Compound Probiotics Improve the Diarrhea Rate and Intestinal Microbiota of Newborn Calves

Effects of kefir fermented with or without 1% autolyzed yeast powder on dry matter intake, intestinal permeability, and rumen fermentation profile of Holstein calves

Co-fermenting kefir with Saccharomyces cerevisiae has been shown to enhance the exopolysaccharides (EPS) produced by lactic acid bacteria during fermentation, which may further promote intestinal development in the calf. Four different concentrations (0%, 0.25%, 0.5%, 1%) on a weight/weight basis (g/20 g kefir grain) of either dried, activated distiller's yeast or autolyzed yeast powder were evaluated for EPS optimization in kefir, and inclusion of 1% autolyzed yeast powder resulted in the greatest EPS yield. In a randomized, complete block design, 81 Holstein heifers were enrolled at 3 d of age, blocked by birth weight, and randomized within block to receive either 125 mL salable whole milk (CON), 125 mL of kefir (KEF), or 125 mL of kefir fermented with 1% autolyzed yeast powder (YAK) in milk replacer 1x/d until 28 d of age. Feed intake and health scores were recorded daily for each calf through 1-week postweaning (63 d of age). Growth measurements were recorded weekly until 9 wk. Indigestible markers D-mannitol and Cr-EDTA were administered at 15, 29, and 50 d to a subset of calves (n = 36) and recovered in plasma and serum to measure intestinal permeability. Rumen fluid was collected from calves (n = 35) via gastric tube at 63 ± 2 d to measure pH and VFA concentrations, as well as serum BHB at 14, 28, 42, 56, and 63 d. While health outcomes (diarrhea, respiratory illness, dehydration) were not affected by treatment, supplementation with YAK significantly improved starter DMI and BW in the preweaning period compared with CON and KEF, and postweaning DMI was significantly improved in both KEF and YAK compared with CON. Increased butyrate was observed in rumen fluid of calves fed YAK, though serum BHB was not affected. This work contributes to further understanding kefir as a promoter of gastrointestinal development in calves and the potential benefits of EPS in the developing ruminant.

The investigation of the mechanism underlying variations in oxidative stress tolerance of Lacticaseibacillus paracasei resulting from fermentation methods through endogenous CRISPR-Cas9 editing methodology

The probiotic effects of lactic acid bacteria make them widely used in human and animal breeding industry. However, the presence of oxidative stress during the production and application process can cause bacterial damage or even death, significantly compromising the functionality of probiotics. Despite its potential for broader application scenarios that could provide a more comprehensive understanding of bacteria's internal adaptation strategies, there is a lack of research investigating oxidative stress from the perspective of culture methods. In this study, the tolerance to oxidative stress was compared between bacteria cultivated through solid-state fermentation (SSF) and liquid-state fermentation (LSF), and the physiological and transcriptional disparities between these two bacterial strains were investigated. Additionally, a novel and efficient gene editing method was developed to elucidate the genetic basis underlying these differences in tolerance. The results demonstrated a significantly higher tolerance to oxidative stress in SSF bacteria compared to LSF bacteria, along with a stronger capacity for maintaining intracellular microenvironment stability and the activity of key metabolic enzymes. It is noteworthy that the bacteria from SSF significantly enhance the transport of carbohydrate substances and facilitate intracellular metabolic flow. Gene editing experiments have confirmed the crucial role of genes glpF and glpO in regulating the glycerol metabolism pathway, which is essential for enhancing the tolerance of bacteria from SSF to oxidative stress. Based on these findings, the mechanism underlying the disparity in oxidative stress tolerance resulting from different culture methods has been summarized. Furthermore, investigation into different culture modes has revealed that moderate oxygen levels during cultivation significantly influence variation in bacterial tolerance to oxidative stress. Importantly, these variations are species-specific and depend on the ecological niche distribution of Lactobacilli. These findings elucidate a novel mechanism by which Lacticaseibacillus paracasei Zhang tolerates oxidative stress, and also suggest that distinct cultivation and processing methods should be tailored based on the specific Lactobacilli groups to achieve optimal application effects in production.

