Genetic parameters for reproduction and lamb production and their components and liveweight, fat depth and wool production in Hyfer sheep

1994 ◽  
Vol 45 (2) ◽  
pp. 443 ◽  
Author(s):  
NM Fogarty ◽  
LD Brash ◽  
AR Gilmour
Keyword(s):  
Genetic Correlation ◽  
Litter Size ◽  
Genetic Parameters ◽  
Genetic Correlations ◽  
Production Traits ◽  
Wool Production ◽  
Reproduction Traits ◽  
Component Traits ◽  
Lamb Survival ◽  
Fleece Weight

Hyfer is a new composite breed suited to specialized lamb production and developed from Dorset (+), Booroola Merino (+)and Trangie Fertility Merino (+) genotypes. Genetic parameters estimated by restricted maximum likelihood methods are reported for liveweight, wool production and a range of reproduction and lamb production traits. Estimates of heritability were 0 44 � 0.10, 0.222 � 0-08 and 0.28 � 0.08 for liveweight, ultrasonic fat depth (C site) and fat depth adjusted for liveweight respectively, for 1454 rams averaging 14 months of age, which were the progeny of 130 sires. The genetic correlation for ram liveweight and fat depth was 0.06 � 0.17 and -0.30 � 0.16 with adjusted fat depth. Estimates of heritability for ewe liveweight at 12-18 months of age and greasy fleece weight at 11-19 months of age were 0.61 � 0.10 and 0.38 � 0.08 respectively, with a genetic correlation of 0.35 � 0.13, based on 1619 ewes, which were the progeny of 135 sires. A maternal effect was significant for ewe liveweight and its inclusion in the model reduced the estimate of heritability to 0.44 � 0.09. Young ewes were joined three times in two years in an accelerated 8-monthly lambing system, and joinings commenced in mid-February, late October and mid-June. The estimates of heritability for overall ewe performance were for lambs born 0.09 � 0.03, lambs weaned 0.04 � 0.02 and weight of lamb weaned 0 -06 � 0.02 (all per ewe joined). Heritabilities for the component traits were: fertility 0 -03 � 0 02, litter size 0.19 � 0.04 and lamb survival 0.07 � 0.03. Estimates of repeatability for the corresponding traits ranged from 0.11 to 0.15, except for litter size (0.26 � 0.02). Estimates of heritability for lambs born, lambs weaned and weight weaned were higher for the first joining than when estimates were based on three joining records. This was associated with higher heritability for fertility from first joining (0.10 � 0.06) than for all three records and the reverse for lamb survival. Estimates of heritability for mean ewe performance were considerably higher and in agreement with the values predicted from the repeatability analyses and number of records, illustrating the value of using repeated ewe records for selection. The genetic correlations between the component traits and overall measures of lamb production were not high enough to consider using component traits as indirect selection criteria. The genetic correlations of liveweight with reproduction traits were positive, but generally not significant, and ranged from 0.01 to 0.63, except for litter size (-0.19 � 0.17). The genetic correlations of greasy fleece weight with reproduction traits were generally smaller than those for liveweight, were not significant and ranged from -0.12 to 0.32. These results, together with others, will be used to compile parameter sets for use in LAMBPLAN to provide meatsheep breeders with comprehensive breeding objectives incorporating growth, leanness, wool and reproduciton.

Genetic parameters for Australian maternal and dual-purpose meatsheep breeds. I. Liveweight, wool production and reproduction in Border Leicester and related types

1994 ◽  
Vol 45 (2) ◽  
pp. 459 ◽  
Author(s):  
LD Brash ◽  
NM Fogarty ◽  
SA Barwick ◽  
AR Gilmour
Keyword(s):  
Genetic Correlation ◽  
Litter Size ◽  
Genetic Parameters ◽  
Genetic Correlations ◽  
Heritability Estimate ◽  
Reproductive Traits ◽  
Phenotypic Correlation ◽  
Data Set ◽  
Reproduction Traits ◽  
Fleece Weight

