Evaluation Of Production Performance In Different Genotype Dairy Cattle And Determination Of Relationships Of SNP's In GH And GHR To Milk Production Traits

The gene of excellent bull rapid expansion within global range with the popularity of artificial insemination technology, the genetic gains of dairy cattle was accelerated. Strict selection on bulls lead to inbreeding and genetic antagonisms of performances with functional traits for Holstein-Friesian are accompanied by unwanted side effects in metabolism, fertility, health, and longevity. Recently, changes in milk pricing have rewarded herds with high fat and protein percentages, and this has enhanced the ability of other breeds and breed crosses to compete with Holsteins on an economic basis. Crossbreeding may be an effective option for reducing the impact of inbreeding depression and improving the reproduction performance, health status and life span, to increasing the economic benefits.The objectives of this study were to compare three different genetic groups (Hybrids, Improved-hybrids and Pure Holsteins) and their offspring for milk performance, growth performance and reproduction performance, to evaluate the genetic improvement effects, and to reveal the essence of genetic improvement of different genetic groups from molecular level by detecting the single nucleotide polymorphisms (SNPs) of Growth Hormone (GH) and Growth Hormone Receptor (GHR) genes. In order to explore the method of combining phenotype selection and maker assistant selection (MAS) for dairy population improvement in current production system, and to provide the theoretical and practical basis for making optimum program of dairy population improvement in china conditions.The results were as followed:1. Milk and growth performances of different genetic groups were improved significantly by excellent Holstein bulls sired.2. The Improved-hybrids and pure Holsteins were not significantly different for milk yield and mature weight, but Improved-hybrids had significantly less birth weight and fewer days open, days to first breeding than pure Holsteins. Improved-hybrids is a viable choice to match the genotype of dairy herds to farm management in china conditions.3. Milk and growth performances of different genetic groups were improved with the degree of breeding, but there were antagonisms of milk performances with days open and days to first breeding.4. The polymorphism of GH was detected in the 4th intron, caused by C→T transition at 2017bp position. The T allele was positive effects for milk performances and the frequencies were rise gradually with the degree of breeding. The polymorphism of GH could be considered as the genetic maker for the milk performances.5. The polymorphism of GHR in the 8th exon was based on the mutation of T→A in 4962bp position, lead the phenylalanine changed to tyrosine. The polymorphism of the locus was no relationship with milk performances.