ESTIMATION OF (CO) VARIANCE COMPONENTS OF EWE PRODUCTIVITY TRAITS IN KERMANI SHEEP

Slovk J. Anim. Sci., 46, 2013 (2): 45-51 2013 CVŽV ISSN 1337-9984 ESTIMATION OF (CO) VARIANCE COMPONENTS OF EWE PRODUCTIVITY TRAITS IN KERMANI SHEEP M. R. MOHAMMADABADI*, R. SATTAYIMOKHTARI Deprtment of Animl Science, Fculty of Agriculture, Shhid Bhonr University of Kermn, Kermn, Irn ABSTRACT The present study ws crried out to estimte (co)vrince components nd genetic prmeters for some productivity trits of Kermni ewes using dt collected during 16-yer period (1995-2011) t Breeding Sttion of Kermni sheep, locted in Shhrebbk city, Kermn province, Irn. The trits studied were: conception rte (CR), litter size t birth per ewe exposed (LSB/EE), litter size t wening per ewe exposed (LSW/EE), totl litter weight t birth per ewe exposed (TLWB/EE) nd totl litter weight t wening per ewe exposed (TLWW/EE). Genetic nlysis of the studied trits ws performed pplying restricted mximum likelihood (REML) procedure under uni- nd multivrite repetbility models. Ewe ge t lmbing nd lmbing yer hd significnt effects on ll the studied trits (P<0.01). Wening ge of lmbs hd significnt effect on TLWW/EE s liner covrite (P<0.01). Estimtes of direct heritbility for CR, LSB/EE, LSW/EE, TLWB/EE nd TLWW/EE were 0.08, 0.06, 0.07, 0.11 nd 0.15, respectively, while corresponding repetbility estimtes were 0.25, 0.19, 0.18, 0.25 nd 0.31, respectively. There were found no ntgonist reltionship mong the studied trits in terms of phenotypic, genetic nd environmentl effects. Direct genetic correltion estimtes mong the studied trits vried from low estimte of 0.16 for CR-TLWB/EE to high estimte 0.95 for CR-LSB/EE. Low to medium phenotypic correltion estimtes of 0.07 (LSB/EE-TLWW/EE) nd 0.46 (TLWB/EE-TLWW/EE) were found. It seems tht selection bsed on TLWW/EE, s n efficient selection criterion bring bout genetic progress for ewe productivity trits in Kermni sheep. Key words: reproductive performnce; heritbility; genetic correltion; sheep INTRODUCTION Smll ruminnts, especilly ntive breed types, ply n importnt role to the livelihoods of considerble prt of humn popultion in the tropics from socioeconomic spects. Therefore, integrted ttempt in terms of mngement nd genetic improvement to enhnce production is of crucil importnce (Kosgey nd Okeyo, 2007). Economicl nd biologicl efficiency of sheep production enterprises generlly improves by incresing productivity nd reproductive performnce of ewes. The profitbility per ewe is minly determined by reproductive rte nd ewe productivity, where mutton nd lmb production hve sizble influences on profitbility (Wng nd Dickerson, 1991). Mutton is the min source of red met in Irn nd its production does not meet the incresing demnd of the consumers. Generlly, the more intensive mutton production system requires the more production of lrge numbers of lmb per breeding ewe. Reproductive chrcteristics re of outstnding importnce in sheep production enterprises due to their effect on profitbility (Mtos et l., 1997), especilly when met production is the chief trget. The Irnin indigenous sheep breeds re minly kept by locl pstorlists under extensive production systems bsed on rngelnds of low qulity nd quntity. In such production system low efficiency is common nd is cused by severl fctors, e.g. low reproductive efficiency (Esmilizdeh et l., 2009). Litter weight wened per ewe exposed considered s n pproprite indictor of overll ewe productivity nd one of the most importnt economic contributions *Correspondence: E-mil: mmohmmdbdi@yhoo.com M. Mohmmdbdi, Deprtment of Animl Science, Fculty of Agriculture, Shhid Bhonr University of Kermn, 7116914111, Kemrn, Irn Tel.: +0098 913 398 7534 Fx: 00983413222043 Received: September 10, 2012 Accepted: Mrch 25, 2013 45