Analyses of two separate Border Leicester data sets are reported. In the first set, genetic parameters were estimated for 14 month liveweight and greasy fleece weight from 1312 ewe and ram records representing 75 sires of the Border Leicester and Glen Vale breeds (a related genotype) using derivative-free REML procedures. The heritability estimate for liveweight was 0.24 � 0.07 and greasy fleece weight was 0.17 � 0-05, with the genetic correlation being -0 21 � 0 -30 and phenotypic correlation 0.54 � 0.02. In the second data set, reproductive performance was analysed and genetic parameters were estimated from 7395 joining records for 1604 ewes, representing 165 sires, from two Border Leicester stud flocks. Reproduction traits analysed were fertility (ewes lambing of ewes joined), litter size (lambs born per ewe lambing) and lambs born (per ewe joined). The studs differed in performance for all reproductive traits; fertility (67 v. 82%), litter size (1-27 v. 1-43) and lambs born (85 v. 117%). The estimates of heritability and repeatability respectively for ewe performance were: fertility 0.01 � 0.01 and 0.05 � 0 01, litter size 0.01 � 0.02 and 0.05 � 0.01, lambs born 0.00 � 0.01 and 0.06 � 0.01. Estimates of heritability for average ewe lifetime performance were 0.04% 0.05 for fertility, 0-02 �0.05 for litter size and 0.03 � 0.05 for lambs born, based on averages of 4.6 joining and 3.5 litter size records for ewes. The genetic correlations between lambs born and its components fertility (0.96 � 0.18) and litter size (0.83 � 0.44) were high, with the genetic correlation between fertility and litter size being 0.65 � 0.52. Implications for breeding programs for Border Leicester flocks within LAMBPLAN are discussed.

scholarly journals Genetic parameters of production and reproduetive traits in on a farm tested Danish Large White and Landrace swine in Greece

2000 ◽  
Vol 43 (3) ◽  
pp. 287-298
Author(s):  
J. Bizelis ◽  
A. Kominakis ◽  
E. Rogdakis ◽  
F. Georgadopoulou
Keyword(s):  
Maximum Likelihood ◽  
Genetic Correlation ◽  
Genetic Parameters ◽  
Genetic Correlations ◽  
Production Traits ◽  
Likelihood Methods ◽  
Large White ◽  
Reproduction Traits ◽  
Maximum Likelihood Methods ◽  
Genetic And Phenotypic Correlations

Abstract. Production and reproduetive traits in Danish Landrace (LD) and Large White (LW) swine were analysed by restricted maximum likelihood methods to obtain heritabilities as well as genetic and phenotypic correlations. Production traits were: age, backfat thickness (BT), muscle depth (MD) and the ratio BT/MD, adjusted to Standard bodyweight of 85 kg. Reproduction traits were: number of pigs born (NB) and number of pigs weaned (NW) per sow and parity. Heritabilities for age, BT, MD and BT/MD were 0.60, 0.44, 0.51 and 0.42 for LD and 0.36, 0.44, 0.37 and 0.45 for LW, respectively. Genetic correlations between age and BT were −0.22 in LD and – 0.44 in LW. The genetic correlation between age and MD was close to zero in both breeds. Genetic correlation between BT and MD were −0.36 and −0.25 in LD and LW, respectively. Heritabilities for NB were 0.25 in LD and 0.13 in LW while heritabilities for NW were close to zero in both breeds. Genetic correlation between NB and NW was 0.46 and 0.70 in LD and LW, respectively.

