Thesis (MScAgric)--University Stellenbosch, 2001. / ENGLISH ABSTRACT: The aim of this study was to estimate genetic parameters as well as to evaluate the
influence of some genetic factors on preweaning growth traits in a multi breed beef cattle
population. These preweaning growth traits were birth weight (BW), weaning weight
(WW) and average daily gain (ADG). Three aspects were addressed in this particular
study; namely the Estimation of (co)variance components and genetic parameters, the
effect of sire breeds and dam genotypes and the contribution of Charolais and Angus
breeding levels on weaning traits in a multibreed beef cattle herd.
Variance components and resulting genetic parameters of BW, WW and ADG in the
population were estimated by Restricted Maximum Likelihood (REML) procedures. Four
different unitrait and multitrait animal models were fitted ranging from a simple model
with the animal direct effects as the only random effect to the model allowing for both
genetic and permanent maternal environmental effects. The model that included directgenetic and permanent maternal environmental effects generally best described the data
analysed. The simple model ignoring maternal effects most likely inflated direct
heritability estimates. Direct heritability estimates were 0.11, 0.19, and 0.15 for BW,
WW and ADG, respectively, fitting a multitrait model that comprised of both the genetic
and maternal environmental effects. Under this comprehensive model, maternal
heritabilties were low under both analyses, ranging from 0.02 to 0.10. Permanent
maternal environmental effects were more important than maternal additive genetic
effects for WW and ADG. Direct and maternal genetic correlations range from 0.42 to
0.44 for BW, -0.22 to -0.25 for WW and -0.17 to -0.23 for ADG, while the corresponding
estimates ofunitrait analysis varied from 0.58 to 0.61 for BW, -0.43 to-0.53 for WW and
-0.49 to -0.79 for ADG.
The effect of Charolais and Hereford sires and dam breed genotypes on BW and WW in
calves of Hereford, F I, two and three breed rotational as well as terminal crosses among
the Charolais, Hereford, Angus and Bonsmara breeds were investigated. BW and WW of
the Charolais sired calves were significantly (P<O.OOl) heavier than the Hereford sired
calves. Angus dams produced calves of smaller (P<0.05) BW than those of purebred and
crossbred dams. The majority of the crossbred dams were not significantly different in
BW of calves. With regard to WW, with the exception of 3/4H1I4A, all crossbred dams
were superior (P<0.05) to Angus and Hereford dams. Calves of crossbred dams were on
the average 8% heavier at weaning than calves of purebred dams. Crossbred dams, with
intermediate Charolais contribution tend to wean heavier calves.
Data collected were also analysed to determine the optimum breeding levels of Charolais
and Angus, fitting a unitrait animal model. Further, the estimated heritabilities were
subsequently used to predict direct and maternal breeding values (Best linear unbiased
predictions) for individual animals. Best linear unbiased estimates (BLUEs) were also
calculated for the traits. BLUEs, direct and maternal breeding values per genetic group
estimated were regressed on proportions of Charolais and Angus breeding, respectively.
BLUEs of BW, WW and ADG increased with increasing the proportion of Charolais
while they decreased with increasing Angus breeding levels. In general, maternal
breeding values increased with increasing the proportions of both breeds. Direct breeding
values of Charolais increased and reached maximum values at 35, 38, and 45%
proportion of Charolais for BW, WW and ADG, respectively. No optimal Angus
proportion was found within these specific environmental conditions. In this herd it may
be suggested that increasing the proportion of Charolais to intermediate levels would tend
to improve the performances of preweaning traits. / AFRIKAANSE OPSOMMING: Die doel van die studie was om genetiese parameters in 'n meerras vleisbeeskudde te
beraam, sowel as om die invloed van sekere genetiese faktore te evalueer. Die voorspeense
groei-eienskappe het geboortegewig (BW), speengewig (WW) en gemiddelde daaglikse
toename (ADG) ingesluit. Drie aspekte is in dié betrokke studie ondersoek, naamlik; die
beraming van (ko )variansiekomponente en genetiese parameters, die invloed van ras van
vader en moedergenotipe en die invloed van Charolais en Angus bydrae op
speeneienskappe in 'n meerras vleisbeeskudde.
