Wool Sulfur Concentration and Output in Fleeceweight-selected and Control Romney Rams

Transcription

1 Aust. J, Agric. Res., 1991, 42, Wool Sulfur Concentration and Output in Fleeceweight-selected and Control Romney Rams R. J. Antr~rn,~,~ S. N. McCutcheon, A,D H. T B1aicA J. LeeB and L. A. ~cclelland*~~ A Department of Animal Science, Massey University, Palmerston North, New Zealand. Biotechnology Division, DSIR, Palmerston North, New Zealand. Present address: New Zealand Wool Board, Private Bag, Wellington, New Zealand. Reprint requests. Present address: Ag-Canada Research Station, PO Box 3000 Main, Lethbridge, Alberta, Canada TlJ4B1. Abstract Wool sulfur concentration and output of Romney sheep from fleeceweight-selected and control lines were measured with a view to determining their potential use as genetic markers for fleeceweight. Midside wool samples were collected at 28 day intervals from 4 to 14 months of age from 35 fleeceweight-selected and 30 control rams. Clean wool growth during each sampling period was calculated. Wool samples were digested using an open wet digestion method and the wool sulfur concentration was determined by plasma emission spectrometry. Fleeceweight-selected rams had significantly greater midside wool growth than the control animals throughout the trial except on day 56. Average wool sulfur concentration in both lines increased over the sampling period to a peak at day 308. The wool sulfur concentration of control rams was significantly higher than that of fleeceweight-selected rams only on days 28 and 280. Total sulfur output (the product of midside wool growth rate and sulfur concentration) was significantly higher in the fleeceweight-selected than in the control rams on days (March-May) and (June-October). It is concluded that midside wool sulfur concentration and output of 4 to 14 month-old-romney hoggets are unlikely to be useful genetic markers for fleece production. Introduction In many wool production systems, ram and ewe replacements are selected primarily on the basis of their own hogget (yearling) fleeceweight. This system has a number of disadvantages. The heritability of hogget fleeceweight is only moderately high (Blair et al. 1985), as a result of which phenotypic fleeceweight does not accurately predict genetic merit. In addition, to allow for selection at hogget shearing, a large number of animals must be carried through the winter when feed is scarce. The need for an accurate method of predicting genetic merit for fleeceweight at an early age has led to studies aimed at identifying genetic markers for this trait. A genetic marker for fleeceweight may be defined as a characteristic of the animal, other than its own fleeceweight, which can be used to predict the genetic merit of that animal for wool production. As noted by Blair et al. (1990), identification of genetic marker(s) could allow more accurate selection of superior animals at an early age (e.g. prior to puberty), thus decreasing the generation interval, increasing the genetic gain per year and possibly reducing breeding costs.