Effects of Bacillus amyloliquefaciens FD777 and Macleaya cordata Extract on Performance, Immunity, Gastrointestinal System Microbiome, and Profitability in Holstein Calves

This study was performed to determine the effects of dietary supplementation of Bacillus amyloliquefaciens FD777 (BA) and Macleaya cordata extract (MCE) on the performance, morbidity and mortality rates, body measurements, immunity, rumen parameters, antioxidant parameters, microbiome level, and profitability of calves during the pre-weaning period. In the study, 51 calves were divided into three groups as one control and two treatment groups considering their age (1 day old), gender (nine females and eight males in each group), and birth weight (37.7 ± 0.4 kg). The calves in the control group (CON) were fed milk without supplements whereas the first treatment group (BA) was fed milk containing 10 mL/day/head of Bacillus amyloliquefaciens FD777 and the second treatment group (MCE) was fed milk containing 2 g/day/head of MCE. As a result, supplementing BA and MCE to calf milk had no significant effect on body weight (BW), dry matter intake (DMI), feed efficiency (FE), morbidity and mortality rates, rumen pH, IgG, IgA, and IgM values, and gastrointestinal microbiota (p > 0.05). On the other hand, it was determined that body weight gain (BWG), body length, body depth, rump width, withers height change, rump height change, rump width change, and serum GSH level increased significantly in the BA group compared to the control group (p < 0.05). According to the partial budget analysis, despite the additional cost of supplementing BA to the calf milk, no calf deaths and lower disease were observed in this group, unlike the other groups, resulting in a lowest calf rearing cost and highest profit. In calves receiving MCE, withers height, rump height, body length, rump width, body depth, chest circumference change, withers height change, rump height change, and rump width change values increased significantly compared with the control group (p < 0.05). In conclusion, the results obtained not only reveal the positive effects of BA and MCE on calves during the pre-weaning period, but also encourage the necessity of investigating their effects on the long-term performance of animals and farm economies.

Machine learning-enhanced assessment of potential probiotics from healthy calves for the treatment of neonatal calf diarrhea

Neonatal calf diarrhea (NCD) remains a significant contributor to calf mortality within the first 3 weeks of life, prompting widespread antibiotic use with associated concerns about antimicrobial resistance and disruption of the calf gut microbiota. Recent research exploring NCD treatments targeting gut microbiota dysbiosis has highlighted probiotic supplementation as a promising and safe strategy for gut homeostasis. However, varying treatment outcomes across studies suggest the need for efficient treatment options. In this study, we evaluated the potential of probiotics Limosilactobacillus reuteri, formally known as Lactobacillus reuteri, isolated from healthy neonatal calves to treat NCD. Through in silico whole genome analysis and in vitro assays, we identified nine L. reuteri strains, which were then administered to calves with NCD. Calves treated with L. reuteri strains shed healthy feces and demonstrated restored gut microbiota and normal animal behavior. Leveraging a machine learning model, we evaluated microbiota profiles and identified bacterial taxa associated with calf gut health that were elevated by L. reuteri administration. These findings represent a crucial advancement towards sustainable antibiotic alternatives for managing NCD, contributing significantly to global efforts in mitigating antimicrobial resistance and promoting overall animal health and welfare.

Effects of Bacillus subtilis on Growth Performance, Metabolic Profile, and Health Status in Dairy Calves

This study focused on assessing whether the inclusion of probiotics (B. subtilis) as feed additives during the preweaning stage can enhance the body weight and metabolic condition of neonatal calves. A total of 50 Holstein calves, all born on the same farm, were randomly divided into two homogeneous treatment groups after birth. The calves in the control group (CG) were fed a milk replacer (n = 25) (13 females and 12 males) and those in the B. subtilis-supplement-treated group (TG), (n = 25) (13 females and 12 males) were fed a milk replacer with 7.5 mL/calf/day of B. subtilis probiotic (complied with the manufacturer's guidelines). The probiotic was administered 24 h post-birth, signifying the start of the experimental period. It took one month to collect the animals. Body weight was measured at birth for all animals. A local veterinarian, working on the farm, conducted daily health checks of the calves, recording health parameters and any antibiotic treatments. Blood samples were collected from each calf at birth and 30, 60, and 90 days by puncturing the jugular vein using 10 mL evacuated serum tubes before morning feeding. Significant differences in body weight were observed between the CG and the TG at 30, 60, and 90 days of age. At 30 days, the TG had a 4.11% higher average body weight than the CG (54.38 kg vs. 52.71 kg). At 60 days, the TG's average weight was 3.75% higher (79.21 kg vs. 76.34 kg), and at 90 days, the TG had a 2.91% higher average weight (112.87 kg vs. 109.67 kg). At 30 days of age, the TG showed significantly lower AST activity, with a 41.12% decrease compared to the CG (51.02 IU/L vs. 72.00 IU/L). Conversely, GGT activity was significantly higher in the TG by 64.68% (40.64 IU/L vs. 14.35 IU/L). Phosphorus concentration at 30 days was also significantly higher in the TG by 9.36% (3.27 mmol/L vs. 2.99 mmol/L). Additionally, the TG had a significantly lower total protein concentration, with a 21.63% decrease at 30 days (46.32 g/L vs. 56.34 g/L) and a 20.28% decrease at 60 days (48.32 g/L vs. 58.12 g/L) compared to the CG. These findings indicate that dairy calves given conventional milk replacer along with a daily dose of 7.5 mL of B. subtilis probiotic experienced enhanced growth performance and a more favourable metabolic profile during the first 90 days of their lives.

