A genetic evaluation of production traits in Nguni cattle

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Date
2003-06
Authors
Van Niekerk, Michiel
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University of the Free State
Abstract
English: Genetic parameters may well aid the prediction of selection and correlated response when selection is based on production traits. The animal model, fitting an additional random factor such as the permanent maternal environmental effect is common practice to increase the accuracy of estimates. As selection in a beef breed such as the Nguni takes place in various environmental conditions, the inclusion of an additional random factor i.e. herd-year-season x sire interaction seems justified. Production traits analyzed included records of birth weight (BW), weaning weight (WW), yearling weight (YW) and eighteen-month weight (EW). Herd-year-season, sex, age at recording (except BW) and age of dam had a significant effect. Herd-year-season x sire interaction (HYSxS) was included as an additional random factor. Estimates obtained by univariate analyses were used as starting values in the multivariate analyses. In multivariate analyses another data set was used which included only herds linked with at least two other herds through sires used. This data set was also used in two bivariate analyses being the analyses between the maternally influenced traits (BWand WW) and WW and YW to gain knowledge as to a possible carry-over effect of the maternal genetic effect. Genetic trends were calculated using the regression of the average breeding value estimates . (EBV) on year of birth. Direct heritability estimates for BW, WW, YW and EW obtained by multivariate analyses were 0.31, 0.32, 0.23 and 0.27 respectively. Genetic correlations between direct and maternal effects for BW and WW were mostly low to moderate and negative (-0.35 to - 0.59 and -0.17 to -0.50 for BW and WW respectively), while direct genetic correlations among the four growth traits were moderate to high (0.51 to 0.95). The maternal genetic correlation between BW and WW was moderate (0.49). It was concluded that selection on WW alone would be undesirable as all other weights would increase. In review, breeding values for production traits should be seen in conjunction with one another so as to take into account undesirable effects on other traits. Genetic trends derived showed no major change. Nguni cattle, like most other beef producing breeds, are kept under a wide variety of extensive environments throughout South Africa. Based on this, a genotype x environment interaction (G x E) in this breed may be expected. Three most important aspects while considering the nature of interactions are the ranking order of the genotypes, the relative magnitudes of genotypic, environmental and interaction effects and the statistical significance of interaction effects. Because of limitations in the data set, only weaning weight (WW) records were used. Records from herds were allocated to one of three veld types that described the specific region in which each berd was situated, i.e. sweetveld (Region 1), sourveld (Region 2) and mixed veld (Region 3). Bivariate analyses of WW in the three different regions were carried out to determine the (co)variance components and weighted direct heritability estimates obtained ranged from 0.23 to 0.45. Direct genetic correlations of Regions 2 and 3 with Region I were significant and were 1.00 and 0.71 respect ivcly. This indicates that no Cl x E occurred between Regions I and 2, but indeed between Regions I and 3. The genetic correlation between Regions 2 and 3 (0.60) were non-sign ificant. Correlation coefficients between breeding values of sires, obtained by multivariate analyses and the different bivariate analyses, was also calculated (range 0.77 to 0.8]) indicating no major re-ranking of sires when selection is based on breeding values obtained by multivariate analyses which include a HYSxS interaction. Top performing sires showed more re-ranking.
