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dc.contributor.advisorVan Wyk, J. B.
dc.contributor.advisorOlivier, J. J.
dc.contributor.authorKebede, Solomon Abegaz
dc.date.accessioned2017-03-22T08:51:47Z
dc.date.available2017-03-22T08:51:47Z
dc.date.issued2002-11
dc.identifier.urihttp://hdl.handle.net/11660/5957
dc.description.abstractEnglish: Genetic analyses of economically important traits were carried out using data collected for 20 years (1978-1997) from a flock of Horro sheep at Bako Research Center, Ethiopia. (Co)variance components and genetic and environmental parameters were estimated for pre- and post- weaning average daily gain (ADGl, ADG2) and Kleiber ratio (KRl, KR2), birth weight (BWT), weaning weight (WWT) and bi-monthly weights to 12 months of age (WT2 to WTI2), and weight at 18 months of age (WTI8). using ASREML. Twelve models, formed with inclusion or exclusion of the maternal genetic, permanent environmental, and temporary (litter) environmental variance components and the covariance between the direct and maternal additive effect on the basic direct additive genetic model, were used. Bivariate analyses were also done. Maternal genetic and temporary environmental components were found to be important (P<0.05) sources of variation for ADG 1 and KRl while only the temporary environmental component was found to be important for ADG2 and KR2. Total heritability estimates for ADGl, ADG2, KRl and KR2, were 0.13±0.04, 0.04±0.03, 0.13±0.03, and 0.01±0.02 respectively. For weights to about six months of age, the inclusion of the temporary maternal effect in the models was found to have significant (P<0.05) contribution to the total variance. Maternal genetic components were important for weights until about eight months of age, while the direct-maternal covariance was important for BWT, WT2, WWT and ADGl. Direct genetic correlations of ADGl with BWT, WWT and WT6 were 0.04±0.21, 0.96±0.02 and 0.92±0.09 while with KRl they were -0.41±0.21, 0.74±0.10 and 0.66±O.16 respectively. The inclusion of maternal genetic, temporary and permanent environmental effects in analytical models for early weights improved model fit. Heritability estimates of average daily gains and Kleiber ratios are low to moderate. The correlations with weight traits, with the exception of BWT, are moderate to high. Thus, it seems more practical to select on weight traits to improve gain and efficiency. Genetic and maternal environmental parameters of perinatal, pre- and post-weaning survival in Horro lambs were studied using 3864 lamb records. The perinatal period covered the first three days after birth (3DS) while pre-weaning (3MS) and post- weaning (3-6MS) survival were taken as survival in the pre- and post-weaning three-month periods respectively. Cumulative survival to six months of age (6MS) was also considered. The same twelve linear genetic models used for growth traits were applied. Additionally logit and probit analyses were carried out. The most appropriate model was chosen which was consistently superior in all of the analytical methods and used to estimate genetic and environmental parameters. A bivariate analyses between survival on the observed scale and birth weight was carried out. For survival to all ages, the model, which included the direct genetic and maternal temporary (litter) environmental effect was found to be the most consistent of all the models compared. Heritability estimates for 3DS, 3MS, 6MS and 3-6MS were 0.00±0.00,O.02±0.03, 0.05±0.03 and 0.07±0.03 respectively. Genetic correlations with birth weight were 0.20±0.23, 0.68±0.34, 0.26±0.17 and 0.45±0.26 respectively, for 3DS, 3MS, 6MS and 3-6MS. The low heritability estimates of survival in this study suggest acceptable progress with respect to this trait through selection will be difficult to attain. The relatively higher genetic correlation of 3MS with birth weight indicates survival may be improved indirectly through selection for birth weight. Despite the low rate of prolificacy (34% twinning) there exists a sizeable litter effect on survival. This should be looked into, since this may entail a separate management for twin born lambs. Genetic parameters of productivity expressed as ewe fertility, incidence of twinning, number of lambs weaned, and total lamb weight at birth (TBW) and at weaning (TWW) per ewe per