Originl pper Slovk J. Anim. Sci., 46, 2013 (2): 45-51 tht genetics cn mde to ny sheep breeding system (Vnimisetti et l., 2007). It is complex trit, influenced by severl fctors such s ge t puberty, ovultion rte, mothering bility, lmb growth nd survivl (Snowder nd Fogrty, 2009). Dugum et l. (2002) stted tht improvement in ewe productivity could to some extent be chieved by incresing the number nd weight of lmbs produced per ewe within specific yer. Knowledge of genetic prmeters for these decisive trits is of gret importnce from genetic improvement stndpoint. Genetic prmeters for reproductive trits of severl sheep breeds hve been reported (Rosti et l., 2002; Ekiz et l., 2005 Vtnkhh et l., 2008; Rshidi et l., 2011). The genetic chrcteriztion of the ntive breeds is of crucil importnce for the conservtory considertions nd building up efficient selection nd breeding progrms (Mtik et l., 2003). Efficient genetic improvement progrms cn boost profitbility nd efficiency for smllholders, within breed selection is n lterntive for genetic improvement of smll ruminnts in the trditionl, low-input production systems of the tropics (Kosgey nd Okeyo, 2007). Accurte estimtes of (co)vrince components for economiclly importnt trits, such s reproductive ones, re pre-requisites for efficient designing of such strtegy. Kermni sheep is one of the most importnt Irnin ntive sheep breeds nd is well-dpted to hrsh environmentl conditions of south-estern prt of country, where dry nd hot wether is prevlent nd pstures re of low qulity nd quntity. Kermni sheep is ft-tiled, dul purpose (met nd wool) with mutton production is of primry importnce, medium-sized nd white-wool breed. In previous study genetic prmeters for some reproductive trits of Kermni sheep, in ewe lmbed bsis, were estimted by Mokhtri et l. (2010). However, estimtion of genetic prmeters nd (co)vrince components for reproductive trits in ewe exposed bsis hs not been reported. Such estimtes re of biologicl importnce nd provide more relistic mesures for genetic improvement of ewe productivity with considering conception rte. Therefore, the present study ws performed t iming estimtion of genetic prmeters including heritbility, repetbility nd genetic correltion for reproductive trits of Kermni ewe in ewe-exposed bsis using niml model. MATERIAL AND METHODS The dt set nd pedigree informtion used in the present study were collected for 16 yer period from 1995 to 2011 from experimentl flock t the Breeding Sttion of Kermni sheep, locted in Shhrebbk city, Kermn province, south-est of Irn. A controlled mting strtegy ws designed. During the breeding seson - period lsting from mid-august to mid-september, single sire pens were used llocting 25-35 ewes per fertile rm. The ewes were kept in flock for mximum of 5 prities (pproximtely until the ge of 7 yers old). In order to void inbreeding, rms were llocted rottionlly to ech group of the ewes in different yers. The flock ws minly kept on pstures of low qulity nd quntity, supplementry feeding ws offered especilly round mting nd during winter (nimls kept indoors). The supplementl feeds consist of 1.5 kg lflf, 0.5 kg whet strw nd 0.2 kg brley per hed per dy. The miden ewes were exposed to the rms t the ge of 18 months. Lmbing occurs from mid-jnury to mid- Februry nd new-born lmbs were weighed nd er-tgged