J.J. Olivier

Direct and maternal (co) variance components and heritability estimates for body weight at different ages and fleece traits in Afrino sheep

Abstract Data, consisting of 4325 lamb records, the progeny of 146 sires and 946 dams, collected on the Carnarvon Afrino flock over the period 1975 to 1992, were used for this study. Variance components resulting from direct additive genetic effects, maternal additive genetic effects, maternal permanent environmental effects, as well as the relationship between direct and maternal effects for birth weight, monthly body weight from weaning at 4 months to 12 months of age, 18 month body weight, 16 month clean fleece weight and 16 month mean fibre diameter were estimated by REML procedures. By ignoring or including maternal genetic or environmental effects, five different models of analysis were fitted in order to determine the most effective model for each trait. The direct heritability estimate for body weight increased from birth (0.22 ± 0.04) up to 8 months of age (0.59 ± 0.06), where it seemed to stabilise. Maternal heritability estimates for body weight, on the other hand, increased from birth (0.09 ± 0.04) to 5 months of age (0.17 ± 0.02), whereafter it decreased gradually. The maternal permanent environmental effect was significant only for birth weight (0.12 ± 0.03). Direct heritability estimates of 0.62 ± 0.04 and 0.73 ± 0.03 were obtained for clean fleece weight and mean fibre diameter, respectively. Maternal effects had no significant influence on clean fleece weight or mean fibre diameter.

Genetic and phenotypic trends and parameters in reproduction, greasy fleece weight and liveweight in Merino lines divergently selected for multiple rearing ability

Genetic and phenotypic trends and parameters were estimated for reproduction, fleece weight and liveweight in a South African Merino population, divergently selected from 1986, either for (H line) or against (L line) maternal multiple rearing ability. Annual reproduction, ewe greasy fleece weight and pre-joining liveweight data were recorded on 809 Merino ewes, from 1986 to 2002. Phenotypic trends indicated divergence in reproduction traits between the H and L lines. The direct additive variance ratio (h2 ± s.e.) for day of lambing was 0.08 ± 0.02. Estimates of h2 for reproduction traits were: 0.10 ± 0.02 for number of lambs born per ewe; 0.04 ± 0.02 for number of lambs weaned per ewe; and 0.04 ± 0.02 for weight of lamb weaned per ewe, corrected for the gender of the lamb. Corresponding h2 estimates for annual production were 0.57 ± 0.06 for greasy fleece weight and 0.48 ± 0.06 for ewe liveweight at joining. Service sire only exerted a significant (P<0.05) effect on day of lambing, but it accounted for merely 2% of the overall phenotypic variation. Ewe permanent environment variance ratios (c2ewe) for the reproduction traits were: 0.07 ± 0.03 for number of lambs born per ewe; 0.11 ± 0.03 for number of lambs weaned per ewe; and 0.11 ± 0.03 for total weight of lamb weaned per ewe. Corresponding c2ewe estimates for annual production traits were 0.14 ± 0.05 for greasy fleece weight and 0.27 ± 0.06 for ewe joining weight. Genetic and ewe permanent environmental correlations between measures of reproduction exceeded 0.7. Genetic correlations of reproduction traits with greasy fleece weight were low and variable in sign. Genetic correlations of reproduction traits with ewe joining weight were positive and particularly high for weight of lamb weaned. Permanent environmental correlations of reproduction traits with greasy fleece weight and joining weight were generally low to moderate. Genetic trends for the H and L lines (derived from averaged direct breeding values within birth years) were divergent (P<0.01) for all reproduction traits. Expressed as percentage of the overall least squares means of the respective traits, breeding values in the H line increased annually, with 1.3% for lambs born per ewe, 1.5% for lambs weaned per ewe and by 1.8% for weight of lamb weaned per ewe. Corresponding trends in the L line were, respectively, –0.6%, –1.0% and –1.2% per year. Substantial genetic progress in annual lamb output was attainable, despite relatively small h2 estimates. This response was achieved without unfavourable genetic changes in wool and liveweight.

Genetic parameter estimates for total weight of lamb weaned in Afrino and Merino sheep

A study was undertaken to estimate genetic parameters for total weight of lamb weaned in Afrino and Merino sheep. Data collected on the Carnarvon Afrino flock, the Carnarvon Merino flock and the Grootfontein Merino stud were used. For Afrino sheep, heritability estimates of 0.061 (0.043), 0.054 (0.055) and 0.170 (0.074) were obtained for total weight of lamb weaned after the first (TWW1), second (TWW2) and third (TWW3) parities respectively. Corresponding estimates for Carnarvon Merino sheep ranged from 0.090 (0.025) for TWW1 to 0.257 (0.047) for TWW4. Similar estimates of 0.084 (0.027), 0.045 (0.029), 0.132 (0.048) and 0.100 (0.054) were obtained for Grootfontein Merino sheep. High positive genetic (rG) and phenotypic (rp) correlations were estimated between first parity and lifetime reproductive performance in all three flocks. For the Carnarvon Afrino flock, rG increased from 0.609 (0.367) between TWW1 and TWW2 to 0.791 (0.206) between TWW1 and TWW3. The corresponding rp, however, decreased from 0.735 (0.019) to 0.613 (0.026). Similar decreases in rp from 0.708 (0.011) and 0.696 (0.013) (Between TWW1 and and TWW2) to 0.549 (0.017) and 0.510 (0.022) (between TWW1 and TWW4) were observed for the Carnarvon and Grootfontein Merino flocks respectively. Genetic correlation estimates of 0.866 (0.127), 0.913 and 0.736 (0.272) were obtained between TWW1 and TWW2, TWW3 and TWW4 for the Grootfontein Merino flock. The results of this study, obtained with two different breeds and in two different environments in flocks with a high and a low reproductive rate, indicate that selection for increased lifetime reproductive performance could be based on total weight of lamb weaned after the first parity.