2 R. J. Antram et al. The examination of physiological and other differences between lines of animals divergently selected on the basis of production traits provides a useful first approach to the identification of such markers (Blair et al. 1990). An inverse relationship between wool sulfur concentration and genetic merit for fleece production has been observed in Merino lines divergently selected for fleeceweight (Piper and Dolling 1966; Reis et al. 1967) and crimp frequency (Campbell et al. 1972). An inverse phenotypic relationship between fleeceweight and wool sulfur concentration has also been observed (Reis et al. 1967). The lower wool sulfur concentration of sheep genetically predisposed to high fleece production is not due simply to a dilution of the same amount of sulfur in a greater amount of wool, since the total wool sulfur output is generally greater in high genetic merit sheep (McGuirk 1979). It appears that, in the Merino at least, wool sulfur concentration or output has potential as a genetic marker for fleeceweight. However, little is known about the relationship between wool sulfur concentration or output and genetic merit for fleece production in New Zealand Romney sheep. Furthermore, even in the Merino there is no information on the variation in wool sulfur concentration with age/season in genetically divergent strains. The purposes of this study were therefore to determine whether there are differences in wool sulfur concentration or output between Romney sheep of high versus low genetic merit for fleeceweight and to evaluate possible genotype by age/season interactions in wool sulfur concentration and output. Materials and Methods Animals The animals used in the study were from the Massey University fleeceweight-selected (FW) and control (C) lines. Management and selection procedures in these lines have been described in detail by Blair et al. (1984, 1985). Briefly, the lines were established in 1956 when mixed-ages ewes from an interbred base flock of New Zealand Romneys were randomly allocated to three lines. The lines were closed in 1958 and have since been maintained at 80 ewes with four 18-month-old rams being used for mating each year. Replacements are chosen at random for the C line whereas, in the FW line, rising two-year-old replacements are selected on the basis of high greasy fleeceweight at hogget shearing (14 months of age). The third line, in which selection was based on face cover (Blair et al. 1984), was not used in this study. After 27 years of single trait selection in the FW line, ewe greasy fleeceweight had increased by about 1 kg and average lifetime wool production by approximately 20% relative to the C line (Blair 1986). Wool Samples The wool samples used in this study were from the experiment of McClelland et a/. (1987) who described sampling procedures in detail. Samples came from 35 FW and 30 C ram hoggets used in that study. On day 1 of the trial (mid-december), when the animals were approximately 4-months-old, a right midside patch (approximately 8 cmx8 cm) was clipped to skin level. Midside samples were collected at 28 day intervals from this time until hogget shearing in mid-october (day 308). Samples were taken by clipping the midside patch whilst the ram lay on its side on a table. The boundaries of the patch were defined by tattooing to ensure accurate definition of the area to be sampled. Patch area was calculated from lengths of the four sides of the patch plus one diagonal (i.e. summing the areas of two triangles with a common side on the diagonal). Wool samples were detergent-scoured then rinsed in hot distilled water, conditioned at 65% relative humidity for at least 72 h and weighed. Conditioned wool contained 10.5%

3 Wool Sulfur in Romney Rams moisture as determined by oven drying to a constant weight. The clean wool growth (mg/cm2) in each 28 day period was calculated by dividing the clean wool weight of the midside sample by the patch area. Samples were stored in paper envelopes in a dark room until sampled for wool sulfur analysis. Wool Sulfur Assay The wool from the midside patch was randomly sampled by using tweezers to pluck fibres and about 200 mg of wool was accurately weighed into a 150 ml conical flask. The wool was digested using an open wet digestion method to oxidize the organic sulfur of wool to inorganic sulfate-sulfur. Oxidizing agent (5 ml of 10% bromine in carbon tetrachloride) was added to each flask and a funnel was placed on the flask. The contents of the flask were mixed by swirling at 5-min intervals for the next 30 min. Concentrated (70%) nitric acid (10 ml) was then added through the funnel and mixed by swirling as above. All reagents were Analar grade. After standing for approximately 16 h, the samples were heated on a heating block at 75 C for 2 h. The temperature was then raised to 10O0C, and the volume was reduced to near dryness (about 5 ml). Hydrochloric acid (2 M, 10 ml per flask) was added to each of the samples, and they were then heated at 75 C for 10 min. The samples were made up to volume in a 50 ml volumetric flask with 2 M hydrochloric acid and mixed thoroughly to evenly disperse any residues. A 15 ml-aliquot was removed and its sulfur concentration determined by plasma emission spectrometry (Model 34000, Applied Research Laboratories, Sunland, L.A., CA; Pritchard and Lee 1984). Each batch of digestions contained an in-house wool standard. The intra- and inter-assay coefficients of variation (CV) were 1.4% and 2.6% respectively. Intra-assay CV were calculated on the results of 18 wool samples assayed in duplicate within one assay and inter-assay CV from 10 samples included in two or more assays. Statistical Analyses Wool sulfur concentration was expressed as a percentage of total clean scoured wool weight while sulfur output for each sampling period was calculated as the product of wool sulfur concentration and midside wool growth. Data from each sampling period were subjected to analysis of variance to determine the significance of the effects of rearing rank (single v. twin), date of birth, dam age (2 to 5 years), selection line and line by rearing rank interactions on midside wool growth, wool sulfur concentration and wool sulfur output. All main effects were treated as fixed. Data were analysed using the statistical package 'REG' (Gilmour 1985). Results Midside Wool Growth Midside wool growth (expressed as weight of wool grown per cm2 per 28 days) of FW and C rams reared as singles or twins is shown in Fig. 1. In both lines, wool growth rate fell from lamb shearing (December) to reach a minimum in the 28 days to day 196 (25 July). The FW rams had significantly (P < 0.05) greater wool growth rates than the C rams throughout the trial, except on day 56. The effect of rearing rank (single v. twin) was significant (P < 0 05) in March and April (days 84 and 11 2). There was also a significant (P < 0.05) line by rearing rank interaction in wool growth at days 56, 168, 252, and 280. Thus fleeceweight-selected rams reared as singles had wool growth rates consistently higher than those of FW rams reared as twins, whereas the wool growth of C rams was not influenced by rearing rank.

