ORCID Profile
0000-0002-4548-5633
Current Organisation
Stellenbosch University
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Publisher: Elsevier BV
Date: 12-2003
Publisher: African Journals Online (AJOL)
Date: 25-07-2008
Publisher: African Journals Online (AJOL)
Date: 28-11-2007
Publisher: CSIRO Publishing
Date: 2014
DOI: 10.1071/AN13140
Abstract: Poor lamb survival pre-weaning is a major source of reproductive inefficiency in Australian sheep flocks. While nutrition and management options have been extensively researched and promoted to improve lamb survival, the present review focuses on the prospects for obtaining genetic gain and helps identify selection strategies for boosting such gains to improve overall reproductive efficiency in the Australian sheep industry. Estimated heritability for lamb survival using linear model analysis is low, although use of threshold models suggests that heritability could be higher, which, if true, could help explain the substantial genetic gains obtained in long-term selection experiments. Epigenetic mechanisms may hinder selection and quantitative trait-loci identification through confounding and/or masking genetic variances and co-variances. With sufficient information, these effects could be considered in genetic evaluations by identifying those components that are amenable to selection. Regarding indirect selection, finding effective criteria for improving lamb survival has proved elusive. Most measures of maternal behaviour, temperament and lambing difficulty researched are poorly correlated genetically with lamb survival. Of lamb behaviours and thermo-genic indicators studied, latency to bleat following handling by humans is moderately genetically correlated with lamb survival, as is neonatal rectal temperature. Industry application remains to be adequately explored for the more promising of these measures. Finally, in lieu of direct selection for lamb survival, there is merit in selecting for multiple-rearing ability or its equivalent, possibly with additional selection criteria for lamb survival and reproductive efficiency.
Publisher: Elsevier BV
Date: 11-2005
Publisher: African Journals Online (AJOL)
Date: 11-06-2004
Publisher: Elsevier BV
Date: 05-1970
Publisher: African Journals Online (AJOL)
Date: 17-02-2014
Publisher: African Journals Online (AJOL)
Date: 2003
Publisher: Informa UK Limited
Date: 06-2012
Publisher: Elsevier BV
Date: 07-2012
DOI: 10.1016/J.MEATSCI.2012.02.010
Abstract: The slaughter and meat quality traits of 20-month-old wool (Merino), dual-purpose (Dohne Merino and South African Mutton Merino [SAMM]) and mutton (Dormer) type sheep were compared. Average live weights of SAMM and Dormer sheep were 23% heavier than those of Dohne Merinos which were 28% heavier than Merinos. Fat depths at the thirteenth rib and lumbar regions of Merino and Dohne Merino sheep were lower than those of SAMM and Dormer sheep. The cooking loss, drip loss and shearing value from the M. longissimus dorsi did not differ between breeds. The initial juiciness and sustained juiciness of meat from Merinos were rated significantly lower by sensory analysis. Meat from Dohne Merino was rated significantly more tender for the attribute first bite. It was demonstrated that Dormer and SAMM sheep had heavier but fatter carcasses than Merinos and Dohne Merinos, with differences in meat quality between breeds.
Publisher: African Journals Online (AJOL)
Date: 2000
Publisher: African Journals Online (AJOL)
Date: 22-09-2006
Publisher: African Journals Online (AJOL)
Date: 08-03-2004
Publisher: CSIRO Publishing
Date: 2009
DOI: 10.1071/EA08255
Abstract: This review summarises the research that has been published on factors that influence the various aspects of ostrich leather quality, a vital aspect to the economic viability of the commercial ostrich industry. The review is ided into three main sections: discussing intrinsic, pre-slaughter and post-slaughter factors that influence leather quality. Only one literature source that investigated the morphology of ostrich skin could be found. The high vascularity near the surface of the skin was indicated in making the skin susceptible to bruising, which influences skin quality, while the strength and flexibility of ostrich leather was attributed to the three-dimensional cross-weave arrangement of collagen fibres. Various studies reported a high degree of variation in quality within and between ostrich skins. The potential of genetic selection for improved skin quality was also considered, and it was demonstrated that most ostrich leather traits exhibited significant genetic variation. Findings on pre-slaughter factors, such as the effects of age, weight, nutrition and management practices, are also summarised. Few research reports on post-slaughter factors that influence leather quality were found. A few studies looked at the effect of storage on ostrich skin quality, but literature on the effect of processing techniques are lacking. Research priorities identified include the development of methods to assess skin quality on-farm and finding objective methods of evaluating ostrich leather quality.
Publisher: African Journals Online (AJOL)
Date: 15-10-2010
Publisher: Elsevier BV
Date: 06-2008
DOI: 10.1016/J.MEATSCI.2007.10.022
Abstract: Meat derived from three genotypes of ostrich, resulting from breeding South African Black (Black) ostriches and Zimbabwean Blue (Blue) ostriches as well as their hybrid, was analysed for physical and sensory quality. Ostriches of a commercially standard slaughter age of 14 months, raised under the same environment were used. The pH(24) was the highest in the pure Blue genotype and therefore meat from this genotype was the darkest and the percentage drip loss and cooking loss the lowest. When comparing the pure Blue genotype to the pure Black genotype, 70% of the muscles had a higher pH(24), 50% of the muscles were redder and significantly less saturated in colour, 67% of the muscles had a lower percentage drip loss and 50% of the muscles had a lower percentage cooking loss. No significant genotypic differences were found regarding the instrumental toughness, nor the sensory attributes of the meat.
