The Effect of Time of Shearing on Wool Production and Management of a Spring-lambing Merino Flock

Transcription

1 The Effect of Time of Shearing on Wool Production and Management of a Spring-lambing Merino Flock Angus John Dugald Campbell, BVSc(Hons) BAnimSc Submitted in total fulfilment of the requirements of the degree of Doctor of Philosophy November 2006 University of Melbourne School of Veterinary Science Angus Campbell, 2006

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3 ABSTRACT Choice of shearing time is one of the major management decisions for a wool-producing Merino flock and affects many aspects of wool production and sheep health. Previous studies have investigated the effect of shearing on only a few of these factors at a time, so that there is little objective information at the flock level for making rational decisions on shearing time. This is particularly the case for flocks that lamb in spring, the preferred time in south-eastern Australia. A trial was conducted in a self-replacing, fine wool Merino flock in western Victoria, from January 1999 to May 2004, comparing ewes shorn annually in December, March or May. Within each of these shearing times, progeny were shorn in one of two different patterns, aligning them with their adult shearing group by months of age. Time of shearing did not consistently improve the staple strength of wool. December-shorn ewes produced significantly lighter and finer fleeces (average 19.1 µm, 3.0 kg clean weight), whereas fleeces from March-shorn ewes were heavier and coarser (19.4 µm, 3.1 kg). Fleeces from ewes shorn in May were of similar weight to fleeces from March-shorn ewes (3.1 kg), but they were of significantly broader diameter (19.7 µm). In young sheep, beneficial changes in some wool characteristics for each shearing group were offset by undesirable changes in others. Shearing ewes in March or May, and weaners in March, May or June, significantly increased the risk of post-shearing mortality about three- and four-fold, respectively, compared to unshorn sheep. Substantial, highly significant associations in young sheep between post-weaning mortality, bodyweight and growth rate were also quantified using various survival analysis techniques. For example, the lightest 20% of weaners at weaning contributed 31% of all deaths in the year following weaning, and increasing average growth rate over summer and autumn from 250 to 500 g/month reduced the risk of death by 74%. These results could be used to develop supplementary feeding systems that efficiently reduce weaner mortality, which is a significant animal welfare issue in many Australian Merino flocks. Mortality effects were incorporated into estimates of the total value of wool produced by the different shearing times between birth and culling at 6¼ years of age. Using median historical ( ) wool prices, shearing ewes in March and their progeny first in June, or October (weaner)-december (ewe) shearing produced the greatest total value of wool ($111/head). March (weaners)-march (ewes) shearing had a wool value of $107/head and December (weaners)-december (adults) shearing $103/head. May-shorn ewes produced the smallest value of wool, irrespective of whether their progeny were first shorn in May or July ($93 96/head). i

4 No shearing time consistently improved all animal health measures. May-shorn ewes had significantly more fleece rot in late autumn than the other shearing groups (odds ratio 2.5) and were up to 0.4 condition score lighter during winter, although they had a lower cost of dag (average $0.64/head) and significantly less breech strike risk in spring, compared to December-shorn ewes (odds ratio 0.18). December-shorn ewes had the greatest cost of dag ($1.50/head). March-shorn ewes had an intermediate cost of dag ($1.03/head) but significantly less breech strike than May-shorn ewes (odds ratio 0.38). Overall, December and March shearing were shown to be appropriate alternatives for a self-replacing Merino flock in south-eastern Australia, whereas May was an undesirable shearing time. ii

5 DECLARATION This is to certify that: (i) the thesis comprises only my original work (ii) due acknowledgement has been made in the text to all other material used, (iii) the thesis is less than 100,000 words in length, exclusive of tables, maps, bibliographies and appendices Angus JD Campbell iii

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7 All we like sheep have gone astray; we have turned every one to his own way; and the Lord hath laid on him the iniquity of us all. Isaiah 53:6 v

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9 ACKNOWLEDGEMENTS I wish to thank the Vizard Foundation and Mr Maurice and Mrs Jill Glover, who generously made their farms, facilities and sheep available for this trial, and the staff of South Roxby, particularly Mr Peter Lindeman, for the day-to-day management of the sheep. This work received financial support from the Vizard Foundation and the Australian Sheep Industry Cooperative Research Centre (CRC). The CRC also kindly supported me with a top-up scholarship. I am very grateful to my supervisors, Dr John Larsen and Associate Professor Andrew Vizard, for their guidance and assistance throughout the study. Associate Professor Vizard devised and designed the trial and it was overseen by Dr Larsen, along with other members of the Mackinnon Project at the University of Melbourne, from December 1998 to January 2002, when I took over. Mr Garry Anderson happily and ably provided me with guidance for the statistical analyses that I performed, for which I am very thankful. The amassing of such a large amount of data is due in no small part to the dedicated and meticulous work of Ms Dianne Rees. I will be eternally grateful for her technical assistance and cheerful smile, which made 5am starts on shearing days bearable. I would also like to thank the following people, who generously provided me with information or assistance during my work: Mr Rod Agar (Australian Wool Testing Authority Ltd) for helping with processing of the dyebanded wool samples; Dr Renick Peres (Department of Primary Industries, Geelong) for providing the weather data; and Dr Roger Thompson (Pasture and Veterinary Institute, Hamilton) for kindly providing me with the results of his lamb shearing experiments. This work is dedicated to my partner, Sarah, for her abiding love and support, and to my son, Callum, for making anything I do worthwhile. vii