lambing were estimated using direct additive and repeatability models. Fertility and twinning were analyzed by a logit analysis, using similar models. In the analysis of fertility, service sire was included either as random or fixed effect. Additionally cumulative total weight of lamb weaned in the first four parities (TWW4) was also analyzed, using the direct additive model. Except for fertility where service sire was considered as random effect, the repeatability model was found to have a better fit than (P<0.05) the direct animal model. Bivariate analyses were done, using the direct animal model. Direct heritability estimates for fertility, twinning and total weight of lambs at birth and at weaning were 0.02±0.02, 0.15±0.03, 0.08±0.02 and 0.04±0.02 respectively. Where service sire was considered as fixed effect, heritability estimate of fertility from a direct model increased to 0.06. Heritability estimates for number of lambs weaned were 0.03 and 0.00 for the direct and repeatability models respectively. Repeatability estimates were 0.10, 0.07, 0.16, 0.06, 0.02 and 0.08 for TBW, TWW, twinning, litter size weaned and fertility under random and fixed sire models respectively. Estimate of the variance ratio in fertility attributed to service sire was 0.16±0.02. Heritability estimate for TWW4 was 0.05. Genetic correlations among TBW, TWW, twinning and number of lambs at weaning were in the range of 0.57 to 0.86. Except for twinning, heritability estimates were very low. Twinning was found to have medium heritability and repeatability, and moderate to high genetic correlation with number of lambs weaned, TBW, and TWW. These suggest that twinning can be used as a selection criterion for improvement in productivity despite increase in lamb mortality with increase in twinning. Weight (kg)-age (days) data of 524 Horro sheep surviving past 3.5 years of age were fitted to Brody's function to estimate growth curve parameters. Genetic and phenotypic parameters of the curve parameters and their relationships among themselves and with birth weight (BW), weaning weight (WW), 6-month weight (WT6) and yearling weight (YW) were estimated using direct univariate and bivariate animal models. Least squares means of growth curve parameters: A (asymptotic mature weight, kg), B (proportion of mature weight attained after birth) and k (rate of maturity, kg gain k-1 body weight day-1) were 37.6, 0.88 and 0.27x10-2 respectively. Female and male Horro sheep have asymptotic mature weights of 33.3 kg and 41.8 kg respectively. Heritability estimates were 0.29±0.10, 0.18±0.09 and 0.14±0.09 for A, Band k respectively. Genetic correlations between A and B, A and k, and B and k were 0.39±0.31, -0.07±0.34 and 0.25±0.39 respectively. Genetic correlations of A with BW, WW, WT6 and YW were 0.27±0.34, 0.34±0.27, 0.44±0.20 and 0.67±0.17 respectively. Genetic correlations of k with BW, WW, WT6, and YW were -0.13±0.69, 0.37±0.35, 0.61±0.25 and 0.66±0.22 respectively. Presence of medium heritability for A and k indicates that progress in improving these traits can be made through selection. WT6 and YW have medium genetic correlations (with reasonable standard error) with the growth curve parameters and these may allow the use of these weights as an indirect selection criterion to shorten generation interval. Weight data from birth to about one year (maximum of 408 days) were analyzed using the random regression model. A total of22149 weight records of 1951 lambs were used. Three different orthogonal (legendre) polynomial orders (three, four and five) of fit for additive genetic and animal permanent environmental effect were considered along with two different error measures. The residual error for weight at the different ages was assumed to be either homogeneous (one error measure) throughout the growing period or heterogeneous (four error measure classes: birth, 10 to 90 days, 91 to 180 days and >180 days). Likelihood ratio test (LRT) and Akaike's Information Criteria (AIC) were used for model comparison. Model fit improved with increased order of fit and with assumption of heterogeneity of error variance. Sizeable differences were found in heritability estimates from the different models, particularly for weight at birth and early age. Components for both additive genetic and animal permanent environmental covariances