Selection For Reproductive Traits Research Articles

The Reproduction Performance in Domestic Animals Controlled by Genetic Mechanism: A Review

Reproduction in domestic animal is a very complex process. The process starts from gamete formation, release, gamete transport, fertilization, embryo and fetal development until delivery of the offspring by the dam. Reproduction holds the most important role in determining the success of livestock farming, profit or loss. The genetic selection of the reproductive traits became an important program to find out the merit candidate dam and bulls. At early time, the selection for reproduction traits was based on the visually phenotypic performance, and this is maintained for long time until present time. In the next phase, the values of heritability for reproduction traits was chosen as a basis of selection. The molecular aspect used for reproductive mechanism and expression was noted beginning in the 2000s using Polymerase Chain Reaction – Restricted Fragment Length Polymorphism (PCR-RFLP) and Single Nucleotide Polymorphism (SNP). The newest technique is to explore not only the role of DNA in the programming the reproductive mechanism, but the the expression of gen (nucleic DNA) at the Ribonucleic Acid (RNA) at the outside level of the cell nucleus.
 Keywords: genetic factor, genetic material, SNP, reproduction process

REPRODUCTIVE TRAITS SELECTION IN NELORE BEEF CATTLE

Genetic breeding programs of beef cattle in Brazil are including new features, mainly related to reproductive efficiency.Thus, it is necessary to study the effectiveness of selection and quantify genetic gain for these traits in herds. This study estimated genetic and phenotypic parameters and genetic trends for reproductive traits used in breeding programs for Nelore beef cattle. The traits studied were the scrotal circumference (SC) at 365 and 450 days of age (SC365 and SC450), age at first calving (AFC) and gestation length, as a cow trait (GLcow) and a calf trait (GLcalf). The (co)variance components were obtained with the Restricted Maximum Likelihood Methodology in a single and double-trait analysis of the animal model. For scrotal circumference (SC365 and SC450), positive and favorable genetic gains were observed. For AFC, GLcow and GLcalf, the trends were favorable for selection, but without significant genetic gain. Selection for large SC may reduce AFC and improve female reproductive efficiency. The selection for reproductive traits (SC365, SC450, AFC and GL) may improve reproductive and productive efficiency of Nelore cattle, if used as a selection criterion.

Genetic Basis of Prolificacy in Sheep

The aim of any animal breeder is to get maximum possible profit from the domestic livestock. This can be achieved by improving the genetic potential by appropriate selection methods. The selection aimed at increasing fecundity will ultimately improve the reproduction rate and production efficiency in small ruminants. But selection for reproduction traits is usually difficult to achieve due to their low heritability values. So alternative selection method (Marker Assisted Selection) with higher accuracy in prediction of breeding value can be adopted for these traits. Therefore research community constantly searches some major genes that can act as marker influencing fertility in animals.

Selection for reproductive traits in white egg stock using independent culling levels

The objective of this study was to report the response to selection for fertility and hatchability in white egg layers strains, based on sire and dam performance, and the effects of inbreeding on these traits. Two selected white egg strains (CC and DD) from Embrapa´s poultry program under multiple trait selection were compared to a control strain (CCc). The control strain was established by randomly mating one male from each sire family to a non-related female from each dam family and was used to monitor genetic change in the selected lines. CC and DD were selected using family and individual information on hen-day egg production up to 40 weeks of age, egg weight, sexual maturity and 16-week-old body weight over five generations. Independent culling levels (ICL) were also used during population expansion to eliminate sires and dams with low fertility (FERT) and hatchability (HATC). Initially, FERT and HATC were over 90.0% in both selected and control strains. FERT and HATC of the selected and the control strains were compared during the last generation. FERT averages were 93.8, 93.8 and 94.4%, and HATCH averages were 93.2, 91.6 and 93.1% for CC, DD and CCc respectively. FERT and HATCH means were not different among strains. Estimated inbreeding increased at a rate of 0.4% per generation in all strains. Selection using ICL was able to effectively maintain the high initial FERT and HATC levels, and provide potential for high selection intensity in other traits. Inbreeding depression was not observed for any trait, indicating that selection compensated for any negative effects of inbreeding.

Lessons for the poultry industry gleaned from experiences with other commodity species

Do breeders really know how well or poorly they are managing reproduction? Poultry breeders could benefit from application of proven concepts of reproductive management used to exploit elite mammalian males, via selection for reproductive traits and extensive use of AI. Use of elite males could dramatically increase the impact of genes of economic importance transferred to the producer level. Testes weight has up to a 35-fold range among males within most lines of poultry, as does number of sperm that can be harvested from a male. These observations should not be ignored. Males with small testes will provide few sperm and they should be culled. Similarly, identification and elimination of males whose sperm are likely to have low fertilizing potential should be beneficial. Approaches to maximize harvest of those sperm produced by an elite male and minimize wastage of these valuable cells are emphasized. To this end, semen should be extended to allow insemination of a minimal volume containing just sufficient sperm consistent with the breeder's goal. Presumably, the goal should be obtaining the maximum number of offspring from a unique male or great-grandparent family, while minimizing cost of producing each chick. This goal might not require maximizing “fertility”. A 10-fold increase in dissemination of DNA from elite males to the next generation is realistic. Over three generations, this increase equals a 1,000-fold increase in the number of birds with the desirable traits! Appropriate biotechnology is available. Will decision makers evaluate new (to them) approaches and progress into the next millennium using modern technology, when cost-effective, or will they continue to manage reproduction with methods more than 50 yr old? Those who choose the latter path may risk extinction.

Implications of genetic changes in body composition on beef production systems

Changing the body composition of beef has implications for the entire beef production system. The dynamic nature of an animal's body composition and the production system itself make predictions of the implications of genetic change in body composition difficult. The cow-calf, stocker, and feeder segments of the production system will be affected differently. Leaner cattle tend to be slaughtered at heavier weights. Heavier weights effectively reduce composition differences of slaughter beef to less than the genetic differences. The effects of four pricing scenarios on slaughter weight and composition were evaluated for two leaner genotypes, one with no change in marbling and one with reduced marbling. A genetic difference of 1.0 yield grade at the same carcass weight resulted in slaughter beef that differed by .4 to 1.0 yield grade because of increased slaughter weights. Separate analyses suggested the stocker segment of beef production will be least affected by changes in body composition. Genotypes that are best fitted to slaughter requirements will have the most flexibility in types of stocker systems that can be used. The cow-calf segment of beef production has several options to adapt to leaner cattle. Management to reduce nutritional stress on leaner cows may be required by some producers. Increased selection for reproductive traits in cow genotypes may be needed. An alternative to selection for reproduction is terminal crossing to partially disassociate the slaughter animals' genotype from the cow's genotype.