Effects Of The Ratio Of Dietary Concentrate To Forage On Blood Indices,Rumen Fermentation And Intestinal Microflora Of Cows During Early Gestation

The present experiment was conducted to investigate the effects of dietary the ratio of concentrate to forage ratio on blood indices,rumen fermentation and intestinal microbiota of cows during early pregestation.In order to provide theoretical basis for scientific feeding of cows in early pregnancy,the optimal ration of concentrate to forage was tested.Sixty healthy Angus cows during the first trimester of pregnancy（pregnancy 30+/-3 days）were randomly divided into three groups:low concentrate group（concentrate to forage ratio 40:60）,medium concentrate group（concentrate to forage ratio 50:50）and high concentrate group（concentrate to forage ratio 60:40）.The details are as follows:Experiment 1:The initial and final body weights of cows were measured at the beginning and end of the experiment,and the whole period weight gain,average daily gain,weight and body size indexes of calves were calculated.The feed intake and nutrient digestibility of cows were measured.With the increase of concentrate ratio in diet,total weight gain,average daily gain,dry matter（DM）digestibility,dry matter intake（DMI）and organic matter（OM）digestibility were significantly increased（P<0.05）,while neutral detergent fiber（NDF）digestibility was decreased（P<0.05）,and no significant differences were found in other indexes（P>0.05）.Experiment 2:Jugular vein blood samples were collected on an empty stomach in the morning of the last day of the experiment,and blood biochemical indexes were determined.With the increase of concentrate ratio,the contents of total protein（TP）,albumin（ALB）,insulin（INS）,growth hormone（GH）and progesterone（P）in serum of cows were significantly increased（P<0.05）.The contents of total cholesterol（TC）,high density lipoprotein（HDL-C）,insulin-like growth factor-1（IGF-I）,leptin（LEP）,adiponectin（ADPN）and luteinizing hormone（LH）were significantly decreased（P<0.05）;With the increase of concentrate ratio in diet,the contents of immunoglobulin A（Ig A）,immunoglobulin G（Ig G）,immunoglobulin M（Ig M）,interleukin-2（IL-2）and interleukin-4（IL-4）in serum of cows were significantly increased（P<0.05）.The content of tumor necrosis factor-α（TNF-α）was significantly decreased（P<0.05）;With the increase of concentrate ratio in diet,the contents of total antioxidant capacity（T-AOC）,superoxide dismutase（SOD）,glutathione peroxidase（GSH-Px）and catalase（CAT）in serum of cows were significantly increased（P<0.05）,while the content of malondialdehyde（MDA）was significantly decreased（P<0.05）.There were no significant differences in other indexes（P>0.05）.Experiment 3:Rumen fluid samples were collected after feeding for 2 hours on the day of blood collection,and p H value,ammonia nitrogen（NH₃-N）,microbial protein（BCP）and volatile fatty acid（VFAs）contents were determined.Rumen p H value of cows was significantly decreased with the increase of concentrate ratio（P<0.05）;The contents of butyric acid,isobutyric acid,valeric acid and isovaleric acid in rumen were significantly increased（P<0.05）,while the content of acetic acid and the ratio of acetic acid to propionic acid were significantly decreased（P<0.05）.With the increase of concentrate ratio in diet,the contents of NH₃-N and BCP in rumen were significantly increased（P<0.05）.Experiment 4:The fresh and pollution-free intestinal contents were collected by rectal fecal method,and the content of volatile fatty acids（VFAs）was determined.The composition of intestinal flora of experimental cattle was detected by 16S r RNA method.With the increase of concentrate ratio in diet,the concentrations of acetic acid,propionic acid,valeric acid,iso-valeric acid and total SCFA in rumen of cows were significantly increased（P<0.05）;In terms of intestinal microflora diversity,the ACE index and Chao1index of the middle and low-concentrate groups were significantly higher than those of the high-concentrate group（P<0.05）,and the Shannon and Simpson indexes of the middle sperm group were significantly higher than those of the high-concentrate group（P<0.05）.The relative abundance of Spirochaete was significantly increased with the increase of concentrate ratio（P<0.05）.In addition,the relative abundance of Desulfobacterota in the low-concentrate group was significantly higher than that in the high-precision and medium-concentrate groups（P<0.05）.With the increase of concentrate ratio,the relative abundance ofChristensenellace AE＿R-7＿group,Bacteroidesand norank＿f＿＿Eubacterium＿coprostanoligenes＿group decreased significantly.The relative abundances of three bacteria genera in the intestinal tract of cows in low-concentrate group were significantly lower than those in the other two dietary groups（P<0.05）.With the increase of concentrate ratio,the relative abundance of Rikenellaceae＿RC9＿gut＿group,Alistipes and Lachnospiraceae＿NK4A136＿group increased significantly.The relative abundances of three species of bacteria in intestinal tract of cows in high-concentrate group and medium-concentrate group were significantly higher than those in low-concentrate group（P<0.05）.In conclusion,increasing the ratio of concentrate to forage in pre-gestation diets can improve the body condition,performance,immune antioxidant capacity,rumen homeostasis and intestinal microflora diversity of cows under the experimental conditions.