4 R. J. Antram et al. Date of birth was significantly (P < 0.05) related to the amount of wool grown in the first three sampling periods, and in the periods to day 224 and to hogget shearing (day 308). Earlier born rams grew more wool than those born later in the season. Dam age was also included in the model, but it was not significant (P> 0.10) except at day 224. At this time, rams born to 3- or 4-year-old ewes had a higher wool growth rate than those born to 2-year-olds or to ewes aged greater than 4 years (P < 0.05). Sampling time (days) Fig. 1. Clean wool growth of fleeceweight-selected (--)-and control (--.) Romney rams during 28 day periods between lamb shearing in December (day 1) and hogget shearing in the following October (day 308). 0, reared as singles; 0, rams reared as twins; vertical bars, pooled standard errors about the mean. Wool Sulfur Concentration The average wool sulfur concentration in both the lines increased over the sampling period from a low at day 28 to a peak at day 308 (Fig. 2). The wool sulfur concentration of C animals was higher than that of FW animals at the first sample (P < 0-10). The lines then converged and wool sulfur concentration was similar in FW and C rams until about day 168. From this time until hogget shearing the C animals had a higher average wool sulfur concentration than the FW animals, but the difference was significant (P < 0.05) only at day 280. There was no significant rearing rank effect or line by rearing rank interaction in wool sulfur concentration at any sampling time. Date of birth affected wool sulfur concentration significantly (P < 0.05) at days 252 and 280 (August-September), the earlier born animals having a lower wool sulfur concentration than those born later in the season. Dam age had

5 Wool Sulfur in Romney Rams 273 a significant (P < 0.05) effect on wool sulfur concentration at days 196 and 308. At these times rams born to 3 or 4-year-old ewes had higher wool sulfur concentrations than rams born to ewes aged 2 or greater than 4 years. Phenotypic correlations between midside wool growth rate and wool sulfur concentration at individual sampling times ranged from to c0.19 and were all nonsignificant. Sampling time (days) Fig. 2. Sulfur concentration of wool from fleeceweightselected (---) and control (-) Romney rams during 28 day periods between lamb shearing in December (day 1) and hogget shearing in the following October -(day 308). 0, rams reared as singles; 0, rams reared as twins; vertical bars, pooled standard errors about the mean. Total Sulfur Output Fig. 3 shows the total wool sulfur output (the product of wool growth rate and sulfur concentration) of FW and C rams reared as twins or singles. Average total wool sulfur output of both lines decreased from day 56 to day 112 before increasing to a maximum value at hogget shearing (day 308). FW rams had a significantly (P < 0.05) higher sulfur output than C rams at days (March-May) and (June-October). The effect of rearing rank was not significant, but there was a significant line by rearing rank interaction during days During this time the FW rams reared as singles had a higher wool sulfur output than those reared as twins, but there was no effect of rearing rank in control rams.

6 2 74 R. J. Antram et al. Date of birth had a significant (P < 0.05) effect on wool sulfur output immediately after lamb shearing (days 28 and 56) and at hogget shearing (day 308). During these periods, lambs born early in the season had a lower sulfur output than those born late in the season. Dam age was significant (P < 0.05) at days 196, 224, and 280. The relationship between dam age and total wool sulfur output was the same as for dam age and wool sulfur concentration, rams born to 3 and 4-year-old ewes having a higher total sulfur output than those born to 2-year-olds or ewes aged greater than 4 years. Sampling time (days) Fig. 3. Total wool sulfur output of fleeceweight-selected (-1 and control (---) Romney rams during 28 day periods between lamb shearing in December (day 1) and hogget shearing in the following October (day rams reared as singles; 0, rams reared as twins; vertical bars, pooled standard errors about the mean. Discussion The results of this study indicate that significant differences in the wool sulfur concentration of FW and C Romney rams were apparent only at particular times of the year, namely, days 28 (January) and 280 (September). Where they occurred, differences were consistent with those observed in Merino studies (Piper and Dolling 1966; Reis et al. 1967), animals with a high genetic merit for fleece production having a low wool sulfur concentration. Wool sulfur concentration showed substantial variation with age/season, increasing from a minimum near the beginning of the trial to a peak at hogget shearing (October). In both lines, temporal variation in wool sulfur concentration appeared to occur independently of corresponding variation in midside wool growth rate.

