Genetic factors affecting milk production, growth and reproduction traits in Bos indicus x Bos taurus crosses in Ethiopia
Abstract
English: Five separate studies were conducted to investigate the genetic factors affecting
growth, milk production and reproduction traits in Bos indicus x Bos taurus
crosses in Ethiopia. The first three studies were based on early growth data
collected from the purebred Boran (Bo), Barca (Ba), Horror (Ho) (Bos indicus)
and their crosses with the Friesian (F), Jersey (1) and Simmental (S) breeds (Bos
taurus). Early growth data were for calves that were representing three purebred
Bos indicus and 38 crossbred genotypes and were separated from their dams one
day after birth and fed milk from a bucket. The fourth and fifth studies were
based on milk and reproduction data collected from cows of two purebreds
(Boran and Friesian) and eight crossbred (crosses of Friesian and Jersey with
Boran) genotypes.
In the first study, five genetic models were evaluated for goodness of fit and
estimation of crossbreeding parameters. These models were: 1) Dominance
model, 2) Dickerson's model (recombination loss), 3) Additive x dominance
interaction model, 4) Dominance x dominance interaction model and 5)
Kinghom's model (x). Models 2 to 5 are epistatic models that included all effects
in model one plus one type of epistatic interaction based on a two-locus gene
model. The models were evaluated using data for birth, weaning, yearling
weights and preweaning average daily gain. All five models tested provided high
levels of fit, with adjusted R2 values averaging 93% over traits. All the epistatic
models fit the data significantly (P<0.05) better than the dominance model for all
the traits. Among the epistatic models, Dickerson's model (Model 2) gave
significantly (P<0.05) higher R2 values compared to the other epistatic models.
Crossbreeding parameters estimated from this model has relatively lower
sampling correlations and correspondingly lower standard errors. This model
could, therefore, be considered as the most appropriate one for parameter
estimation and prediction of performances of untested genotypes for future
crossbreeding decisions for the breeds involved in this study.
In the second study, breed difference, heterosis and recombination loss were
estimated for birth weight (BWT), weaning weight (WWT), preweaning average
daily gain (ADG) and yearling weight (YWT), fitting an animal model.
Differences between genotypes were significant (P<0.01) for all traits. Genetic
group means adjusted for environmental effects ranged from 20 to 30 kg for
BWT, 88 to 114kg for WWT, 122 to 157kg for YWT and 358 to 492g for preweaning
average daily gain (ADG). The breed additive effect of the F as a
deviation from the Bo was significant (P<0.01) and positive for all traits.
Relative to the Bo mean, the additional breed additive contribution of the F breed
on BWT, WWT, ADG and YWT was 39.3, 16.5, 9.3 and 10.3%, respectively.
On the other hand, the breed additive effects of the Ho and J breeds were
significantly (P<0.01) negative for all traits. The heterotic effects were
significantly negative (P<0.01) for BWT for all F and S crosses, but positive
(P<0.01) for all other traits for all types of crosses. The average heterosis
estimated within the F, J and S breeds were: -2.1±0.6, 0.2±0.6 (P>0.05) and
-2.3±0.6 kg for BWT, 8.8±2.1, 11.8±2.3 and 13.7±2.4 kg for WWT, 60.4±11.3,
64.8±12.3 and 90.6±12.7 g for ADG and 19.8±2.6, 19.5±2.8 and 20.8±2.9kg for
YWT, respectively. The recombination effects were significant (P<0.01) for the
majority of crosses for all traits. The estimates for the recombination loss were
negative for all traits, except for BWT. The average recombination effects
estimated within the F, J and S breeds were: 2.6±0.8, 2.9±0.9 and 2.4±1.0 kg for
BWT, -13.6±3.2, -4.2±3.4 (P>0.05) and -16.0±4.0 kg for WWT, -88.0±17.1,
-39.4±18.4 and -102.2±21.3 g for ADG and -14.4±4.0, -0.1±4.4 (P>0.05) and
-17.5±4.9 kg for YWT, respectively.