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11 TABLE OF CONTENTS Abstract...ii Declaration...ii Acknowledgements...ii Table of Contents...ii List of Tables...ii List of Figures...ii C h a p t e r 1 General Introduction Background Determinants of Wool Enterprise Profitability & Their Relationship to Shearing Time Stocking Rate Wool Production per Sheep Average Price per Kilogram of Wool Enterprise Costs...2 C h a p t e r 2 Literature Review The Effect of Shearing Time on Wool Quality Staple Strength & Position of Break Components of Staple Strength & Position of Break Fibre Diameter Properties Intrinsic Fibre Strength Fibre Shedding Associations between Staple Strength, Position of Break & Shearing Time Shearing Time & Recurring Factors Affecting Staple Strength Fleece Weight, Yield & Fibre Diameter Staple Length Vegetable Matter Contamination Time of Shearing & Wool Quality Summary The Effect of Shearing Time on Flock Management & Sheep Health Sheep Nutritional Requirements & Farm Stocking Rate Reproductive Efficiency Shearing During Mating Shearing & Lamb Birthweight Shearing & Ewe Sheltering Behaviour Fleece Rot Dag Flystrike Other Health Issues Mortality Mortality of Weaner Merino Sheep The Extent of Merino Weaner Mortality in Australia Limitations of Weaner Mortality Investigations Causes of Mortality & Illthrift Factors Associated with Weaner Mortality Bodyweight Growth Rate Bodyweight & Death from Causes Other Than Malnutrition Physiology Underlying the Association between Mortality & Bodyweight Season & Year of Birth Disease Maternal Factors Sex...2 ix

12 2.3.5 Weaner Mortality Summary Methodologies for Analysing Survival & Mortality Conclusion...2 C h a p t e r 3 Experiment Introduction and Materials & Methods Introduction & Trial Overview Experimental Site Animals Flock Management Shearing Periodic Wool Growth Measurement Analysis Wool Production Body Condition & Weight Dag Fleece Rot Flystrike Ewe Reproduction Mortality Multivariate Weaner Survival Analysis Calculation of Fleece Values Lifetime Wool Production...2 C h a p t e r 4 Results Weather Observations & Wool Production Weather Observations Overview of Sheep Numbers & Wool Production Results Staple Strength & Position of Break Ewes Weaners Fleece Weight & Yield Ewes Patterns of Annual Wool Growth in Ewe Shearing Groups Weaners Fibre Diameter Ewes Weaners Staple Length Ewes Weaners Summary of Wool Characteristics Fleece Value Ewes Weaners Lifetime Wool Production Results...2 C h a p t e r 5 Discussion Wool Production Staple Strength Ewes Weaners Fibre Diameter & Fleece Weight Fleece Value Ewes Weaners Lifetime Fleece Value...2 C h a p t e r 6 Results Sheep Health & Mortality Body Condition & Growth Rate Ewe Condition Score Weaner Growth Rate Following Shearing Fleece Rot Ewes Weaners...2 x

13 6.3 Dag & Crutching Ewes Weaners Flystrike Ewes Weaners Reproduction Mortality Ewes Weaners Summary Mortality Data Mortality & Bodyweight Mortality & Mean Seasonal Growth Rate Mortality and sex Mortality & Weaner Shearing Time Multivariate Survival Analyses Value of Lifetime Wool Production, Accounting for Survivorship...2 C h a p t e r 7 Discussion Sheep Health & Mortality Body Condition & Growth Rate Ewes Weaners Fleece Rot Dag & Crutching Flystrike Reproduction Mortality Ewes Weaners Value of Lifetime Production, Accounting for Survivorship...2 C h a p t e r 8 Conclusion...2 Bibliography...2 A p p e n d i c e s...2 A p p e n d i x 1 Fertiliser Application & Pasture Management Details on Farm A...2 A p p e n d i x 2 Fleece Values Based on First & Ninth Decile Historical Micron Basis Prices...2 A2.1 Ewes...2 A2.2 Weaners...2 A2.3 Lifetime Fleece Values...2 A p p e n d i x 3 Price Schedules Used to Calculate Fleece Values...2 xi

14 List of Tables C h a p t e r 1 Table 1.1: Summary of shearing times reported in different regions of Australia...2 C h a p t e r 2 Table 2.1: Summary of experiments comparing shearing time and staple strength in Merinos, measured by % of tender fleeces, N/ktex and/or position of break...2 Table 2.2: Summary of results of studies comparing greasy fleece weight (GFW), fibre diameter (FD) and clean fleece yield of Merinos shorn annually at different times of the year...2 Table 2.3: Summary of trials comparing the net returns per head from shearing young Merino sheep once (shearing B only) or twice (shearing A then shearing B)...2 Table 2.4: Summary of the results of studies examining changes in sheep feed requirements following shearing at different times of the year...2 Table 2.5: Mortality of Merino and Merino-cross sheep between weaning and approximately 18 months of age reported in Australian commercial enterprises or field experiments...2 Table 2.6: Summary of methodologies of studies reporting risk factors for post-weaning mortality...2 Table 2.7: Post-weaning mortality of sheep in different nutritional groups reported by Allden (1968c).2 Table 2.8: Mortality of weaners with different weaning weights and autumn growth rates reported by Hodge (1990)...2 Table 2.9: Maternal factors associated with weaner mortality...2 C h a p t e r 3 Table 3.1: Calendar of flock management procedures and shearing times...2 Table 3.2: Statistical methods used to analyse differences between shearing groups in ewe and weaner results, and corresponding Stata (StataCorp 2005) commands...2 C h a p t e r 4 Table 4.1: Number of ewes in each age group, and mean age and standard deviation (years) of the ewe flock at each shearing...2 Table 4.2: Duration of wool growth (days) between, and dates of, shearings in each ewe shearing group...2 Table 4.3: Duration of wool growth (days) between birth and shearing 1, and shearing 1 and shearing 2 for weaner shearing groups in each birth-year cohort...2 Table 4.4: Least squares mean greasy fleece weight (GFW), yield, clean fleece weight (CFW), fibre diameter (FD), staple length (SL), staple strength (SS) and percentage of mid-breaks of wool from the ewe shearing groups...2 Table 4.5: Least squares mean greasy fleece weight (GFW), yield, clean fleece weight (CFW), fibre diameter (FD), staple length (SL), staple strength (SS) and percentage of mid-breaks of wool produced at shearing 1 and 2 by each weaner shearing group...2 xii