t the birth time. The lmbs were kept indoors during the winter nd fed mnully. Flocks were grzed during the dy nd housed t night. Wening Tble 1: Descriptive sttistics for the studied reproductive trits Item Trits CR LSB/EJ LSW/EJ TLWB/EJ TLWW/EJ No. of records 2683 2683 2683 2658 2597 No. of ewes 993 993 991 991 989 No. of sire of the ewes 71 71 71 71 71 No. of dms 535 535 535 534 534 No. of dms with progeny 507 507 507 504 499 Men 0.87 0.91 0.84 2.96 17.02 S.D. 0.32 0.40 0.47 1.35 8.96 C. V. (%) 36.78 43.96 47.62 45.61 52.64 CR: conception rte LSB/EJ: litter size t birth per ewe exposed; LSW/EJ: litter size t wening per ewe exposed; TLWB/EJ: totl litter weight t birth per ewe exposed; TLWW/EJ: totl litter weight t wening per ewe exposed 46

Slovk J. Anim. Sci., 46, 2013 (2): 45-51 Originl pper ws t pproximtely 3 months of ge. All lmbs were wened t the sme dy, without necessity t the sme ge. Trits investigted cn be ctegorized into two clsses; bsic nd composite. Conception rte (CR) ws bsic nd binry trit tht is mesured with vlues of 0 ( ewe exposed to rm did not lmb) nd 1 ( ewe exposed to rm did lmb). Other considered trits were composite including litter size t birth per ewe exposed (LSB/EE=CR x LSB), litter size t wening per ewe exposed (LSW/EE=CR x LSW), totl litter weight t birth per ewe exposed (TLWB/EE=CR x TLWB) nd totl litter weight t wening per ewe exposed (TLWW/ EE=CR x TLWW). LSB/EE ws the number of lmbs born per ewe exposed within specific yer (0, 1 or 2) nd LSW/EE ws the number of lmbs wened per ewe exposed within specific yer (0, 1 or 2). TLWB/EE refers to the sum of the birth weights of ll lmbs born per ewe exposed nd TLWW/EE refers to the sum of the weights of ll lmbs wened per ewe exposed. The dt structure of the studied trits is presented in tble 1. Generl liner model (GLM) procedure of SAS pckge (SAS, 2002) ws employed for lest squre nlyses nd determining of significnt fixed effects to be included in finl model. The model ccounting for fixed effects included lmbing yer in 17 levels (1995 2011) nd ewe ge t lmbing in 6 clsses (2 7 yers old). Age of lmb t wening (in dys) ws fitted s liner covrite for corresponding trits. The interction between lmbing yer nd ewe ge ws not significnt nd ws removed from the finl model. All trits contined lmb weights t birth nd/or t wening were pre-djusted for sex of lmbs using pproprite multiplictive djustment fctors. The (co)vrince components nd genetic prmeters were estimted by restricted mximum likelihood (REML) method, pplying AI-REML method with convergence criterion of 10-8 using WOMBAT progrm of Meyer (2007) fitting the following repetbility model: y= Xb+ Z+Wpe+ e where y is vector of records for ech trits; b,, pe nd e re vectors of fixed effects, direct dditive genetic effects, permnent environmentl effects relted to repeted records of ewes nd residul effects, respectively. Design mtrices of X, Z nd W relte the corresponding effects to the vector of y. It ws ssumed tht dditive genetic effects, permnent environmentl effects relted to repeted records of ewes nd residul effects to be normlly distributed with men of zero nd vrinces of Aσ 2, I d σ 2 pe nd I n σ2 e respectively. Also σ2, σ2 pe nd σ2 e re direct dditive genetic vrince, service sire vrince, permnent environmentl vrince relted to repeted records of the ewes nd residul vrince, respectively. A is the dditive numertor reltionship mtrix, I d nd I n re identity mtrices with order equl to the number of ewes nd records, respectively. In order to estimte the genetic, environmentl nd