Reproductive performance and genetic parameters for Australian Dorset Sheep

1994 ◽  
Vol 45 (2) ◽  
pp. 427 ◽  
Author(s):  
LD Brash ◽  
NM Fogarty ◽  
AR Gilmour
Keyword(s):  
Litter Size ◽  
Reproductive Performance ◽  
Genetic Improvement ◽  
Genetic Correlations ◽  
Reproductive Traits ◽  
Reproductive Rate ◽  
Parameter Estimates ◽  
Reproduction Traits ◽  
Component Traits ◽  
Lamb Survival

Reproductive performance of ewes in a large Dorset stud flock is reported. The data included 2488 ewes with 10016 joining records over 25 years. Average performance for reproductive traits were: fertility 92%, litter size 1.31, neonatal lamb survival 91%, lamb survival to weaning 85%, with overall lambs born 1.20 and lambs weaned 1.02 per ewe joined. Differences between breeds (Poll Dorset and Dorset Horn), season of birth (spring and autumn) and season of joining (spring and autumn) were significant for most reproduction traits. Linear and quadratic regressions for age of ewe at joining were highly significant for all traits (P < 0.001) with maximum performance between three and six years of age. Estimates of heritability for ewe reproductive traits were: 0.062 � 0-02 for number of lambs born and 0.04 � 0.01 for number of lambs weaned per ewe joined, and component traits, 0.02 �0 -01 for fertility, 0 08 � 0 -02 for litter size and 0.00 � 0.01 for lamb survival. Estimates of repeatability were less than 0.14 for all the reproduction traits, which resulted in substantially higher predicted heritabilities when repeated records were used. Heritability estimates for average ewe lifetime performance, with approximately four records, were 0.08 � 0 06 for lambs born, 0.12 � 0.05 for lambs weaned, 0.08 � 0.04 for fertility, 0.l9 � 0 -04 for litter size and zero for lamb survival. The genetic correlations between litter size and lambs born and weaned were close to unity, whereas those for fertility were lower and declined from lambs born (0.6l � 0.22) to lambs weaned (0-45 � 0.30). The estimated heritability for ewe longevity, defined as the number of years the ewe remained in the breeding flock, was 0.00 � 0.03. The potential for genetic improvement in reproductive rate is discussed in relation to other reports in the literature and in the context of the roles of the Dorset breed in the Australian lamb industry. Increased reproductive rate in Dorset flocks impacts on stud profitability and the rate of genetic improvement from selection for other traits such as liveweight. The parameter estimates derived will be used in compiling breed-specific parameter sets for genetic evaluation in LAMBPLAN.

Genetic parameters for Australian maternal and dual-purpose meatsheep breeds. II. Liveweight, wool and reproduction in Corriedale sheep

1994 ◽  
Vol 45 (2) ◽  
pp. 469 ◽  
Author(s):  
LD Brash ◽  
NM Fogarty ◽  
AR Gilmour
Keyword(s):  
Litter Size ◽  
Genetic Correlations ◽  
Fibre Diameter ◽  
Dual Purpose ◽  
Scrotal Circumference ◽  
Average Fibre Diameter ◽  
Reproduction Traits ◽  
Component Traits ◽  
Average Fibre ◽  
Fleece Weight

Performance of sheep from a large Corriedale stud flock was assessed. Weaning and yearling liveweights, greasy and clean fleece weights, clean fleece yield and average fibre diameter records on approximately 3000 animals representing 64 sires were analysed. Also scrotal circumference of 1009 rams representing 27 sires were analysed. Some 3740 reproduction records over 11 years, for 980 ewes representing 114 sires, were also analysed. Heritability estimates were 0 34 �0.07 for weaning liveweight, 0.132 � 0.04 for yearling liveweight, 0.32 � 0.07 for greasy and 0.29 � 0.07 for clean fleece weights, 0.534 � 0 10 for clean fleece yield, 0-56 � 0 10 for yearling and 0 62 � 0 - 14 for hogget fibre diameters and 0.l5 � 0.11 for scrotal circumference. The genetic correlations between liveweight and fleece weight ranged from 0.13 to 0.34, and those for liveweight and fibre diameter were close to zero. The genetic correlations of scrotal circumference with liveweight and wool traits were positive and moderate. Reproductive performance in the flock was high, with fertility 92% and litter size 1.62, resulting in 148% lambs born and 130% lambs tagged alive of ewes joined. Estimated heritabilities for reproduction traits were 0-03 � 0.02 for lambs born and for lambs tagged, and the component traits, fertility 0 01 � 0 -02, litter size 0.04 � 0.03 and neonatal lamb survival was zero. Lambing date had a heritability of 0.06 � 0.03. Estimates of repeatability ranged from 0-04 � 0-01 for fertility to 0.07% 0.02 for lambs tagged and lambing date. Predicted heritabilities for the average of 3.8 records per ewe generally agreed with those estimated for average ewe lifetime performance, which ranged from 0.02 � 0.08 for fertility to 0.12 � 0.09 for lambs tagged and 0.l3 � 0.09 for lambing date.