In the third study, variance components and direct and maternal heritabilities
were estimated for weight at birth, weaning and yearling and preweaning average
daily gain. Data were analysed using six alternative animal models (direct and
including or excluding maternal effects). The direct heritability estimates from
the "best" model for each trait were: 0.14±0.03 for birth weight, 0.08±0.03 for
weaning weight, 0.06±0.02 for preweaning average daily gain and 0.13±0.03 for
yearling weight. The direct maternal heritability estimates were small, but
significantly different from zero for only birth weight (0.07±0.02), weaning
weight (0.04±0.02) and preweaning average daily gain (0.04±0.02). Direct
genetic correlations between birth weight and the other three traits were:
0.66±0.08, 0.55±0.19 and 0.50±0.12 with weaning weight, preweaning average
daily gain and yearling weight, respectively. The genetic correlation between
weaning weight, preweaning average daily gain and yearling weight was high
and ranged from 0.82±0.11 to 0.97±0.O1. Small, but non-zero maternal
heritabilities estimated for weaning and preweaning average daily gain for
artificially reared calves in this study should be interpreted cautiously because of
potential bias from unaccounted breed additive and non-additive effects of the
dam. Results of this study also showed that estimates of variance components
and genetic parameters suitable for general use can be obtained from mixed
purebred and crossbred data after appropriately accounting for breed additive and
non-additive effects.
In the fourth study, breed additive and non-additive effects plus heritabilities and
repeatabilities for milk yield per lactation (LMY), milk yield per day (DMY),
lactation length (LL), annual milk yield (AMY), annual milk yield per metabolic
body weight (AMYBW) and cow weight at calving (BW) were estimated. In
addition, genetic, phenotypic and permanent environmental correlations were
estimated between AMY and LL, AMY and BW and LL and BW. Data for each
trait were analysed, using two equivalent repeatability animal models: first,
fitting genotype as a fixed group effect and in the second model substituting
genotype with breed additive, heterotic and recombination effects as fixed
covariates. Among the genotypes the Bo had the lowest and the F the highest
performance for all traits. The least-squares means for the Bo breed were 529±65
kg for LMY, 2.8±0.1 kg for DMY, 193±6 d for LL, 514±61 kg for AMY,
7.8±0.7 for AMYBW and 304±3 kg for BW. Both F and J breed additive effects,
measured as a deviation from the Bo breed were significant (P<0.01) for all
traits, except for BW of the J. The F and J additive contributions were 2774±89
and 1473±362 kg for LMY, 7.1±0.2 and 4.8±0.8 kg for DMY, 146±8 and 81±7 d
for LL, 2345±71 and 1238±319 kg for AMY, 20.6±0.9 and 18.9±4.3 kg for
AMYBWand 140±4 and -21±22 kg (P>0.5) for BW, respectively. The heterotic
contributions to the crossbred performance were also positive and significant
(P<0.01) for all traits, except for BW in the F x Bo crosses. The Fl heterosis
expressed as a deviation from the mid-parent values were 22 and 66 % for LMY,
11 and 20% for DMY, 29 and 29% for LL, 21 and 64 % for AMY, 42% (P>0.05)
and 42 % for AMYBW and 2% (P>0.5) and 11% for BW for the F x Bo and J x
Bo crosses, respectively. The recombination effect estimated for the F x Bo
crosses was negative and significant for LMY (-526±192 kg, P<0.01), DMY (-
3.0±0.4 kg, P<0.01)AMY (-349±174, P<0.05) and BW (-68±11 kg, P<0.001).
For the J x Bo crosses the recombination loss was only significant and negative
for DMY (-2.2±0.7 kg, P<0.05) and BW (-33±17, P<0.05). The direct
heritabilities (h2) and repeatabilities (r2) estimated for each trait after correcting
for the fixed environmental and breed additive and non-additive effects were
0.24±0.04 and 0.39±0.02 for LMY, 0.19±0.03 and 0.30±0.02 for DMY,
0.13±0.03 and 0.19±0.02 for LL, 0.23±0.04 and 0.37±0.02 for AMY, 0.17±0.05
and 0.39±0.02 for AMYBW and 0.10±0.03 and 0.34±0.02 for BW, respectively.
The estimated genetic correlations between AMY and LL, AMY and BW, LL
and BW were 0.71±0.08, 0.17±0.18 and 0.23±0.20, respectively.
In the fifth study, estimates of breed additive differences, heterosis and
recombination loss, as well as heritabilities were obtained for age at first calving
(AFC), calving interval (Cl), days open (DO) and number of services per
conception (SPC). The genetic parameters were estimated using a repeatability
animal model for Cl, DO and SPC and a unitrait animal model for AFC. The
overall least-squares means estimated were: 38.3±0.26 months, 435±4 days,
145±10 days and 1.58±0.03 (number) for AFC, Cl, DO and SPC, respectively.
The breed additive effects of F and J were only significant (P<0.01) for AFC.