Variansiekomponente en afgeleide genetiese parameters vir BW, WW en ADG in die
kudde is met behulp van die Beperkte Maksimum Waarskynlikheidsprosedure (REML)
beraam. Vier verskillende enkel- en meereienskapmodelle is gepas, wat vanaf 'n
eenvoudige model wat slegs die direkte effek as enigste toevallige effek, tot dié model
waarin beide die genetiese en permanente mateme omgewingseffekte ingesluit is. Die
model wat beide die direkte en permanente mateme effekte ingesluit het, het die data die
beste gepas. Die eenvoudige model, wat die mateme effekte nie insluit nie, het in alle
waarskynlikheid die direkte oorerflikhede oorberaam. Die direkte oorerflikheidsberamingsas onderskeidlik 0.11, 0.19 en 0.15 vir BW, WW en ADG met dié meereienskapmodel
wat beide genetiese en mateme effekte ingesluit het. Met die omvattende model was die
mateme oorerflikhede laag en het van 0.02 tot 0.10 gewissel. Die permanente mateme
omgewingseffekte was belangriker as die direkte mateme effekte vir WW en ADG. Die
genetiese korrelasies tussen direkte en mateme effekte het vir BW tussen 0.42 en 0.44, vir
WW tussen -0.22 en -0.25 en vir ADG tussen -0.49 en -0.79 gewissel.
Die invloed van Charolais en Hereford bulle en moederrasgenotipes op BW en WW van
Hereford, F 1, twee- en drieras rotasie sowel as terminale kruisings tussen die Charolais,
Hereford, Angus en Bonsmara is ondersoek. BW en WW van kalwers van Charolais bulle
was betekenisvol (P<O.OOl) swaarder as kalwers van Hereford bulle. Angus koeie het
kalwers met laer (P<0.05) BW as die van ander suiwer en kruisraskoeie geproduseer.
Kalwers van die meerderheid kruisraskoeie het egter nie in BW verskil nie. Wat WW
betref, maar met die uitsondering van %HYtA, was alle kruisraskoeie beter (P<0.05) as
beide Angus en Hereford koeie. Kalwers van kruisraskoeie was gemiddeld 8 % swaarder
met speen as kalwers van suiwerraskoeie. Kruisraskoeie met intermediêre vlakke van
Charolaisbydrae het geneig om die swaarste kalwers te speen.
Die data is verder ook geanaliseer om die optimum vlakke van Charolais en Angus, deur
die passing van 'n enkeleienskap dieremodel, te bepaal. Die beraamde oorerflikhede is
vervolgens gebruik om direkte en mateme teelwaardes (Beste liniêre onsydige voospellers )
vir individuele diere te voorspel. Beste liniêre onsydige beramings (BLUE's) is ook vir
elke eienskap bereken. Die regressies van BLUE's, direkte en mateme teelwaardes per
genetiese groep bereken, is vervolgens op proporsie Charolais en Angus bydraes
onderskeidelik gepas. BLUE's vir BW, WW en ADG het met toename In
Charolaisproporsie toegeneem, terwyl dit met toename in Angusbydrae afgeneem het. In
die algemeen het mateme teelwaardes met toename in die bydrae van beide rasse
toegeneem. Direkte teelwaardes van die Charolais het toegeneem en maksimum waardes
by 35, 38 en 45 % proporsie Charolais vir onderskeidelik BW, WW en ADG bereik. Vir
die Angus is geen optimum proporsie in dié spesifieke omgewing gevind nie. In dié kudde
word intermediêre Charolais vlakke vir die verbetering van voorspeense eienskappe
aanbeveel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52285 |
| Date | 12 1900 |
| Creators | Melka, Hailu Dadi |
| Contributors | Schoeman, S. J., Stellenbosch University. Faculty of AgriScience. Dept. of Animal Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 69 p. : ill. |
| Rights | Stellenbosch University |
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