increased with an increase in age. Heritability estimates from the 'best' model have shown declining and increasing values at different parts of the trajectory. The lowest estimate was 0.14 for weight at birth, while the highest estimate was 0.40 for weight at about 400 days of age. The ratio of permanent environmental variance to the total variance increased from 0.42 at birth to 0.67 at about 270 days and decreased slightly thereafter. With the exception of weight at birth and at about yearling, heritability estimates from this study were lower than estimates from univariate studies where maternal effects were considered. The difference between estimates decreased with age, implying the higher estimates from this study are a result of ignoring maternal genetic and environmental (temporary and permanent) effects. Therefore consideration of maternal genetic and environmental effects needs attention. Choice of appropriate order of polynomial has significant influence and increased order of polynomial may need to be tested to refine estimates with a larger data set (additional weights per animal).en_ZA
dc.description.abstractAfrikaans: Genetiese analises van ekonomies belangrike eienskappe is uitgevoer op data ingesamel vir 'n periode van 20 jaar (1978-1997) van 'n kudde Horro skape te Bako Navorsingssentrum, Etiopië. (Ko)variansie-komponente en omgewingsparameters is beraam vir voor- en naspeense gemiddelde daaglikse toename (GDT1 en GDT2) en Kleiberverhouding (KV1,KV2) deur gebruik te maak van ASREML. Twaalf modelle is gebruik, wat opgebou is deur in- ofuitsluiting van die maternaal genetiese permanente en tydelike (werpsel) omgewingsvariansiekomponente en die ko-variansie tussen die direken maternaal additiewe effek op die basiese direk-additiewe genetiese model. Dieselfde modelle is aangewend om die beste model te identifiseer en die belangrikheid te bereken van maternale omgewingseffekte op geboortegewig (Ggew), speengewig (Sgew) en tweemaandelikse gewigte tot 12 maande ouderdom (Gew2 tot Gew12), en gewig op 18 maande ouderdom (Gew 18). Dubbelveranderlike ontledings is gedoen tussen GDT1, GDT2, KV1 en KR2 en met Ggew, Sgew Gew6, Gew12 en Gew18. Maternaal-genetiese en tydelike omgewingskomponente het geblyk belangrike (P< 0.05) bronne van variasie vir GDT2 en KV1 te wees. Onder die beste model was direk-additiewe, maternaaladditiewe en tydelike omgewingskomponente verantwoordelik vir ongeveer 15,20 en 13 persent onderskeidelik van die totale fenotipiese variansie vir GDT1 en 9,8 en 19 persent onderskeidelik vir KV1. Vir GDT2 en KV2 was die bydrae tot die totale variansie van tydelike omgewingseffek 22 en 20 persent onderskeidelik. Totale oorerflikheidsberamings vir GDT1 en GDT2, KV1 en KV2 was 0.13 ± 0.04, 0.04±0.023, 0.13±0.03 en 0.01±0.02 onderskeidelik. Vir gewigte tot ongeveer sesmaande ouderdom is gevind dat die insluiting van die tydelike omgewingsvariansiekomponent in die modelle betekenisvolle (P< 0.05) bydrae tot die geheelvariansie gelewer het. Die permanente omgewingskomponent was betekenisvol (P< 0.05) belangrik vir Gew2 en Sgew. Maternale genetiese komponente was belangrik vir gewigte tot ongeveer agtmaande ouderdom, terwyl die direk-maternale ko-variansie belangrik was vir Ggew, Gew2, Sgew en GDT1. Direkte genetiese korrelasies van GDT1 met Ggew, Sgew en Gew6 was 0.04±0.21, 0.96±0.02 en 0.92±0.09, terwyl met KV1 dit -0.41±0.214, 0.74±0.10 en 0.66± 0.16 onderskeidelik was. Die insluiting van maternale genetiese en tydelike en permanente omgewingseffekte in ontledingsmodelle vir vroeë gewigte het die pas van die model verbeter. Oorerflikheidsberamings van gemiddelde daaglikse toenames en Kleiberverhoudings is laag tot matig. Die korrelasies met gewigseienskappe, geboortegewig uitgesluit, is matig tot hoog. Seleksie op gewigeienskappe blyk dus 'n beter opsie te wees vir verbetering in toename en doeltreffendheid. Genetiese en maternale omgewingsparameters van na-geboortelike en voor- en naspeense oorlewing in Horro-Iammers is van 3864 lamrekords bestudeer wat gedurende die periode 1978 - 1997 versamel is. Die na-geboortelike periode het oor die eerste drie dae na geboorte (3D) gestrek, terwyl voorspeense (3M) en na-speense (3-6M) oorlewing beskou is as oorlewing in die voor- en naspeense driemaande-periodes onderskeidelik. Kumulatiewe oorlewing tot by sesmaande ouderdom is ook in aanmerking geneem. Dieselfde twaalf lineêre genetiese modelle wat op groei-eienskappe toegepas is, is gebruik. Logit- en probit-ontledings is bykomend uitgevoer. Die model wat deurgaans voortreflik in drie van die ontledingsmetodes vertoon het, is as die mees geskikte gekies. Genetiese en omgewingsparameters is van die betrokke model beraam met 'n logitontleding (beramings van probit-ontledings was dieselfde). 