The effect of heterogeneity for yearling weights measured in different test phases of the South African National Beef Cattle Improvement Scheme

In animal breeding, animals originating from different environments are often considered in selection decisions. Production data in these groups may differ both in mean and variance. In South Africa, yearling weights of beef cattle are recorded in two different phases of the National Beef Cattle Improvement Scheme (NBCIS). The aim of this study was to assess changes in the ranking of animals in the selection process where animals are selected on estimated breeding values (EBVs) for yearling weight before and after correcting for heterogeneity between the two phases. Yearling weights are measured in Phases B and D of the NBCIS. Yearling weights recorded in Phase D were adjusted according to the standard deviation and heritabilities of yearling weights in Phase B. To determine whether the adjustment was justified, two VCE REML analyses were performed on combined Phase B and D data to estimate breeding values. The first analysis involved unadjusted Phase D data, while the second run involved Phase D yearling weights, adjusted for heterogeneity. The ranking correlation between EBVs derived from the two runs, was 99% indicating almost no re-ranked after adjustment. It is concluded that Afrikaner yearling weights in Phase B and D can be analysed jointly without any pre-adjustments when estimating breeding values. South African Journal of Animal Science Vol.32(3) 2002: 171-17

Heritabilities of reproductive traits in a beef cattle herd using multitrait analysis

(South African J of Animal Science, 2000, 30, Supplement 1: 140-141

Heritability estimates derived from threshold analyses for reproduction and stayability traits in a beef cattle herd

The object of this study was to estimate heritabilities and sire breeding values for stayability and reproductive traits in a composite multibreed beef cattle herd using a threshold model. A GFCAT set of programmes was used to analyse reproductive data. Heritabilities and product-moment correlations between predicted breeding values for stayability at 36, 48, 60, 72 and 84 months of age, calving success and longevity were estimated. The estimated heritabilities on the underlying scale for these traits were 0.06, 0.10, 0.06, 0.03, 0.11, 0.03 and 0.08 respectively. Product-moment correlations between breeding values for stayability traits were low. The highest correlation of 0.22 was obtained between the ages of 36 and 48 months. Heritability estimates and correlations between traits appear to be of such a low magnitude that selection for these characteristics would result in limited genetic improvement, and also indicate that sires had little influence on the stayability, longevity or calving success of their daughters. (South African Journal of Animal Science, 2001, 31(1): 25-32

Genetic parameters for reproductive traits in a beef cattle herd estimated using multitrait analysis

The object of this study was to estimate heritabilities and genetic correlations for reproductive traits in a composite multibreed beef cattle herd using multitrait analysis. A REML procedure fitting a multitrait animal model was used to analyse data. Heritabilities and genetic correlations for calving interval (CI), calving date (CD), calving date with a penalty score (CDP) and age at first calving (AFC) were estimated as traits of the dam. The estimated heritabilities for CI, CD, CDP and AFC obtained in this study were 0.01, 0.04, 0.06 and 0.40 respectively with a repeatability of 0.07, 0.12 and 0.13 for CI, CD and CDP. Genetic correlations between traits varied from low to moderate, except for high correlations between CD and CDP (0.98), CI and CD (0.75) and between CI and CDP (0.79). Heritabilities, genetic correlations and repeatabilities of CD and CDP obtained in this study suggest that CD and CDP are the same traits and that selection for CDP rather then for CD does not have any additional advantages. Due to the additional advantages of CD over CI and the fact that CD is a less biased measurement of the female reproductive complex, CD and AFC (because of its high heritability) may be considered as selection criteria for improvement of reproduction in beef cattle herds. (South African Journal of Animal Science, 2001, 31(1): 41-48

Genetic parameters for reproductive traits in a beef cattle herd estimated using multitrait analysis

The object of this study was to estimate heritabilities and genetic correlations for reproductive traits in a composite multibreed beef cattle herd using multitrait analysis. A REML procedure fitting a multitrait animal model was used to analyse data. Heritabilities and genetic correlations for calving interval (CI), calving date (CD), calving date with a penalty score (CDP) and age at first calving (AFC) were estimated as traits of the dam. The estimated heritabilities for CI, CD, CDP and AFC obtained in this study were 0.01, 0.04, 0.06 and 0.40 respectively with a repeatability of 0.07, 0.12 and 0.13 for CI, CD and CDP. Genetic correlations between traits varied from low to moderate, except for high correlations between CD and CDP (0.98), CI and CD (0.75) and between CI and CDP (0.79). Heritabilities, genetic correlations and repeatabilities of CD and CDP obtained in this study suggest that CD and CDP are the same traits and that selection for CDP rather then for CD does not have any additional advantages. Due to the additional advantages of CD over CI and the fact that CD is a less biased measurement of the female reproductive complex, CD and AFC (because of its high heritability) may be considered as selection criteria for improvement of reproduction in beef cattle herds.Articl

Heritability estimates derived from threshold analyses for reproduction and stayability traits in a beef cattle herd

The object of this study was to estimate heritabilities and sire breeding values for stayability and reproductive traits in a composite multibreed beef cattle herd using a threshold model. A GFCAT set of programmes was used to analyse reproductive data. Heritabilities and product-moment correlations between predicted breeding values for stayability at 36, 48, 60, 72 and 84 months of age, calving success and longevity were estimated. The estimated heritabilities on the underlying scale for these traits were 0.06, 0.10, 0.06, 0.03, 0.11, 0.03 and 0.08 respectively. Product-moment correlations between breeding values for stayability traits were low. The highest correlation of 0.22 was obtained between the ages of 36 and 48 months. Heritability estimates and correlations between traits appear to be of such a low magnitude that selection for these characteristics would result in limited genetic improvement, and also indicate that sires had little influence on the stayability, longevity or calving success of their daughters.Articl

Management development in education: fact or fiction – some preliminary findings

Whether behaviour dimensions in a management context can be changed by means of training programmes is a debatable issue. Little if any research has been done in this regard and, in the education setting, it appears no research at all has been done. Against this background the first experimental research project of its kind was launched in South Africa. The research design made provision for an experimental and a control group, both consisting of an equal number of secondary school principals. As a first step, both groups were exposed to a recognised assessment centre (ACEL) during which certain management dimensions were evaluated. The second step was to put the experimental group through a management training programme followed by the third step, namely, a second assessment for both groups. According to the statistical results, two behaviour dimensions of the experimental group showed a significant difference before and after the training programme, whilst no significant difference was recorded for the control group. This research project does not claim that management dimensions of educational leaders can be changed by means of training. The work should rather be regarded as a pilot study and the first empirical attempt of this kind in the field of education management. The findings are therefore preliminary and can only be verified by a longitudinal study. (South African Journal of Education: 2002 22(2): 132-135