Genetic diversity and estimation of genetic parameters for economically important traits in Zambian cattle

Abstract

Current genetic erosion of indigenous breeds is common. Globally, this has become a major concern. In Zambia, genetic improvement programs rely upon traditional selection and breed substitution, and do not utilise local animal genetic resources. The aim of this work was to provide information for genetic improvement strategies, including the preferred traits of cattle breeders, estimating genetic diversity and genetic parameters, to improve and conserve local well-adapted indigenous cattle. This study used quantitative survey data, collected between September 2012 and December 2012. Both parametric and non-parametric tests were conducted to test if there were significant differences in preferences for traits between three regions of Zambia, namely Namwala, Chipata and Lundazi. The tests revealed that there were no significance differences for the traits preferred between the regions. However, large-scale farmers preferred larger sized animals and emerging small-scale cattle farmers preferred fertility traits. Genetic data from 274 alleles generated using 32 microsatellite markers from 72 individuals representing three indigenous Zambian cattle breeds (Angoni, Tonga and Barotse) was used to assess genetic diversity and population structure. Although, Zambian indigenous cattle breeds did not exhibit a high and unique breed’s purity, cattle exhibited a higher level of genetic diversity within breeds than between breeds. Despite the evidence of a close gene flow between the three populations, inbreeding was largely insignificant going by the Bayesian cluster at K=2. It may be further evidence of existing divergent and multi-loci genetic admixtures between and within breeds. If accurate, the uniqueness of the population clustering offers valuable information on the gene pool available for selection within breeds for utilisation, genetic improvement and conservation. However, Tonga and Barotse breeds appeared to exhibit lower genetic diversity than Angoni. To measure the genetic parameters for growth, data for 266 Angoni and 606 Boran weaning weights for 15 years were used in linear mixed models to estimate variances and heritabilities. The change in the log-likelihood was used to test for improvements when comparing models. Fixed effects of sex, breed, and age were determined on weaning weight. Random effects included breed by animal and breed by dam. Separate breed variances were not significant and so the overall direct heritability and maternal heritability was moderate (20% and 19%, respectively) using the best model (6). Thus, these heritability estimates of direct and maternal effects on weaning weight indicate it should be possible to make good genetic progress for this trait. Zambian indigenous cattle provide rich genetic resources, exhibiting moderately heritability, and therefore, have the potential to be improved by using appropriate planning and flexible breeding programs. This is important because the current trends show a substantial increase in demand for meat worldwide and if farmers in Zambia wish to develop an export market, beef production must be improved. However, Zambia will require separate breeding objectives and genetic parameter estimates for large-scale farmers and emerging small-scale farmers in order to exploit the wide range of diversity through genetic selection. This could be through focusing on different breed for each group.