Model comparisons and genetic and environmental parameter estimates of growth and the Kleiber ratio in Horro sheep

No Abstract. South African Journal of Animal Science Vol. 35 (1) 2005: pp.30-4

Estimates of genetic and environmental (co)variances for live weight and fleece traits in yearling South African Mutton Merino sheep

No Abstract. South African Journal of Animal Science Vol. 34 (1) 2004: pp.37-4

Genetic parameters for growth traits in South African Brahman cattle

Genetic parameters for growth traits in the South African Brahman breed were estimated using ASREML from data records of birth weight (BWT) = 41 509, weaning weight (WWT) = 37 705, yearling weight (YWT) = 22 682 and final weight (FWT) = 13 055 collected between 1985 and 2002. The direct additive contribution to BWT, WWT, YWT and FWT were 0.28, 0.14, 0.14 and 0.18 respectively. The corresponding maternal heritability estimates were 0.11, 0.06, 0.05 and 0.03 respectively. The maternal permanent environmental component due to the dam contributed 3-7% of the total phenotypic variances of the traits under consideration. The corresponding contribution of herd-year-season x sire interaction ranges from 5% to 6%. The genetic correlation between animal effects was -0.36 for BWT. The prospects of improvement of these traits by selection seem possible and contribution of maternal permanent environment due to dam is of considerable importance as maternal effects. South African Journal of Animal Science Supp 2 2004: 44-4

Revised models and genetic parameter estimates for production and reproduction traits in the Elsenburg Dormer sheep stud

Genetic parameters for production and reproduction traits in the Elsenburg Dormer sheep stud were estimated using records of 11743 lambs born between 1943 and 2002. An animal model with direct and maternal additive, maternal permanent and temporary environmental effects was fitted for traits considered traits of the lamb (birth and weaning weight and survival). Fixed effects were sex, birth status, year and age of dam. Weaning weights were pre-adjusted to a 100-day equivalent. For reproduction traits (considered as traits of the ewe), which included number and weight of lambs born and weaned, repeatability models were fitted. The random part consisted of direct additive and ewe and sire permanent environmental effects. Direct and maternal heritability estimates were 0.13 and 0.23 for birth weight and 0.07 and 0.09 for weaning weight. Corresponding proportions of total phenotypic variance due to maternal permanent and temporary environment were 0.09 and 0.28 and 0.06 and 0.22 respectively. The genetic correlation between animal effects was -0.23 in the case of birth weight. The results showed that temporary environment (full sibs within a year) generally has a major effect on all pre-weaning traits. The direct heritability estimate of survival was 0.02 while the temporary maternal environmental variance as a proportion of phenotypic variance was 0.10. The estimates obtained for number and weight of lambs born and weaned were generally low, ranging from 0.03 for number of lambs born to 0.11 for total weight at birth. The permanent environmental effect of the ewe accounted for 6-7% of the total phenotypic variance. Genetic correlations of total weight of lamb weaned with the other reproduction traits were generally high (0.64 to 0.92) with low standard errors. The corresponding phenotypic, environmental and ewe permanent environmental correlations were all medium to high and estimated with a fair deal of accuracy according to low standard errors. The genetic relationship between weaning weight of the ewe and her lifetime reproduction (accumulated over four lambing chances) ranged between 0.40 and 0.67. Correlations between number of lambs weaned per ewe and weight of lamb weaned per ewe were particularly high (0.8 - 0.9). It was concluded that the maternal environmental effect should be partitioned into two components (permanent and temporary) when data sets involving multiple births over many generations are considered. Keywords: Dormer sheep, Genetic parameters, Temporary and permanent environmental effects, Early growth, Survival and reproduction traits South African Journal of Animal Science Vol.33(4) 2003: 213-22

Is genetic selection for skin nodule traits of ostriches feasible?

Preliminary genetic parameters for nodule traits of ostrich skins were estimated to examine whether genetic improvement of skin quality is feasible. Average nodule size and density per dmยฒ were determined on five localities on each of 439 ostrich skins. An animal model with random animal and skin permanent environmental effects was fitted for the traits considered. Fixed effects were locality on skin, age, year of hatch and gender. Locality significantly influenced nodule size and nodule density. Nodule size increased with an increase in slaughter age, while nodule density decreased. Estimates for heritability were low at 0.10 for both traits, but still differed significantly from zero. The genetic correlation between nodule density and average nodule size was very high at -0.72. The skin permanent environmental correlation was -0.33, the environmental correlation -0.17 and the phenotypic correlation was -0.28. More research into genetic variation within localities and correlations with other easily measurable traits is indicated for genetic improvement of ostrich leather quality. South African Journal of Animal Science Supp 2 2004: 29-3

Short Communication Inbreeding in the Dohne Merino breed in South Africa

The actual level of inbreeding and the effect of inbreeding depression on yearling body weight and fleece traits in the South African Dohne Merino population were investigated. All available pedigree data, which comprised of 266 268 records (302 169 animals including base parents) for the period 1975 to 2003 were used for calculating individual inbreeding coefficients. Inbreeding depression was estimated as the regression of performance (corrected for fixed effects) on the individual and dam inbreeding coefficients, fitting an animal model. The rate of inbreeding (ΔF) was estimated as the difference between the individual inbreeding (Ft) and the inbreeding of the parents (Ft-1) divided by (1-Ft-1). The level of inbreeding (F) in the SA Dohne Merino sheep population is very low. The proportion of animals that was inbred to some extent increased from 0.00 (average F = 0) in 1980 to 0.38 in 2003 (average F = 0.012). No significant inbreeding depression on body weight and fleece traits could be found. In general the results suggest that inbreeding at present is not a serious problem in the South African Dohne Merino breed. Keywords: Dohne Merino sheep; inbreeding depression South African Journal of Animal Science Vol. 37 (3) 2007: pp.176-17