Performance of crossbred progeny of Trangie Fertility Merino and Booroola Merino rams and Poll Dorset ewes. 3. Reproduction, liveweight and wool production of adult ewes

1995 ◽  
Vol 35 (8) ◽  
pp. 1083 ◽  
Author(s):  
NM Fogarty ◽  
DG Hall
Keyword(s):  
Birth Weight ◽  
Litter Size ◽  
Significant Variation ◽  
Ovulation Rate ◽  
Average Birth Weight ◽  
Wool Production ◽  
Component Traits ◽  
Lamb Survival ◽  
Fleece Weight ◽  
Almost All

Reproduction, liveweight and wool production are reported for 4 cohorts of 377 Trangie Fertility x Dorset (TD) and 261 Booroola x Dorset (BD) ewes over 6 years. The BD ewes were 3-4 kg lighter (P<0.001) and had a higher ovulation rate prior to joining in February-March (2.37 � 0.03 v. 1.65 � 0.03) than TD ewes. This resulted in a higher litter size (2.07 � 0.03 v. 1.66 � 0.04) and number of lambs born per ewe joined (1.92 � 0.04 v. 1.56 � 0.04) for the BD ewes. Lamb survival was lower from BD than TD ewes (0.71 � 0.02 v. 0.85 � 0.02), so that the 2 ewe strains weaned the same number of lambs. The growth rate of lambs was lower from the BD ewes and overall they weaned 3.8 kg less (P<0.001) weight of lamb than TD ewes. Chill (index of environmental conditions at lambing), litter size and average birth weight of lambs in the litter (linear and quadratic) affected (P<0.001) lamb survival. At moderate levels of chill there was little difference in survival of single and twin lambs from BD and TD dams when birth weight was 4-5 kg, but survival declined more rapidly for progeny of BD ewes at lower birth weight. Under severe lambing conditions survival was depressed more for lambs born from BD ewes than TD ewes. Almost all ewes expressed oestrus over the 3, 6-week periods, December-January, January-February and March (joining). There was significant variation (P<0.001) in incidence of oestrus due to year and age (linear and non-linear), but not liveweight at joining, and there was little difference between ewe strains. Similarly, for post-lambing oestrus (to fit 8-monthly joining) and post-lambing anoestrous interval, there was little difference between strains, but year and age were highly significant (P<0.001). BD ewes had a lower (P<0.001) greasy fleece weight (3.76 v. 3.86 kg), than TD ewes. BD ewes were classified as either carriers (F+) or non-carriers (++) of the FecB gene, which was significant (P<0.001) for ovulation rate (+1.14 ovulations), litter size (+0.8 lambs), lamb survival (-18%), lambs born per ewe joined (+0.64 lambs) and total weight of lamb born per ewe joined (0.5 kg, P<0.01). The effect of the FecB gene was non-significant for lamb survival when litter size and lamb birth weight (P<0.001) were included in the model. Repeatability estimates based on over 3 records per ewe were about 0.2 for lambs born, weight of lamb born, lambs weaned and weight of lamb weaned per ewe joined. Component traits ranged from 0.27 for litter size to 0.10 for lamb survival, with fertility intermediate (0.15). Greasy fleece weight (0.72) and ovulation rate (0.41) had high repeatabilities with post-lambing anoestrous interval being low (0.11). Repeatability for ovulation rate was reduced to 0.34 when F+ ewes were excluded.