Afrikaans: Genetiese parameters is van kardinale belang by die voorspelling van seleksie en gekorreleerde respons wanneer seleksie vir produksie-eienskappe plaasvind. 'n Dieremodel, waarby '11 addisionele toevallige effek soos die petmanente maternale effek, ingesluit word is algemeen om die akkuraatheid van beramings te verhoog. Aangesien seleksie by vleisbeeste soos die Nguni-ras, in verskillende omgewingstoestande plaasvind, blyk die insluiting van 'n addisionele toevallige effek nl. kudde-Jaar-seisoen x vaar interaksie geregverdig te wees. Produksie-eienskappe wat gebruik is het ingesluit geboortegewig (BW), speengewig (WW), 12- maande gewig (YW) en l S-maande gewig (EW). Kudde-jaar-seisoen, geslag, ouderdom by meting (behalwe BW) en ouderdom van die moer het almal 'n betekenisvolle effek gehad. Kudde-jaarseisoen x vaar interaksie (HYSxS) is as 'n addisionele toevallige effek ingesluit. Enkeleienskap ontledings sowel as twee twee-eienskapontledings is uitgevoer en het BW en WW (eienskappe met maternale invloed) ingesluit asook WW en YW (orn die moontlikheid van 'n oordrag-effek van die maternale komponent vas te stel). Enkeleienskapwaardes is as beginwaardes in '11 veelvoudige eienskapontleding gebruik om die (ko)variansie-komponente van en/of tussen die verskillende eienskappe te beraam. Genetiese tendense is bereken deur die regressie van die gemiddelde teelwaardeberamings op jaar van geboorte. Direkte oorerflikhede vir BW, WW, YW en EW verkry deur veelvoudige-eienskapontleding was onderskeidelik 0.31, 0.32, 0.23 en 0.27. Genetiese korrelasies tussen die direkte- en maternale effek vir BW en WW was laag tot medium en negatief (-0.35 tot -0.59 en -0.17 en -0.50 vir BW en WW onderskeidelik), terwyl die direkte genetiese korrelasies tussen die vier eienskappe medium tot hoog was (0.51 tot 0.95). Die maternale genetiese korrelasies tussen BW en WW was medium (0.49). Daar is tot die gevolgtrekking gekom dat seleksie vir WW alleen ongewens sal wees aangesien alle ander gewigte ook sal toeneem. Ten slotte behoort teelwaardes vir produksie-eienskappe in afhanklikheid met mekaar beskou te word orn sodoende rekening te hou met die ongewensde effek op ander eienskappe. Genetiese tendense het geen noemenswaardige verandering getoon nie. Nguni-beeste, soos meeste ander vleisbeeste, word onder 'n wye verskeidenheid omgewings aangehou regdeur Suid-Afrika. Gebaseer hierop kan 'n moontlike genotipiese omgewingsinteraksie (G x E) in die ras dus verwag word. Drie belangrike faktore moet oorweeg word wanneer die effek van interaksies bestudeer word, nl. die rangorde van die genotipes, die relatiewe omvang van genotipiese-, omgewings- en interaksie-effekte asook die statistiese betekenisvolheid van die interaksie-effekte. As gevolg van beperkinge ten opsigte van die datastel, kon slegs WW-rekords gebruik word. Rekords van kuddes is toegewys aan een van drie veldtipes wat die spesifieke omgewing waarin elke kudde produseer beskryf, nl. Soetveld (Streek I), Suurveld (Streek 2) en Gemengde veld (Streek 3). Twee-eienskapontledings van WW in die drie verkskillende streke is gedoen om die (ko )variansie-komponente te beraam. Geweegde direkte oorerflikheidsberamings hierdeur verkry het gestrek van 0.23 tot 0.45. Direkte genetiese korrelasies van Streke 2 en 3 met Streek 1 was betekenisvol en was onderskeidelik 1.00 en 0.71. Hierdie resultate dui aan dat daar geen G x E tussen Streke 1 en 2 bestaan nie, maar wel tussen Streke 1 en 3. Die direkte genetiese korrelasie tussen Streke 2 en 3 (0.60) was nie betekenisvol nie. Korrelasie-koëffisiënte tussen teelwaardes van vaars, afkomstig van veelvoudige-eienskapontleding en die verskillende dubbeleienskapontledings, is ook bereken (omvang 0.77 tot 0.81) en dui aan dat geen wesenlike herrangskikking van vaars sal voorkom nie wanneer seleksie gebaseer word op teelwaardes verkry van veelvoudige-eienskapontleding, wat 'n HYSxS interaksie insluit. Die toppresterende vaars het 'n meer drastiese herrangskikking getoon.
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Nguni cattle, Indigenous cattle, Genetic parameters, Genotype x environment interaction, Herd-year-season x sire interaction, Genotype x ecological region interaction, Environmental sensitivity, Growth traits, Dam line, Nguni cattle -- South Africa -- Breeding, Dissertation (M.Sc.Agric. (Animal, Wildlife and Grassland Sciences))--University of the Free State, 2003
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