Heterogeneity of variance and its implications on dairy cattle breeding

Milk yield data (n = 12307) from 116 Holstein-Friesian herds were grouped into three production environments based on mean and standard deviation of herd 305-day milk yield and evaluated for within herd variation using univariate animal model procedures. Variance components were estimated by derivative free REML algorithm, and significance tests done using the Fmax procedure. Phenotypic, additive genetic and residual variances were heterogeneous across production environments. The estimates of variances in kg2 were 708349.9, 966853.7 and 2229338.9; 112266.9, 209949.9 and 689942.1; and 512660.0, 734854.5 and 1317808.3 for phenotypic, additive genetic and residual variances, respectively for production environments 1, 2 and 3. The heritability estimates were 0.15 ± 0.04, 0.22 ± 0.05 and 0.31 ± 0.03, respectively. The magnitude of estimated breeding values for sires and their ranking was influenced by production environment. Each production environment had a unique set of superior sires. The more variable production environments contributed more bull-dams at various selection intensities. Effects of heterogeneous variances need to be accounted for in genetic evaluation for Holstein-Friesian in Kenya. Keywords: Variance components; heterogeneity; milk yield; Holstein-Friesian South African Journal of Animal Science Vol. 37 (3) 2007: pp.170-17

Genetic parameter estimates for growth traits of Large White pigs in Kenya

Variance components and genetic parameter were estimated for piglet growth traits of Large White (LW) pigs managed under intensive production systems in Kenya. Data were on piglet performance of LW pigs born between 1982 to 1996. Growth performance traits of the piglets that were considered, were body weight (BW, in kg) at birth (BW0), three weeks (BW3), eight weeks at weaning (BW8), 12 weeks ( BW12), 24 weeks (BW24) and 36 weeks (BW36); and average daily gain (g/day) from birth to eight weeks (DG0-8) and from weaning to 24 weeks (DG8-24). Variance components and genetic parameters were estimated using univariate and multivariate animal models. Direct heritability estimates from univariate analyses were 0.38, 0.24, 0.47, 0.39, 0.36 and 0.26 for BW0, BW3, BW8, BW12, BW24 and BW36, respectively. Maternal heritabilities were 0.42, 0.25 0.15 and 0.18 for BW0, BW3, BW8 and DG0-8, respectively. Genetic correlations among growth traits were positive and ranged from 0.45 to 0.98 while phenotypic correlations ranged from 0.54 to 0.95. Early piglet growth was highly heritable and under the influence of maternal effects. Selection programmes for genetic improvement of early growth performance should be based on models that account for direct and maternal genetic and litter effects. Keywords: Additive genetic effects, body weight, swine, litter effects, maternal effectsSouth African Journal of Animal Science Vol. 38 (3) 2008: pp. 166-17

Genomic composition factors affect codon usage in porcine genome

The objective of the study was to determine the codon usage bias in the porcine genome and decipher its determinants. To investigate the underlying mechanisms of codon bias, the coding sequence (CDS) from the swine reference sequence (ssc10.2) was extracted using Biomart. An in house built Perl script was used to derive various genomic traits and codon indices. Analysis was done using R statistical package, and correlations and multivariate regressions were performed. We report the existence of codon usage bias that might suggest existence of weak translational selection. The codon bias is feebly related to nucleotide composition (GC%, GC3, CDS length). This study can be explored for designing degenerate primers, necessitate selecting appropriate hosts expression systems to manipulate the expression of target genes in vivo or in vitro and improve the accuracy of gene prediction from genomic sequences thus maximizing the effectiveness of genetic manipulations in synthetic biology.Key words: Coding sequence, synomynous codons, selection, translational mutation, pig genom

Indigenous Thai Beef Cattle Breeding Scheme Incorporating Indirect Measures of Adaptation: Sensitivity to Changes in Heritabilities of and Genetic Correlations Between Adaptation Traits

A model Indigenous Thai beef cattle breeding structure consisting of nucleus, multiplier and commercial units was used to evaluate the effect of changes in heritabilities of and genetic correlations between adaptation traits on genetic gain and profitability. A breeding objective that incorporated adaptation was considered. Two scenarios for improving both the production and the adaptation of animals where also compared in terms of their genetic and economic efficiency. A base scenario was modelled where selection is for production traits and adaptation is assumed to be under the forces of natural selection. The second scenario (+Adaptation) included all the information available for base scenario with the addition of indirect measures of adaptation. These measures included tick count (TICK), faecal egg count (FEC) and rectal temperature (RECT). Therefore, the main difference between these scenarios was seen in the records available for use as selection criteria and hence the level of investments. Additional genetic gain and profitability was generated through incorporating indirect measures of adaptation as criteria measured in the breeding program. Unsurprisingly, the results were sensitive to the changes in heritabilities and genetic correlations between adaptation traits. However, there were more changes in the genetic gain and profitability of the breeding program when the genetic correlations of adaptation and its indirect measures were varied than when the correlations between these measures were. The changes in the magnitudes of the genetic gain and profit per cow stresses the importance of using reliable estimates of these traits in any breeding program

Biotechnology in livestock production: Overview of possibilities for Africa

Livestock production is expected to grow tremendously in line with the projected demand for animal products. Therefore, the methods of livestock production must change to allow for efficiency andimprovement in productivity. Biotechnology is important if the world is to respond to the pressure to produce more food from animals for the ever-growing human population. In general, biotechnology inlivestock production can be categorised as the biological, chemical and physical techniques that influence animal health (survival), nutrition, breeding and reproduction. These techniques have been applied mostly in developed countries but their application in Africa is minimal due to reasons related to economic growth such as poor infrastructure, technical and educational capacity. However, Africa can still benefit from tailor-made technologies that simplify complex techniques into applicable form through strategic packaging. Public concerns on food safety, environment and ethics are issues that cannot be ignored

Genetic relationship between lactation curve traits in the first three parities of dairy cattle

In Kenya, selection of dams for the national contract mating scheme is based on 305-day lactation milk yield (TMY) performance across parities. At farm level, only cows that had good TMY performance in previous parity are retained for the subsequent lactation. This strategy has resulted in improved milk production performance, although increased incidences of physiological disorders, mastitis and reduced fertility have been reported in high-yielding cows. Records on functional traits relative to milk yield are scant. Properties of lactation curves could be used indirectly to explain the productive and functional efficiency of dairy cows. This study assesses the relationship between lactation traits, based on the lactation curve, to evaluate the effects of selection for TMY on lactation curve properties and to assess the effects of selection decisions based on first lactation on performance in later lactations. A repeatability analysis revealed negative genetic correlations between peak milk yield (MYmax) and persistency (S); MYmax and days in milk at peak (DIMP); and TMY and DIMP. Genetic correlations were positive between DIMP and S, and TMY and MYmax. This implies that selection for high TMY would result in high MYmax and a reduction in DIMP. This alters the shape of the lactation curve, shifting production pressure to early lactation, which aggravates a negative energy balance, thus compromising the physiological integrity of the cow. Continuous selection for high TMY could be responsible for the reported decline in reproductive efficiency and lactation physiology. Correlation estimates between traits in different parities were bidirectional (correlation estimates changed signs (+/-) in different parities), implying that selection decisions made in lactation 1 may not have similar outcomes in lactations 2 and 3. Selection at farm level should be optimised by using records from three parities, as is done in the contract mating scheme.Keywords: Correlation estimates, reproductive performance, test-day milk yiel