Intake of compound probiotics accelerates the construction of immune function and gut microbiome in Holstein calves

Acquired immunity is an important way to construct the intestinal immune barrier in mammals, which is almost dependent on suckling. To develop a new strategy for accelerating the construction of gut microbiome, newborn Holstein calves were continuously fed with 40 mL of compound probiotics (containing Lactobacillus plantarum T-14, Enterococcus faecium T-11, Saccharomyces cerevisiae T-209, and Bacillus licheniformis T-231) per day for 60 days. Through diarrhea rate monitoring, immune index testing, antioxidant capacity detection, and metagenome sequencing, the changes in diarrhea incidence, average daily gain, immune index, and gut microbiome of newborn calves within 60 days were investigated. Results indicated that feeding the compound probiotics reduced the average diarrhea rate of calves by 42.90%, increased the average daily gain by 43.40%, raised the antioxidant indexes of catalase, superoxide dismutase, total antioxidant capacity, and Glutathione peroxidase by 22.81%, 6.49%, 8.33%, and 13.67%, respectively, and increased the immune indexes of IgA, IgG, and IgM by 10.44%, 4.85%, and 6.12%, respectively. Moreover, metagenome sequencing data showed that feeding the compound probiotics increased the abundance of beneficial strains (e.g., Lactococcus lactis and Bacillus massionigeriensis) and decreased the abundance of some harmful strains (e.g., Escherichia sp. MOD1-EC5189 and Mycobacterium brisbane) in the gut microbiome of calves, thus contributing to accelerating the construction of healthy gut microbiome in newborn Holstein calves.

IMPORTANCE

The unstable gut microbiome and incomplete intestinal function of newborn calves are important factors for the high incidence of early diarrhea. This study presents an effective strategy to improve the overall immunity and gut microbiome in calves and provides new insights into the application of compound probiotics in mammals.

How does active yeast supplementation reduce the deleterious effects of aflatoxins in Wistar rats? A radiolabeled assay and histopathological study

The aim of this study was to investigate the mechanisms by which yeasts (Saccharomyces cerevisiae) control the toxic effects of aflatoxins, which are not yet fully understood. Radiolabeled aflatoxin B1 (AFB13H) was administered by gavage to Wistar rats fed with aflatoxin (AflDiet) and aflatoxin supplemented with active dehydrated yeast Y904 (AflDiet + Yeast). The distribution of AFB13H and its metabolites were analyzed at 24, 48 and 72 h by tracking back of the radioactivity. No significant differences were observed between the AflDiet and AflDiet + Yeast groups in terms of the distribution of labeled aflatoxin. At 72 h, for the AflDiet group the radiolabeled aflatoxin was distributed as following: feces (79.5%), carcass (10.5%), urine (1.7%), and intestine (7.4%); in the AflDiet + Yeast the following distribution was observed: feces (76%), carcass (15%), urine (2.9%), and intestine (4.9%). These values were below 1% in other organs. These findings indicate that even after 72 h considerable amounts of aflatoxins remains in the intestines, which may play a significant role in the distribution and metabolism of aflatoxins and its metabolites over time. The presence of yeast may not significantly affect this process. Furthermore, histopathological examination of hepatic tissues showed that the presence of active yeast reduced the severity of liver damage caused by aflatoxins, indicating that yeasts control aflatoxin damage through biochemical mechanisms. These findings contribute to a better understanding of the mechanisms underlying the protective effects of yeasts against aflatoxin toxicity.

Probiotics in milk replacer affect the microbiome of the lung in neonatal dairy calves

Introduction

Probiotics have been investigated for their many health benefits and impact on the microbiota of the gut. Recent data have also supported a gut-lung axis regarding the bacterial populations (microbiomes) of the two locations; however, little research has been performed to determine the effects of oral probiotics on the microbiome of the bovine respiratory tract. We hypothesized that probiotic treatment would result in changes in the lung microbiome as measured in lung lavage fluid. Our overall goal was to characterize bacterial populations in the lungs of calves fed probiotics in milk replacer and dry rations from birth to weaning.