15 C h a p t e r 6 Table 6.1: Mean condition score prior to joining in March (join), during winter in July (wint) and at weaning in December (wean) of each ewe shearing treatment...2 Table 6.2: Mean fleece-free bodyweight at weaning and 95% CI (kg) of progeny from each ewe shearing group...2 Table 6.3: Mean growth rate and 95% CI (kg/month) between May and December (8 15 months old) of weaners that, in May, were shorn (MAY-MAY), or were carrying two (MAR-MAR) or five (DEC-DEC) months wool...2 Table 6.4: Prevalence of severe fleece rot (score 3) in ewe shearing groups...2 Table 6.5: Odds ratios (95% CI) of weaner shearing groups having severe fleece rot, relative to unshorn weaners or weaners carrying 12 months wool, at different times between 6 and 20 months of age..2 Table 6.6: Mean cost of dags (cents/head) in each dag score category; mean cost in each shearing group, weighted by prevalence of each dag score category, in (only crutched prior to shearing) and (crutched prior to lambing and shearing); and mean total annual cost of dag...2 Table 6.7: Odds (95% CI) of severe dag (score 3) in weaner shearing groups in March, October & March (6, 13 & 18 months old, respectively), relative to unshorn weaners or weaners carrying 12 months wool...2 Table 6.8: Flystrike prevalence in ewe shearing groups during November and early December...2 Table 6.9: Proportion of weaners in each shearing group affected by flystrike in May (8 months old) in two years of the trial...2 Table 6.10: Proportion of weaners in each shearing group affected by flystrike and odds of flystrike, relative to DEC-DEC weaners, in November (14 months old) in three years of the trial...2 Table 6.11: Proportion of weaners in each shearing group affected by flystrike and odds of flystrike, relative to MAR-MAR weaners, in March (18 months old) in two years of the trial...2 Table 6.12: Proportion of ewes in each shearing group lactating at lamb marking and odds (95% CI) of ewes lactating at marking, relative to DEC ewes...2 Table 6.13: Number of lambs weaned, number of ewes and weaning percentage in each year...2 Table 6.14: Mean weaning weight and 95% CI (kg) of weaners dying and surviving during the postweaning period in each year-trial cohort...2 Table 6.15: Number of weaners in each weaning weight quintile (range in kg) that died and were at risk during the post-weaning period, total mortality, cumulative mortality rate, and mortality risk (95% CI), relative to the middle quintile...2 Table 6.16: Average weaner growth rate (kg/month; GR ) at different times throughout the postweaning period (PWP) and total mortality...2 Table 6.17: Total mortality, cumulative mortality rate (deaths/1000 weaners/month) and mortality risk of males relative to females...2 Table 6.18: Mortality rate (deaths/1000 weaners/month) of shorn and unshorn weaners, mortality rate difference, and mortality rate ratio between shorn and unshorn weaners at each shearing...2 Table 6.19: Coefficients of statistically significant terms in Weibull, Cox, cubic spline, log-logistic and interval-censored Weibull survival analysis models, in analyses of a) all data, and b) Trial 2 data only...2 Table 6.20: Mean annual (Ann.) and cumulative (Cum.) survival prior to each shearing of sheep in each shearing group between birth and 6 years old (y.o.)...2 xiii

16 A p p e n d i c e s Table A-1.1: Annual fertiliser application and pasture management details for Farm A...2 Table A-3.1: First, median and ninth decile basis prices in the period July 1992 February 2006 for wool of specified fibre diameter (FD; µm), and first, median and ninth decile percentage changes from basis price for wool of specified staple length (SL; mm) and staple strength (SS; N/ktex)...2 xiv