Genetic and phenotypic trends and parameters in reproduction, greasy fleece weight and liveweight in Merino lines divergently selected for multiple rearing ability

2004 ◽  
Vol 44 (8) ◽  
pp. 745 ◽  
Author(s):  
S. W. P. Cloete ◽  
A. R. Gilmour ◽  
J. J. Olivier ◽  
J. B. van Wyk
Keyword(s):  
Genetic Correlations ◽  
Annual Production ◽  
Production Traits ◽  
Genetic Progress ◽  
Additive Variance ◽  
Genetic Changes ◽  
Environmental Correlations ◽  
Breeding Values ◽  
Reproduction Traits ◽  
Fleece Weight

Genetic and phenotypic trends and parameters were estimated for reproduction, fleece weight and liveweight in a South African Merino population, divergently selected from 1986, either for (H line) or against (L line) maternal multiple rearing ability. Annual reproduction, ewe greasy fleece weight and pre-joining liveweight data were recorded on 809 Merino ewes, from 1986 to 2002. Phenotypic trends indicated divergence in reproduction traits between the H and L lines. The direct additive variance ratio (h2 ± s.e.) for day of lambing was 0.08 ± 0.02. Estimates of h2 for reproduction traits were: 0.10 ± 0.02 for number of lambs born per ewe; 0.04 ± 0.02 for number of lambs weaned per ewe; and 0.04 ± 0.02 for weight of lamb weaned per ewe, corrected for the gender of the lamb. Corresponding h2 estimates for annual production were 0.57 ± 0.06 for greasy fleece weight and 0.48 ± 0.06 for ewe liveweight at joining. Service sire only exerted a significant (P<0.05) effect on day of lambing, but it accounted for merely 2% of the overall phenotypic variation. Ewe permanent environment variance ratios (c2ewe) for the reproduction traits were: 0.07 ± 0.03 for number of lambs born per ewe; 0.11 ± 0.03 for number of lambs weaned per ewe; and 0.11 ± 0.03 for total weight of lamb weaned per ewe. Corresponding c2ewe estimates for annual production traits were 0.14 ± 0.05 for greasy fleece weight and 0.27 ± 0.06 for ewe joining weight. Genetic and ewe permanent environmental correlations between measures of reproduction exceeded 0.7. Genetic correlations of reproduction traits with greasy fleece weight were low and variable in sign. Genetic correlations of reproduction traits with ewe joining weight were positive and particularly high for weight of lamb weaned. Permanent environmental correlations of reproduction traits with greasy fleece weight and joining weight were generally low to moderate. Genetic trends for the H and L lines (derived from averaged direct breeding values within birth years) were divergent (P<0.01) for all reproduction traits. Expressed as percentage of the overall least squares means of the respective traits, breeding values in the H line increased annually, with 1.3% for lambs born per ewe, 1.5% for lambs weaned per ewe and by 1.8% for weight of lamb weaned per ewe. Corresponding trends in the L line were, respectively, –0.6%, –1.0% and –1.2% per year. Substantial genetic progress in annual lamb output was attainable, despite relatively small h2 estimates. This response was achieved without unfavourable genetic changes in wool and liveweight.

Genetic and phenotypic parameters for reproduction, production and bodyweight traits in Australian fine-wool Merino sheep

2018 ◽  
Vol 58 (2) ◽  
pp. 207 ◽  
Author(s):  
S. Dominik ◽  
A. A. Swan
Keyword(s):  
Genetic Relationships ◽  
Genetic Correlations ◽  
Fibre Diameter ◽  
Careful Consideration ◽  
Production Traits ◽  
Merino Sheep ◽  
Wool Production ◽  
Phenotypic Correlations ◽  
Reproduction Traits ◽  
Definition Of

