Phenotypic and genetic parameters for production traits of Merino sheep in central western Queensland

Abstract

Proc. Aust. Soc. Anim. Prod. 1996 Vol. 21 PHENOTYPIC AND GENETIC PARAMETERS FOR PRODUCTION TRAITS OF MERINO SHEEP IN CENTRAL WESTERN QUEENSLAND MARY ROSE and P.M. PEPPER Dept of Primary Industries, Animal Research Institute, Yeerongpilly, Qld 4105 SUMMARY The heritability of and the phenotypic and genetic correlations among production characters, greasy fleece weight (GFW), yield (YLD), clean fleece weight (CFW), fibre diameter (DIAM) and live weight at 15 months of age (LWT), were estimated in a flock of medium Peppin Merino sheep in central western Queensland. The effects of year of birth and birthtype were significant factors for all characters except yield while sex affected all characters. Most estimates. were in general agreement with the published range. Heritabilities for GFW, YLD, CFW, DIAM and LWT were respectively 0.26, 0.58, 0.33, 0.62 and 0.27 respectively. Keywords: Merino sheep, production characters, heritabilities, genetic correlations, phenotypic correlations INTRODUCTION Accurate estimates of genetic and phenotypic parameters for production characters are necessary for the design of efficient sheep breeding programmes as is a knowledge of the effects of environmental factors on these characters in the accurate selection of animals based on measurement. Mortimer (1987) provided a review of the published estimates of genetic parameters for wool production and quality traits with special reference to Australian Merino flocks and Robertson (1987) for hogget live weight. These reviews showed that most characters were moderately to highly heritable. In the environment of this study, Beattie (1962) reported offspring-dam regression estimates for medium Peppin sheep in north west Queensland based on mixed-age animals of both sexes and uncorrected data. The National Performance Recording Scheme for Merino and other wooled sheep breeding flocks (formerly WOOLPLAN), uses 'accepted' values for the phenotypic and genetic parameters based on published values (Ponzoni 1988). There are few published values for flocks in Queensland so values derived in a flock in central western Queensland, where many of the state' largest Merino studs are situated, are of interest. In this paper we s report preliminary results from a flock at Longreach, central western Queensland, being recorded for studies into the selection of better acclimatised sheep for the area. The effects of year of birth, sex and birth type on fleece production and live weight at 15 months of age and estimates of genetic and phenotypic parameters for these characters are reported. MATERIALS AND METHODS Environment Studies were carried out at Rosebank Research Station, Longreach, in central western Queensland. The environment and levels of production in this area have been described by Moule (1954) and Smith (1964). Sheep The flock was of locally bred, mature age, medium Peppin ewes which were mated to rams bred in the area. The ewes were allocated randomly using stratification on age and live weight to 18 sire groups, each sire being mated to approximately 35 ewes. Sires were replaced each year so there were 54 sires mated over the 3 years, 1992-94. Ewes were run as a single mob except at joining and lambing when they were allotted to 18 individual paddocks for ease of management and data collection. Records Complete records of greasy fleece weight (GFW), percentage yield (YLD), clean fleece weight (CFW), average diameter (DIAM), and live weight (LWT) at 15 months were available for 1241 sheep, the progeny, born in 1992, 1993 and 1994, of 54 sires. There were 643 males and 598 females. There were 1045 born as singles, 192 animals born as twins and 4 born as triplets. Statistical analyses These data were analysed using the model: 170 Yroc. Aust. Sot. Anim. Prod. 1996 Vol. 21 where yijkhn = the individual measurement; m Yri 2, GI Bin eijklmn = = = = = = = population mean; year of birth; the effect of sire nested within year; the effect of dam; the effect of sex; the effect of the birthtype; the random error. Except for Sij and dk (which were treated as random), all other effects were treated as fixed. Analyses were carried out using the programme REML (Thompson 1977) as implemented by Genstat 5 Release 3 (1993). The significance of the fixed effects, year of birth, sex and birth type was tested using the Wald Statistic (Genstat 5 