Across flock genetic parameter estimation for yearling body weight and fleece

Accurate genetic parameter estimates are needed upon which to perform multiple-trait across flock breed analyses. Genetic parameters for yearling body weight (BW), clean fleece weight (CFW) and mean fibre diameter (MFD) were estimated using records of 107 389 individuals (the progeny of 1 530 sires and 45 178 dams) collected between 1992 and 2004 in the South African Dohne Merino population. Fixed effects included in the model were flock-year-season-sex-management group (1 594 classes), type of birth (singles, multiples), age of dam (2 - 7+ years) and age at measurement, fitted as a linear covariate (385 ± 12 days). Six different single-trait animal models were fitted, where different combinations of the following random effects were fitted: direct additive, the sire-flock interaction, the sire-flock-year-season interaction (SFYS), the dam genetic effect, the direct-maternal correlation and the dam permanent environmental effect. These analyses were followed by a three-trait analysis structured according to the log likelihood ratios obtained for the single-trait analysis. This analysis allowed the calculation of relevant correlations among traits together with their respective standard errors. Direct heritability estimates from the three-trait analysis were 0.17 for BW, 0.19 for CFW and 0.45 for MFD. Maternal heritability estimates were 0.01 for BW and 0.006 for CFW, with corresponding dam permanent environmental ratios of respectively 0.03 and 0.02. The genetic correlation between animal effects amounted to 0.48 for BW. Derived proportions of the total phenotypic variance due to SFYS were 0.02, 0.02 and 0.02, respectively. Genetic correlations of BW with CFW and MFD were 0.11 and 0.13, respectively, and of CFW with MFD 0.16. It was concluded that the inclusion of some form of a genotype by environmental interaction as part of the national evaluation is essential, although it controlled only a modest portion of the overall phenotypic variation. Keywords: Direct heritability, maternal effects, genotype x environment interaction, correlationsSouth African Journal of Animal Science Vol. 38 (1) 2008: pp. 31-3

Genetic parameters and trends for birth weight, birth coat score and weaning weight in Merino lines divergently selected for ewe multiple rearing ability

Data were recorded for birth weight, birth coat score and weaning weight of between 2018 and 4235 Merino lambs born over a 17-year interval from 1986 to 2002. The resource population was divergently selected from the same base population since 1986, either for (H line) or against (L line) maternal multiple rearing ability. Direct additive genetic variances - expressed as a ratio of the total phenotypic variance (h2, direct heritability) - were estimated at 0.12 + 0.03 for birth weight, 0.70 + 0.05 for birth coat score and 0.13 + 0.04 for weaning weight. Maternal genetic variance ratios (m2) were estimated at 0.23 + 0.04 for birth weight and 0.10 + 0.04 for weaning weight. It was not significant for birth coat score. Maternal permanent environmental variance ratios (c2) for the respective traits amounted to 0.08 + 0.03 for birth weight, 0.04 + 0.02 for birth coat score and 0.08 + 0.03 for weaning weight. No consistent phenotypic or genetic differences in favour of either line were found for birth weight or birth coat score. Compared to L line lambs, phenotypic means for weaning weight were heavier in favour of H line lambs from 1995. This trend was confirmed by divergence in yearly averaged direct breeding values in the H and L lines. Expressed as percentage of the overall phenotypic mean for weaning weight, genetic changes amounted to +0.23% in the H line and -0.26% in the L line. A corresponding maternal genetic trend amounting to -0.19% of the overall phenotypic mean for weaning weight was found in the L line, while no maternal genetic change could be discerned in the H line. Divergent selection for multiple rearing ability thus did not influence birth weight and birth coat score, while the correlated response in weaning weight was favourable. Keywords: Direct heritability, Genetic trends, Maternal heritability, Parameter estimation, Smoothing splines South African Journal of Animal Science Vol.33(4) 2003: 248-25

Tumour invasiveness, the local and systemic environment and the basis of staging systems in colorectal cancer

background: The present study aimed to examine the relationship between tumour invasiveness (T stage), the local and systemic environment and cancer-specific survival (CSS) of patients with primary operable colorectal cancer. methods: The tumour microenvironment was examined using measures of the inflammatory infiltrate (Klintrup-Makinen (KM) grade and Immunoscore), tumour stroma percentage (TSP) and tumour budding. The systemic inflammatory environment was examined using modified Glasgow Prognostic Score (mGPS) and neutrophil:lymphocyte ratio (NLR). A 5-year CSS was examined. results: A total of 331 patients were included. Increasing T stage was associated with colonic primary, N stage, poor differentiation, margin involvement and venous invasion (P<0.05). T stage was significantly associated with KM grade (P=0.001), Immunoscore (P=0.016), TSP (P=0.006), tumour budding (P<0.001), and elevated mGPS and NLR (both P<0.05). In patients with T3 cancer, N stage stratified survival from 88 to 64%, whereas Immunoscore and budding stratified survival from 100 to 70% and from 91 to 56%, respectively. The Glasgow Microenvironment Score, a score based on KM grade and TSP, stratified survival from 93 to 58%. conclusions: Although associated with increasing T stage, local and systemic tumour environment characteristics, and in particular Immunoscore, budding, TSP and mGPS, are stage-independent determinants of survival and may be utilised in the staging of patients with primary operable colorectal cancer