phenotypic correltions multivrite nlysis ws performed. The fixed effects included in the multivrite niml model were those in univrite nlyses. Tble 2: Lest squre mens with stndrd error for the studied reproductive trits Fixed effects Trits CR LSB/EJ LSW/EJ TLWB/EJ TLWW/EJ Overll men 0.86±0.02 0.94±0.03 0.87±0.01 2.95±0.05 18.26±0.34 Ewe ge (yer) ** ** ** ** ** 2 0.63±0.02 c 0.69±0.01 c 0.62±0.03 c 1.94±0.05 c 11.21±0.34 d 3 0.88±0.01 b 0.92±0.03 b 0.86±0.01 b 2.90±0.04 b 17.43±0.36 c 4 0.91±0.01 b 0.95±0.01 0.88±0.01 b 3.23±0.06 18.61±0.35 b 5 0.94±0.02 0.99±0.01 0.94±0.02 3.24±0.07 18.90±0.33 b 6 0.95±0.03 1.00±0.04 0.96±0.03 3.36±0.09 20.11±0.42 7 0.86±0.05 b 0.87±0.06 b 0.84±0.07 b 2.91±0.19 b 17.54±1.06 c Lmbing yer ** ** ** ** ** Birth dte b - ns ns - 0.04**±0.01 Abbrevitions of the trits re described in footnote of Tble 1. b Regression coefficient on dy of lmb birth. c resulted from multivrite nlysis Mens with similr letters in ech subclss within column do not differ. ns Non significnt (P > 0.05). ** Significnt effect t P < 0.01. 47

Originl pper Slovk J. Anim. Sci., 46, 2013 (2): 45-51 RESULTS AND DISCUSSION The lest squre mens for studied trits re shown in tble 2. All trits significntly influenced by lmbing yer nd ewe ge t lmbing (P<0.01). Age of the lmb t wening (in dys) significntly influenced TLWW/ EE (P<0.01). Lmbing dte turned out not to hve ny significnt effect on LSB/EE nd LSW/EE (P>0.05). Vrince components nd genetic prmeters for considered trits under univrite nlysis re presented in tble 3. Low direct heritbility (h 2 ) estimtes were d obtined for ll trits rnging from 0.06 for LSB/EE to 0.15 for TLWW/EE. Estimtes of rtio of permnent environmentl vrince due to repeted records of ewe on phenotypic vrince (pe 2 ) were lso low nd vried from 0.11 for LSW/EE to 0.17 for CR nd repetbility estimtes from 0.18 for LSW/EE to 0.31 for TLWW/EE. Estimtes of direct heritbility, obtined from multivrite nlysis, re presented in tble 4 (ondigonl vlues). Corresponding estimted vlues were lower thn those of obtined under univrite nlysis nd were 0.06, 0.04,.0.04, 0.07 nd 0.08 for CR, LSB/ EE, LSW/EE, TLWB/EE nd TLWW/EE, respectively. Correltion estimtes (phenotypic, genetic nd environmentl) mong the trits re presented in tble 4. Low to high genetic correltion estimtes found mong the trits tht were rnged from 0.16 for CR-TLWB/EE to 0.95 for CR-LSB/EE. While, phenotypic correltion estimtes were low (0.07 between LSB/EE nd TLWW/ EE) to medium (0.46 between TLWB/EE nd TLWW/ EE). Also, environmentl correltion estimtes were low to medium in mgnitude nd vried from 0.06 for LSW/ EE to 0.31 for CR-LSB/EE. Tble 3: Estimtes of genetic prmeters nd vrince components for the studied reproductive trits Trits σ 2 σ 2 pe σ2 e σ2 p h2 d ± S.E. pe2 ± S.E. r CR 0.0085 0.0180 0.0795 0.1060 0.08 ± 0.03 0.17 ± 0.03 0.25 LSB/EJ 0.0085 0.0184 0.1148 0.1417 0.06 ± 0.02 0.13 ± 0.03 0.19 LSW/EJ 0.0119 0.0188 0.1400 0.1707 0.07 ± 0.03 0.11 ± 0.02 0.18 TLWB/EJ 0.1632 0.2078 1.1131 1.4841 0.11 ± 0.02 0.14 ± 0.05 0.25 TLWW/EJ 8.2101 8.7474 37.7766 54.7341 0.15 ± 0.04 0.16 ± 0.02 0.31 σ 2: direct genetic vrince; σ2 : permnent environmentl vrince; pe σ2: residul vrince; e σ2: phenotypic vrince; p h2 : direct heritbility; d pe 2 : rtio of permnent environmentl vrince on phenotypic vrince; r: repetbility; S. E.: stndrd error. Abbrevitions of the trits re described in footnote of Tble 1. Tble 4: Phenotypic, genetic nd environmentl correltion b estimtes nd direct heritbility c estimtes for the studied reproductive trits Trits CR