S.W.P. Cloete

Genetic parameters and trends for lamb survival and birth weight in a Merino flock divergently selected for multiple rearing ability.

Data of 5,390 Merino lambs born from 1986 to 2007 (approximately 6.9 generations) were used to derive genetic parameters and trends for age-specific and overall lamb survival on the underlying scale, as well as for lamb birth weight, using Gibbs sampling. The majority of lambs were descended from lines that were divergently selected for the ability of ewes to rear multiples. The line selected in the upward direction was denoted as the high line (H line), whereas the line selected in the downward direction was the low line (L line). Analyses included the covariance between direct and maternal genetic effects, except where it was not estimable owing to small direct additive variance components, a high incidence of lambs surviving, or both. Direct heritability estimates were 0.02 for lamb survival at birth, 0.12 for lamb survival from birth to tail docking, 0.39 for lamb survival from docking to weaning, 0.28 for overall lamb survival, and 0.17 for birth weight. Corresponding estimates for the maternal genetic effect were 0.26, 0.14, 0.16, 0.14, and 0.29. Dam permanent environmental variance ratios were, respectively, 0.14, 0.09, 0.05, 0.07, and 0.07. Estimates of the direct-maternal genetic correlation were -0.60 for lamb survival from docking to weaning, -0.61 for overall lamb survival, and -0.15 to -0.23 for birth weight. Genetic, maternal genetic, and dam permanent environmental correlations between lamb birth weight and overall or age-specific lamb survival were not different from zero. Expressed relative to overall means, annual direct genetic change in the H line amounted to -0.01% per annum for lamb survival at birth, 0.52% per annum for lamb survival from birth to docking, and 1.3% per annum for lamb survival from docking to weaning. Corresponding trends in the L line were, respectively, -0.01, -0.42, and 0.042% per annum. Maternal genetic trends amounted to, respectively, 0.23, -0.11, and -0.24% per annum in the H line and -0.78, -0.50, and -0.16% per annum in the L line. It was concluded that sustained genetic progress in lamb survival is feasible if directed selection is applied to a correlated trait such as the ability of ewes to rear multiples.

A mathematical modelling study of fluid flow and mixing in full-scale gas-stirred ladles

A full-scale, three-dimensional, transient mathematical model for application to gas-stirred ladles was developed. Multiphase aspects were accounted for by employing the Lagrangian Discrete Phase Model (DPM) in describing the bubble plume and the Eulerian Volume of Fluid (VOF) model for tracking the free surface of the melt. The standard k?e (SKE) model was used for modelling turbulence. Further research is required to refine the turbulence modelling approach, but validation experiments showed that the present approach yielded accurate information on bulk fluid flow and mixing in the ladle. The resulting model is easily generalised and computationally efficient.

Twice daily collection yields greater semen output and does not affect male libido in the ostrich

The success of an artificial insemination program in ostriches is highly dependent on the yield of viable semen. We, therefore, tested how semen output is affected by three different collection frequencies: once every 2d (48h interval), daily (24h interval), and twice a day (6h interval). Ejaculates were collected from seven male ostriches (aged 2-4 years) for 10 consecutive days using the dummy female method. We assessed semen characteristics (sperm motility, volume, concentration, number of sperm per ejaculate and sperm viability) and male libido (the delay between the presentation of the dummy and ejaculation, and the willingness to mount the dummy). The total daily output of semen and the number of sperm were greater at the 6h collection interval than at the 24h or 48h interval while sperm motility and viability were not affected. At the 6h interval, the number of live normal sperm increased over the treatment period while the number of live abnormal sperm was reduced. Furthermore, the time that males took to mount the dummy and their willingness to copulate with the dummy were unaffected by collection frequency. Across males we observed great individual variation in both semen characteristics and libido suggesting there is the potential to increase the efficiency of semen collection by selecting superior males. These results indicate not only that two collections per day yield maximum semen output and may improve semen viability, but also that quantifying variation between males may help further increase semen collection efficiency.

