Effect Of Feeding Bacillus On Growth Performance And Gastrointestinal Flora Of Lactating Holstein Female Calves

The feeding of dairy calves has an extremely important impact on the production of dairy farms,especially the female calves which will affect the later production efficiency,so the healthy growth of calves is the basis of the development of dairy industry.In order to reduce calf morbidity and improve calf performance,this experiment investigated the effects of Bacillus cereus and Bacillus licheniformis on growth performance,nutrient apparent digestibility,blood parameters,health status,rumen fermentation and gastrointestinal microflora of Holstein female calves,with the aim of providing theoretical basis for better calf breeding with Bacillus subtilis and Bacillus licheniformis supplementation.In this trial,a completely randomized compartmentalized experimental design was used to divide 24 Holstein female calves(means ± SD;38.25 ± 1.27 kg)at birth into six separate compartmentalized groups,each containing two treatments,the control group(CON)and the probiotic group(PG).Fresh water and adequate starter were provided daily during the trial period.Calves were weaning at 56 days of age when the trial ended.Experiment 1: Effects of feeding Bacillus on growth performance and blood parameters of dairy calvesThere was a tendency for calf height to decrease at 56 days of age in the PG group compared to the CON group(P=0.06),and there was no difference in calf feed efficiency(FE)between the two groups(P=0.90).In addition,feeding Bacillus cereus improved the digestibility of feed dry matter(P=0.08)and crude protein(P=0.05).At 28 days of age,there were no significant differences in immunological,antioxidant and biochemical parameters of calves’ blood between the two groups.At 56 days of age,calves in the PG group had significantly higher plasma levels of immunoglobulin G(Ig G)than calves in the control group(P=0.04),and there was a trend toward an increase in total antioxidant capacity of TAOC(P=0.08),as well as in albumin content(P=0.09).Experiment 2: Effects of feeding Bacillus on rumen fermentation and microbiota of dairy calvesRuminal fluid p H(P=0.35),total volatile fatty acid(VFA)concentration(P=0.81),and NH3-N concentration(P=0.72)were not significantly different among treatment groups,but there was a tendency for the ratio of acetic acid to propionic acid to increase at 56 days of age(P=0.07).The Shannon index(P=0.03)and the Simpson index(P=0.04)of calves in the PG group at day 28 were significantly lower than those in the CON group.At 28 days of age,calves in the PG group had a significantly lower Shannon index(P=0.03)and Simpson’s index(P=0.04)was significantly lower than that of the CON group.At 28 days of age,calves in the PG group showed a significant decrease in Succiniclasticum(P=0.01)and Ruminococcus(P=0.02)and Anaerovibrio(P=0.01)and a significant increase in Subdoligranulum abundance(P=0.03)relative to the CON group.At 56 days of age,calves in the PG group showed a significant decrease in abundance of Actinobacteriota(P=0.03)and Bifidobacterium(P=0.03)and a significant increase in relative abundance of Selenomonas(P=0.05)relative to the CON group.The relative abundance of Patescibacteria decreased significantly with increasing age(P<0.01);the relative abundance of Prevotella and Succiniclasticum increased significantly with increasing age(P<0.01)Experiment 3: Effects of feeding Bacillus on diarrheal condition and fecal microbiota of dairy calvesThere was a trend towards a lower rate of diarrhea in calves in the PG group between 28 and 56 days of age(P=0.09),with no significant differences in fecal score(P=0.34)or number of treatments(P=0.56).There was no difference in α-diversity and β-diversity between the two treatment groups at 28 and 56 days of age(P>0.1).For calves at 28 days of age,there was a significant increase in calves in the PG group relative to the CON group for Cyanobacteria(P=0.04)and Gastranaerophilales(P=0.04)and a significant decrease in GCA-900066575 abundance(P=0.02).56-day-old calves,calves in the PG group showed an increasing trend in relative abundance of Desulfovibrio(P=0.07)and Candidatus＿Stoquefichus(P=0.09)relative to the CON group.The relative abundance of Firmicutes,Clostridia＿UCG-014 and Butyricicoccus decreased significantly(P<0.01)with increasing age,while the relative abundance of Fusobacteriota increased significantly(P<0.01)with increasing age.It was concluded that:(1)The tendency of feeding Bacillus to increase the digestibility of dry matter and crude protein in calves;it also increased the levels of plasma Ig G and T-AOC capacity of calves;(2)Feeding Bacillus reduced the α-diversity of rumen microbes in 28-day-old calves;(3)Feeding Bacillus cereus has a tendency to dreduce the number of days of diarrhea in calves;(4)Feeding Bacillus increased the proportion of some beneficial flora(Cyanobacteria,Gastranaerophilales,Desulfovibrio)in the gut.