Browsing by Author "Muller, Anieka"

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    Feather and skin development of ostriches Struthio camelus
    (AOSIS, 2018-12-05) Brand, Tertius S.; Kritzinger, Werne J.; Van der Merwe, Daniel A.; Muller, Anieka; Hoffman, Louw C.; Niemann, Gert J.
    Information on feather and skin growth is important for the development of mathematical optimisation nutritional models for ostriches. Ostriches (n = 65) were subjected to a four-stage formulated growth diet programme (pre-starter, starter, grower and finisher), with declining protein and energy content. Nine birds were weighed, stunned, exsanguinated, defeathered, skinned and eviscerated at 1, 54, 84, 104, 115, 132 and 287 days of age. Feathers from four pre-selected locations on the body were harvested and weighed. The wet skin weight, wet unstretched skin size and wet unstretched crown size were measured at each slaughter stage. The live weight, feather and skin yields of the birds increased with age at slaughter, as did feather shaft diameter. Prediction models were developed to estimate the yield of the skin in terms of live weight and of empty body protein weight to aid in diet formulation. The allometry of feather growth was determined from total feather weight, as the maturation rates of the feathers differ from that of the ostrich body. Results from this study will aid in setting up a mathematical optimisation nutritional model for ostriches.
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    Studies on the environmental and genetic parameters for lamb survival, growth and wool traits of the Elsenburg Dormer and SA Mutton Merino flocks
    (Stellenbosch : Stellenbosch University, 2020-12) Muller, Anieka; Cloete, Schalk W. P.; Brand, T. S.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Environmental and genetic parameters and trends of the Elsenburg South African Mutton Merino (SAMM) and Dormer resource flocks were estimated. The breeds were also compared for lamb survival, growth, wool, carcass and meat quality traits. Early growth and lamb survival data over a 64-year period (1955 - 2019) and yearling weight and wool data over a 36-year period (1983 - 2019) were used in the study for SAMM sheep. Single-trait heritability estimates of SAMM lambs amounted to 0.07 for birth weight (BW), 0.03 for weaning weight (WW), 0.02 for lamb survival (LS), 0.24 for yearling weight (YW), 0.58 for clean yield (CY), 0.37 for clean fleece weight (CFW), 0.34 for staple length (SL), 0.55 for coefficient of variation of fibre diameter (CVFD) and 0.68 for fibre diameter (FD). Maternal heritability estimates were 0.15 for BW, 0.06 for WW and 0.01 for LS. Multi-trait heritability estimates compared well with the single-trait estimates. Genetic correlations among weight traits ranged from 0.04 for BW and YW to 0.81 for WW and YW. Low to moderate correlations among yearling traits accorded with previous literature for wool breeds. Genetic trends showed favourable but extremely slow genetic responses. Data from 1943 to 2019 were used to investigate genetic and environmental parameters and trends for early growth traits and LS in the Dormer flock. Yearling live weight- and wool traits were recorded for a shorter period from 2008 to 2018. Direct single-trait heritability estimates were 0.15 for BW, 0.06 for WW, 0.02 for LS, 0.19 for YW, 0.63 for CY, 0.56 for CFW, 0.59 for SL, 0.59 for SS, 0.60 for CVFD and 0.80 for FD. Maternal genetic effects amounted to 0.21 for BW, 0.08 for WW and 0.06 for YW. Genetic correlations among live weight traits ranged from low (-0.11) between BW and YW to very high (0.93) for WW and YW. Genetic correlations among wool traits were mostly low. Genetic trends for all weight traits suggested significant positive trends with time. Expressed relative to the overall phenotypic mean, these trends amounted to 0.12% for BW, 0.16% for WW and 0.45% for YW. Selection from 2013 for direct-, maternal- and a combination of direct and maternal breeding values up to 2019 resulted in genetic trends amounting to 0.07% for BW, 0.79% for WW and 1.01% for YW in the line selected on direct breeding values for WW. Corresponding genetic trends amounted to respectively -0.51%, 0.17% and 0.27% in the line selected on maternal breeding values for WW and respectively -0.20%, 0.41% and 0.58% in the line selected for a combination of direct and maternal breeding values. Maternal genetic trends were markedly smaller in magnitude even in those lines were selection was based on maternal breeding values. Results indicated that SAMM lambs were heavier at birth compared to their Dormer contemporaries (4.19 vs. 4.13 kg). Dormers were heavier than SAMMs at weaning (27.3 vs. 25.0 kg) and also when weighed as yearlings (49.7 vs. 47.8 kg). Dormer lambs had a higher survival rate than SAMM lambs at 0.89 and 0.81, respectively. Clean fleece weight was the only wool trait not affected by breed. Dormer yearlings had a higher CY and SL than SAMM yearlings. In contrast, SAMM yearlings had a lower CVFD and finer wool than their Dormer contemporaries (respectively 22.4 vs. 28.6 μm). The two breeds did not differ for slaughter weight, carcass weight or dressing percentage. Dormers had a thicker subcutaneous fat cover at the rump than SAMM contemporaries (5.00 vs 4.18 mm). It was concluded that all traits considered were variable and heritable, although selection responses to traits such as lamb survival and weaning weight in SAMMs may be slow. Breed differences for economically important traits were consistent with the roles of the two breeds, with the Dormer as a coarse-woolled terminal sire breed and the SAMM as a dual-purpose breed.