Farm management strategies for improving the quality of fine wool

Abstract

The effects of a range of farm management strategies on the characteristics of the wool produced by Merino sheep in southern Australia were investigated. The physical and financial responses induced by the different strategies were examined under a variety of seasonal and market conditions using a model of a self-replacing flock of Merino ewes. Historical climatic and financial data collected in Hamilton, western Victoria, were used to determine the conditions experienced over a period of 23 consecutive years.

An existing model of a sheep flock was extended to provide the detailed predictions of fibre diameter, staple length and staple strength required to assess the strategies under test. Fibre diameter and staple length were predicted as a function of wool growth rate, with the variation in cross-sectional area along the length of the fibre used to predict staple strength. An analysis of historical records of variation in the level of vegetable matter contamination of wool sold in Victoria was used to relate the level of contamination to both the time the sheep were shorn and the fibre diameter.

The accuracy of the model in predicting the characteristics of the wool produced under a wide range of conditions was assessed by comparing the predictions with an extensive set of field data. The model successfully mimicked the pattern of pasture and sheep liveweight change over three consecutive years and for a wide range of stocking rates. There was no evidence of bias in the predictions of fleece weight or the characteristics of the wool produced so that, in general, the assessment of the performance of the model was very favourable.

In a preliminary analysis, the importance of individual wool characteristics as determinants of the price of Merino wool was assessed, these being fibre diameter, staple length, staple strength and vegetable matter level. Two methods of determining the value of each characteristic were employed. The first method used present day values of the wool characteristics and the second used procedures developed recently for predicting the processing performance of the wool as a means of forecasting its future value. Fibre diameter was identified as the most important determinant of the price of Merino wool, regardless of which of these methods was used. Furthermore, the effects of management changes on fibre diameter were found to have the opposite effect on price to the effect of changes in staple length and staple strength.

The effects of a range of management strategies on the physical and financial responses of flocks composed of Peppin or South Australian Merino ewes were assessed in a series of four simulated experiments. Of the strategies tested, changing from the traditional practice of lambing in autumn to a winter lambing time produced the best overall improvement in fleece characteristics. Not only was the wool produced by ewes lambing in June/July of higher price than those lambing in May, their higher reproduction rate and lower supplementary feed requirements, together with the improved financial returns from wool, increased the net cash income by more than 17%. Ewes lambing in May often had little or no green pasture available in late pregnancy and their wool growth rate, staple length and staple strength were depressed during autumn, particularly in years when there was a late start to the pasture growing season.

Increasing the quantity of supplementary feed provided during periods when there was insufficient pasture available to meet animal requirements, increased fleece weight, staple length and staple strength. However fibre diameter was also increased, this having a negative impact on the value of the wool such that there was no net effect of the changes in wool characteristics on price. The increase in fleece weight alone was often not sufficient to cover the cost of the additional supplementary feed provided.

Increasing the reproduction rate or stocking rate of the breeding ewes decreased their fleece weight, staple length and staple strength. However, there was again no net effect on wool price, with the decrease in fibre diameter countering the deterioration in the other fleece characteristics. The effect of the reduction in fleece weight on financial returns was small in comparison to the beneficial effects of the additional sheep shorn and sold. For the range of reproduction rates and stocking rates considered in this study, the increase in production per unit area easily outweighed the decline in production per animal.

These analyses have highlighted the importance of the interactions between the fleece characteristics in their response to changes in management, as well as interactions between wool and other components of production. Future attempts to devise farm management strategies for improving wool quality should pay special attention to these interactions and to the relative effects of individual fleece characteristics on wool price.