Relative to the Bo, both the F and the J additive contributions for AFC were
-5.4±0.5 and -5.5±1.9 months, respectively. Crossing the F and J breeds with the
Bo breed also resulted in significant heterosis (P<0.05) ranging from I0ta 21%
in all traits. The estimated recombination loss was only significant for AFC
(2.8±1.0 months) for the F x Bo crosses. Heritability estimates were high for
AFC (0.44±0.05) and low for Cl (0.08±0.03), DO (0.04±0.03) and SPC
(0.08±0.02). The corresponding estimates for the repeatability (r2
) were
0.14±0.02 and 0.14±.0.02 for Cl and DO, respectively. The repeatability estimate
for SPC was zero. Afrikaans: Vyf afsonderlike studies is uitgevoer om die genetiese faktore te ondersoek wat
groei, melkproduksie en voortplantingseienskappe in Bos indicus x Bos tauruskruisings
in Ethiopië affekteer. Die eerste drie studies is op vroeë groeidata wat
versamel is van suiwergeteelde Boran (Bo)-, Barca (Ba)-, Horro (Ho)-rasse (Bos
indicus) en hul kruisings met Fries (F)-, Jersey (J)- en Simmentaler (S)- rasse (Bos
taurus) versamel is gebaseer. Vroeë groeidata was van kalwers wat drie
suiwergeteelde Bos indicus en 38 kruisgeteelde genotipes verteenwoordig het en
wat een dag na geboorte van hulle moeders geskei is en melk uit 'n emmer gevoer
is. Die vierde en vyfde studies is gebaseer op melk- en voortplantingsdata
gebaseer wat van koeie van twee suiwergeteelde (Boran en Fries) en agt
kruisgeteelde (Boran met Fries en Jersey) genotypes versamel is.
In die eerste studie is vyf genetiese modelle geëvalueer vir geskiktheid van
passing en beraming van kruistelingsparameters. Hierdie modelle was: 1)
dominansiemodel, 2) Dickerson se model (rekombinasie verlies), 3) additiewe x
dominansie interaksie-model, 4) dominansie x dominansie interaksie-model en 5)
Kinghom se model (x). Modelle 2 tot 5 is epistatiese modelle wat al die effekte in
modeilingesluit het, plus een tipe epistatiese inter-aksie gebaseer op 'n tweelocus
gene-model. Die modelle is geëvalueer deur gebruik te maak van data vir
geboorte-, speen- en jaaroudgewigte, asook voorspeense gemiddelde daaglikse
toename. Al vyf modelle wat getoets is het hoë vlakke van passing vertoon, met
aangepaste R2 -waardes wat 'n gemiddeld van 93% oor eienskappe bereik het. Al
die epistatiese modelle het die data betekenisvol (P<0.01) beter vir al die
eienskappe gepas as die dominansiemodel. Vandie epistatiese modelle het
Dickerson se model betekenisvol (P<0.01) hoër Ri-waardes getoon, vergeleke met
die ander. Kruistelingparameters wat van hierdie model beraam is het relatief laer
monsteringkorrelasies en ooreenstemmend laer standaardfoute gehad. Hierdie
model kan derhalwe beskou word as die mees geskikte vir parameterberamings en
voorspelling van die prestasie van ongetoetste genotipes Vir toekomstige
teeltbesluite oor raskruisings wat in hierdie studie betrokke is.
In die tweede studie is rasverskille, heterose en rekombinasieverliese Vir
geboortegewig (Ggew), speengewig (Sgew), voorspeense gemiddelde daaglikse
toename (GDT) en jaaroudgewig (Jgew) deur 'n dieremodel te gebruik beraam.
Verskille tussen genotipes was betekenisvol (P<0.01) vir alle eienskappe.