17 List of Figures C h a p t e r 1 Figure 1.1: Average contribution of individual factors to variation in quarterly clean wool price April 1996 June 1998, after Hatcher (2000)...2 C h a p t e r 2 Figure 2.1: An example of the effect of rate of change of fibre diameter on staple strength. The two wool fibres have a similar minimum fibre diameter and peak breaking force, but the bottom fibre has a greater linear density and therefore a lower staple strength...2 Figure 2.2: An example of how shearing time (dotted arrows) locates position of break (POB) on a wool fibre. ABCD is the pattern of diameter change along the wool fibre. Shearing at A & C places POB in the middle of the fibre. Shearing at B & D places POB at the end of the fibre...2 Figure 2.3: Price discounts due to staple length of 18 µm, 35 N/ktex wool at first, median and ninth decile prices from Figure 2.4: Average vegetable matter levels in Australian states (Source: AWEX sale data to , inclusive, compiled by B. Swain)...2 Figure 2.5: Mortalities in Merino weaner sheep, classified by weight at weaning, from: 3 12 months of age on pasture (Lloyd Davies 1983), 3 6 months of age in a drought feedlot (Lloyd Davies et al. 1988), and 4½ 6 months of age on pasture (Holmes 1992)...2 C h a p t e r 3 Figure 3.1: Timing of ewe and progeny shearing treatments (age in months at weaner shearings)...2 C h a p t e r 4 Figure 4.1: Monthly cumulative rainfall and average daily maximum and minimum temperatures at Farm A during the Time of Shearing Trial...2 Figure 4.2: Mean staple strength of fleeces from ewe shearing groups (error bars indicate 95% confidence interval (CI); LSM: least squares means)...2 Figure 4.3: Mean proportion of staple mid-breaks in fleeces from ewe shearing groups (error bars indicate 95% CI)...2 Figure 4.4: Mean staple strength of fleeces from shearing 1 and shearing 2 of each weaner shearing group (error bars indicate 95% CI)...2 Figure 4.5: Mean proportion of staple mid-breaks in fleeces from shearing 1 and shearing 2 of each weaner shearing group (error bars indicate 95% CI)...2 Figure 4.6: Mean greasy fleece weight of ewe shearing groups, adjusted to 365 days growth (excluding October-shorn maiden ewes; error bars indicate 95% CI)...2 Figure 4.7: Mean clean fleece yield of ewe shearing groups (error bars indicate 95% CI)...2 Figure 4.8: Mean clean fleece weight of ewe shearing groups, adjusted to 365 days growth (excluding October-shorn maiden ewes; error bars indicate 95% CI)...2 xv

18 Figure 4.9: Mean clean wool growth rates of ewes from each shearing group in each dyeband period ( denotes shearing)...2 Figure 4.10: Mean weight of clean fleece grown by ewes in each shearing group during each dyeband period ( denotes shearing)...2 Figure 4.11: Mean clean fleece weight of each weaner shearing group at shearing 1 ( ) and shearing 2 ( ) (LSM: least squares means)...2 Figure 4.12: Mean clean wool growth rates of each weaner shearing group between birth and shearing 1 ( Shearing 1 ) and shearings 1& 2 ( Shearing 2 ). Error bars indicate 95% CI....2 Figure 4.13: Mean yields of clean fleece from shearing 1 and 2 of each weaner shearing group (error bars indicate 95% CI)...2 Figure 4.14: Mean fibre diameter of ewe shearing groups (error bars indicate 95% CI)...2 Figure 4.15: Mean fibre diameter of weaner shearing groups at shearing 1 and shearing 2 (error bars indicate 95% CI)...2 Figure 4.16: Mean staple length of ewe shearing groups, excluding October-shorn maiden ewes (error bars indicate 95% CI)...2 Figure 4.17: Mean staple lengths of each weaner shearing group from shearing 1 and shearing 2 (error bars indicate 95% CI)...2 Figure 4.18: Estimated fleece value of each ewe shearing group, based on median historical basis price and median, first decile (lower bar) and ninth decile (upper bar) staple length and strength premiums and discounts...2 Figure 4.19: Estimated fleece values from first ( ) and second ( ) shearing of each weaner shearing group, calculated using median historical micron basis prices and length & strength discounts...2 C h a p t e r 5 Figure 5.1: Significant seasonal events during years 1 & 2, and hypothesised fibre diameter profile, showing the effect of different shearing times on the position of break and measured staple strength...2 C h a p t e r 6 Figure 6.1: Mean condition score of ewes in each shearing group at different times during the trial (bars indicate 95% CI)...2 Figure 6.2: Mean fleece-free bodyweight of weaner shearing groups between weaning and 15 months of age (December to December; bars indicate 95% CI)...2 Figure 6.3: Proportion of each weaner shearing group with severe fleece rot (score 3) between weaning and 20 months of age, amongst weaners born in 2000, 2001 and Figure 6.4: Proportion of each ewe shearing group with no (dag score (DS) 0), mild (DS 1 2) and severe (DS 3 5) dag (arrows indicate time of crutching or shearing)...2 Figure 6.5: Proportion of each weaner shearing group with severe dag (score 3) between weaning and 20 months of age, amongst weaners born in 2001 and Figure 6.6: Cumulative mortality rates of ewes in each shearing group at different times of the year...2 Figure 6.7: Turnbull survival estimates of year-trial cohorts...2 Figure 6.8: Number of lambs weaned and deaths in each censoring interval of the PWP, by year-trial cohort (timelines not to scale)...2 Figure 6.9: Turnbull survival estimates of within-cohort weaning weight quintiles...2 Figure 6.10: Turnbull survival estimates of males and females...2 xvi

