Effects Of Concentrate Supplement Protein Levels On Lactation Performance,Rumen Fermentation And Microflora In DHF1

Protein is one of the material foundations of life,and it has been widely used to improve the production performance of animals by adjusting the protein source and protein content in the diet.The dairy sheep industry is in its infancy in my country,and there is no clear standard for dairy sheep breeding.Therefore,the experiment was conducted to investigate the effects of concentrate supplementation on lactation performance,rumen fermentation and rumen microflora of first-generation of East Friesian and Hu crossbred dairy sheep,and to provide scientific basis for dietary protein level formulation of dairy sheep.Twenty-four dairy sheep（F1:East Friensian sheep♂×Hu sheep♀）（2nd parity,2nd lactation month）were randomly divided into 4 groups with 3 replicates per group and 2 sheep per replicate.The dietary protein level were 16%（low protein group）,18%（medium low protein group）,20%（medium high protein group）and 22%（high protein group）,respectively.Concentrate supplemention was fed quantitatively（1.8kg/d）and roughage was freely consumed.The experiment lasted for 75 days,and the pre-experiment lasted for 15 days and the formal experiment lasted for 60days.Mainly the following results are obtained:1.Effects of protein levels of concentrate supplementation on lactation performance and nutrient apparent digestibility of DHF1 dairy sheep（1）The dietary protein level had no significant effects on Average daily gain（ADG）and Dry matter intake（DMI）（P>0.05）.When the protein level was higher than 16%,the average daily protein intake of DHF1 was significantly increased with the increase of dietary protein level（P<0.01）.（2）At days 11 to 20 and 0 to 60 during the formal experiment,the average daily milk yield in 20%CP group was higher than that in 16%CP group and 18%CP group（P<0.05）,but there was no significant difference between 20%CP group and 22%CP group;The average milk yield（1.28 kg/d）in 20%CP group was the highest in the whole experiment period;Different protein levels had no significant effect on milk composition.（3）The concentrate supplementation of different protein levels had no significant effects on DM,Neutral detergent fiber（NDF）,Acid detergent fiber（ADF）and CP digestibility among all groups（P>0.05）.However,CP digestibility increased with the increase of dietary CP level.2.Effects of protein levels of concentrate supplementation on rumen fermentation and microflora of DHF1 dairy sheep（1）Protein level of concentrate supplementation had no significant effect on microbial Shannon index,Simpson index and Pielou＿e index of rumen fluid（P>0.05）.The index of Chao1 in 18%CP group at the 30th day was significantly lower than that of the other three groups（P<0.05）.Observed species index of 20%CP group was significantly higher than that of 18%CP group（P<0.05）.The Chao1 index of 20%CP group at the 60th day was significantly higher than that of 16%CP group and 18%CP group（P<0.05）.（2）There was no significant difference in dominant bacteria among the four groups,which were Firmicutes and Bacteroidetes.The dominant bacteria in the rumen of each treatment group were Prevotella＿1 and Prevotella＿7 at the 30th day of the trial period.The abundance of Prevotella＿7 in 18%CP group was significantly higher than that in 16%CP group and 22%CP group（P<0.05）;The abundance of Christensenellaceae＿R-7＿group in 16%CP group was significantly higher than that in 18%CP group（P<0.05）.The relative abundance of Ruminal clostridium＿6 in 20%CP group was significantly higher than that in the other three groups（P<0.05）.The relative abundance of Muribaculaceae and[Ruminococcus]＿Gauvreauii＿group in 22%CP group was significantly higher than that in the other three groups（P<0.05）.At the60th day of the trial period,the dominant bacteria among the four groups were Ruminococcaceae＿UCG-014 and Rikenellaceae＿RC9＿gut＿group,but there was no significant difference among the four groups（P<0.05）.（3）Different protein levels had no significant effects on rumen p H,ratio of acetic acid to propionic acid,isobutyric acid,valeric acid and isovaleric acid（P<0.05）.At the 30th day of the trial period,the concentration of NH₃-N in20%CP group was significantly higher than that in 18%CP group（P<0.05）.The acetic acid content in 20%CP group was significantly higher than that in 18%and 22%CP groups（P<0.01）,significantly higher than that in 16%CP group（P<0.05）.The content of total volatile fatty acids（TVFA）in 20%CP group was significantly higher than that in the other three groups（P<0.01）,the butyric acid content in 20%CP group was significantly higher than that in the other three groups（P<0.05）.At the 60th day of the trial period,the concentration of NH₃-N in 16%CP group was significantly lower than that in 20%CP group and 22%CP group（P<0.05）.The contents of acetic acid and TVFA in 16%CP and 20%CP groups were significantly higher than those in 18%CP group（P<0.05）,the propionic acid content in 16%and 20%CP groups was significantly higher than that in 18%CP groups（P<0.01）.（4）p H,NH₃-N,acetic acid,propionic acid,butyric acid,isobutyric acid,valeric acid,isovaleric acid and TVFA were significantly correlated with rumen bacteria（P<0.05）.There was no significant correlation between milk yield and rumen bacteria at the 30th day of the trial period（P<0.05）,The milk yield at the 60th day was positively correlated with Shuttleworthia,Christensenellaceae＿R-7＿group,Ruminococcus＿gauvreauii＿group,Ruminococcus＿UCG-010,Family＿XIII＿AD3011＿group and Ruminococcaceae＿UCG-004,and was significantly negatively correlated with the relative abundances of[Eubacterium]＿Ruminantium＿group,Prevotella＿7 and Ruminococcus＿1（P<0.05）.This study showed that the dietary protein level did not affect the dominant bacteria in rumen fluid,but 20%CP group could improve the relative abundance of probiotics,significantly increase the rumen NH₃-N,acetic acid and total volatile fatty acid contents,provide more energy for the body,significantly increase milk yield of DHF1 dairy sheep.Therefore,the 16%,18%,20%and 22%CP levels for DHF1 dairy sheep,the optimal crude protein level of concentrate supplemention is 20%.