Publisher: Elsevier BV
Date: 04-2005
DOI: 10.1016/J.MEATSCI.2004.10.016
Abstract: Commercially reared ostriches (n=84) were randomly allocated to one of two groups. The first group (stressed: n=38) was deprived of food for a period of 2.5 days prior to slaughter, to simulate the stress experienced by slaughter ostriches held in holding pens (lairage) at a commercial ostrich abattoir over a weekend. The second group (control: n=46) was fed normally until 24 h prior to slaughter. Initial live weight as well as hot and cold drumstick weight were independent (P>0.05) of treatment. Stressed birds lost on average (±SE) approximately three times more weight than control birds over the experimental period (-3.2±0.6 vs. -1.0±0.5 kg, respectively). Full stomach and alimentary tract weights did not differ between treatments although there was a tendency for that derived from stressed birds to have lower stomach contents. The intra-muscular (Muscularis iliofibularis) pH(f) of stressed birds was 0.22 units higher (P<0.01) than that of contemporaries in the control group 1 h post-slaughter (6.03±0.06 vs. 5.81±0.05, respectively). After 26.5 h in a refrigerated room, this difference still remained at 0.25 units (6.46±0.07 vs. 6.21±0.07, respectively P 0.05) by the withholding of food for 2.5 days. It can thus be concluded that withholding feed from ostriches on lairage over a period of 2.5 days does not have any negative influence on the meat yield or physical quality traits thereof.
Publisher: Public Library of Science (PLoS)
Date: 30-06-2023
DOI: 10.1371/JOURNAL.PGEN.1010801
Abstract: Sex chromosomes have evolved repeatedly across the tree of life and often exhibit extreme size dimorphism due to genetic degeneration of the sex-limited chromosome (e.g. the W chromosome of some birds and Y chromosome of mammals). However, in some lineages, ancient sex-limited chromosomes have escaped degeneration. Here, we study the evolutionary maintenance of sex chromosomes in the ostrich ( Struthio camelus ), where the W remains 65% the size of the Z chromosome, despite being more than 100 million years old. Using genome-wide resequencing data, we show that the population scaled recombination rate of the pseudoautosomal region (PAR) is higher than similar sized autosomes and is correlated with pedigree-based recombination rate in the heterogametic females, but not homogametic males. Genetic variation within the sex-linked region (SLR) (π = 0.001) was significantly lower than in the PAR, consistent with recombination cessation. Conversely, genetic variation across the PAR (π = 0.0016) was similar to that of autosomes and dependent on local recombination rates, GC content and to a lesser extent, gene density. In particular, the region close to the SLR was as genetically erse as autosomes, likely due to high recombination rates around the PAR boundary restricting genetic linkage with the SLR to only ~50Kb. The potential for alleles with antagonistic fitness effects in males and females to drive chromosome degeneration is therefore limited. While some regions of the PAR had ergent male-female allele frequencies, suggestive of sexually antagonistic alleles, coalescent simulations showed this was broadly consistent with neutral genetic processes. Our results indicate that the degeneration of the large and ancient sex chromosomes of the ostrich may have been slowed by high recombination in the female PAR, reducing the scope for the accumulation of sexually antagonistic variation to generate selection for recombination cessation.
Publisher: Elsevier BV
Date: 03-2021
Publisher: African Journals Online (AJOL)
Date: 17-02-2014
Publisher: CSIRO Publishing
Date: 13-04-2023
DOI: 10.1071/AN22464
Abstract: Context Coping with high levels of cold stress should be beneficial to survival of lambs, given the high mortality rate associated with severe winter storms. The Elsenburg Merino selection experiment involved ergent selection for reproduction. Phenotypic results comparing the positively selected H-Lines and negatively selected L-Lines suggested that cold-stress adaption could have contributed to the favourable genetic trends for survival of H-Line lambs. However, observing the genetic merit of better adapted animals depends on the presence of cold stress at the time of recording. A genotype by environment component (G × E) could, thus, be important when assessing survival/mortality phenotypes. Aim This study proposed the genetic analysis of this possible G × E component and compared the H- and L-Lines in this regard. Methods The sire model allowed the use of progeny phenotypes for neonatal mortality recorded during different levels of cold stress, and the possible G × E could be investigated through the reaction-norm approach. Genetic parameters were evaluated as random regression components by implementing a Gibbs s ling approach. A data set of 5723 in idual lamb records was analysed as the progeny of 213 sires. Results A modelled G × E component played an important role in mortality outcomes, with the mean estimate (and 95% confidence interval) for the slope ( σ s b 2 = 0.113 [ 0.0019 – 0.28 ] AN22464_IE1.gif) only marginally smaller than the corresponding estimate for the intercept ( σ s a 2 = 0.124 [ 0.003 – 0.26 ] AN22464_IE2.gif). The reaction-norm model showed a higher heritability (h2 ± posterior standard deviation) for mortality at 3 days of age during high cold-stress (0.22 ± 0.16 at ~1100 KJm−2h−1) than during mild (0.13 ± 0.10 at ~960 KJm−2h−1) conditions, suggesting a greater ability to discriminate between sires at increasing stress levels. Conclusions Failure to account for this G × E component putatively contributes to the low h2 commonly reported for survival traits. The higher h2 at increased levels of cold stress could have played an important part in the higher survival of the H-Line progeny, who were better at coping with cold, wet and windy conditions. Implications Larger studies representing a wider environmental trajectory are recommended. This should be very feasible since cold stress can be derived from commonly available weather-station data.
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