The present study estimated phenotypic and genetic relationships between wool production, reproduction and bodyweight traits in Australian fine-wool Merino sheep. The data for the study originated from the CSIRO Fine Wool Project, Armidale, Australia. Data on wool characteristics, measured at ~10 and 22 months of age, bodyweight and several reproduction traits across consecutive lambing opportunities were analysed. The genetic correlations were moderately negative between fibre diameter measured as yearling and adult, and lamb survival (rg = –0.34 ± 0.15 and rg = –0.28 ± 0.14 respectively) and total number of lambs weaned (rg = –0.32 ± 0.21 and rg = –0.40 ± 0.21 respectively). The genetic correlations of yearling and adult greasy and clean fleece weights with number of lambs weaned and fecundity showed moderately to highly negative relationships and a moderately negative correlation with the number of fetuses at pregnancy scanning. Phenotypic correlations between reproduction and wool production traits were estimated to be zero, with the exception of bodyweight showing low to moderate positive phenotypic correlations with total number of lambs born and weaned. Genetic variances were generally low for the reproduction traits and resulted in low heritability estimates (from h2 = 0.03 ± 0.01 to h2 = 0.12 ± 0.13), with the exception of total number of lambs born (h2 = 0.25 ± 0.03). The study indicated that parameter estimation and trait definition of lifetime reproduction records require careful consideration and more work in this area is required.

The genetic foundation of fitness and reproduction traits in Australian pig populations. 2. Relationships between weaning to conception interval, farrowing interval, stayability, and other common reproduction and production traits.

1996 ◽  
Vol 47 (8) ◽  
pp. 1275 ◽  
Author(s):  
E Tholen ◽  
KL Bunter ◽  
S Hermesch ◽  
HU Graser
Keyword(s):  
Genetic Parameters ◽  
Performance Test ◽  
Genetic Relationships ◽  
Average Daily Gain ◽  
Genetic Correlations ◽  
Data Sets ◽  
Production Traits ◽  
Breeding Programs ◽  
Reproduction Traits ◽  
Daily Gain

Data sets from 2 large Australian piggeries were used to estimate genetic parameters for the traits weaning to conception interval (WCIi-l,i) and farrowing interval (FIi-l,i), number born alive (NBAI), average piglet birthweight (BWi), 21-day litter weight (W21i), and sow stayability (STAYli) recorded for each ith parity, as well as sow average daily gain (ADG) and backfat (BF) recorded at the end of performance test. Over parities and herds, heritabilities for each trait were in the ranges: WCI/FI, 0.0-0.10; NBA, 0.09-0.16; BW, 0.11-0.35; W21, 0.12-0.23; STAYli, 0.02-0.09; ADG, 0.35-0.37; BF, 0.36-0.45. Genetic correlations between NBAl and NBA from later parities were significantly different from 1. In addition, in 1 herd negative genetic correlations (rg = -0.04 to -0.25) were found between sow stayability traits and NBA1, but not NBA recorded in later parities. Stayability was Unfavourably correlated with ADG and BF, and favourably correlated with WCI12. However, WCI12 was unfavourably correlated genetically with BF (rg = -0.24) but uncorrelated with ADG. Antagonistic relationships also existed between NBA and BW, NBA and W21, and BW and STAY. In addition to the traditional traits currently included in pig-breeding programs (e.g. ADG, BF, and NBA), traits such as WCI, BW, and STAY should also be considered as selection criteria to minimise the detrimental effects of antagonistic genetic relationships between traits.

Genetic parameters for lamb weight at different ages and wool production in Baluchi sheep

1997 ◽  
Vol 65 (2) ◽  
pp. 247-255 ◽  
Author(s):  
M. H. Yazdi ◽  
G. Engström ◽  
A. Näsholm ◽  
K. Johansson ◽  
H. Jorjani ◽  
...  
Keyword(s):  
Weight Gain ◽  
Genetic Correlation ◽  
Genetic Parameters ◽  
Genetic Correlations ◽  
Phenotypic Variance ◽  
North East ◽  
Native Breed ◽  
Fleece Weight ◽  
Maternal Heritability ◽  
Weight Gain Measures

