Clean wool growth of Merino sheep selected as fine or broad wool within 2 strains

Abstract

Proc. Aust. Soc. Anim. Prod. I994 Vol. 20 CLEAN WOOL GROWTH OF MERINO SHEEP SELECTED AS FINE OR BROAD WOOL WITHIN TWO STRAINS P.J. MURRAYA, I.W. PURVISA, I.H. WILLIAMSA and P.T. DOYLE B *Faculty of Agriculture (Animal Science), University of Western Australia, Nedlands, W.A. 6009 *Sheep Industries Branch, Dept of Agriculture, Albany, W.A. 6330 SUMMAR Y The hypothesis tested was that fine and broad wool Merino sheep, from within a stud, would have the same clean wool growth, yield and staple length growth when consuming the same amount of feed. This was tested using sheep from a Bungaree and a Peppin stud known to produce relatively broad and fine wool, respectively. Within each stud sheep were selected which differed in fibre diameter (fine and broad groups), but not fleece weight and liveweight (LW). Animals from the different studs had different mean LWs and fleece weights. The 4 groups of sheep (Bungaree fine, Bungaree broad, Peppin fine, Peppin broad) were fed a pelleted diet based on lucerne and lupin grain in an experiment that comprised 3 levels of feeding (1.5% or 2.2% of individual LW or ad libitum) and 3 periods of 8 weeks. The design was a double change-over latin square with each sheep receiving each diet in 1 of the periods. Because there were significant (P < 0.01) carryover-effects of the preceding treatment in periods 2 and 3, the results were analysed as 1.5% of LW to 2.2% and ad libitum; 2.2% to 1.5% and ad libitum; and ad libitum to 1.5% and 2.2%. Snippet fibre diameter (SFD) was determined from a 2 mm long snippet clipped from the wool staples at the end of each period. Clean wool growth rate and yield were determined from midside patches clipped at the end of each period. Staple length grown during each period was measured from dyebands placed in the wool at the end of each period. The 4 groups of sheep maintained their SFD ranking irrespective of the treatments. The treatments had significant effects on clean wool growth rate, fibre diameter and staple length growth, but did not affect yield. There were differences in wool growth rate between the strains and the diameter extremes, with the Peppin broad wool sheep producing less wool than the Peppin fine wool sheep, and both groups producing less wool than the Bungaree sheep. Keywords: Merino, genotypes, wool growth, fibre diameter, staple length. INTRODUCTION Murray et al. (1994) reported significant differences in liveweight (LW) gain and feed conversion efficiency for fine and broad wool animals selected within commercial Bungaree and Peppin strains. The fine wool groups within strains gained LW at a higher rate than the broad wool sheep, and the Bungaree strain were less efficient in converting feed into LW than the Peppins. A large number of the studies on the effects of diet and feed intake on fibre characteristics of sheep have been undertaken with non-Merino sheep or with Merinos from closed flocks or single trait selection flocks (eg. Allden 1979; Reis 1979). It is not known whether current commercial Merino sheep of similar fleece and LW, selected on mean fibre diameter (MFD) at the extremes of a population, would maintain their ranking and produce similar weights of clean wool of similar yields and staple lengths when compared at different nutrient intakes. The hypothesis tested in this study was that sheep with different MFD within and between strains would increase or decrease wool growth, MFD and staple length growth at the same rate when fed a ration at the same proportion of LW. MATERIALS AND METHODS At weaning 200 sheep were obtained from a Bungaree and a Peppin stud and were grazed together on annual pasture for 8 months. The 2 studs were chosen as they differed by 3 pm in MFD in a study of strain, stud and environmental effects on hogget performance (Lewer et al. 1990). Prior to the start of the experiment all animals were shorn and weighed. The MFD was measured on midside wool samples. Within each strain 24 sheep were selected into 2 groups which were fine and broad in MFD, but similar in mean fleece weight and LW. The 48 sheep were allocated to single pens in an enclosed shed. The experiment used a double change-over latin square design (Patterson 1952; Cochran and Cox 1957) with a 4 week introductory period then 3 periods of 8 weeks at 3 levels of intake. Full details of the experimental design are given by Murray et al. (1994). In each period 4 sheep from each group (ie. Bungaree fine and broad wool; Peppin fine and broad wool) were fed at 1.5% or 2.2% of their LW or ad Zibitum. The 1.5% and 