Genetiese groepgemiddeldes aangepas vir omgewingseffekte het van 20 tot 30kg
gewissel vir Ggew, 88 tot 114 kg vir Sgew, 122 tot 157 kg vir Jgewen van 358 tot
429g vir voorspeense gemiddelde daaglikse toename (GDT). Die ras-additiewe
effek van F as 'n afwyking van die Bo, was betekenisvol (P<0.01) en positief vir
alle einskappe. Relatief tot die Bo-gemiddelde was die bykomende additiewe
bydrae van die F-ras op Ggew, Sgew, GDT en Jgew onderskeidelik 39.3, 16.5,
9.3 en 10.3%. Hierteenoor was die additiewe effekte van die Ho- en J-rasse
betekenisvol (P<0.01) negatief vir alle eienskappe. Die heterose-effekte was
betekenisvol negatief (P<0.01) vir Ggew vir alle F- en S-kruisings, maar positief
(P<0.01) vir alle ander eienskappe vir alle tipe kruisings. Die gemiddelde heterose
wat binne die F-, J- en S-rasse beraam is, was onderskeidelik -2.l±0.6, 0.2±0.6
(P>0.05) en -2.3±0.6 vir Ggew, 8.8±2.1, 11.8±2.3, en 13.7±2.4 kg vir Sgew,
60.4±11.3, 64.8±12.3 en 90.6±12.7 g vir GDT en 19.8±2.6, 19.5±2.8 en 20.8±2.9
kg vir Jgew. Die rekombinasie-effekte was betekenisvol (P<O.OI) vir die
meerderheid van kruisings vir alle eienskappe. Die beramings van die
rekombinasie-verlies was negatief vir alle eienskappe, behalwe vir Ggew. Die
gemiddelde rekombinasie-effekte wat beraam is binne die F-, J- en S-rasse was
onderskeidelik 2.6±0.8, 2.9±09 en 2.4±1.0 kg vir Ggew, -13.6±3.2, -4.2±3.4
(P>0.05) en -16.0± 4.0 kg vir Sgew, -88.0±17.l, -39.4±18.4 en -102.2±21.3 g vir
GDT en -14.4±4.0, -0.l± 4.4 (P>0.05) en -17.5±4.9 kg vir Jgew vir genoemde drie
rasse onderskeidelik.
In die derde studie is variansiekomponente en direkte en maternale oorerflikhede
vir gewig by geboorte, speen en jaaroud en voorspeense gemiddelde daaglikse
toename onderskeidelik beraam. Data is deur die passing van ses alternatiewe
dieremodelle (direk en met in- of uitsluiting van maternale effekte) ontleed. Die
direkte oorerflikheidsberamings van die "beste" model vir elke eienskap was:
0.14±0.03 vir geboortegewig, 0.08±0.03 vir speengewig, 0.06±0.02 vir
voorspeense gemiddelde daaglikse toename en 0.13±0.03 vir jaaroudgewig, Die
direkte maternale oorerflikheidsberamings was klein, maar betekenisvol
verskillend van slegs zero vir geboortegewig (0.07±0.02), speengewig (0.04±0.02)
en voorspeense gemiddelde daaglikse toename (0.04±0.02). Direkte genetiese
korrelasies tussen geboortegewig en die ander drie eienskappe was onderskeidelik
0.66±0.08, 0.55±0.19 en 0.50±0.12 met speengewig, voorspeense gemiddelde
daaglikse toename en jaaroudgewig. Die genetiese korrelasies tussen speengewig,
voorspeense gemiddelde daaglikse toename en jaaroudgewig was hoog en het
tussen 0.82±0.11en 0.97±0.0l gewissel. Klein, maar nie-zero maternale
oorerflikhede wat speengewig en voorspeense gemiddelde daaglikse toename vir
kunsmatig-grootgemaakte kalwers in hierdie studie beraam is, moet met
omsigtigheid geïnterpreteer word vanweë die potensiële sydigheid van
onverklaarde ras-additiewe en -nie-additiewe effekte van die moeder. Resultate
van hierdie studie het ook getoon dat beramings van variansie-komponente en
genetiese parameters wat geskik is vir algemene gebruik, verkry kan word van
gemengde, suiwergeteelde en kruisgeteelde data na behoorlike inagneming van
ras-additiewe en -nie-additiewe effekte.