7 Wool Sulfur in Romney Rams Conversely, a substantial variation in wool sulfur concentration, which followed very closely the temporal pattern of wool growth, has been reported in 2-year-old Merino wethers that varied phenotypically in wool-producing ability (Reis and Williams 1965). Ross (1964) found an inverse temporal relationship between wool sulfur concentration and wool growth rate in Romney ewes, but the relationship was apparent in only one year of that study. Wool sulfur concentrations in the FW and C ram hoggets (average of 2.5 to 2-9%) were generally lower than the values (2.7 to 4.2%) reported previously for Merino sheep (Piper and Dolling 1966; Reis et al. 1967; Campbell et al. 1972). This can be explained partially, but not completely, by the fact that in this study sulfur concentration was expressed as a proportion of conditioned wool weight, whereas in the Merino studies it was expressed in proportion to oven-dry weight. Low sulfur concentrations in wool do not appear to be a characteristic of the Massey University selection lines, since previous estimates of sulfur concentration in 2-year-old rams from these lines (McCutcheon et al. 1987) were similar to, or higher than, estimates from unselected Romneys (Ross 1964) and from Merinos (Piper and Dolling 1966; Reis et al. 1967). However, the animals used in this study were 4 to 14-months-old, and wool sulfur concentration increased progressively through the study (i.e. with increasing age), whereas animals in previous studies were generally greater than 2-years-old. The low wool sulfur concentrations in our animals may therefore be a consequence of their being younger than those used previously. Wool sulfur output was significantly greater in the FW rams than in the C rams at days (March-May) and (June-October). This is consistent with the results of Merino trials which reported a generally greater wool sulfur output from high genetic merit animals (McGuirk 1979). Temporal variation in the wool sulfur output closely followed the corresponding pattern of wool growth. Total wool sulfur output of both lines decreased from day 56 to day 112 before increasing to a maximum value at day 308. Line by rearing rank interactions in wool sulfur output reflected the corresponding interactions in wool growth rate. It may be that competition for nutrients during foetal life and/or early postnatal life (pre-weaning) impedes the ability of FW twins to reach their genetic potential for wool growth at a later stage. Since control animals have a lower potential wool growth, the effects of this competition may be less marked in control rams reared as twins than in twins from the FW line. The results of this study are not encouraging with respect to the use of wool sulfur concentration as a genetic marker for wool production in the Romney. Differences between the lines were initially apparent only at day 28 and, by the time differences again appeared at day 280, the animals were past puberty and had already been retained over the winter when feed availability is at a minimum. Furthermore, by day 280 they were close to hogget shearing, at which time fleeceweight data would normally be available. While post-winter selection of replacement stock on the basis of wool sulfur concentration would have few benefits (unless wool sulfur concentrations could be used in an index with hogget fleeceweight to improve the accuracy of selection), selection prior to puberty would decrease the number of animals that were required to be retained over the winter. Given that a difference between the lines in wool