Methods

A group of 20 dairy calves was split into two treatment groups: probiotic (TRT; N = 10, milk replacer +5 g/d probiotics; Bovamine Dairy, Chr. Hansen, Inc., Milwaukee, WI) and control (CON; N = 10, milk replacer only). On day 0, birth weight was obtained, and calves were provided colostrum as per the dairy SOP. On day 2, probiotics were added to the milk replacer of the treated group and then included in their dry ration. Lung lavages were performed on day 52 on five random calves selected from each treatment group. DNA was extracted from lavage fluid, and 16S ribosomal RNA (rRNA) gene hypervariable regions 1-3 were amplified by PCR and sequenced using next-generation sequencing (Illumina MiSeq) for the identification of the bacterial taxa present. Taxa were classified into both operational taxonomic units (OTUs) and amplicon sequence variants (ASVs).

Results

Overall, the evaluation of these samples revealed that the bacterial genera identified in the lung lavage samples of probiotic-fed calves as compared to the control calves were significantly different based on the OTU dataset (p < 0.05) and approached significance for the ASV dataset (p < 0.06). Additionally, when comparing the diversity of taxa in lung lavage samples to nasal and tonsil samples, taxa diversity of lung samples was significantly lower (p < 0.05).

Discussion

In conclusion, analysis of the respiratory microbiome in lung lavage samples after probiotic treatment provides insight into the distribution of bacterial populations in response to oral probiotics and demonstrates that oral probiotics affect more than the gut microbiome.

The Effect of Probiotics in a Milk Replacer on Leukocyte Differential Counts, Phenotype, and Function in Neonatal Dairy Calves

Probiotics have been investigated for many health benefits; however, few studies have been performed to determine the effects of oral probiotics on peripheral blood and respiratory immune cells in cattle. Our objectives were to determine changes in health and growth status, differential blood cell counts and function, and blood and lung cell function using flow cytometry and PCR in dairy calves fed a milk replacer with (PRO, N = 10) or without (CON, N = 10) the addition of probiotics to the milk replacer and dry rations from birth to weaning. Performance and clinical scores were not different between the treatment groups. Treatment-by-day interactions for peripheral blood leukocyte populations differed in cell number and percentages. A greater percentage of leukocytes expressed the cell surface markers CD3, CD4, CD8, CD11b, and CD205 on d 21 in CON animals. Lung lavages were performed on five animals from each treatment group on d 52. There were no differences between treatment groups for the expression of cytokines and Toll-Like Receptors as measured using Polymerase Chain Reaction, possibly due to the small sample size. Oral probiotics appear to affect peripheral blood immune cells and function. Their effect on overall calf health remains to be determined.

Effects of lactic acid bacteria isolated from Tibetan chickens on the growth performance and gut microbiota of broiler

Lactic acid bacteria (LAB) are organic supplements that have several advantages for the health of the host. Tibetan chickens are an ancient breed, which evolve unique gut microbiota due to their adaptation to the hypoxic environment of high altitude. However, knowledge of LAB isolated from Tibetan chickens is very limited. Thus, the purpose of this study was to assess the probiotic properties of Lactobacillus Plantarum (LP1), Weissella criteria (WT1), and Pediococcus pentosaceus (PT2) isolated from Tibetan chickens and investigate their effects on growth performance, immunoregulation and intestinal microbiome in broiler chickens. Growth performance, serum biochemical analysis, real-time PCR, and 16S rRNA sequencing were performed to study the probiotic effects of LP1, WT1, and PT2 in broiler chickens. Results showed that LP1, WT1 and PT2 were excellent inhibitors against Escherichia coli (E. coli ATCC25922), meanwhile, LP1, WT1, and PT2 significantly increased weekly weight gain, villus height, antioxidant ability and gut microbiota diversity indexes in broilers. In addition, LP1 and PT2 increased the relative abundance of Lactobacillus and decreased Desulfovibrio in comparison with T1 (control group). Additionally, oral LAB can reduce cholesterol and regulate the expression of tight junction genes in broiler chickens, suggesting that LAB can improve the integrity of the cecal barrier and immune response. In conclusion, LAB improved the growth performance, gut barrier health, intestinal flora balance and immune protection of broiler chickens. Our findings revealed the uniqueness of LAB isolated from Tibetan chickens and its potential as a probiotic additive in poultry field.

