A crossbreeding program between Ardi Saudi goats (A) with the Syrian goats (Damascus, D) was started in
2006 in two experiments (Jouf and Qassim) applying bio-techniques of estrous synchronization and artificial
insemination to improve milk and meat production. In rabbits, few numbers of new lines were synthesized in our
Arabian countries using different criteria and methods of selection and crossbreeding. In this concept, Saudi 2 and
APRI rabbits (as maternal lines) and Alexandria and Saudi 3 (as paternal lines) and Moshtohor (as multipurpose
line) were being formed to be convenient in hot climate. The most common selection criteria used in selection
programs to develop new maternal lines were related with litter size at birth or at weaning and milk production,
while in paternal lines, post-weaning daily gain or marketing weight are commonly selected individually. Spanish
V-line rabbits genetically selected for more than 35 generations were introduced in various developing countries (as
alive animals or as frozen embryos) and by using recent bio-techniques and applying selection and /or crossbreeding
programs with local lines, this line was widely distributed in some hot countries of the world like Egypt and Saudi
Arabia.
In rabbits, direct selection had little or moderate effects on litter and lactation traits, while it had considerable effects
on post weaning growth and feed conversion. Direct heterotic effects were evidenced for litter size, litter weight, and
milk yield. Crossbred does and dams gave favourable heterotic effects on litter traits, milk yields and components
and milk conversion ratio. Direct heterosis for body weights raised in hot countries were mainly positive and
ranging from 1.3 to 14.5 %, but the estimates for maternal heterosis were mainly low and ranging from 0.2 to 5.3 %.
Crossbred dams gave moderate maternal heterotic effects ranging from 4.8 to 18.7%. Neither individual heterosis,
nor maternal heterosis were evidenced for meat quality traits. Crossbred bucks were associated with an existence of
heterotic effects in ejaculate volume (11.6%), sperm concentration (10.5 %), percentages of motile (9.8%) and living sperms, along with a reduction in percentages of abnormal (-10.8%) and dead sperms (-23.5%). Crossbred dams gave maternal heterotic effects on some semen parameters in their progeny of crossbred bucks. The recent molecular technologies were used only in developing countries to detect the associations between phenotypic traits and genetic markers and three markers were detected for litter and milk traits and body weights. In goats, the favourable estimates of direct and maternal heterosis for some litter and lactation traits and most growth traits would be an encouraging factor for the goat producers in hot climate countries to use crossbred does and dams on commercial scale. Crossbred dams had considerable maternal heterotic improvements in their crossbred daughters in terms of larger litter size, heavier litter weight at birth and weaning, pre-weaning mortality and milk production and components (2.4 to 28.1 %). Crossbred dams could produce crossbred bucks characterized by higher volume of ejaculate, higher semen quality with more concentration and motile sperms, along with lesser percentages of abnormal sperms and dead sperms than their crossbred daughters. Direct recombination losses were of little importance for the majority of the traits and they were generally lower than the estimates of direct heterosis.
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