Does selecting for finer wool result in. higher incidence of creeping belly in the South African Dohne Merino sheep breed?

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1 Does selecting for finer wool result in higher incidence of creeping belly in the South African Dohne Merino sheep breed? P Naidoo 1, JJ Olivier1, #, J Morris 2 and SWP Cloete 1,2 1 Directorate: Animal Sciences: Western Cape Department of Agriculture, Private Bag X1, Elsenburg, Department of Animal Sciences, Stellenbosch University, Private Bag X1, Matieland, 7602 # Corresponding author: bukso@elsenburg.com Take home message One of the breeding objectives of the Dohne Merino breed in South Africa is to decrease fibre diameter while maintaining fleece weight. It was postulated that selection for fine wool would increase the incidence of creeping belly (a condition where belly fleece encroaches into the woolly area of the sheep s body) and as a result decrease the financial value of the fleece. This study found that selection for finer wool with high wool quality score can result in a higher incidence of creeping belly and it is therefore important to place a cap on clean fleece weight selection and monitor the incidence of creeping belly. Keywords: Dohne Merino, reproduction, wool quality, dual-purpose sheep breed. Introduction Small stock farming uses the large proportion of agricultural land in South Africa (SA) that is not suitable for intensive agricultural production (Schoeman et al., 2010). Extensive small stock production in the large arid areas of SA contributes about 8% to the total gross value of animal products (Cloete et al., 2014, Schoeman et al., 2010). While the monetary contribution of the sheep industry is relatively minor in comparison to other animal products, the industry is important in the regional context and of strategic importance in rural areas of South Africa (Cloete and Olivier, 2010, Cloete et al., 2014). The Merino industry produces wool for the international market and meat for local consumption, with mutton providing 60-70% of gross income to a commercial Merino enterprise depending on fluctuations in the meat:wool price ratio (Olivier, 1999). The result of this dual-purpose enterprise is that South African breeders favour dualpurpose breeds. The dual-purpose Dohne Merino breed was established (ca. 1939) locally as a hardy and versatile genotype from a cross between the Merino and the German Mutton Merino (now known as the SA Mutton Merino) (Cloete et al., 1998, van Wyk et al., 2008). Although originally bred for semi-intensive farming in the Eastern Cape grassland regions, the Dohne Merino s ability to thrive under various conditions has resulted in the breed s popularity and expansion to other areas in South Africa (Cloete et al., 1998, van Wyk et al., 2008). The Dohne Merino breed accounts for 27,8% of the recorded portion of the South African small stock genetic resource as represented by weaning weight records submitted to the National Small Stock Improvement Scheme (NSSIS) (Cloete et al., 2014). Dohne Merinos have also been exported to other major sheep producing countries. In a study of the across-flock genetic parameter estimation for body weight and fleece traits in the South African Dohne Merino population, van Wyk et al. (2008) concluded that wool quality and quantity Vol 13 No

2 may not be compromised as a correlated response to selection for meat production traits. However, the demand for finer wool for the clothing industry has led to more emphasis being placed on the production of finer wool in the Dohne Merino breed (Olivier, 2009). There is a tendency for belly type wool to creep up the sides of the animal into the fleece wool in dual-purpose and wool breeds (Snyman and Olivier, 2015); thus reducing the economic value of the wool. Olivier et al. (2010) reasoned that the threshold for selection for decreased fibre diameter within the Grootfontein Dohne Merino flock had been reached due to the higher incidence of creeping belly (assessed subjectively using a linear scale) and low staple strength estimated in their study. The occurrence of creeping belly has also been assessed in the Carnarvon Afrino sheep flock (Snyman and Olivier, 2002). Selection for finer wool is one of the main breeding objectives for the South African Dohne Merino industry. Current estimates of genetic parameters are required to construct genetic improvement plans for the industry to improve viability, productivity and profitability (Snyman and Olivier, 2002). This study evaluated objectivelyassessed production traits and subjectivelyappraised creeping belly (CBS) and wool quality (WQS) scores for the Dohne Merino stud maintained at Mariendahl Experimental Farm of Stellenbosch University (South Africa) with the intention to address the question: does selecting for finer wool result in a higher incidence of creeping belly in the South African Dohne Merino sheep breed? Materials and methods Data used for this study was collected from the Dohne Merino stud maintained at the Mariendahl experimental farm of the Stellenbosch University. A seven-trait linear-threshold animal model was fitted to the data (n = 2290), with live weight (LW), clean fleece weight (CFW), mean fibre diameter (MFD), staple length (SL), coefficient of variation of fibre diameter (CV) and subjectively-appraised creeping belly (CBS) and wool quality (WQS) scores as variables. Production year, sex, birth type and dam age were the fixed effects considered and direct, additive animal effects were the only random effects considered in this analysis. The objectively-assessed production traits were included as linear traits; with the subjective scores defined as binary traits with two categories (1 depicted as unacceptable score and 2 as acceptable scores in both cases). As the data contained both categorical and continuous traits, THRGIBBS1F90 and POSTGIBBSF90 software (Misztal, 2008) were used for the analyses. Descriptive statistics for objective production traits in Dohne Merino yearlings (Table 1) Results and Discussion Table 1. Descriptive statistics for objective production traits in Dohne Merino yearlings Trait Number of observations Mean ± SD Coefficient of variation Range LW (kg) ± CFW (kg) ± MFD (μm) ± SL (mm) ± CV (%) ± CBS ± WQS ± Vol 13 No

