Abstract:
Proc. Aust. Soc. Anim. Prod. 1996 Vol. 21 NUTRITIONAL RESPONSES IN WOOL SULPHUR BY FOUR MERINO GENOTYPES OF DIFFERING WOOL GROWTH PERFORMANCE G.J. LEE and A. J. WILLIAMS NSW Agriculture, Agricultural Research and Veterinary Centre, Orange, N.S.W. 2800 SUMMARY Sheep from 4 Merino flocks, different in annual clean fleece production when grazed together, were given several nutritional treatments to compare the relationships of wool sulphur with nutrient intake, and with wool growth and plasma cystine. The sheep were selected from a finewool (Fl), a strong wool (S), and 2 medium-Peppin (MP6 and MPlO) flocks. The nutritional treatments varied intakes of 2 pelleted diets - B and F. Diet B consisted of oat grain, lucerne chaff, and oaten straw, while diet F was as for B but fortified with fishmeal. The concentration of sulphur in wool was positively but curvilinearly related to N intake. Sheep from flock Fl had higher levels of sulphur in wool than those from the other flocks at any particular level of N intake. The rate at which wool sulphur concentration increased with either increasing N intake or increasing plasma cystine concentration did not differ between the flocks. However, the daily output of sulphur @g/cm'> by flock Fl was less than that of the other flocks, reflecting the relative wool growth rates. Over 90% of the variation in the daily output of sulphur was attributable to variation in wool growth rate. Keywords: wool sulphur, wool growth, plasma cystine, Merino sheep INTRODUCTION In an earlier paper (Lee and Williams 1994) we reported the nutritional responses in wool growth by genotypes of differing wool growth performance. It was apparent that the responses of wool growth and plasma cystine concentration to (N) intake varied among the flocks both quantitatively and in nature. In particular, the capacity for wool growth of the low producing finewool flock sheep was not limited by their capacity to consume feed and their plasma cystine concentration responded curvilinearly to (N) intake reaching a maxima within the range of experimental intakes. The plasma cystine levels of the other flocks increased with intake over the range of intakes included in this study, as did their wool growth rate. In addition, the wool growth rate of the low producing genotypes was less influenced by a nutritionally altered plasma cystine concentration than was that of the high producing genotypes. As both wool growth rate and wool sulphur content reflect the rate that cystine is utilised by the follicles, the opportunity was taken to measure the sulphur content of the wool grown by these sheep. This paper reports the response of wool sulphur to nutritional treatments, and the relationship of wool sulphur with wool growth and plasma cystine concentrations. METHODS AND MATERIALS Four flocks were chosen from the multiple bloodline Merino flock at the Agricultural Research Centre, Trangie, on the basis of their hogget wool production (Mortimer and Atkins 1989). The 4 flocks were a Saxon finewool bloodline (Fl), a medium-strong South Australian bloodline (S), and 2 medium Peppin bloodlines (MP6 and MPlO). Flocks Fl and MPlO produced lower clean fleece weights annually than flocks S and MP6 when the flocks grazed together. Seventy eight randomly selected ewes (non-pregnant and non-lactating) aged 4-5 years from the 4 flocks were individually penned and treated with a broad spectrum anthelmintic. The 2 pelleted diets (B and F) used in this experiment are fully described by Lee and Williams (1994). Briefly, diet B consisted of 230 g oat grain, 450 g luceme chaff, and 300 g oaten straw, /kg, while diet F was as for B but fortified with 100 g fishmeal/kg, at the expense of 50 g oat grain and 50 g luceme chaff/kg. Fishmeal was used as the protein supplement for its resistance to ruminal degradation and ability to supply sulphur amino acids (eg Hennessy et al. 1983). A 6 week pre-experimental period was used to reduce environmental differences between ewes by standardising the diet, level of feeding, and housing prior to the experimental period. During this period, the ewes were offered 900 g of diet B at 1000 hours daily. Wool growth during the pre-experimental period was clipped from midside patches (8 cm x 8 cm) with Oster small animal clippers with a No. 40 cutting 123 Proc. Aust. Sot. Anim. Prod. 1996 Vol. 21 assembly, using the procedures described by Lee and Williams (1993). At the end of the pre-experimental period, venous blood samples were collected into evacuated heparinised tubes from each ewe on 4 occasions - 09M (prefeeding), 1100, 1300 and 1500 hours. After centrifugation, plasma was collected and stored at - 15OC untii determination of total cystine levels (Williams et al. 1986). At the start of the experimental period, the ewes within each flock were randomly allocated to 5 groups, which were then each allotted one of the following 5 treatments: 600,900 or 1200 g air dry Diet B/day, or 900 or 1200 g Diet F/day. All ewes were fed their experimental diet daily at 1000 hours for 13 weeks. Clipping of the patches was repeated in the 8th and 13th weeks of feeding the experimental diets and the wool grown between weeks 8 and 13 kept for sulphur determination. At the end of the experimental period, a further 4 blood samples were collected from each ewe as previously described. Wool sulphur (S) was determined on wool grown during the pre-experimental period and between weeks 8 and 13 of the experimental period by ICP-AES following digestion of 50mg samples of clean wool in 0.5ml nitric acid at 90�C and then diluting the digests to 1Oml with distilled water. The instrument was calibrated with aqueous standards in 2% nitric acid. Flock differences in the S content of wool grown during the pre-experimental period were tested using least square methods (REG - Gilmour 1988). This procedure was also used to analyse the wool S content of wool grown during the experiment (between weeks 8 and 13) statistically but using the pre-experimental