In die vierde studie is ras-additiewe en -nie-additiewe effekte beraam, asook
oorerflikhede en herhaalbaarhede vir melkopbrengs per laktasie (LMO),
melkopbrengs per dag (DMO), lengte van laktasie (LL), jaarlikse melkopbrengs
(lMO), jaarlikse melkopbrengs per metaboliese liggaamsgewig (lMOLgew), en
koeigewig met kalwing (Lgew). Bykomend is genetiese, fenotipiese en
permanente omgewingskorrelasies tussen lMO en LL, lMO en Lgew en LL en
Lgew beraam. Data vir elke eienskap is ontleed deur twee ekwivalente
herhaalbaarheids-dieremodelle te gebruik: eerstens, deur genotipe as 'n vaste
groep-effek te pas en in die tweede model genotipe te vervang deur ras-additiewe,
heterose en rekombinasie-effekte as vaste ko-veranderlikes. Van die genotipes het
die Bo die laagste en die F die hoogste prestasie vir al die eienskappe gehad. Die
kleinste vierkantgemiddeldes vir die Bo-ras was 529±65 kg vir LMO, 2.8±0.1 kg
vir DMO, 193±6d vir LL, 514±61 kg vir JMO, 7.8±0.7 vir JMOLgew en 304±3
kg vir Lgew. Beide F en J ras-additiewe effekte, wat gemeet is as 'n afwyking van
die Bo-ras was betekenisvol (P<0.01) vir alle eienskappe, behalwe vir Lgew van
1. Die F en J additiewe bydraes was onderskeidelik 2774±89 en 1473±362 kg vir
LMO, 7.l±0.2 en 4.8±0.8 kg vir DMO, 146±8 en 81±7 d vir LL, 2345±71 en
1238±319 kg vir JMO, 20.6±0.9 en 18.9±4.3 kg vir JMOLgew en 140±4 en -
21±22 kg (P>0.5) vir Lgew. Die heterose-bydrae tot die kruisteeltprestasie was
ook positief en betekenisvol (P0.01) vir alle eienskappe, behalwe vir Lgew in die
FxBo kruisings. Die FI heterose, uitgedruk as 'n afwyking van middelouerwaardes
was onderskeidelik 22 en 66 % vir LMO, 11 en 20% vir DMO, 29 en
29% vir LL, 21 en 64% vir JMO, 42% (P>0.05) en 42% vir JMOLgew en 2%
(P>0.5) en 11% vir Lgew vir F x Bo- en J x Bo- kruisings. Die rekombinasieeffek
vir F x Bo kruisings was negatief en betekenisvol vir LMO (-526± 192 kg,
P<0.01), DMO (-3.0±0.4kg, P<0.01),JMO (-349±174, P<0.05) en Lgew (-68±11
kg, P<0.001). Vir J en Bo- kruisings was die rekombinasie-verlies slegs
betekenisvol en negatief vir DMO (-2.2±0.7 kg, P<0.05) en Lgew (-33±17,
P<0.05). Die direkte oorerflikhede (h2) en herhaalbaarhede (r2) wat vir elke
eienskap beraam is nadat vir die vaste omgewings- en ras-additiewe en -nieadditiewe
effekte gekorrigeer is, was onderskeidelik 0.24±0.04 en 0.39±0.02 vir
LMO, 0.19±0.03 en 0.30±0.02 vir DMO, 0.l3±0.03 en 0.l9±0.02 vir LL,
0.23±0.04 en 0.37±0.02 vir JMO, 0.l7±0.05 en 0.39±0.02 vir JMOLgew en
0.10±0.03 en 0.34±0.02 vir Lgew. Die beraamde genetiese korrelasies tussen JMO
en LL, JMO en Lgew, LL en Lgew was onderskeidelik 0.71±0.08, 0.17±0.18 en
0.23±0.20.
In die vyfde studie is beramings van ras-additiewe verskille, heterose en
rekombinasie-verliese, sowel as oorerflikhede gemaak vir ouderdom met eerste
kalwing (OEK), kalwings-interval ( Cl) , dae oop (DO) en aantal dekkings per
bevrugting (DPB). Die genetiese parameters IS beraam deur 'n
herhaalbaarheidsdieremodel vir Cl, DO en DPB en 'n enkeleienskap-dieremodel
vir OEK te pas. Die algehele kleinste kwadraatgemiddeldes wat beraam is, was
onderskeidelik 38.3±0.26 maande, 435±4 dae, l45±10 dae en 1.58±0.03 (getal)
vir OEK, Cl, DO en DPB. Die ras-additiewe effekte van F en J was slegs vir
OEK betekenisvol (P<0.01). Relatief tot die Bo, was beide die F en J additiewe
bydraes vir OEK onderskeidelik -5.4±0.5 en -5.5±1.9 maande onderskeidelik.
Kruising van die Bo met die F- en J-rasse het ook betekenisvolle heterose tot
gevolg gehad (P<0.05) wat van 10 tot 21% in alle eienskappe gewissel het. Die
beraamde rekombinasie-verlies was slegs vir OEK (2.8±1.0 maande) vir F- en Bokruisings
betekenisvol. Beramings van oorerflikheid was hoog vir OEK
(0.44±0.05) en laag vir Cl (0.08±0.03), DO (0.04±0.03) en DPB (0.08±0.02). Die
ooreenstemmende beramings vir die herhaalbaarhede (r2) was onderskeidelik
0.14±O.2 en 0.14±0.02 vir Cl en DO. Permanente omgewingseffek vir DPB was
zero.