'n Dubbelveranderlike ontleding tussen oorlewing op die waargenome skaal en geboortegewig is uitgevoer. Vir oorlewing tot by alle ouderdomme is die model wat die additief-direkte en additiefmaternale (werpsel) omgewing en die foutkomponent ingesluit het as die mees konsekwente van al die modelle wat vergelyk is bevind. Oorerflikheidsberamings was 0.00±0.000,.02±0.03, 0.05±0.03 en 0.07±0.03 vir 3D, 3M, 6M en 3-6M onderskeidelik. Genetiese korrelasies met geboortegewig was 0.20±0.23, 0.68±0.34, 0.26±0.17 en 0.45±0.26 onderskeidelik vir 3D, 3M, 6M, en 3-6M. Die lae oorerflikheidberamings van oorlewing in hierdie studie dui daarop dat aanvaarbare vordering ten opsigte van hierdie eienskap deur kunsmatige seleksie moeilik haalbaar sal wees. Die relatief hoë genetiese korrelasie van 3M met geboortegewig dui aan dat oorlewing indirek verbeter kan word deur seleksie vir geboortegewig. Ten spyte van die lae vrugbaarheidsgraad (34% tweelinge) is daar 'n aansienlike werpseleffek op oorlewing. Dit regverdig verdere aandag, aangesien dit aparte bestuur vir tweelinggebore lammers mag behels. Genetiese parameters van produktiwiteit uitgedruk as ooivrugbaarheid, voorkoms van tweelinge, aantal lammers gespeen en totale lamgewig met geboorte (TGgew) en met speen (TSgew) per ooi per lamkans is beraam. Direkte additiewe en herhaalbare modelle is gebruik. Vrugbaarheid en voorkoms van tweelinge is ontleed deur 'n logit-ontleding waar enerse modelle gebruik is. In die ontleding van vrugbaarheid is diensvaar óf as toevallige óf as vaste effek ingesluit. Bykomend is die kumulatiewe totale gewig lammers gespeen in die eerste vier lamkanse (TSgew4) ook ontleed, deur die direkte additiewe model te gebruik. Op die basis van log-aanneemlikheid verhoudingstoets is die herhaalbaarheidsmodel betekenisvol (P< 0.05) verskillend van die direkte model in alle gevalle gevind. Behalwe vir vrugbaarheid waar diensvaar as toevallige effek gereken is, is gevind dat die herhaalbaarheidsmodel beter gepas het as die direkte dieremodel. Dubbelveranderlike ontledings is gedoen, deur gebruikmaking van die direkte dieremodel. Direkte oorerflikheidsberamings vir vrugbaarheid, voorkoms van tweelinge en totale gewig van lammers met geboorte en speen was 0.02±0.02, 0.15±0.03, 0.08±0.02 en 0.04±0.02 onderskeidelik. Waar diensvaar as vaste effek gereken is, het oorerflikheidsberaming van vrugbaarheid van 'n direkte model verhoog na 0.06. Oorerflikheidsberamings vir aantallammers gespeen was 0.03 en 0.00 vir die direkte en herhaalbaarheidsmodelle onderskeidelik. Herhaalbaarheidsberamings was 0.10, 0.07, 0.16, 0.06, 0.02 en 0.08 vir TGgew, TSgew, tweelinggeboortes, grootte van werpsel gespeen en vrugbaarheid onder toevallige en vaste modelle onderskeidelik. Beraming van die variansie-verhouding in vrugbaarheid wat aan diensvaar toegeskryfis was 0.16 ± 0.02. Die oorerflikheidsberaming vir TSgew4 was 0.05. Genetiese korrelasies tussen TGgew, TSgew, voorkoms van tweelinge en aantallammers met speen was tussen 0.57 en 0.86. Behalwe vir tweelinggeboortes, was oorerflikheidsberamings baie laag. Tweelinggeboortes het geblyk medium oorerflikheid en herhaalbaarheid te hê en matige tot hoë genetiese korrelasie met aantal lammers gespeen, TGgew en TSgew. Dit dui daarop dat voorkoms van tweelinge as 'n seleksiekriterium vir verbetering in produktiwiteit gebruik kan word. Gewigs (kg)-ouderdom (dae) data van 524 Horro-skape wat tot na 3.5 jaar oorleef het, is in Brody se funksie ingebou om groeikurweparameters te beraam. Genetiese en fenotipiese parameters van die kurwe-parameters en hul verhouding met hulself en met geboorte- gewig (Ggew), speengewig (Sgew), sesmaande-gewig (Gew6) en jaaroudgewig (Jgew) is beraam. en Direkte dieremodel is in alle enkel- en dubbelveranderlike ontledings gebruik. Lineêre korrelasies is bereken tussen groeikurwe-parameters en totale gewig gespeen per ooi vir die eerste tot vierde lamkanse (TGSI, TGS2, TGS3 