19 Figure 6.11: Mortality rate ratio of shorn and unshorn weaners, with different growth rates during the early ( GR(early) ) or middle ( GR(mid) ) post-weaning period, estimated by the cubic spline ( ) and Cox ( ) models (bars indicate 95% CI)...2 Figure 6.12: Effect of shearing in March on death rates of female weaners with GR early = 1 kg/month ( ) or 2 kg/month ( ), estimated by the cubic spline model*...2 Figure 6.13: Mortality rate ratio for a 2 kg increase in weaning weight or time-varying bodyweight (BWT) from the labelled value, estimated by Weibull, Cox and cubic spline models (bars indicate 95% CI)...2 Figure 6.14: Mortality rate ratio for a 0.25 kg/month increase in GR early from the labelled value for Weibull, Cox and cubic spline models (bars indicate 95% CI)...2 Figure 6.15: Smoothed mortality rate estimate from all data, and estimated Weibull & cubic spline hazard functions for female weaners with median covariate values (weaning weight 17 kg; GR early, GR mid and GR late = 0.9, 1.6 and 2.8 kg/month, respectively)...2 Figure 6.16: Smoothed curve of the scaled Schoenfeld residuals for growth rate early in the postweaning period (GR early ) vs. time since weaning...2 Figure 6.17: Per head value of wool production of each shearing group to 6.25 years of age, accounting for cumulative survival, at median historical micron basis prices using first, median and ninth decile historical staple length and strength premiums and discounts...2 A p p e n d i c e s Figure A-2.1: Estimated fleece value ($/head) produced by each ewe shearing group, based on median, first decile (lower bar) and ninth decile (upper bar) micron basis prices and median staple length and staple strength discounts...2 Figure A-2.2: Estimated fleece values ($/head) from shearing 1 ( ) and shearing 2 ( ) of each weaner shearing group, calculated using first decile historical basis prices and median staple length & strength premiums and discounts...2 Figure A-2.3: Estimated fleece values ($/head) from shearing 1 ( ) and shearing 2 ( ) of each weaner shearing group, calculated using ninth decile historical basis prices and median staple length & strength premiums and discounts...2 Figure A-2.4: Estimated value ($/head) of wool produced over the lifetime (from birth to 75 months of age) of ewes shorn in each weaner and ewe shearing combination, net of shearing costs, at first, median and ninth decile historical micron basis prices with median staple length and strength premiums and discounts...2 Figure A-2.5: Estimated value ($/head) of wool produced over the lifetime of ewes shorn in each weaner and ewe shearing combination, net of shearing costs & accounting for cumulative survival, at first, median and ninth decile historical micron basis prices with median staple length and strength discounts...2 xvii

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21 C H A P T E R 1 GENERAL INTRODUCTION The question of When should I shear? is one which should be considered seriously by every grazier for such a decision will affect farm efficiency, labour, markets, and returns. Sheep & Wool Branch, Tasmanian Journal of Agriculture Background The two most important management decisions at the discretion of a wool producer with a selfreplacing Merino flock are when to lamb and when to shear (Morley 1994). In the winter rainfall zone of Australia, there is a large body of research to demonstrate that spring is the preferred lambing time (Lloyd Davies 1987; Foot and Vizard 1993). However, there is little holistic, objective evidence of a preferred time of shearing for spring-lambing flocks. Table 1.1: Summary of shearing times reported in different regions of Australia Location & Stock Time of shearing Reference Class Victoria central Victoria majority (>80%) August November Foot & Vizard (1993) Gippsland spring: 57% Irving (1991) summer: 25% autumn: 7% winter: 2% state-wide spring: 52% summer: 18% autumn: 13% winter: 17% Court and Lawless (1995) Tasmania Ewes Wethers Weaners Western Australia spring: 36% summer: 25% autumn: 22% winter: 17% mainly later winter; also significant numbers late autumn and late spring majority spring more in spring but remainder spread throughout the year Statham (2004) McFarland & Shaw (1998); Bell (1993) South Australia ~50% summer or autumn Ashton (1992) Victoria, NSW & South Reeve & Thompson (2004) Australia 1

22 General Introduction On Australian farms, adult Merinos are usually shorn annually. Shearing times vary widely within and between regions in Australia (Table 1.1). In surveys of Victorian and South Australian woolgrowers, availability of labour was the most common reason given for choosing a particular shearing time, although flystrike risk, reliability of weather and available daylight hours were also considered to be important (Irving 1991; Ashton 1992). Notably, wool quality issues were not cited as important determinants of shearing time, but this may be because these surveys were conducted before staple strength was commonly measured. Studies have shown that shearing time affects many aspects of wool production and sheep health. For example, time of shearing affects wool quality characteristics such as staple strength, position of break, fleece weight, yield and fibre diameter (Arnold et al. 1984). It can also influence stocking rate, a key determinant of farm profitability, by affecting the pattern of nutrient demand of the flock and the timing of cull stock sales (Dabiri et al. 1996; Salmon et al. 2006). Time of shearing can also influence the susceptibility of sheep to diseases such as flystrike and fleece rot (Raadsma 1988). These studies have investigated the effect of changing time of shearing on each of these factors in isolation. However, no study has estimated the combined effect of shearing time on all of the factors influencing wool enterprise profitability. Therefore, the aim of this study was to examine the totality of effects of shearing time on a spring-lambing, self-replacing Merino enterprise in south-eastern Australia. The remainder of Chapter 1 provides an overview of the important determinants of profitability for a wool enterprise in south-eastern Australia. Chapter 2 reviews the literature on the relationship between time of shearing and these factors. 1.2 Determinants of Wool Enterprise Profitability & Their Relationship to Shearing Time Together, stocking rate, wool production per sheep, average price received for wool and enterprise costs determine the gross margin of a wool enterprise (Quinn et al Equation 1.1). GM = SR ( W p E )...Equation 1.1 where: GM = gross margin ($/ha) SR = stocking rate (DSE/ha) W = wool production per sheep (kg/dse) p = average wool price received per kilogram of wool ($/kg) E = enterprise costs ($/DSE) The factors influencing each of these will be examined in turn Stocking Rate Stocking rate refers to the number of sheep grazed per unit area. It is commonly expressed as the number of dry sheep equivalents (DSE) per hectare, where DSE is the amount of feed consumed by an 2