LSB/EJ LSW/EJ TLWB/EJ TLWW/EJ CR 0.06±0.05 0.95±0.26 0.74±0.34 0.16±0.21 0.34±0.23 LSB/EJ 0.44±0.08 (0.31±0.06) 0.04±0.03 0.76±0.29 0.35±0.19 0.28±0.17 LSW/EJ 0.27±0.09 (0.16±0.04) 0.36±0.09 (0.16±0.02) 0.04±0.01 0.39±0.27 0.49±0.26 TLWB/EJ 0.11±0.04 (0.08±0.02) 0.21±0.06 (0.12±0.02) 0.23±0.04 (0.06±0.02) 0.07±0.05 0.87±0.15 TLWW/EJ 0.15±0.04 (0.19±0.05) 0.07±0.03 (0.14±0.04) 0.32±0.03 (0.14±0.04) 0.46±0.04 (0.22±0.05) 0.08±0.04 Abbrevitions for the trits re presented in footnote of Tble 1. b Genetic correltions (bove digonl), phenotypic (below digonl) nd environmentl in the prenthesis c resulted from multivrite nlysis 48

Slovk J. Anim. Sci., 46, 2013 (2): 45-51 Originl pper A generl tendency for improvement of the studied trits with the increse of ewe ge ws observed until the ge of 7 yers old (Tble 2) nd it cn be explined prtly by differences in mternl effects, nursing nd mternl behvior of ewe t different ges. Fourie nd Heydenrych (1983) reported tht twinning rte nd conception rte generlly increse with ge, followed by decrese in reproductive performnce fter pproximtely 5 prities. Significnt effects of ewe ge on reproductive trits of sheep hve been reported in the literture (Rosti et l., 2002; Ekiz et l., 2005, Rshidi et l., 2011). The significnt effect of lmbing yer my be scribed to vrition in climtic conditions nd mngeril prctices through different yers. Significnt effect of lmbing yer on ewe productivity trits hs been well documented by others (Boujenne et l., 1991; Bromley et l., 2001; Ekiz et l., 2005; Vtnkhh et l., 2008; Mokhtri et l., 2010; Rshidi et l., 2011). A low estimte of 0.08 ws obtined for direct heritbility of CR, which ws in ccordnce with estimtes of Rosti et l. (2002) nd Sfri et l. (2005). Lower estimte of 0.01 ws found by Vtnkhh et l. (2008) for direct heritbility of CR in Lori-Bkhtiri sheep tht ws lower thn estimted vlue in the present study. The low estimte my be due to the effect of rndom environmentl fctors on vribility of the observtions nd becuse of the ctegoricl expression of the trit. Therefore, improvement of CR through selection would be difficult even though CR is of gret economic importnce. Low estimtes of direct heritbility were found for LSB/EE (0.06) nd LSW/EE (0.07) tht generlly greed with severl uthors (Fogrty, 1995; Rosti et l., 2002; Sfri et l. 2005; Vtnkhh et l., 2008). Therefore, the possibility to chieve rpid genetic gin through selection for these trits would be limited. Direct dditive genetic vrince constitutes 11 % nd 15 % of phenotypic vrince for TLWB/EE nd TLWW/ EE, respectively. TLWB/EE indictes the cpcity of the ewes to produce weight of lmbs t birth fter exposure to the rm without tking the number of lmbs born into ccount (Rosti et l., 2002). Direct heritbility estimte of TLWB/EE (0.11) ws in generl congruence with estimte of Rosti et l. (2002) nd Vtnkhh et l. (2008). TLWW/EE mesures the bility of the ewe to produce wening weight of lmb fter exposure to the rm nd is trit of gret economic importnce in ny sheep breeding production system. Obtined direct heritbility (0.15) ws concordnt with estimte of Rosti et l. (2002) nd Sfri et l. (2005). Lower estimte of 0.07 ws obtined by Vtnkhh et l. (2008) in Lori-Bkhtiri sheep. The TLWW/EE could be considered s n efficient selection criterion becuse it is in sense, mesure of totl productivity of the ewe for lmb-met production during specific breeding yer (Rosti et l., 2002). Furthermore, it is high economic importnce composite trit (Ercnbrck nd Knight, 1998) nd hd components such s fertility, number