Release 3 1993). RESULTS AND DISCUSSION Table 1. MeaIls for greasyfleece weight (GFW), yield (YLD), clean fleece weight and live weight (LWT) of 15month medium Peppin Merino sheep (CFW, average diameter (DIAM) Effects of environmental factors Table 1 shows the means for fleece characters and live weight for each of the environmental factors, year of birth, sex and birth type. Year of birth significantly affected all characters with the exception of yield. There were large differences between the best and worst years in most characters. All production characters, except yield, were greatest for the 1993 drop and least for the 1994 drop. Year of birth and year of measurement are confounded and differences in production reflect the season experienced in the year of measurement. With the exception of live weight and yield, year of birth had the major effect on the other characters. Sex was a significant factor in all characters. It was the dominant effect on live weight. Rams were heavier at 15 months and had heavier fleece weights and lower yields and diameters than ewes. Birth type was the least important environmental factor. However it had a significant effect on fleece weight and fibre diameter at 15 months. Sheep born as singles had heavier fleece weights but had slightly finer wool. This would support the use of data corrected for birth type to improve the accuracy of selection. Phenotypic and genetic parameters Table 2 shows the means and the genetic and phenotypic parameters for each of the production characters. 171 Proc. Aust. Sot. Anim. Prod. 1996 Vol. 21 Table 2. Phenotypic and genetic parameters (GE) for greasy fleece weight (GFW), yield (YLD), clean fleece weight (CFW), average diameter (DIAM) and live weight (LWT) of 15month medium Peppin Merino sheep Heritability estimates suggest all characters were moderately to highly heritable. The estimates for these production characters are within the range reported for other medium Peppin flocks (Beattie 1962; Mortimer 1987; Turner and Young 1969). Estimates of phenotypic correlations between wool characters are generally within the published range, except the correlation between GFW and YLD which is lower than those published for Peppin Merinos. The correlation between GFW and DIAM is at the high end of the range and between YLD and CFW at the lower end. The correlations between hogget LWT with both GFW and CFW are much higher than those reported by Robertson (1987). All estimates of genetic correlations were within the published range (Mortimer 1987). CONCLUSIONS Parameters are specific to the particular flock or population in which they are estimated, although for the important production characters in Merino sheep in Australia there appears to be general agreement with a published range. Obtaining further estimates from Merino flocks is, however, appropriate in confirming the use of 'accepted' values in performance recording and when additional characters are introduced into sheep breeding programmes. The estimates of parameters for a flock in central western Queensland in this study are in general agreement with the 'accepted' values in the National Performance Recording Scheme for Australian Merino sheep, although the estimates of heritability in this study are slightly lower than those currently used for LWT (0.40) and for GFW and CFW (0.35 and 0.40 respectively) and higher than that for fibre diameter (0.50). ACKNOWLEDGEMENTS It is a pleasure to thank David Cobon, Quenton Scott and other staff who managed the sheep at Longreach; Quenton Scott, Joanne Bailey and Susan Peart who collected samples and weighed sheep and Annette Cotton who kept the database and collated the data. REFERENCES BEATTIE, A.W. (1962). Qd J. Agric. Sci. 19: 17-26. GENSTAT (1993). Genstat 5 Release 3 (Oxford Science Publications, Clarendon Press: Oxford). MORTIMER, S.I. (1987). ` 'Merino Improvement Programs in Australia', (Ed. B.J. McGuirk) pp. 159-73 In (Australian Wool Corporation: Melbourne). MOULE, G.R. (1954). Aust. Vet. J. 30: 153-71. PONZONI, R.W. (1988) Wool Technol. Sheep Breed. 36: 70-5. ROBERTSON, D.E. (1987). In 'Merino Improvement Programs in Australia', (Ed. B.J. McGuirk) pp. 2 19-26 (Australian Wool Corporation: Melbourne). SMITH, I.D. (1964). Proc. Aust. Sot. Anim. Prod. 5: 100-6. THOMPSON, R. (1977). Biometrics 33: 485-95. TURNER, H.N. and YOUNG, S.S.Y. (1969). 'Quantitative genetics in sheep breeding' (The Macmillan Company of Australia: Melbourne). 172