Deriving a preliminary breeding objective for commercial ostriches: an overview

Ostrich farmers rely on skins and meat as their most important sources of revenue, with feathers being of secondary importance. This paper provides a summary of parameter estimates (heritabilities and genetic correlations) estimated from the resource flock held at the Oudtshoorn Research Farm. Traits considered were egg production, chick production, mature liveweight, offspring slaughter weight and skin traits. Feather weight of mature breeding birds was not included, as revenue received for this commodity is comparatively low, and mostly reliant on quality. All the traits considered were moderately to highly heritable, and reproduction traits in particular were highly variable. No substantial unfavourable genetic correlations were noted, and worthwhile gains in all traits appear to be achievable within a selection objective based on economic principles. Economic weights for key traits were obtained from a bio-economical input-output simulation model that was prepared for the industry. A simple preliminary selection index including chick production (as a hen reproductive trait) and slaughter weight (as a measure of growth) appears to be adequate for the present needs, given the limited availability of routinely recorded traits. A key performance trait that is currently missing from the economic assessment is chick survival, which is known to be low and highly variable among ostrich flocks. Further information will be added as it becomes available.

Genetic and phenotypic correlations of total weight of lamb weaned with body weight, clean fleece weight and mean fibre diameter in three South African Merino flocks

Data collected on three South African Merino flocks were used to estimate genetic and phenotypic correlations of total weight of lamb weaned over three parities (TWW) with two-tooth body weight at 14 to 17 months of age (BW), clean fleece weight (CFW) and mean fibre diameter (MFD). The flocks included were maintained under widely divergent environmental conditions, and included the Tygerhoek Merino flock (n=1360), the Grootfontein Merino stud (n=1535) and the Klerefontein Merino flock (n=1971). The arid environment of Klerefontein supported mean (±SD) performance levels of 32.0±5.6 kg, 2.6±0.7 kg, 19.8±1.9 μm and 37.7±21.7 kg for BW, CFW, MFD and TWW respectively. Performance levels under more favourable environmental and less extensive conditions at Grootfontein were markedly higher (respectively 42.8±7.0 kg, 4.8±1.1 kg, 23.0±2.1 μm and 91.1±35.9 kg), with Tygerhoek generally intermediate in this regard. Phenotypic correlations of TWW with BW varied from 0.15±0.04 at Tygerhoek to 0.32±0.02 at Klerefontein. Corresponding genetic correlations were positive and high, ranging from 0.67±0.13 at Grootfontein to 0.80±0.04 at Tygerhoek. Phenotypic correlations of TWW with CFW and MFD were relatively low (rp<0.10). The genetic correlations of TWW with CFW were variable, ranging from 0.06±0.11 at Klerefontein to 0.41±0.11 at Tygerhoek. Corresponding correlations with MFD were more stable, ranging from 0.18±0.13 at Tygerhoek to 0.26±0.20 at Grootfontein. It was concluded that progress in all these economically important traits would be feasible in a well-designed breeding programme for South African Merino sheep. The estimation of further, more precise, genetic correlations from larger data sets may also be regarded as a priority for the Merino industry.

Genetic parameters for ewe reproduction with objectively measured wool traits in Elsenburg Merino flock

Reproduction is important for sustainable lamb production in Merino sheep. Data from a Merino flock maintained at Elsenburg Research Farm in the Western Cape, South Africa, were used to investigate the genetic parameters for ewe reproduction traits and their relationship with objectively measured wool traits. Traits included number of lambs born during the first lambing opportunity (NLB1), number of lambs weaned during the first lambing opportunity (NLW1), total weight of lamb weaned during the first lambing opportunity (TWW1), number of lambs born during a ewe’s lifetime (NLB3), number of lambs weaned during a ewe’s lifetime (NLW3), and total weight weaned per ewe’s reproductive life (TWW3) Fixed effects of selection line, birth type, sex, age of the dam in years, year of birth, and the sex*birth year interaction had significant effects on all bodyweight and objectively measured wool traits. Only year of birth and selection line affected ewe reproduction traits. Heritability estimates amounted to 0.10 ± 0.03 for NLB1, 0.07 ± 0.02 for NLW1, 0.10 ± 0.04 for TWW1, 0.25 ± 0.04 for NLB3, 0.12 ± 0.03 for NLW3, and 0.18 ± 0.04 for TWW3. Wool traits were moderately heritable at 0.28 ± 0.05 (staple strength) to 0.60 ± 0.03 (clean yield (CY)) and coefficient of variation of fibre diameter (CVFD). Relationships among ewe reproduction traits were high, ranging from 0.74 between TWW1 and NLB3 to 1.00 between NLW1 and TWW1. The genetic relationships of ewe reproduction traits with wool weights and staple length were positive. Fibre diameter (FD) and CY were unfavourably related to ewe reproduction traits. It seems possible to improve ewe reproduction when selecting on NLB, NLW, and TWW in Merino sheep without unwanted correlated response to selection in wool traits, with the exception of FD and CY. Keywords : Bodyweight, heritability, relationships