ELSENBURG JOURNAL A note on factors that affect the skin nodule development in ostriches+

T S Brand1,2 and W J Kritzinger2,3

1 Directorate Animal Sciences, Department of Agriculture, Western Cape Government, Private Bag X1, Elsenburg 7607

2Department of Animal Sciences, Stellenbosch University, Private Bag x1, Elsenburg 7607

3Animal Scientist, Bex Group (Pty) Ltd, 29 Electron Road, Technopark, Stellenbosch, 7600

+This note is an extract from the thesis by W J Kritzinger, “Allometric description of ostrich (Struthio camelus) growth and development”, 2004. MSc-study. University (Study leaders: T S Brand, LC Hoffman and F D Mellett)

Introduction

Nodules are the result of feather follicles on the skin and make it unique both in appearance and to the touch. Nodules are also the factor that distinguishes ostrich leather from competitors. Although no formal standards are available, the size, shape and distribution of these nodules are expected to have an effect on the marketability of the leather product (Cloete et al., 2004). Cloete et al. (2004) reported that age has an effect on some nodule traits in birds ranging from 5 to 14 months of age. Mellett et al. (1996) reported an increase in nodule size with age and stated that the optimum size is only achieved at 14 to 16 months of age. Van Schalkwyk et al. (2001) showed that both body weight and age have an influence on nodule size. They also reported that an acceptable nodule size could be obtained at around 11 months of age. Swart (1981 as cited by Van Schalkwyk, 2008) stated that “green” body feathers or blood feathers cause inferior nodules and nodule shape is determined by the stage of feather growth at slaughter. Swart (1981) investigated the effect of forced feather removal on nodule development and showed that nodule development may be correlated with feather development.

Brand et al. (2018) published a detailed description of the skin and feather development in ostriches.

The correlation coefficients between the explanatory variables affecting the growth and development of nodules found by Kritzinger (2011) are given in Table 1.

In order to understand the correlations among the explanatory variables, a principal component factor analysis was done. Age, live weight, EBPW (empty body protein weight), wing feather shaft diameter, skin size, skin weight and total feather weight were transformed to the natural logarithmic form. All the explanatory variables except wing feather shaft diameter were co-linear and loaded onto the first factor (Table 2). Only two factors were identified (Table 2). The second factor loads only on the wing feather shaft diameter. A multiple linear regression model with independent variables, live weight and wing feather shaft diameter was firstly constructed (explaining 93% variation in nodule size) and then improved with response surface regression to include a quadratic term, thus yielding the equation: y = 2.63 + 0.561x - 0.00111 x 2 + 0.133 z (R 2 = 0.93), where y = nodule size (mm), x = live weight (kg) and z = wing feather shaft diameter (mm)

All correlations are significant at p < 0.05

+Wing feather shaft diameter

Significant contributions for each factor are in bold type.

A multiple linear regression model with independent variables, age and wing feather shaft diameter was also constructed (explaining 88 % variation) and yielded the following equation:

The study by Kritzinger (2011), identified several factors that affect nodule development on ostrich skins. The current model allows the accurate prediction of nodule size of ostrich skin up to an age of 287 days when using body weight and wing shaft diameter (R2 = 0.93%) or age and wing feather shaft diameter (R2 = 88%). AP

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References

Brand, T S, Kritzinger J, Van der Merwe, D A, Muller A, Hoffman C and Niemann, G J., 2018. Feather and skin development of ostriches (Struthio camelus). Journal of the South African Veterinary Association, Vol 89 pg. 1556. DOI: https://doi.org/10.4102/jsava.v89i0.1556

Cloete, S. W. P., van Schalkwyk, S. J., Hoffman, L. C., and Meyer, A., 2004. Effect of age on leather and skin traits of slaughter ostriches. South African Journal of Animal Science, 34 (2), pp. 80-86.

Kritzinger, W J., 2011. Allometric description of ostrich growth and development. MSc thesis. Stellenbosch University. (Study leaders: T S Brand, LC Hoffman and F D Mellett)

Mellett, F. D., Fisher, P., and Böhme, H. M., 1996. Grading of ostrich skins. Proc. Europ. Ostrich Conf., November, Henglo, The Netherlands, European Ostrich Association, Banbury.

Swart, D., 1981. Die evaluering van die ekonomiese waarde van die vel, vleis en vere op die lewendige slagvolstruis. Ongepubliseerde verslag, Departement van Landbou en Visserye, Suid-Afrika.

Van Schalkwyk, S. J., 2008. Factors affecting ostrich leather traits. Ph.D. Thesis, Stellenbosch University, South Africa.

Van Schalkwyk, S. J., Cloete, S. W. P., Brand, T. S., & Hoffman, L. C., 2001. Die implikasie van ’n jonger of ouer slagstadium. Volstruisboeredag, Oudtshoorn Proefplaas, 1 Augustus 2001.

For more information, contact Prof Tertius Brand: tertius.brand@westerncape.gov.za