of lmbs t wening per ewe exposed nd number of lmbs born. For ll prcticl purposes, it is more desirble to select component trit thn composite one when component trit bers high genetic correltion with composite trit, higher heritbility nd coefficient vrition compred to the composite one (Snowder nd Fogrty, 2009). Comprison between component trit nd composite one in terms of selection response cn be done by compring the product of the heritbility nd coefficient of vrition (Smith, 1969). Such product cn be useful in determining the credence of selection bsed on composite trit reltive to selection bsed on its components (Snowder nd Fogrty, 2009). Using the obtined vlues in the present study, the product of the heritbility nd coefficient vrition for TLWW/EE is 7.89, compred with 2.94 for CR, 2.64 for LSB/EE nd 3.33 for LSW/EE. Therefore, response to selection for TLWW/EE would be greter thn the responses expected for its component trits. Estimtes of repetbility were higher thn the heritbility ones suggesting tht trits re ffected more by non-dditive genetic effects (dominnce nd epitsis) nd permnent environmentl effects. Therefore, the ccurcy of selection for these trits especilly for TLWW/EE on the first lmbing should be medium s repetbility mesures correltion between performnce records in different lmbing of the ewe. Repetbility estimte of CR (0.25) ws medium. Contrry to us, Vtnkhh et l. (2008) estimted low estimte of 0.10 for repetbility of CR in Lori-Bkhtiri sheep. LSB/EE nd LSW/EE hve reltively similr in mgnitude repetbility vlues of 0.19 nd 0.28, respectively. Higher estimtes were obtined for repetbility of TLWB/EE (0.25) nd TLWW/EE (0.31). Corresponding lower estimtes were found by Vtnkhh et l. (2008). Genetic correltion estimtes mong the studied trits were positive nd higher thn those of phenotypic nd environmentl ones. CR hd high genetic correltion with LSB/EE (0.95) nd LSW/EE (0.74), probbly becuse it is mjor component of these trits. Lower genetic correltion estimtes of CR with TLWB/EE (0.16) nd TLWW/EE (0.34) could be explined to some extent by the fct tht these trits hve records different from zero, only if conception rte is successful (Rosti et l., 2002; Vtnkhh et l., 2008). Obtined genetic correltions mong CR nd other studied trits were in generl greement with estimtes of Rosti et l. (2002). LSB/EE nd LSW/EE hve positive nd reltively high genetic correltion (0.76). Similr to our estimte, Vtnkhh et l. (2008) obtined corresponding vlue of 0.77 in Lori-Bkhtiri sheep. A lower estimte of 0.29 ws found by Rosti et l. (2002). Medium estimtes 49

Originl pper Slovk J. Anim. Sci., 46, 2013 (2): 45-51 of genetic correltions for LSB/EE-TLWB/EE (0.35) nd LSB/EE-TLWW/EE (0.28) were generlly lower thn those of obtined by Vtnkhh et l. (2008) but generlly were in greement with Rosti et l. (2002). Estimtes of genetic correltions for LSW/EE- TLWB/EE (0.39) nd LSW/EE-TLWW/EE (0.49) were generlly greed with those of obtined by Vtnkhh et l. (2008) nd higher thn estimtes of Rosti et l. (2002). A high genetic correltion (0.87) ws estimted between TLWB/EE nd TLWW/EE. This high genetic correltion suggests tht genes resulting in hevy birth weight of litters, through number nd weight of lmbs re responsible for genes ffecting milk production performnce nd mternl behvior of ewes throughout pre-wening period. Selection for TLWB/EE my be desirble, even if the direct heritbility is not high becuse of the high genetic correltion between TLWB/ EE nd TLWW/EE. Recording of TLWB/EE hve tken some weeks erlier thn