Comparative Study On Performance,Serum Biochemical Indices And Rumen Fermentation Parameters Of Lactating Dairy Cows With Different Genotypes

The purpose of this study was to investigate the differences in production performance,serum biochemical indexes,and rumen fermentation parameters in different genotypes of Chinese Holstein lactating cows.First,the Beta Casein（β-CN）genotype of 80 Chinese Holstein cows was identified by tail vein blood sampling.Usually,cows containing only A1β-casein are called A1A1 cows,those containing only A2 β-casein are called A2A2 cows,and those containing both A1 β-casein and A2 β-casein are called type A1A2 cows.According to the identification results of β-casein genotype of dairy cows,the dairy cows were divided into three groups:A1A1,A2A2 and A1A2.Eight cows were selected for each group and fed the same diet.The adaptation period was 7 d and the formal period was 56 d.Feed intake and milk production of the cows were recorded during the trial and feed,fecal,milk,blood and rumen fluid samples were collected and used for later analysis.The results are as follows:1.Identification of β-casein genotype in Chinese Holstein cows.The results showed that there were two genotypes of β-casein,A1 β-casein and A2 β-casein,in 80 Chinese Holstein dairy cows.Among them,there were 14 A1A1 cows,22 A2A2 cows and 44 A1A2 cows,the A2 allele frequency was 55%,the A1 allele frequency was 45%,and the A2 allele was slightly dominant.2.Comparison of growth performance,milk composition and apparent nutrient digestibility in different genotypes of cows.The results showed that:（1）There were no significant differences in dry matter intake（DMI）,milk yield and feed conversion rate（FCR）of A1A1,A2A2 and A1A2 cows（P>0.05）.（2）There were no significant differences in the lactose rate,total milk solids,milk urea nitrogen content and somatic cell count of A1A1,A2A2 and A1A2 cows（P>0.05）,the milk fat rate and milk protein rate of A2A2 cows were significantly higher than those of A1A1 and A1A2 cows（P<0.05）.（3）There was no significant difference in the digestibility of dry matter（DM）,crude protein（CP）,neutral detergent fiber（NDF）and acid detergent fiber（ADF）in A1A1,A2A2 and A1A2 cows（P>0.05）.3.Comparison of blood routine and serum biochemical indexes in different genotypes of cows.The results showed that:（1）There was no significant difference in blood routine indexes between A1A1,A2A2 and A1A2 cows（P>0.05）.（2）There was no significant difference in serum biochemical indexes among A1A1,A2A2 and A1A2 cows（P>0.05）.4.Comparison of rumen fermentation parameters and rumen microorganisms in different genotypes of cows.The results showed that:（1）The rumen fermentation parameters of A1A1,A2A2 and A1A2 cows were pH value,ammonia nitrogen（NH3-N）,microbial protein（MCP）,volatile acid（VFA）,acetic acid,propionic acid and butyric acid were not significantly different（P>0.05）.（2）There was no significant difference in Observed species,Shannon,Simpson,Chao 1 and ACE index between A1A1,A2A2 and A1A2 cows（P>0.05）.（3）The dominant flora at the rumen microbial phylum level of A1A1,A2A2 and A1A2 cows are Bacteroidetes,Firmicutes and Proteobacteria,and the dominant genus at the genus level is Prevotella.In conclusion,the β-casein of Chinese Holstein cows is polymorphic,and the A2 allele is dominant.Under the same diet and management conditions,A2A2 cows have better milk production traits than A1A1 and A1A2 cows,and can more effectively use the milk precursors in the rumen to synthesize milk fat and milk protein,which has higher utilization value.