Effects Of Supplementary Forage On Growth Performance,Rumen Fermentation And Gastrointestinal Tract Microorganisms Of Pre-Weaning Calves

As a reserve force for lactating dairy cattle,the success or failure of calf feeding management is related to the sustainability and profitability of a dairy farm in the future.Pre-weaning calves have the characteristics of high nutritional demand,rapid growth and development,great development potential and low immune ability.Therefore,excellent feeding and management mode is the key to ensure the rapid and healthy growth of calves.Perfect rumen development is an important goal of calf breeding.Studies had confirmed that volatile fatty acids（VFA）,especially propionate and butyrate,after concentrate fermentation can effectively stimulate the development of rumen epithelium.However,some studies had confirmed that if the calves were fed only milk and starter,when the intake of starter was large,the rumen pH value and nutrient digestibility of calves would be reduced,which is not conducive to the growth development and health of calves.According to previous studies,fed calves with a small amount of high-quality forage before weaning helped to improve their rumen environment,alleviate diarrhea and appropriately improved their growth performance.In this study,alfalfa hay and oat hay were added to the diet of calves before weaning,and the feed intake,body weight,rumen pH and plasma were measuredβ-hydroxybutyric acid（BHBA）,rumen and fecal microorganisms were used to comprehensively evaluate the effects of forage supplementation on the growth and development,rumen fermentation and gastrointestinal microorganisms of pre-weaning calves,so as to provide a theoretical basis for the nutritional regulation of pre-weaning calves.Exp.1 Effects of forage supplementation on growth,ruminal environment and bacterial composition in pre-weaning calvesSixty 23 day old female calves were randomly divided into three groups:the control group（CON group）fed with starter without forage;Alfalfa hay（AH group）added with 75 g/d（dry matter basis）or oat hay（OH group）added with 75 g/d（dry matter basis）on the basis of starter,and the three groups were provided the same amount of milk.Starter and water were provided ad libitum.The pre-test period starts from 23 days old,enters the trial period at 30 days old for 6 weeks,and ends the test at 73 days old.The body weight and body size were recorded continuously two days before the start of the trial period as the initial value.The intake of milk,starter and forage were recorded every day during the trial period.The body weight and body size were recorded for two consecutive days in the second,fourth and sixth weeks（W2,W4and W6）of the trial period.The feed efficiency（FE）was calculated according to the total solid intake and average daily gain（ADG）.The FE was calculated every two weeks after morning feeding,During the trial period,the samples of jugular vein blood and rumen fluid of each test cow were collected every two weeks at 2 hours after morning feeding,and the plasma biochemical indexes,pH value of rumen fluid,fermentation indexes and microflora were measured.Rectum fecal samples were collected continuously in the last three days of the trial period to determine the apparent digestibility of total gut nutrients.The results showed that the intake of forage of AH group was greater than that of OH group（P<0.05）.Compared with the control group and AH group,oat hay supplement significantly increased the total solid feed intake（P<0.05）.Ah group and OH group did not affect the body size,body weight,ADG,FE and apparent digestibility of gut nutrients in pre-weaning calves（P>0.05）.Compared with the CON group and the AH group,the OH group significantly increased the concentration of BHBA in plasma（P<0.05）.Compared with the control group,the AH group and the OH group had significant lower LDH in plasma,the concentration of total VFA,propionate,valerate and NH₃-N at W6 in rumen.Compared with the AH group and the CON group,the Chao1 index and PD whole tree index of the rumen microbes in the OH group at W6 were significantly increased（P<0.05）.Compared with the CON group,The relative abundance of Tenerictes,Ruminococcaceae＿NK4A214＿group,Blautia,Lachnoclostridium＿1 and Christensenellaceae＿R-7＿group in Rumen was significantly decresed（P<0.05）.Exp.2 Effects of forage supplementation on body health and fecal microorganisms in pre-weaning calvesThe aim of this experiment was to investigate the effect of forage supplementation on diarrhea and fecal microorganisms in pre-weaning calves.Animal feeding was the same as in Exp.1,and feces were scored every day.On the last day of the trial period,feces were collected from the rectum with sterile cotton swabs.Incidence of diarrhea was calculated from fecal scores,and fecal samples were used for 16S r RNA sequencing.The results showed that in the trial period,the incidence of diarrhea decreased with the increase of age.The incidence of diarrhea in the AH group was lower than the CON group in the whole trial period,and the OH group was lower than the CON group in the first 5 weeks.The highest relative abundance of fecal microorganisms in phyla were Firmicutes,Bacteroidetes,Actinbacteria,Proteobacteria,Spirochaetes and Tenericutes,and the genus with the highest relative abundance were Ruminococcaceae＿UCG-005,Bacteroides,Blautia.The microbial composition of the OH group was significantly different from that of the CON group and the AH group（R=0.048,P=0.048）.Compared with the CON group,the relative abundances of Cyanobacteria,Prevotellaceae＿UCG-003,Oscillibacter,Eubacterium＿coprostanoligenes＿group and Ruminococcaceae＿UCG-004 in the feces of the AH group were significantly decreased（P<0.05）,the relative abundances of Prevotella＿9 and Alloprevotell were significantly increased（P<0.05）,The relative abundance of Prevotella＿9 and Oscillibacter in the feces of the OH group was significantly decreased,and the relative abundance of Odoribacter was significantly increased（P<0.05）.This study showed that supplementary forage did not affect the growth and development of pre-weaning calves,but could increased rumen pH.Alfalfa hay supplementation can reduce the incidence of diarrhea;Oat hay supplementation increased total solid intake,beneficial to the rumen development,increased the relative abundance of beneficial bacteria such as blautia and christensenellaceae in rumen,which can promote the function of rumen epithelial barrier,which has a positive impact on the health of pre-weaning calves.