A comparison between slaughter traits and meat quality of various sheep breeds: Wool, dual-purpose and mutton

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.

The development of ratite production through continued research

This paper summarises research on farmed ratites and their industries over the past 100 years. Commercial ratite products include meat, skins, feathers and oil. Research on ratites has attempted to enhance the quantity and quality of these products by focusing on the disciplines of breeding and genetics, reproduction and incubation, assisted reproduction, nutrition and animal welfare. Advances in these disciplines are discussed, and directions for future research are provided.

Cortisol production in sheep is influenced by the functional expression of two cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17) isoforms.

In commercial production systems, the full expression of the genetic potential of an animal is limited by its intrinsic and extrinsic environment. It is therefore necessary to include robustness as a breeding goal because robustness is defined as the ability of an animal to express a high production potential in a wide variety of environmental conditions. The ability of mammals to produce sufficient cortisol on stimulation of the hypothalamic-pituitary-adrenal (HPA) axis is vital in its adaptation to stress. The biosynthesis of cortisol is dependent on the enzymatic activity of the microsomal enzyme, cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17). Two isoforms for sheep (Ovis aries) CYP17, previously identified in 2 independent studies, differ by 2 nucleotides, resulting in 2 AA differences (Ser210Gly and Tyr464Asn). The present study investigates the effect of these differences on cortisol production as a function of the HPA axis activity by comparing the catalytic activities of these isoforms. The activities of the CYP17 isoforms were compared by expressing the enzymes in vitro. The kinetic constants, Vmax and Km, which were determined for pregnenolone and progesterone (in the absence of cytochrome b(5)), showed no significant difference (P > 0.05) between the CYP17 isoforms. In contrast, a time course of the metabolism of pregnenolone, 17-hydroxypregnenolone, and progesterone, assayed in the presence and absence of ovine cytochrome b(5) overexpression, showed significant differences (P < 0.05) between the isoforms. Wild-type 1 CYP17 (WT1, GenBank accession number L40335) yielded more cortisol precursors than wild-type 2 (WT2, GenBank accession number AF251388). Site-directed mutagenesis indicated that a tyrosine residue at position 464 of WT1 increased the 17α-hydroxylation of progesterone compared with an asparagine residue at that position of WT2. In a subsequent insulin-induced hypoglycemic stress test, the presence of WT1 resulted in a greater cortisol output from the sheep adrenal than the presence of WT2, as homozygous WT1/WT1 sheep produced more cortisol than heterozygous WT1/WT2 sheep. The SNP located within the WT1 allele may therefore have a potential application in marker-assisted selection of sheep exhibiting a greater release of cortisol from the adrenal gland in response to stressors.

Ostrich chick humoral immune responses and growth rate are predicted by parental immune responses and paternal colouration

One of the most important measures of offspring performance is growth rate, which is often traded off against another important survival trait, immune function. A particular feature of ostrich chicks maintained in farmed environments is that cohorts of chicks vary widely in size. As parents can have a profound effect on the phenotype and fitness of their offspring, we investigated whether chick growth and immune defence were related to variation in levels of immune defence in their genetic parents. As secondary sexual traits of sires could serve as indicators of male quality, and be used in female mating decisions, we also investigated whether chick growth rate and immune defence were related to male plumage and integumentary colouration. We found that offspring growth rates and humoral responses were related to the humoral responses of their parents, suggesting that at least some components of humoral immune capacity are heritable. The white colour of male ostrich feathers was correlated to the humoral response and growth rate of their offspring, suggesting that this visual cue involved in the male courtship display could serve as an important signal to females of male quality, thereby forming the basis of mate choice in this species.

