| dc.description.abstract | Growth data from 6,800 progeny of straight breds, intermediate crosses between
Toggenburg (T), Anglo-Nubian (N), Small East African (E) and Galla (G) breeds in
equal proportions and the resulting composites from 1982 to 2004 were used to evaluate
growth performance from birth to yearling. The aim of the study was to assess the effects
of genetic and non genetic factors on early growth performance as well as estimate the
additive and non additive genetic parameters.
A fixed effects least squares model (Harvey, 1990) was used to estimate the effects of
non genetic factors. Pedigree Viewer programme of the Derivative-Free-Restricted
Maximum Likelihood, DFREML, (Meyer, 1998) was used for pedigree analyses and
calculation of inbreeding coefficient for individual animals. Additive and non additive
genetic parameters were simultaneously estimated by fitting an animal model using
DFREML algorithm (Meyer, 1998), in which linear coefficients for non additive effects
were substituted for genetic group and fitted as regression covariates in the model.
Two-breed crosses performed best in all traits while the straight breds had the least
performance. Mean birth weight (BWT) for the two composites was the same (2.69 ±
0.49 and 2.69 ± 0.46 for composite 1 and 2 respectively). Mean weaning weight (WWT)
for the composites was 9.89 ± 2.38 kg and 9.29 ± 2.17 kg with mean pre-weaning
average daily gains (ADG1) of 55.51 ± 9.39 and 52.10 ± 9.13 g/day in composite 1 and 2
respectively. Mean yearling weights (YWT) were 17.32 kg, 18.67 kg and 17.85 kg with
mean post-weaning average daily gains (ADG2) of 36.72, 40.42, and 35.88 g/day for the
straight breds, two- and four-breed crosses respectively. Sex, type of birth, period and
season of kidding, age of the dam and period and season of weaning significantly
Xl
affected early growth traits in varying degrees (P < 0.05 - P < 0.001) in the different
genotypes.
The mean proportion of inbred animals over the study period was 7.04 %, with an
average inbreeding coefficient of 3.6 % and insignificant (P>0.05) annual change of -
0.001 ± 0.0001. The effect of inbreeding on the growth traits was not significantly
different from zero (P>0.05). Heritability estimates ranged from 0.10± 0.02 to 0.24 ±
0.01 for post-weaning and pre-weaning average daily gains respectively. Phenotypic
correlations between BWT and WWT and between BWT and ADG1 were equal and
negative (-0.02 ± 0.001) while the respective genetic correlations were positive but very
low (0.15 ± 0.04 for BWT and WWT and 0.001 ± 0.02 for BWT and ADG1,
respecti vel y).
Anglo-Nubian had the greatest effect on WWT (+1.69 kg), YWT (+1.74 kg) and ADG1
(+ 13.28 g/day). Between the indigenous breeds, Galla breed performed better in all traits
except YWT. Effect of individual heterosis was greater in BWT (+0.05 kg) and ADG2
(+0.36 and +3.04 g/day for YWT and ADG2 respectively). Maternal heterotic effects
were positive in pre-weaning traits (+0.04 kg and +0.39 gI day for WWT and ADG 1
respectively.
The study establishes that early growth performance of KDPG composites is affected by
environmental influences such as nutrition which should be appropriately adjusted for
optimal performance. The effect of retained recombination loss has been reducing the
performance of the composites hence the programme did not optimize on the potential
benefits of crossbreeding. | en |