8 R. J. Antram et al. sulfur concentration was observed at the commencement of this trial, further studies are required to determine whether differences exist between the lines prior to this time (i.e. before 4 months of age). Reis (1965) has reported differences in the sulfur concentration of wool samples from different sites on Merino sheep. No information is available on the variation in wool sulfur concentration across the body of Romney sheep or in sheep differing in genetic merit for fleece production (i.e. the possibility of genotype x site interactions). Further studies are needed to determine whether sulfur concentration varies in wool selected from different sampling sites on Romney sheep and, in particular, whether the midside is the most appropriate site for measuring wool sulfur concentration as a potential predictor of genetic merit for fleece production. Although there were significant differences between the lines in wool sulfur output on days (March-May), wool sulfur output has little advantage over wool growth or sulfur concentration alone as a genetic marker. Measurement of wool sulfur output requires both the assay of wool sulfur concentrations and the measurement of wool growth and much of the between-line variation in sulfur output could be attributed to variation in midside wool growth. In conclusion, selection for high hogget greasy fleeceweight in the Massey University Romney selection lines has been accompanied by a divergence in wool sulfur output, but this primarily reflects the corresponding divergence in wool growth rate. No consistent differences were observed between the lines in wool sulfur concentration. Thus the sulfur concentration of midside wool samples collected from animals aged 4-14 months is unlikely to be useful as a genetic marker. Further studies are required to determine whether differences exist between the lines prior to this time. Acknowledgments The authors gratefully acknowledge the technical assistance of Miss M. F. Scott, Miss Y. H. Cottam and Mr G. S. Purchas, and the financial assistance of the New Zealand Wool Board and the C. Alma Baker Trust. References Blair, H. T. (1986). Responses to 27 years of selection for greasy fleeceweight. Proc. 3rd World Congr. Genet. Appl. Livest. Prod. Vol. 12, pp Blair, H. T., Garrick, D. J., Rae, A. L., and Wickham, G. A. (1984). Selection response in New Zealand Romney sheep 1. Selection for wool-free faces. N.Z. J. Agric. Res. 27, Blair, H. T., Garrick, D. J., Rae, A. L., and Wickham, G. A. (1985). Selection responses in New Zealand Romney sheep 2. Selection for yearling greasy fleeceweight. N.Z. J. Agric. Res. 28, Blair, H. T., McCutcheon, S. N., and Mackenzie, D. D. S. (1990). Physiological predictors of genetic merit. Proc. Aust. Assoc. Anim. Breed. Genet, 8, Campbell, M. E., Whiteley, K. J., and Gillespie, J. M. (1972). Compositional studies of highand low- crimp wools. Aust. J. Biol. Sci. 25, Gilmour, A. R. (1985). REG: a generalized linear models programme. Misc. Bull. No. l., Div. Agric. Serv., N.S.W. Dept. Agric. McClelland, L. A., Wickham, G. A., and Blair, H. T. (1987). Efficiency of Romney hoggets from a fleece weight selected flock. Proc. 4th Anim. Sci. Cong. Asian-Australas. Assoc. Anim. Prod. Soc.: 330 (Abstr.).

9 Wool Sulfur in Romney Rams McCutcheon, S. N., Mackenzie, D. D. S., and Blair, H. T. (1987). Nitrogen metabolism and plasma urea concentrations in fleeceweight-selected and control Romney rams. Aust. J. Agric. Res., 38, McGuirk, B. (1979). Selection for wool production in Merino sheep. In 'Selection Experiments in Laboratory and Domestic Animals'. (Ed. A. Roberston.) pp (Commonw. Agric. Bur.: Farnham Royal, U.K.) Piper, L. R., and Dolling, C. H. S. (1966). Variations in the sulfur content of wool of Merino sheep associated with genetic differences in the wool-producing capacity. Aust. J. Biol. Sci. 19, Pritchard, M. W., and Lee, J. (1984). Simultaneous determination of boron, phosphorus and sulphur in some biological and soil materials by inductively-coupled plasma emission spectrometry. Analyt. Chim. Acta, 157, Reis, P. J. (1965). The growth and composition of wool Variations in the sulphur content of wool. Aust. J. Biol. Sci. 18, Reis, P. J., Tunks, D. A., Williams, 0. B., and Williams, A. J. (1967). A relationship between sulphur content of wool and wool production by Merino sheep. Aust. J. Biol. Sci. 20, Reis, P. J., and Williams, 0. B. (1965). Variations in the sulphur content of wool from Merino sheep on two semi-arid grasslands. Aust J. Agric. Res., 16, Ross, D. A. (1964). Wool production and sulphur content. N.Z. J. Agric. Res. 7, Manuscript received 26 March 1990, accepted 27 August 1990