2.2% intakes were adjusted fortnightly to compensate for changes in LW. The 281 Proc. Aust. Sot. Anim. Prod. 1994 Vol. 20 diet used for all treatments has been given by Murray et al. (1994). One week before the start of the experiment all the sheep had a square (ca. 10 cm by 10 cm) tattooed on the right midside. This square was clipped at the beginning and end of each period to measure wool growth rate (mg/cm2.day) and yield. To adjust for strain differences in LW, total wool growth per sheep was calculated by the equation - total wool grown/day = mg/cm?day x 0.088 x LW0mh7 (Bennett 1973). At the start and end of each period wool staples 4 cm anterior to the midside patch were opened and a dyeband placed in the wool at the skin. The distance between dyebands was measured by ruler on 10 staples, cut from this site 1 week after the end of the experiment, to determine staple length growth. The 2 mm of wool above each dyeband was cut to determine snippet fibre diameter (SFD) and the standard deviation of SFD for each sheep on each treatment. There were significant carry-over effects of the preceding treatment on SFD, the standard deviation of the SFD, clean wool growth rate and staple length growth. Consequently, the results were analysed as 6 treatments: 1.5% of LW to 2.2% and ad Zibitum; 2.2% to 1.5% and ad Zibitum; and ad Zibitum to 1.5% and 2.2%. The assumptions made in the statistical analysis were that only the first residual effects were considered (residual effects came from the preceding period only) and these were independent of level of intake in the period in which they were observed. General linear models (Minitab Release 8) were used to test strain, diameter extreme and treatment differences and interactions. RESULTS At shearing, prior to the start of the experiment, the mean LW, greasy fleece weight and MFD for the Bungaree strain were 38.8 + 0.33 kg (5 s.e.), 3.8 ? 0.04 kg and 25.4 2 0.12,~m respectively compared to 30.8 5 0.23 kg, 3.0 + 0.04 kg and 20.7 _ 0.09 ,um for the Peppins (Table 1). + Table 1. Liveweight (kg), greasy fleece weight (kg) and mean fibre diameter @m) for fine and broad wool groups within strains at hogget shearing There were differences in clean wool growth (g/m?day and calculated (Figure 1) and treatments (Table 2) (P < 0.001). There were differences in from the preceding period to that of the treatment being analysed (P < 0.001; strains growing over 5 g more or nearly 4 g less wool than that grown in the g/day) between the strains the amount of wool grown Table 2) with sheep across preceding period. Figure 1. Clean wool growth rate (g/m2.day; filled bars) or as a function of liveweight (g/day; bars with diagonals) for the strains and diameter groups 282 Proc. Amt. Sot. Anim. Prod. 1994 Vol. 20 There was a strain by diameter group interaction for the amount of wool grown on the midside patch (P c 0.05) or on the whole animal (P c 0.05) with the Peppin broad wool producing 13% less than the Peppin fine wool and 29% less than the Bungaree strain (Figure 1). Table 2. Clean wool growth rate (g/m2.day), staple length (mm) and the change in each measured from the preceding period for the 6 treatments (pooled over strains and diameter groups) There was an effect of strain (Bungaree 77.4 + 0.54% and Peppin 74.2 2 0.55%; P < 0.001) and diameter extreme (fine wool 76.8 + 0.56% and broad wool 74.8 + 0.53%; P = 0.009) on yield. The nutritional treatments had no significant effect on yield. Although there was no significant effect of strain or diameter extreme on staple length growth during the treatment periods there was an effect of strain on the overall difference in staple length growth from the preceding period (Bungaree + 0.58 + 0.15 mm and Peppin + 1.00 + 0.15 mm; P c 0.05). The treatments had effects on the staple length growth on the midside of the sheep (P < 0.001; Table 3). The change in staple length from the preceding period ranged from +5.5 to -3 mm for each 8 week period (Table 2). Table 3. Snippet fibre diameter (SFD)@m) for the Bungaree and Peppin sheep, and the standard deviation of the SFD @m) for the fine wool and broad wool groups of sheep measured at the end of each treatment. The change from the end of the preceding period is given for each treatment At the start of the experiment (above the first dyeband) the SFD of the Bungaree fine and broad wool sheep were 21.3 + 0.37 and 24.8 t 0.55 pm (2 s-e.) respectively, compared to 17.2 t 0.29 and 20.9 + 0.36 pm for the Peppins. By the end of the experiment the 4 groups had increased in SFD to 24.0 + 0.59,27.5 + 0.81, 20.1 t 0.71 and 23.3 + 0.49pm. Although the differences in the SFD between the