AbstractThe Baluchi breed is the most common native breed of Iran adapted to harsh environments in the eastern parts of the country. The data used in the present study, collected from two research flocks at the Abbasabad sheep breeding station in north-east Iran, included 20 534 animals descended from 363 sires, 5992 dams, 282 maternal grandsires, and 2865 maternal granddams during the period 1966 to 1989. The traits recorded were: birth weight (BW), weaning weight (WW), weight at 6 months (W6), weight at 12 months (YW), pre-weaning gain (WG), post-weaning gain (PWG), lamb fleece weight (LFW), ewe fleece weight sheared before first joining (FW1) and adult ewe fleece weight (FW). Genetic parameters, estimated with restricted maximum likelihood and a two-trait animal model, were similar in the two flocks. Direct heritabilities for the various body weight traits were moderate and varied between 0·13 and 0·32, while the maternal heritabilities were low and varied between 0·01 and 0·12. Direct and maternal genetic correlations between WW and weights at later ages were moderate to high (0·59 to 0·96). Direct heritabilities of weight gain measures varied between 0·12 and 0·19, while no significant maternal influence on either of these weight gain measures could be detected. The estimates of direct genetic correlation between WG and PWG were positive and varied between 0·54 and 0·74, while negative maternal genetic correlation (0·17 on average) between WG and PWG was detected. For LFW, direct heritability was low and no maternal heritability could be shown. For FW1, both direct and maternal genetic influences were demonstrated (0·07 to 0·26). Direct genetic correlation between LFW and FW1 was very low and close to zero, while maternal genetic correlation was positive and relatively high (0·72 on average). The relative contributions to phenotypic variance from variance components due to common environmental effects ranged from 0·01 to 0·15 for all traits. The repeatability of FW was low (0·03 to 0·12).

Variation in reproduction and production of Poll Dorset ewes

1994 ◽  
Vol 45 (2) ◽  
pp. 415 ◽  
Author(s):  
DG Hall ◽  
AR Gilmour ◽  
NM Fogarty
Keyword(s):  
Litter Size ◽  
Environmental Effects ◽  
Reproductive Performance ◽  
Reproductive Traits ◽  
Late Summer ◽  
Reproductive History ◽  
Reproduction Traits ◽  
Lamb Survival ◽  
Fleece Weight ◽  
One Year

Poll Dorset ewes were joined to Booroola Merino (n = 22) or Trangie Fertility Merino (n = 26) rams in single sire joinings during late summer/autumn of 1978, 1979, 1980 and 1981. Rams were changed each year and there were 1678 individual ewe joinings. A maximum of 527 ewes were used in any one year, and they represented 14 studs and varied in age, reproductive history and liveweight. The traits, litter size, maternal lamb survival, lambs weaned per ewe lambing and weight of lamb weaned per ewe lambing (kg at 100 days) were analysed for the effect of year, stud, age, lambs born and ewe liveweight. Litter size averaged 1-37, maternal lamb survival 0.70, and number of lambs weaned per ewe was 0.94. There were large variations in the reproductive traits due to year and stud and lesser effects due to age. Each extra kilogram of ewe liveweight at joining increased litter size by 0.012 and weight of lamb weaned by 0.39 kg, but had no significant effect on maternal lamb survival or number of lambs weaned. Multiple-bearing ewes weaned 0.72 more lambs and 16 - 2 kg more lamb weight than single-bearing ewes. Lamb survival was similar for singleand multiple-bearing ewes. Greasy fleece weight averaged 2.2 kg ewe-' and single bearing ewes produced 0.19 kg/ewe more than multiple-bearing ewes. Dystocia caused 53% and starvation/mismothering/exposure caused 23% of lamb deaths; the proportion of deaths due to starvation/mismothering/exposure increased with increasing ewe joining liveweight. The large variation between studs in reproductive performance partly reflected genetic differences between Poll Dorset flocks which could be exploited. Estimates of heritabilities ranged from 0.06 to 0.14 � 0.10 for the reproductive traits and were 0.10 � 0.12 for ewe liveweight and 0.16 � 0.20 for greasy fleece weight. However much of the between stud variation may also have arisen from early environmental effects. Estimates of repeatability ranged from 0.06 to 0.l5 � 0 05 for reproduction traits and were 0.44 � 0.06 for ewe liveweight at joining and 0.56 � 0.08 for greasy fleece weight.

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