Economic profit of most livestock enterprises is largely dependent of reproduction performance. Prolificacy is defined as number of offsprings produced in a single litter, is an important aspect of reproduction efficiency in most of farm livestock species. In addition to economic conditions, several environmental factors, including nutrition and health management conditions determine whether twining is needed or not. Generally, reproduction traits have low heritabilities and do not easily respond to classic selection strategies. However, use of genetic markers can efficiently accelerate genetic progression of prolificacy. Reproduction is a complex process which is influenced by many genes. The genes with major effects on fecundity are called fecundity (Fec) genes, which could be detected by genomic studies. Bone morphogenetic protein receptor 1B (BMPR1B), bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are three important fecundity genes. Many quantitative trait loci and causative mutations, associated with reproduction traits, have been reported in different species of the farm animals. However, their presence and effects are largely dependent on species, breeds and populations. Therefore, marker-assisted selection for genetic improvement of reproduction traits should be planned regarding genetic structure of the populations. Moreover, a prolific mother should have enough ability to feed her
