Embryonic mortality rate in pigs, sheep and goats ranges around 30%. It occurs mainly during the first month of pregnancy and mostly before implantation. In pigs, a second less important stage observed about Day 50 of pregnancy is resulting from overcrowding of the uterine horns. In these three species, chromosomal abnormalities such as centric fusions or reciprocal translocations cause the formation of embryos with unbalanced karyotypes which do not survive until parturition. This may considerably increase the basal loss. Several examples of major genes involved in embryonic mortality are reviewed though few cases are conclusive. The between breed and crossbred variability in embryo loss is reviewed. In pigs, large between breed variability independant of the ovulation rate is observed as well as significant individual and maternal heterotic effects. In sheep, this variability is less marked and almost no heterosis is observed. The within breed variability does not include an additive genetic component in the pig but is mainly related to the variability of the ovulation rate due both to genetic correlations and to maternal uterine effects, though the mechanism is not well understood. The success of selection experiments for prolificacy in sheep seems to be due to a lower correlation between ovulation rate and embryonic mortality than exists in the pig. The existence of pig and sheep breeds with low rates of embryonic mortality and the selection of highly prolific lines within these species provide ideal material for studies on embryonic mortality.

Timing and Extent of Embryonic Mortality in Pigs Sheep and Goats: Genetic Variability

The genetics of prenatal survival of pigs and rabbits: a review

Summary A review of recent swine crossbreeding experiments is presented and integrated with earlier work Variation among experiments in observed heterosis for specific crosses was large for reproduction and sow productivity traits However, standard errors of estimates were also large It seems likely that heterosis, expressed in absolute values or in percentage units, is different for specific crosses It is unclear whether these differences are large enough to warrant the use of unique parameter values for comparisons of alternate mating systems In addition to average heterosis values, average direct and maternal genetic effects are given

/pdf/crossbreeding-in-swine-experimental-results-1jdkis2k2q.pdf

Crossbreeding in swine: experimental results

A general review on pig genetics is given. The main topics covered are : karyotype and chromosomal abnormalities, coat colour, hereditary defects and disorders, disease resistance, immunogenetics, biochemical polymorphisms, linkages and syntenies, and quantitative traits of economic importance. As regards the latter field, special emphasis is put on the known influences of marker genes on performance traits. Lists of genes controlling coat colour, blood groups (erythrocyte antigens), and electrophoretic variants of blood serum proteins and blood cell enzymes are tabulated. A list of 29 genetic abnormalities which can be considered as probably monogenic in the pig is also given. The total number of presently identified loci is around 100.

/pdf/pig-genetics-a-review-1hdos66o4l.pdf

Pig genetics: a review

A crossbreeding experiment using Large White (LW) and Meishan (MS) pig strains was conducted. Direct, maternal and and-maternal additive genetic effects along with direct, maternal and paternal heterosis effects were estimated for litter productivity traits: total number born (TNB), number born alive (NBA), number weaned (NW), litter weight at birth (WB) and at 21 days (W21), either adjusted or not for litter size, and survival rate from birth to weaning (SR). Direct, maternal additive and direct heterosis effects were also estimated for sow traits: weight before farrowing (SWF) and at weaning (SWW), weight loss (SWL) and feed consumption (SFC) during lactation. Data from 267 litters farrowed by 117 sows were analysed. Between breeds additive differences in prolificacy are mainly maternal (3.7 ± 0.9, 4.2 ± 0.8 and 2.8 ± 0.8 piglets/litter in favour of MS for TNB, NBA and NW respectively). Maternal effects are also important, but in favour of LW, for adjusted litter weights. However, due to litter size differences, they are non-significant for unadjusted litter weights. Direct and grand-maternal differences are non-significant for all litter traits, except SR where grand-maternal effects are in favour of MS (4.1 ± 1.5%). Large additive differences also exist in sow traits: LW dams are heavier 57 ±

/pdf/estimation-of-crossbreeding-parameters-between-large-white-2zx8mkdk0k.pdf

R. K. Jonhson

Papers

Comparison of Productivity and Performance for Two-Breed and Three-Breed Crosses in Swine