Effect of synbiotics on growth performance, gut health, and immunity status in pre-ruminant buffalo calves

Synbiotics are employed as feed additives in animal production as an alternate to antibiotics for sustaining the gut microbiota and providing protection against infections. Dairy calves require a healthy diet and management to ensure a better future for the herd of dairy animals. Therefore, the present study was carried out to investigate the effect of synbiotics formulation on growth performance, nutrient digestibility, fecal bacterial count, metabolites, immunoglobulins, blood parameters, antioxidant enzymes and immune response of pre-ruminant Murrah buffalo calves. Twenty-four apparently healthy calves (5 days old) were allotted into four groups of six calves each. Group I (control) calves were fed a basal diet of milk, calf starter and berseem with no supplements. Group II (SYN1) calves were fed with 3 g fructooligosaccharide (FOS) + Lactobacillus plantarum CRD-7 (150 ml). Group III (SYN2) calves were fed with 6 g FOS + L. plantarum CRD-7 (100 ml), whereas calves in group IV (SYN3) received 9 g FOS + L. plantarum CRD-7 (50 ml). The results showed that SYN2 had the highest (P < 0.05) crude protein digestibility and average daily gain compared to the control. Fecal counts of Lactobacilli and Bifidobacterium were also increased (P < 0.05) in supplemented groups as compared to control. Fecal ammonia, diarrhea incidence and fecal scores were reduced in treated groups while lactate, volatile fatty acids and antioxidant enzymes were improved compared to the control. Synbiotic supplementation also improved both cell-mediated and humoral immune responses in buffalo calves. These findings indicated that synbiotics formulation of 6 g FOS + L. plantarum CRD-7 in dairy calves improved digestibility, antioxidant enzymes, and immune status, as well as modulated the fecal microbiota and decreased diarrhea incidence. Therefore, synbiotics formulation can be recommended for commercial use in order to achieve sustainable animal production.

Colonization and development of the gut microbiome in calves

Colonization and development of the gut microbiome are crucial for the growth and health of calves. In this review, we summarized the colonization, beneficial nutrition, immune function of gut microbiota, function of the gut barrier, and the evolution of core microbiota in the gut of calves of different ages. Homeostasis of gut microbiome is beneficial for nutritional and immune system development of calves. Disruption of the gut microbiome leads to digestive diseases in calves, such as diarrhea and intestinal inflammation. Microbiota already exists in the gut of calf fetuses, and the colonization of microbiota continues to change dynamically under the influence of various factors, which include probiotics, diet, age, and genotype. Colonization depends on the interaction between the gut microbiota and the immune system of calves. The abundance and diversity of these commensal microbiota stabilize and play a critical role in the health of calves.

Effects of Bacillus licheniformis and Combination of Probiotics and Enzymes as Supplements on Growth Performance and Serum Parameters in Early-Weaned Grazing Yak Calves

Early weaning is an effective strategy to improve cow feed utilization and shorten postpartum intervals in cows; however, this may lead to poor performance of the weaned calves. This study was conducted to test the effects of supplementing milk replacer with Bacillus licheniformis and a complex of probiotics and enzyme preparations on body weight (BW), size, and serum biochemical parameters and hormones in early-weaned grazing yak calves. Thirty two-month-old male grazing yaks (38.89 ± 1.45 kg body weight) were fed milk replacer at 3% of their BW and were randomly assigned to three treatments (n = 10, each): T1 (supplementation with 0.15 g/kg Bacillus licheniformis), T2 (supplementation with a 2.4 g/kg combination of probiotics and enzymes), and a control (without supplementation). Compared to the controls, the average daily gain (ADG) from 0 to 60 d was significantly higher in calves administered the T1 and T2 treatments, and that from 30 to 60 d was significantly higher in calves administered the T2 treatment. The ADG from 0 to 60 d was significantly higher in the T2- than in the T1-treated yaks. The concentration of serum growth hormone, insulin growth factor-1, and epidermal growth factor was significantly higher in the T2-treated calves than in the controls. The concentration of serum cortisol was significantly lower in the T1 treatment than in the controls. We concluded that supplementation with probiotics alone or a combination of probiotics and enzymes can improve the ADG of early-weaned grazing yak calves. Supplementation with the combination of probiotics and enzymes had a stronger positive effect on growth and serum hormone levels, compared to the single-probiotic treatment with Bacillus licheniformis, providing a basis for the application of a combination of probiotics and enzymes.

