Agriculture has carried out set-stocking, high stocking rate experiments in a number of districts and many more are in progress. Farmers intent on achieving better pasture utilisa- tion though raising stocking rates should only do so under the guidance of their local agricultural advisers.
A Final Word on Grazing Management
In the experiment we have described, the grazing management adopted was the simplest of all systems—set stocking. This system was chosen for two main reasons:
• it simplified the design and main- tenance of the experiment;
• with some possible exceptions, no other management system has been shown to offer any worth- while advantage. Some form of grazing control may be of value for breeding ewes, but only at the highest stocking rate.
413
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