S content as a covariate. Flock, the covariate, together with N intake (both linear and quadratic), diet (B or F), the first order interactions of flock with the covariate, intake and diet, and the interactions between intake and diet were fitted in an analysis of variance adjusting for preceding terms. (NB. Feed intakes were relatively constant - Lee and Williams 1994). The object was to find the simplest model that accounted for the most variation in the dependent variable using the least variables, non-significant terms being sequentially deleted. The proportion of variation in wool S output (pg/cm2.day), both in the pre-experimental period and in the experiment, caused by variation in wool growth per unit area (mg/cm2.day) and wool S concentration (mg/g) was determined using the method described by Henderson and Hayman (1960). Daily wool growth per unit area and wool S concentration (both in log form) were regressed on log daily wool S output. Flock and its interaction with log wool S output were included in the model to determined flock effects. Similarly, diet and its interaction with log wool S output together with N intake were included in the model to determine nutritional effects. RESULTS The mean wool S concentrations and daily outputs for each of the flocks during the pre-experimental period are shown in Table 1. Table 1. Flock means (+s.e.) for wool sulphur concentration and wool sulphur output during the pre-experimental period WooZ S content Wool S content was positively and curvilinearly related to N intake over the range of intakes used in this experiment (Table 2). There were no differences between the flocks in the rate of response of wool S concentration to N intake, although sheep from flock Fl had higher concentrations of S in the wool than sheep from the other flocks at the same N intake. After accounting for the N intake of the sheep, there were no significant effects of diet on wool S levels. The response in wool S level to changes in plasma cystine concentration was similar for all flocks, although the wool S concentration of Fl sheep was higher (PcO.05) than that of sheep from the other flocks at the same cystine concentration (Figure 1). 124 Proc. Aust. Sot. Anim. Prod. 1996 Vol. 21 Table 2. Least square regression coefficients and deviations (+ s.e.) for nutritional and flock effects on wool sulphur and daily wool sulphur output of eweS from the 4 Merino flocks Wool s output Wool S output (pg/cm2.day) was also positively and curvilinearly related to N intake over the range of intakes used in this experiment (Table 2). However, there were differences between the flocks in the rate S output responded to N intake, with sheep flock Fl responding at a lower rate than sheep from the other flocks. There were no significant effects of diet on S output after accounting for the N intake of the sheep. Figure 1. Relationship between plasma cystine and wool S content in 4 Merino genotypes (Fl H, S A, MP6 +, and MPlO e) Most of the variation in wool S output (92+5 and 9324 % of the variation in the pre-experimental and experimental periods respectively) was associated with variation in wool growth, after accounting for differences between flocks and nutritional effects (level of intake and diet, in the experimental period). Within flocks, variation in wool sulphur content, including that associated with nutrition, accounted for 16+3 % of the variation in wool S output. There were no differences in these proportions between flocks or diets. 125 Proc. Aust. Sot. Anim. Prod. I996 Vol. 21 DISCUSSION The results confirm previous observations that flocks with a greater genetic capacity for wool growth have both lower wool S and plasma cystine concentrations than flocks with a lesser capacity (Williams 1987). In addition, the positive environmental relationship within flocks of wool S with the rate of wool growth is consistent with reports of Reis and Schinckel(l963, 1964), Reis and Williams (1965) and Lee and Williams (1993). We reported earlier (Lee and Williams 1993) that, within a flock, alterations in plasma cystine levels induced by nutrition are indicative of changes in cystine availability/flux, although we do not know how this relationship may vary between flocks. In the present experiment (Lee and Williams 1994), the responses in plasma cystine levels to nutrition differed between the flocks, but the rate of change in the S content of wool grown associated with increases in plasma cystine concentration did not differ between the flocks. However, the output of S in wool (mg/cm2.day) of the lower producing flocks (Fl and MPlO) was less than that of the higher producing flocks at the same cystine concentration, despite the higher wool S content. This indicates that the relative capacity of the wool follicles to compete for and/or utilise the available SAA (cystine) for fibre growth is lower in the flocks with a lower wool growth capacity, particularly flock Fl. REFERENCES GILMOUR, A.R. (1988). REG - A generalised linear models program. Miscellaneous Bulletin 1. Division of Agricultural Services, Department of Agriculture, New South Wales. HENDERSON, A.E. and HAYMAN, B.I. (1960). Amt. J. Agric. Res. 11: 851-70. HENNESSY, D.W., LEE, G.J. and WILLIAMSON, P.J. (1983). Amt. J. Agric. Res. 34: 453-67. LEE, G.J. and WILLIAMS, A.J. (1993). Amt. J. Agric. Res. 44: 973-91. LEE, G.J. and WILLIAMS, A.J. (1994). Amt. J. Agric. Res. 45: 117 l-87. LENG, R.A. and NOLAN, J.V. (1984). J. Dairy Sci. 67: 1072-89. MORTIMER, S. I. and ATKINS, K.D. (1989). Aust. J. Agric. Rex 40: 433-43. REIS, P.J. and SCHINCKEL, P.G. (1963). Amt. J. Biol. Sci. 16: 218-30. REIS, P.J. and SCHINCKEL, P.G. (1964). Amt. J. BioZ. Sci. 17: 532-47. REIS, P.J. and WILLIAMS, O.B. (1965). Amt. J. Agric. Res. 16: 101 l-20. WILLIAMS, A.J. (1987). In 'Merino Improvement Programs in Australia', (Ed B.J. McGuirk.) pp. 481-94 (Australian Wool Corporation: Melbourne). WILLIAMS, A.J., MURISON, R.D. and CROSS, CC. (1986). Amt. J. Agric. Res. 37: 657-63. 126