23 General Introduction adult Merino sheep in medium body condition (Morley 1994). The use of DSE allows a direct comparison of animals with different feed intakes per head. There is an important interaction between stocking rate and time of lambing. In south-eastern Australia, it is well recognised that more sheep can be grazed per hectare in spring-lambing flocks than in those lambing at other times (Caple et al. 1989; Lean et al. 1997). This is because lambing in spring best matches the flock s peak nutritional requirements during late pregnancy and lactation with the time of highest pasture growth rate. Time of shearing is considered to have considerably less impact on stocking rate than time of lambing and, for this reason, it has been recommended to choose time of lambing before time of shearing (Foot and Vizard 1993). Time of shearing affects farm stocking rate in two different ways. Firstly, the feed requirement of sheep can increase after shearing and thereby influence stocking rate (Black and Bottomley 1980). Secondly, cull and cast-for-age sheep are usually sold soon after shearing, and consequently different times of shearing will result in different seasonal grazing pressures on a farm. These issues are discussed in greater detail in Section Wool Production per Sheep At any given stocking rate, genetics fundamentally determines average wool production per sheep (Morley 1994). Genetic improvement is the dominant method used in Australia to increase per head wool production of Merinos and allows improvements to be made without necessarily compromising other fleece characteristics (Hatcher 2000). Although shearing at certain times of the year can result in a relatively small increase in fleece weight (Lightfoot 1967; Arnold et al. 1984), it is accompanied by an increase in fibre diameter, which lowers the wool s value. Time of shearing has therefore not been considered an important method for increasing wool production per sheep (Arnold et al. 1984). The relationship between shearing time, fleece weight and fibre diameter is discussed further in Section Average Price per Kilogram of Wool Different studies report slightly varying contributions of the various wool quality factors to wool price, but all show that average fibre diameter is the dominant determinant of price received by a grower for their wool (Figure 1.1). Variation in fibre diameter typically accounts for 50 70% of the variation in price received (Couchman et al. 1993; Hatcher 2000). Fibre diameter is one of the more heritable wool characteristics, with a heritability of approximately 0.50 (Morley 1994). Selection indexes can be devised that result in fibre diameter reduction, whilst avoiding or minimising deleterious changes to other aspects of wool production, such as fleece weight, and have been used widely in Australia (Hygate et al. 2006). Shearing time has been shown to influence fibre diameter (Arnold et al. 1984), but because greater, and permanent, progress in decreasing fibre diameter has been achieved through genetic selection, manipulating time of shearing has been a secondary consideration in strategies to lower fibre diameter. 3

24 General Introduction After fibre diameter, wool quality factors that have a large effect on first stage processing performance have the most significant impact on wool price. These factors are staple strength, position of break (the point along the staple where it breaks under tension), vegetable matter content and staple length (Hatcher 2000). Wools with a fibre diameter less than 20.5 µm tend to receive price penalties when staple strength is less than about 36 N/ktex (Oldham 2000). For example, between 1992 and 2006, 19 µm wool with a staple strength of 26 N/ktex received up to a 24% price discount compared to 36 N/tex wool of the same fibre diameter (Independent Commodity Services 2005). Position of break also tends to reduce wool price if more than 55% of tested staples break in the middle, although the discounts are usually only in the order of 1 2% (AWI 2006). The presence of vegetable matter in wool affects processing efficiency and also lowers wool price (Charlton et al. 1981). Wool containing small or linear-shaped vegetable matter particles, such as seed and shive, tended to receive higher price penalties than burr because these contaminants were more difficult to remove (Atkinson 1989). Time of shearing can have substantial and direct effects on staple strength, position of break and vegetable matter contamination (Warr et al. 1979; Arnold et al. 1984; Adams et al. 2000), and hence on the price growers receives for their wool. Wool with staple length less than about 65 mm has received substantial price discounts because it is unsuitable for worsted processing (Adams et al. 2000; Independent Commodity Services 2005). Adult Merinos shorn annually invariably produce wool of adequate length, irrespective of when they are shorn (Arnold et al. 1984). However, sometimes adult sheep are shorn prematurely prior to sale, which can result in wool of short staple length that is heavily discounted (Salmon et al. 2006). Similarly, short staple length wool is commonly produced from young sheep whose shearing time is being aligned Figure 1.1: Average contribution of individual factors to variation in quarterly clean wool price April 1996 June 1998, after Hatcher (2000) 1% 2% 11% 7% 6% 9% 64% Fibre diameter Staple strength Staple length Vegetable matter Colour Style Wool marketing 4

25 General Introduction with the adult flock. Consequently, short shearing interval is a dominant cause of short staple length wool (Donnelly 1991a) Enterprise Costs Enterprise, or variable, costs are those which are directly attributable to a particular enterprise and that vary with its scale (Morley 1994). The main variable costs in a wool enterprise include contract services associated with shearing, supplementary feeding, animal health management and pasture maintenance (Quinn et al. 2005). Shearing time may influence costs by increasing sheep s nutritional requirements and influencing their susceptibility to diseases such as fly strike and fleece rot (Black and Bottomley 1980; Irving 1991). In summary, time of shearing is not considered to be the dominant factor influencing stocking rate, wool production per head, wool price received or enterprise costs, although it impacts upon all to some degree. The only factor primarily influenced by shearing time is staple length. The relatively small and diverse effects of shearing time on many aspects of a wool enterprise, rather than large effects on one or two factors, may partially explain the variety of observed shearing times that occur even within a given region. 5