3 Table 2. Direct additive and residual variance components (σ 2 and a σ2 respectively) and e (co)variance ratios for live weight (LW), clean fleece weight (CFW), mean fibre diameter (MFD), staple length (SL), coefficient of variation of MFD (CV) and subjectively-appraised creeping belly (CBS) and quality scores (WQS) of Dohne Merino yearlings Trait LW CFW MFD SL CV CBS WQS Variance components σ 2 a σ 2 e PSD for σ 2 a (Co)variance ratios (h 2 on the diagonal, rg above the diagonal and re below the diagonal) LW 0.41± ± ± ± ± ± ±0.15 CFW 0.34± ± ± ± ± ± ±0.17 MFD 0.33± ± ± ± ± ± ±0.14 SL 0.21± ± ± ± ± ± ±0.14 CV 0.10± ± ± ± ± ±0.14 CBS -0.14± ± ± ± ± ± ±0.27 WQS 0.07± ± ± ± ± ± ±0.15 were consistent with corresponding results obtained in Dohne Merinos (van Wyk et al., 2008, Olivier et al., 2010). The frequency of animals judged to have creeping bellies (18% of animals) was twice as high as those with poor wool quality (9% of animals). Heritability (h 2 ) estimates for the objective wool traits CFW, MFD and SL were 0.37 ± 0.06, 0.72 ± 0.07 and 0.37 ± 0.05, respectively. Creeping belly score had a relatively low h 2 of 0.16 ± 0.04 while WQS was highly heritable at 0.43 ± Heritability (h 2 ) estimates for live weight and objective wool traits were consistent with comparable results in the literature (van Wyk et al., 2008). At 16%, the h 2 of creeping belly score on the underlying liability scale was somewhat lower that for the other traits. It was also lower that an estimate of 0.38 reported by Snyman & Olivier (2002) for creeping belly in Afrino sheep. It is important to note that the former study used linear scores on a 50-point scale to subjectively score the animals in their study. At >40%, the (h 2 ) of quality score were more than double as high as that of creeping belly score. This (h 2 ) estimate for quality score is also comparable to literature estimates for quality scored on a 50-point linear scale, which often exceeds Snyman & Olivier (2002) reported that related traits, like softness (h 2 =0.51), crimp definition (h 2 =0.47) and evenness across the fleece (h 2 =0.28) had comparable levels of genetic variation. Genetic correlations between objective and subjective traits in Table 2 were mostly similar to those in the literature. The genetic correlations of live weight with fleece weight and fibre diameter were lower than expectations based on the literature, but correlations of a comparable magnitude has been reported for Dohne Merinos in the past (van Wyk et al., 2008, Olivier et al., 2010). Sheep with acceptable scores for wool quality would generally have stronger fleeces, with higher coefficients of variation. Notable correlations were found between WQS and MFD (0.36 ± 0.14); sheep with acceptable wool quality would generally have stronger fleeces. Vol 13 No

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5 Further, the genetic correlation between wool quality and creeping belly scores were fairly strongly negative (-0.55 ± 0.27) indicating that sheep with acceptable quality scores would tend to have poorer scores for creeping belly on the underlying liability scale. The most concerning genetic correlation was between CBS and CFW (-0.29 ± 0.16) as this shows that selecting for lower clean fleece weights can result in a higher incidence of creeping belly. Comparable genetic correlations of creeping belly score with softness, crimp definition and evenness across the fleece amounted to respectively -0.52, and in Afrino sheep when both traits were assessed on a 50-point linear scale (Snyman and Olivier, 2002). Conclusion In conclusion, this study found that selection for finer wool with high WQS can result in a higher incidence of CB and it is therefore important to place a cap on clean fleece weight selection and monitor the incidence of creeping belly. AP References CLOETE, S. & OLIVIER, J South African sheep and wool industries. International Sheep and Wool Handbook, CLOETE, S., OLIVIER, J., SANDENBERGH, L. & SNYMAN, M The adaption of the South Africa sheep industry to new trends in animal breeding and genetics: A review. South African Journal of Animal Science, 44, CLOETE, S., SCHOLTZ, A. & AUCAMP, B Environmental effects, heritability estimates and genetic trends in a Western Cape Dohne Merino nucleus flock. South African Journal of Animal Science, 28, OLIVIER, W Is selection for decreased fibre diameter in a merino flock with overstrong wool viable? Grootfontein Agric., 9. OLIVIER, W., HERSELMAN, M. & VAN HEERDEN, M Production norms of the Grootfontein Dohne Merino flock. Grootfontein Agric., 10. SCHOEMAN, S., CLOETE, S. & OLIVIER, J Returns on investment in sheep and goat breeding in South Africa. Livestock Science, 130, SNYMAN, M. & OLIVIER, W Correlations of subjectively assessed fleece and conformation traits with production and reproduction in Afrino sheep. South African Journal of Animal Science, 32, SNYMAN, M. & OLIVIER, W An analysis of creeping belly in the Carnarvon Afrino sheep flock. Grootfontein Agric., 15. VAN WYK, J., SWANEPOEL, J., CLOETE, S., OLIVIER, J. & DELPORT, G Across flock genetic parameter estimation for yearling body weight and fleece traits in the South African Dohne Merino population. South African Journal of Animal Science, 38, Vol 13 No