en TGS4) en tussen die gemiddeld van aantal lammers gebore (ALG4) en aantal wat oorlewe het (AL04) per lamkans by ooie wat vier en meer lamkanse gehad het. Kleinste kwadraatgemiddeldes van groeikurweparameters: A (asimptotiese volwasse gewig, kg), B (proporsie van volwasse gewig bereik na geboorte) en k (tempo van volwassenheid, kg toename k-1 liggaamsgewig dag-1) was 37.6, 0.88 en 0.27x10-2 onderskeidelik. Die asimptotiese volwasse gewig van vroulike en manlike Horro-skape is 33.3 kg en 41.8 kg onderskeidelik. Oorerflikheidsberamings was 0.29±0.10, 0.18±0.09 en 0.14±0.09 vir A, B en k onderskeidelik. Genetiese korrelasies tussen A en B, A en k en B en kwas 0.39±0.31, -0.07±0.34 en 0.25±0.39 onderskeidelik. Genetiese korrelasies van A met Ggew, Sgew, Gew6 en Jgew was 0.27±0.34, 0.34±0.27, 0.44±0.20 en 0.67±0.17 onderskeidelik. Genetiese korrelasies van kwas -0.13±0.69, 0.37±0.35, 0.61±0.25 en 0.66±0.22 met Ggew, Sgew, Gew6 en Jgew onderskeidelik. Lineêre korrelasies van A en k met TSgew1, TSgew2, TSgew4, ALG4 en AL04 was 0.05 & 0.26,0.28 & 0.20, 0.27 & 0.05, 0.27 & 0.05 en 0.14 & 0.13 onderskeidelik. Die voorkoms van en medium oorerflikheid vir A en k toon aan dat vordering gemaak kan word in die verbetering van hierdie eienskappe deur seleksie. Die groeikurwe-parameters blyk positiewe verhoudings te hê met aanwysers van leeftydsproduksie. Gew6 en Jgew het medium genetiese korrelasies (met redelike standaardfout) met die groeikurwe-parameters, wat dit moontlik maak dat hierdie gewigte as en indirekte seleksie-kriterium gebruik kan word om generasie-interval te verkort. Gewigdata vanaf geboorte tot ongeveer een jaar (maksimum 408 dae) is ontleed deur die toevallige regressiemodel te gebruik. en Totaal van 22149 gewigrekords van 1951 lammers is gebruik. Drie verskillende ortogonale (legendre) veeltermige ordes, (drie, vier en vyf) wat geskik was vir additiewe genetiese en dier- permanente omgewingseffek is in aanmerking geneem, tesame met twee verskillende foutterme. Die fout vir gewig op die verskillende ouderdomme was veronderstel om óf homogeen te wees (een foutterm) reg deur die groeiperiode, óf heterogeen (vier fouttermklasse: geboorte, 10 tot 90 dae, 91 tot 180 dae en >180 dae). Aanneemlikheidverhoudingstoets (AVI) en Akaike se Inligtingskriteria (AlK) is gebruik vir modelvergelyking. Pas van die model het verbeter met verhoging in rangorde van passing en met aanname van ongelyksoortigheid van foutvariansie. Aansienlike verskille is in oorerflikheidsberamings van die verskillende modelle gevind, veral vir gewig met geboorte en op vroeë ouderdom. Komponente vir beide additiewe genetiese en dierpermanente omgewingskovariansie het toegeneem met 'n toename in ouderdom. Oorerflikheidberamings van die "beste" model het afnemende en toenemende waardes getoon in verskillende dele van die trajek. Die laagste beraming was 0.14 vir gewig met geboorte, terwyl die hoogste beraming 0.40 was vir gewig op ongeveer 400-dae ouderdom. Die verhouding van permanente omgewingsvariansie tot die totale variansie het toegeneem van 0.42 by geboorte tot 0.67 op ongeveer 270-dae ouderdom en weer effens afgeneem daarna. Met die uitsondering van gewig by geboorte en teen jaaroud was oorerflikheidsberamings verkry in hierdie studie laer as beramings van enkelveranderlike studies waar maternale effekte in aanmerking geneem is. Die verskille tussen beramings het afgeneem met ouderdom, wat impliseer dat die hoër beramings van hierdie studie 'n gevolg is van die verontagsaming van maternale genetiese en omgewings-( tydelike en permanente) effekte. Inagneming van maternale genetiese en omgewingseffekte behoort dus aandag te geniet. Keuse van gepaste orde van veelterme het betekenisvolle invloed en toenemende orde van veelterme moet miskien getoets word om beramings met 'n groter datastel te verfyn (bykomende gewigte per dier).af
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectSheep -- Breeding -- Ethiopiaen_ZA
dc.subjectSheep -- Geneticsen_ZA
dc.subjectSheep -- Reproductionen_ZA
dc.subjectDissertation (M.Sc.Agric. (Animal, Wildlife and Grassland Sciences))--University of the Free State, 2002en_ZA
dc.titleGenetic evaluation of production, reproduction and survival in a flock of Ethiopian Horro sheepen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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