Beneficial features of pediococcus: from starter cultures and inhibitory activities to probiotic benefits

Pediococci are lactic acid bacteria (LAB) which have been used for centuries in the production of traditional fermented foods. There fermentative abilities were explored by the modern food processing industry in use of pediococci as starter cultures, enabling the production of fermented foods with distinct characteristics. Furthermore, some pediococci strains can produce bacteriocins and other antimicrobial metabolites (AMM), such as pediocins, which are increasingly being explored as bio-preservatives in various food matrices. Due to their versatility and inhibitory spectrum, pediococci bacteriocins and AMM are being extensively researched not only in the food industry, but also in veterinary and human medicine. Some of the pediococci were evaluated as potential probiotics with different beneficial areas of application associated with human and other animals' health. The main taxonomic characteristics of pediococci species are presented here, as well as and their potential roles and applications as starter cultures, as bio-preservatives and as probiotic candidates.

In vitro investigation on lactic acid bacteria isolatedfrom Yak faeces for potential probiotics

In order to evaluate the potential and safety of lactic acid bacteria (LAB) isolated from faeces samples of Ganan yak as probiotic for prevention and/or treatment of yak diarrhea, four strains of LAB including Latilactobacillus curvatus (FY1), Weissella cibaria (FY2), Limosilactobacillus mucosae (FY3), and Lactiplantibacillus pentosus (FY4) were isolated and identified in this study. Cell surface characteristics (hydrophobicity and cell aggregation), acid resistance and bile tolerance, compatibility, antibacterial activity and in vitro cell adhesion tests were also carried out to evaluate the probiotic potential of LAB. The results showed that the four isolates had certain acid tolerance, bile salt tolerance, hydrophobicity and cell aggregation, all of which contribute to the survival and colonization of LAB in the gastrointestinal tract. There is no compatibility between the four strains, so they can be combined into a mixed probiotic formula. Antimicrobial tests showed that the four strains were antagonistic to Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium. Moreover, the in vitro safety of the four isolates were determined through hemolytic analysis, gelatinase activity, and antibacterial susceptibility experiments. The results suggest that all the four strains were considered as safe because they had no hemolytic activity, no gelatinase activity and were sensitive to most antibacterial agents. Moreover, the acute oral toxicity test of LAB had no adverse effect on body weight gain, food utilization and organ indices in Kunming mice. In conclusion, the four LAB isolated from yak feces have considerable potential to prevent and/or treat yak bacterial disease-related diarrhea.

Effects of Milk Replacer-Based Lactobacillus on Growth and Gut Development of Yaks' Calves: a Gut Microbiome and Metabolic Study

The gut microbiota and its metabolic activities are crucial for maintaining host homoeostasis and health, of which the role of probiotics has indeed been emphasized. The current study delves into the performance of probiotics as a beneficial managemental strategy, which further highlights their impact on growth performance, serologic investigation, gut microbiota, and metabolic profiling in yaks' calves. A field experiment was employed consisting of 2 by 3 factorial controls, including two development stages, namely, 21 and 42 days (about one and a half month), with three different feeding treatments. Results showed a positive impact of probiotic supplements on growth performance by approximately 3.16 kg (P < 0.01) compared with the blank control. Moreover, they had the potential to improve serum antioxidants and biochemical properties. We found that microorganisms that threaten health were enriched in the gut of the blank control with the depletion of beneficial bacteria, although all yaks were healthy. Additionally, the gut was colonized by a microbial succession that assembled into a more mature microbiome, driven by the probiotics strategy. The gut metabolic profiling was also changed significantly after the probiotic strategy, i.e., the concentrations of metabolites and the metabolic pattern, including enrichments in protein digestion and absorption, vitamin digestion and absorption, and biosynthesis of secondary metabolites. In summary, probiotics promoted gut microbiota/metabolites, developing precise interventions and achieving physiological benefits based on intestinal microecology. Hence, it is important to understand probiotic dietary changes to the gut microbiome, metabolome, and the host phenotype. IMPORTANCE The host microbiome is a composite of the trillion microorganisms colonizing host bodies. It can be impacted by various factors, including diet, environmental conditions, and physical activities. The yaks' calves have a pre-existing imbalance in the intestinal microbiota with an inadequate feeding strategy, resulting in poor growth performance, diarrhea, and other intestinal diseases. Hence, targeting gut microbiota might provide a new effective feeding strategy for enhancing performance and maintaining a healthy intestinal environment. Based on the current findings, milk replacer-based Lactobacillus feeding may improve growth performance and health in yaks' calves.