strains and the diameter extremes were maintained under all of the 6 treatments (both P c 0.001) there was a strain by treatment interaction (P < 0.05) for the change in SFD from the end of the preceding period to the end of the treatment being analysed. This strain by treatment interaction reflected differences in the magnitude of the change in SFD for the 2 strains. The treatments resulted in a maximum 5.5 pm reduction or a 6.8 ,um increase in SFD over the 8 283 Proc. Aust. Sot. Anim. Prod. I994 Vol. 20 week period for the Bungarees and the corresponding values for the Peppins were 4.5 and 6.2 pm (Table 3). Across treatments the magnitude of this change in diameter was 12% greater for the Bungaree than for the Peppin sheep (Table 3). There were differences between strains (Peppin 4.5 5 O.lOpm and Bungaree 5.7 z O.lOpm; P c 0.001) and diameter extremes (fine wool 4.9 + 0.10 pm and broad wool 5.2 + 0.10 ,um; P c 0.05) for the standard deviation of the SFD. There was also a diameter group by treatment interaction for the standard deviation of the SFD, with the standard deviation of the broad wool and the fine wool groups changing in different directions for the same treatments from the preceding period to the treatment being analysed (P c 0.01; Table 3). DISCUSSION In this experiment, within the Peppins the broad wool sheep did not grow as much wool as the fine wool group. This contrasts with previous studies using sheep from closed selection flocks which found that sheep with broader wool within a population had higher wool growth rates than those with finer wool (see Butler and Maxwell 1984). Our results from commercial flocks, indicate that under ad Zibitum feeding with animals eating similar amounts of feed, broad wool sheep within some strains may not produce as much wool as fine wool sheep. Although sheep from each strain and diameter extreme were eating the same amount of ration, as it was based on their LW (Murray et al. 1994), the Bungaree sheep produced a greater weight of wool per unit area and for the whole fleece (calculated from midside production and LW). The Peppin broad wool sheep not only produced less wool than the fine group, but they increased LW at a lower rate than the fine wool sheep (Murray et al. 1994). This indicates that, in the sheep selected from this stud, the broad wool sheep were less efficient in converting feed into both LW and wool. The results indicate that the 4 groups of sheep maintained their SFD ranking irrespective of the treatments. The treatments showed clearly that the groups had equal potential to reduce or increase their SFD and it was only the magnitude of the change that was dependent on changes in the level of intake. However, the data indicates that the range of fibre sizes, as measured by the standard deviation of the SFD, and measured at the end of each treatment, decreases with increased intake for fine wool animals whereas it increases for broad wool animals. This increase can be explained by the increase in SFD. As the mean gets broader the ` opportunity' for variation in fibre size increases on both sides of the mean and finer wools have a smaller range of fibre sizes less than the mean than do broader wools. The decrease in standard deviation of the SFD with increased intake for the fine wool sheep may reflect differences in the density and secondary to primary fibre ratios between the diameter extremes. The mass of wool produced per unit area of skin is dependent on the follicle density, and the diameter and length of fibres. Given that fibre length is highly correlated to staple length as stated by Gee (1975), although disputed by others (e g. Whan 1973) and as there was no difference in the staple length between strains or diameter extremes then, the differences in wool produced were due in part to differences in both fibre diameter and density. ACKNOWLEDGMENTS One of the authors, P.J.M., was in grateful receipt of an Australian Wool Research Trust Fund Postgraduate Scholarship when this experiment was carried out. REFERENCES ALLDEN, W.G. (1979). 1n 'Physiological and Environmental Limitations to Wool Growth', (Eds J-L. Black and P.J. Reis) pp. 61-78 (U niversity of New England Publishing Unit: Armidale). BENNETT, J.W. (1973). J. Agric. Sci., Camb. 81: 429-32. BUTLER, L.G. and MAXWELL, W.M.C. (1984). Anim. Breed. Abs. 52: 474-85. COCHRAN, W-and COX, G. (1957). 'Experimental Designs' (John Wiley and Sons: New York). GEE, E. (1975). S.A. Wool Text. Res. Inst. BUZZ. 9: 26-35. LEWER, R.P., WOOLASTON, R.R. and HOWE, R.R. (1990). Proc. Aust. Ass. Anim. Breed. &net. 8: 295-8. 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