Genetic improvement of beef cattle in a tropical environment with special reference to the Gudali and Wakwa breeds in Cameroon

[摘要] English:In an attempt to genetically Improve Gudali beef cattle JO Cameroon, two selectionexperiments were conducted between 1968 and 1988 at the Animal Production andResearch Stations of Wakwa, Ngaoundere. The one experiment involved a two-breedsynthetic beef breed, the Wakwa, obtained from inter se matings of the first filialgeneration of American Brahman (50%) x Gudali (50%) crosses. The other experimentinvolved recurrent selection of the indigenous purebred Gudali in an effort to enhance itsbeef production without any serious detrimental effects to its adaptational qualities.In order to assess the genetic progress of the two experiments, a study using mixed modelmethodology was carried out. The objectives were to quantify factors affecting growthtraits, estimate (eo )variance components, predict genetic merit (breeding values) fordirect and maternal performance and determine genetic progress by examining direct andmaternal genetic trends for all animals. A total of 2886 records for birth weight (BWT),2732 for average preweaning daily gain (ADG), 2899 for weaning weight (WWT), 2098for yearling weight (YWT) and 1957 for eighteen months weight (EWT) of Gudali cattlewere used in the study. Corresponding number of records for the Wakwa were 1793,1656,1838, 1372and 1328. The results indicated that sire, sex, season (S), calf birth year (C), herd (H), HxSxCinteraction, cowage group and ages at weaning (WAGE), yearling (YAGE) and eighteenmonths (EAGE), as well as covariates for weaning, yearling and eighteen month weights,were significant (p<0.05) sources of variation for these traits. Therefore, for reliablegenetic parameter estimations and evaluation of genetic merit of individual candidateanimals for selection, these sources of variation should be taken into consideration. Hencethe inclusion of these factors in the mixed model for the estimation of genetic parametersand prediction of breeding values.Estimates obtained for direct, maternal and total heritabilities were 0.37, 0.05 and 0.21 forBWT; 0.24, 0.17 and 0.07 for ADG; 0.27,0.19 and 0.11 for WWT; 0.51, 0.20 and 0.22 forYWT; and 0.18, 0.02 and 0.18 for EWT, respectively, in the Gudali. Corresponding estimatesin the Wakwa were 0.55, 0.23 and 0.18 for BWT; 0.26, 0.07 and 0.12 for ADG; 0.28, 0.09and 0.15 for WWT; 0.18, 0.00 and 0.17 for YWT and 0.14, 0.06 and 0.17 for EWT. Estimatesfor genetic correlations between direct and maternal effects were generally highly negative andranged from -0.76 for ADG to -0.98 for YWT in the Wakwa and from -0.77 for WWT to -0.88 for BWT in the Gudali. However, in both breeds the genetic correlation was nil for EWT.These estimates obtained are indicative that there are distinct possibilities of improving directpreweaning and/or postweaning growth in the both breeds through selection. However, a highselection intensity for direct performance may in the long run be detrimental to maternalperformance as a result of the generally strong genetic antagonism between them.Although some estimates of genetic parameters for preweaning weight from one to sevenmonths traits were not obtained for the Wakwa breed due to limited data, estimatesobtained for the Gudali indicated that the highest, although moderate, estimate formaternal heritability (0.24) was for weight at two months of age. Therefore, an attempt tooptimise direct and maternal performance in the Gudali through selection could be mosteffective at two months and at yearling, respectively. It is suggested that the apparentgenetic antagonism generally found between direct and maternal ability be specificallyinvestigated using more suitable data.An assessment of genetic progress indicated positive and significant (p

[发布机构] University of the Free State