records of TLWW/EE. This time period cn be of breeding decision mking importnt, due to the typicl sesonl breeding ctivity of sheep, sving few weeks my dvnce selection by one breeding seson (Rosti et l., 2002). CONCLUSION Lrge influences of non-genetic effects on the studied trits were observed. Therefore, concentrting on mngeril prctices such s improvement in ewe nutrition round mting nd lte pregnncy cn result in the improvement of reproductive performnce of ewes. In spite of low genetic vritions observed for the studied trits building n pproprite breeding progrm needs to include these trits s n integrl prt of the progrm, due to their considerble influence on the profitbility of production system. In this ccount, TLWW/EE is composite trit incorporting growth bility of lmbs s well s their survivl from birth to wening, mternl bility of the ewes nd conception rte. The existence of positive genetic correltion estimtes between TLWW/ EE nd the other trits suggests tht using TLWW/EE s selection criterion in plotting out breeding progrm would be beneficil nd could promote the overll productivity of the ewes. ACKNOWLEDEGMENT The uthors wish to thnk ll Kermni sheep Breeding Sttion stff, especilly M. Meymnidiniy, who ssisted in mnging the experimentl flock over ll the yers the reserch ws in progress. Contribution from Jehde Keshvrzi Orgniztion of Kermn province, Animl Affirs deputy, for providing the dt set is deeply cknowledged. REFERENCES BOUJENANE, I. KERFAL, M. KHALLOUK, M. 1991. Genetic nd phenotypic prmeters for litter trits of D mn ewes. Anim. Prod., vol. 52, 1991, p. 127-132. BROMLEY, C. M. VAN VLECK, L. D. SNOWDER, G. D. 2001. Genetic correltions for litter weight wened with growth, prolificcy, nd wool trits in Columbi, Polypy, Rmbouillet, nd Trghee sheep. J. of Anim. Sci., vol. 79, 2001, p. 339-346. DUGUMA, G. SCHOEMAN, S. J. CLOETE, S. W. P. JORDAAN, G. F. 2002. Genetic nd environmentl prmeters for productivity in Merinos. South Africn J. of Anim. Sci., vol. 32, 2002, p. 154-159. EKIZ, B. OZCAN, M. YILMAZ, A. CEYHAN, A. 2005. Estimtes of phenotypic nd genetic prmeters for ewe productivity trits of Turkish Merino (Krcbey Merino) sheep. Turkish J. of Veterinry nd Anim. Sci., vol. 29, 2005, p. 557-564. ERCANBRACK, S. K. KNIGHT, A. D. 1998. Responses to vrious selection protocols for lmb production in Rmbouillet, Trghee, Columbi nd Polypy sheep. J. of Anim. Sci.,vol. 61, 1998, p. 1311-1325. ESMAILIZADEH, A. K. DAYANI, O. MOKHTARI, M. S. 2009. Lmbing seson nd fertility of fttiled ewes under n extensive production system re ssocited with live weight nd body condition round mting. Anim. Prod. Sci. vol. 49, 2009, p. 1086-1092. FOGARTY, N. M. 1995. Genetic prmeters for live weight, ft nd muscle mesurements, wool production nd reproduction in sheep: review. Animl Breeding Abstr., vol. 63, 1995, p. 101-143. FOURIE, A. J. HEYDENRYCH, H. J. 1983. Phenotypic nd genetic spects of production in the Dohne Merino. III. The influence of ge of ewe on reproductive performnces. South Africn J. of Anim. Sci., vol. 13, 1983, p. 164-166. KOSGEY, I. S. OKEYO, A. M. 2007. Genetic improvement of smll ruminnts in low-input, smllholder production systems: Technicl nd infrstructurl issues. Smll Ruminnt Reserch, vol. 70, 2007, p. 76-88. MATIKA, O. Vn WYK, J. B. ERASMUS, G. J. BAKER, R. L. 2003. Genetic prmeter estimtes in Sbi sheep. Livestock Prod. Sci., 2003, vol. 79, p. 17-28. MATOS, C. A. P. THOMAS, D. L. GIANOLA, D. TEMPELMAN, R. J. YOUNG, L. D. 1997. Genetic 50

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