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27 C H A P T E R 2 LITERATURE REVIEW This literature review discusses the effects of shearing time on wool quality characteristics and animal health, and survival of sheep after weaning more generally. Wool quality, which is discussed in Section 2.1, is difficult to define, although it may be best measured via the characteristics that most influence spinning performance and yarn quality (Vizard and Hansford 1999). Staple strength, mean fibre diameter, staple length and level of vegetable matter contamination are amongst the most important of these characteristics. The ways in which time of shearing affects sheep nutrition, health and mortality are reviewed in Section 2.2, with a more detailed examination of Merino weaner mortality in Section The Effect of Shearing Time on Wool Quality Staple Strength & Position of Break Staple strength (SS) is a measurement that represents the tensile strength of a staple of wool fibres (Lamb 2004). As outlined in Chapter 1, staple strength influences the price farmers receive for their wool because it is related to the performance of wool when it is processed into top. The adverse effect of low staple strength on processing performance is of considerable manufacturing significance (Bigham et al. 1983). Staple strength is calculated from several fibre measurements. It is the quotient of the tensile force required to break a wool staple and its linear density (Schlink 2000): peak breaking force (N) SS (N/ktex) =...Equation 2.1 linear density(ktex) The linear density of the wool fibre is its average mass per unit length and is measured in kilotex (ktex): clean fibre mass (g) linear density ktex) = fibre length (m) (...Equation 2.2 Staple strength was originally assessed subjectively, according to how easily a staple was broken when subjected to manually applied tension and flicked with a finger. Although this flick test is a crude 7

28 Literature Review estimate of staple strength, it broadly classified wool as being sound (>30 N/ktex) or tender (<30 N/ktex), a distinction that was related to the wool s processing performance (Bigham et al. 1983; Hansford 1987; Couchman et al. 1993). The tender classification can be further divided into parttender (25 30 N/ktex), tender (18 24 N/ktex) or rotten (<18 N/ktex). Objective measurement of staple strength was incorporated throughout the 1990s into the set of objective characteristics that now form the basis for the sale of wool in Australia, a process known as sale by description. Staple strength is routinely measured with either an ATLAS or AgriTest Staple Breaker machine (Vizard et al. 1994), both of which produce comparable results (Schlink 2000). The ATLAS and Staple Breaker machines first measure staple length under a standard extension, then the force required to pull the staple apart. The two resultant pieces are weighed to calculate linear density, and thence staple strength (Adams et al. 2000; Lamb 2004). The location of the staple s breaking point along its length, or position of break (POB), is usually assessed alongside staple strength. As discussed in Section 1.2.3, POB is also an important characteristic of wool quality. It is calculated from the relative weights of the two pieces of broken wool from strength testing, and a minimum of 40 staples are broken to give a result describing the percentage of staples breaking in the lower third (that closest to the skin, or base ), middle ( mid ) or upper third ( tip ) of the staple (Australian Wool Testing Authority 2004). A significant proportion of wool grown in southern Australia has been classified as tender (Couchman et al. 1993). Foot and Vizard (1993) described this as the biggest limitation to quality of wool from ewes and young sheep in south-eastern Australia. For example, when that statement was made, 25% and 35% of the wool sold in Victoria and Western Australia, respectively, was assessed as weak (Doyle et al. 1993). Adams et al. (2000) presented unpublished survey data suggesting that between 35 45% of wool from southern Australia was [financially] penalised (p. 61) for poor staple strength Components of Staple Strength & Position of Break In order to discuss the effect of shearing time on staple strength, it is necessary to consider the physical wool properties that determine staple strength and POB. A great deal of research has investigated the wool fibre properties that determine staple strength, and this has been well summarised in reviews such as those by Bigham (1983) and (1994). Because staple strength is calculated from several different wool staple measurements, it has been described as a summary of several biological properties of the wool fibre (Schlink et al. 2000a p. 21). The properties of interest are (Schlink and Hynd 1994): components of fibre diameter, comprising minimum diameter, and diameter variation along and between fibres intrinsic fibre strength fibre shedding 8

29 Literature Review Although there has been debate in the past about the different factors that influence staple strength, it is now broadly accepted that the wool fibre s size and shape, which are related to fibre diameter, have a greater influence on staple strength than properties of the wool material itself (Yang and Lamb 1997) Fibre Diameter Properties The breaking force of a wool fibre or staple is mostly determined by the size of its minimum crosssectional area, rather than differences in the intrinsic strength or chemical composition of the wool material present in the cross section (Adams et al. 2000). Less force is required to break a wool fibre of small diameter (and hence lower cross-sectional area) than a fibre of large diameter. Initial examinations of the relationship between fibre diameter and staple strength focused on the relationship between minimum fibre diameter and staple strength. Various authors have reported 20 66% of the variation in staple strength is accounted for by variation in minimum fibre diameter (Bigham et al. 1983; Hunter et al. 1983; Denney 1990; Hynd et al. 1997; Thompson and Hynd 1998). However, other studies have shown that rate of change of diameter along the fibre was correlated with staple strength to a similar or greater extent than minimum diameter, with fibres having a larger diameter change in a given length being weaker (Hansford and Kennedy 1988; Hansford and Kennedy 1990b; Friend et al. 1996; Peterson et al. 1998; Brown et al. 2002). Minimum diameter and rate of diameter change along fibres help determine the overall shape of the wool fibre, which is referred to as the fibre diameter profile (Schlink et al. 2000a). Different aspects of the fibre diameter profile affect different components from which staple strength is calculated, explaining the association between staple strength and minimum fibre diameter, as well as rate of fibre diameter change. Minimum fibre diameter determines the fibre s peak breaking force the numerator of Equation 2.1 because it is related to the quantity of wool material present at the fibre s weakest point. On the other hand, diameter variation along the fibre influences its linear density, which is the denominator of Equation 2.1. A fibre whose diameter changes gradually has a lower linear density Figure 2.1: An example of the effect of rate of change of fibre diameter on staple strength. The two wool fibres have a similar minimum fibre diameter and peak breaking force, but the bottom fibre has a greater linear density and therefore a lower staple strength. 16 µm 16 µm 9