Measuring the gut microbiome in birds : Comparison of faecal and cloacal sampling

The gut microbiomes of birds and other animals are increasingly being studied in ecological and evolutionary contexts. Numerous studies on birds and reptiles have made inferences about gut microbiota using cloacal sampling; however, it is not known whether the bacterial community of the cloaca provides an accurate representation of the gut microbiome. We examined the accuracy with which cloacal swabs and faecal samples measure the microbiota in three different parts of the gastrointestinal tract (ileum, caecum, and colon) using a case study on juvenile ostriches, Struthio camelus, and high‐throughput 16S rRNA sequencing. We found that faeces were significantly better than cloacal swabs in representing the bacterial community of the colon. Cloacal samples had a higher abundance of Gammaproteobacteria and fewer Clostridia relative to the gut and faecal samples. However, both faecal and cloacal samples were poor representatives of the microbial communities in the caecum and ileum. Furthermore, the accuracy of each sampling method in measuring the abundance of different bacterial taxa was highly variable: Bacteroidetes was the most highly correlated phylum between all three gut sections and both methods, whereas Actinobacteria, for example, was only strongly correlated between faecal and colon samples. Based on our results, we recommend sampling faeces, whenever possible, as this sample type provides the most accurate assessment of the colon microbiome. The fact that neither sampling technique accurately portrayed the bacterial community of the ileum nor the caecum illustrates the difficulty in noninvasively monitoring gut bacteria located further up in the gastrointestinal tract. These results have important implications for the interpretation of avian gut microbiome studies.

Exploration of the Hypothalamic-Pituitary-Adrenal Axis to Improve Animal Welfare by Means of Genetic Selection: Lessons from the South African Merino

Simple Summary Breeding sheep that are robust and easily managed may be beneficial for both animal welfare and production. Sheep that are more readily able to adapt to stressful situations and a wide variety of environmental conditions are likely to have more resources available for a higher expression of their production potential. This review explores the utilization of one of the stress response pathways, namely the hypothalamic-pituitary-adrenal axis, to locate potential sites where genetic markers might be identified that contribute to sheep robustness. A South African Merino breeding programme is used to demonstrate the potential benefits of this approach. Abstract It is a difficult task to improve animal production by means of genetic selection, if the environment does not allow full expression of the animal’s genetic potential. This concept may well be the future for animal welfare, because it highlights the need to incorporate traits related to production and robustness, simultaneously, to reach sustainable breeding goals. This review explores the identification of potential genetic markers for robustness within the hypothalamic-pituitary-adrenal axis (HPAA), since this axis plays a vital role in the stress response. If genetic selection for superior HPAA responses to stress is possible, then it ought to be possible to breed robust and easily managed genotypes that might be able to adapt to a wide range of environmental conditions whilst expressing a high production potential. This approach is explored in this review by means of lessons learnt from research on Merino sheep, which were divergently selected for their multiple rearing ability. These two selection lines have shown marked differences in reproduction, production and welfare, which makes this breeding programme ideal to investigate potential genetic markers of robustness. The HPAA function is explored in detail to elucidate where such genetic markers are likely to be found.

The effect of temperature and pH on the motility and viability of ostrich sperm

As the chemical environment of semen diluents can have a profound effect on sperm quality, we examined the effect of temperature and pH on the motility and viability of sperm in the ostrich. Semen was collected from four males, each male being replicated three times. Ejaculates were diluted and incubated for 10 min at 20°C and 40°C in four different buffers, temperature adjusted at pH 6, 7, 8 and 9 respectively. Average path velocity (VAP), curvilinear velocity (VCL), straight-line velocity (VSL), linearity (LIN), beat cross frequency (BCF) and amplitude of lateral displacement (ALH) were then recorded for each sample using CASA. The viability of sperm was assessed using nigrosin-eosin staining. Sperm incubated at 40°C had higher motility parameters, except for ALH. At 40°C, VAP, VSL and LIN increased with pH while VCL, BCF and ALH were higher for lower pHs. The viability of sperm was not affected by temperature but decreased at pH values>7. A pH in the neutral range appeared to yield higher quality sperm after in vitro storage at 20°C. However, the effect of different pH levels and temperatures on sperm longevity needs to be investigated further to develop viable ostrich specific diluents.