30 Literature Review than one whose diameter changes suddenly along its length. If the two fibres have the same minimum diameter (i.e. the same peak breaking force), the fibre with the greater rate of fibre diameter change will have be weaker because of its greater linear density (Adams et al. 2000). This is illustrated in Figure 2.1. POB usually occurs at the wool fibre s point of minimum fibre diameter (Bigham et al. 1983; Schlink et al. 1998; Schlink et al. 2000b), although it is possible for it to occur at other locations due to the mechanics of fibre and staple breaking(orwin et al. 1980; de Jong et al. 1985). Fibres with thin regions of varying length will vary in their elongation and load-bearing properties, and thus staple strength. Fibres with a short thin section elongate less, and fail under a lower load, than fibres with a long thin section. Analyses that include fibre elongation have very high correlations with staple strength (Masters et al. 1998; Lamb 2004). This may help to explain why fibres with large diameter variation and short, thin sections have a POB at the sudden diameter change, and are often weaker than ones whose diameter changes more gradually (Brown 1971). Diameter variation between fibres is also related to staple strength, although it is not part of the fibre diameter profile (Adams et al. 1997). Between-fibre variation is thought to be both indirectly and directly associated with staple strength (Lamb 2004). The indirect association occurs because fibres of different diameters tend to also have different lengths. When tested to breaking point, fibres of different lengths come under load at different times (Masters et al. 2000). The direct association occurs because fibres with varying diameters elongate different amounts before breaking (Lamb 2004). The indirect and direct associations have the same result: fibres within the staple do not load simultaneously, so the peak force is shared by fewer fibres at one time. Thus, there is less wool material resisting the breaking force than if all fibres in the cross section were resisting the tension together. As a result, a staple containing fibres of widely differing diameters breaks at a lower peak force than one with less between-fibre diameter variation (Adams et al. 2000; Schlink et al. 2000a, Peterson, 1998 #516) Intrinsic Fibre Strength Historically, great emphasis was placed on an association between intrinsic fibre strength the strength of the wool material itself and staple strength. However, intrinsic fibre strength only varies moderately between individual Merinos (Hunter 1980; Yang and Lamb 1997), and even when variation in intrinsic fibre strength has been observed, it is very poorly correlated with staple strength (Lamb 2004). For example, no correlation between intrinsic fibre strength and staple strength was found in a Western Australian study of fine and broad wool Merino hoggets receiving three different levels of supplementary feeding in summer and shorn in spring (Peterson et al. 1998). Differences in the cellular or chemical composition of wool that are related to staple strength have not been observed in Merinos (Hansford and Kennedy 1990a), although they have been in Romney sheep (Orwin et al. 1980). Even the effects on staple strength of physiological processes such as pregnancy and lactation do not appear to be mediated through changes in intrinsic fibre strength. For example, no 10

31 Literature Review changes in intrinsic fibre strength were observed even when large changes in staple strength were observed in lambing ewes under different nutritional regimens (Hunter et al. 1990). Any relationship between intrinsic fibre strength and staple strength may be overridden by other fibre characteristics that cause more variation in staple strength. Reis (1992) pointed out that the breaking force of wools with the same average fibre diameter vary significantly and proposed that intrinsic fibre strength played a significant role in staple strength. However, this overlooked the possibility that wools with the same average diameter may have different minimum diameters and peak breaking forces, as explained previously Fibre Shedding Fibre shedding occurs when a wool follicle stops producing a wool fibre and is expelled from the follicle before it is shorn off. Shed fibres do not span the distance between the jaws of the testing machine and so do not bear any load but still contribute to the staple s linear density and consequently decrease staple strength (Schlink et al. 2000a). Fibre shedding has been reported to be well correlated in wool of staple strength less than 30 N/ktex, but not in stronger wool (Schlink and Hynd 1994), and its inclusion in analyses does not seem to explain staple strength variation any more than minimum fibre diameter and fibre diameter variation alone (for example, see Hynd et al. 1997) Associations between Staple Strength, Position of Break & Shearing Time Position of break and the along-fibre components of staple strength (minimum diameter and rate of diameter change) occur at specific points in time as wool grows. Thus, these are the components that can potentially interact with shearing time, which also happens at a single point in time along the wool staple. In contrast, other components of staple strength, such as between-fibre variation or intrinsic fibre strength, affect the staple along its entire length. It is therefore unlikely that a single event could interact with them in a consistent way. A number of surveys have shown an association between time of shearing and staple strength. For example, Curtis and Stanton (2000 cited by Oldham 2000) demonstrated a seasonal variation in staple strength of wool produced in all states of Australia, based on average figures from wool sold between 1995 and This analysis assumed that shearing occurred 1 2 months before sale. In Victoria, staple strength was greatest in wool sold in August (and therefore probably shorn in June or July), with an average staple strength of 38 N/ktex, whilst wool sold in December (shorn October or November) had the worst staple strength of 34 N/ktex. The staple strength of wool sold from other states also varied throughout the year, although the timing of the maximum and minimum strength differed between states. South Australia and New South Wales had similar patterns to Victoria. Western Australia had a similarly shaped curve, although the peak coincided with autumn shearing (36 N/ktex) and the trough with spring shearing (31 N/ktex). Queensland wool showed less variation throughout the year: wool sold in spring was strongest (38 N/ktex) and strength wool from the rest of year was only 2 3 N/ktex less. Wool from Tasmania sold between January and July had an average strength of 11