Neonatal Dairy Calves Research Articles

PSI-37 The effects of delaying initial colostrum feeding on gastrointestinal tract growth of neonatal bull dairy calves.

PSI-37 The effects of delaying initial colostrum feeding on gastrointestinal tract growth of neonatal bull dairy calves.

342 The effects of extended colostrum feeding on gastrointestinal tract growth of the neonatal dairy calf.

342 The effects of extended colostrum feeding on gastrointestinal tract growth of the neonatal dairy calf.

The use of ultrasound to measure muscle depth and area in postmortem Holstein dairy calves.

Monitoring growth of neonatal dairy calves is a useful management tool to assist producers in achieving goals for reproduction and performance. The goal of this study was to examine ultrasound as an in vivo tool to quantify longissimus dorsi muscle (ribeye) linear depth and extensor carpi radialis (ECR) and semitendinosus (ST) muscle cross-sectional areas in postmortem preweaned Holstein calves. Postmortem preweaned calves (n = 137, age 13.1 d ± 15.5 SD, body weight 36.5 kg ± 7.2 SD) were obtained from two California calf ranches between April and July 2013. Two operators collected ultrasound images of the ribeye, ECR, and ST muscles using an Aloka 500V equipped with a 5-cm 7.5-MHz linear transducer. Ultrasound ribeye linear depth and ECR and ST cross-sectional areas were calculated using the Ultrasound Image Capture System. Ultrasound measurements were compared to dissected (carcass) measures. Carcass ribeye linear depth was estimated using a ruler. Dissected ECR and ST muscle cross-sectional areas were estimated by tracing muscle cross sections onto transparency paper and then photocopying, cutting out, and weighing individual paper muscle tracings. Weights of the tracings were then converted to areas using the known area of a standard 8.5 × 11 inch paper. Data were analyzed by regressing carcass estimates on observed ultrasound measurements. The coefficient of determination (R2) indicated that ultrasound measurements were most closely associated with carcass measurements for the ST muscle (R2 = 0.60, 0.62 for operator 1 and 2, respectively) when compared to the ribeye and ECR muscles (R2 = 0.27, 0.41 for ribeye and 0.43, 0.32 for ECR for operator 1 and 2, respectively). The mean bias showed consistent underestimation by the ultrasound measurements when predicting carcass measurements for all three muscles and for both operators (ribeye bias = 0.15, 0.40; ECR bias = 0.95, 1.15; and ST bias = 0.73, 0.27 for operator 1 and 2, respectively). Operator contributed significantly in explaining a proportion of the variation in the regression equation for the ST muscle only, whereas calf body weight contributed significantly in explaining a proportion of the variation in the regression equation for all three muscles. The results of this study demonstrated that ultrasound measurements of the ST were the most accurate for quantifying the cross-sectional area when compared to both the ECR and ribeye in postmortem Holstein calves.

Blood immune transcriptome analysis of artificially fed dairy calves and naturally suckled beef calves from birth to 7 days of age

Neonatal calves possess a very immature and naïve immune system and are reliant on the intake of maternal colostrum for passive transfer of immunoglobulins. Variation in colostrum management of beef and dairy calves is thought to affect early immune development. Therefore, the objective of this study was to examine changes in gene expression and investigate molecular pathways involved in the immune-competence development of neonatal Holstein dairy calves and naturally suckled beef calves using next generation RNA-sequencing during the first week of life. Jugular whole blood samples were collected from Holstein (H) dairy calves (n = 8) artificially fed 5% B.W. colostrum, and from beef calves which were the progenies of Charolais-Limousin (CL; n = 7) and Limousin-Friesian beef suckler cows (LF; n = 7), for subsequent RNA isolation. In dairy calves, there was a surge in pro-inflammatory cytokine gene expression possibly due to the stress of separation from the dam. LF calves exhibited early signs of humoral immune development with observed increases in the expression genes coding for Ig receptors, which was not evident in the other breeds by 7 days of age. Immune and health related DEGs identified as upregulated in beef calves are prospective contender genes for the classification of biomarkers for immune-competence development, and will contribute towards a greater understanding of the development of an immune response in neonatal calves.

Genome wide transcriptome analysis provides bases on colonic mucosal immune system development affected by colostrum feeding strategies in neonatal calves

BackgroundDelivery of colostrum within the first several hours after birth is vital for establishing successful passive immunity in neonatal dairy calves. However, it is unclear whether a difference in colostrum feeding strategy can affect the development of the calf gastrointestinal tract. The aim of this study was to evaluate the effect of colostrum feeding time within the first 12 h after birth on the colonic mucosal immune system in neonatal calves using a genome wide transcriptome analysis.ResultsRNA sequencing-based transcriptome analysis of colon tissues collected from 27 male Holstein calves which were randomly assigned to one of three colostrum feeding strategies – (immediately after birth (TRT0); 6 h after birth (TRT6); 12 h after birth (TRT12)) – and euthanized at 51 h of age detected 15,935 ± 210, 15,332 ± 415, and 15,539 ± 440 expressed genes in the colon under three treatments, respectively. The core transcriptome of the colon included 12,678 genes, with enriched “cellular process” and “metabolic process” as the top two biological functions with 802 of them being immune function related genes. Principal component analysis of the colon transcriptomes did not display a clear separation by colostrum feeding strategy and differential abundance analyses showed no significant difference in the expression of immune related genes among the treatments. Additionally, a weighted gene co-expression network analysis identified 4 significant (|correlation| > 0.50 and p ≤ 0.05) gene modules consisting of 122 immune related genes, which were positively or negatively correlated with the abundance of Lactobacillus and Faecalibacterium prausnitzii in the colon.ConclusionTranscriptome analysis indicates that the development of the colonic mucosal immune system in neonatal calves may be independent of the timing of initial colostrum meal within 12 h after birth. Our results also provide a molecular understanding of colonic biological function in neonatal calves and extends knowledge on how host gene expression profiles are associated with the abundance of specific bacterial groups in the colon.

Technical note: Serum total protein and immunoglobulin G concentrations in neonatal dairy calves over the first 10 days of age

Efficacy of passive transfer of immunity in young calves is commonly assessed using total serum protein (STP) or serum immunoglobulin G (IgG) concentration tested within the first few days of life. To our knowledge, no research has measured changes in these concentrations over this period to establish an appropriate age range for testing. The aim of this study was to monitor changes in STP and serum IgG concentrations from birth until 10 d of age to provide a basis for recommendations for when passive transfer of immunity in dairy calves can be measured. Concentrations of STP and IgG of 12 calves were measured at 11 time points: at approximately 30 min before colostrum feeding, at 24 h after colostrum feeding, and daily from d 2 to 10 of age. Mean (± standard deviation) STP and IgG concentrations were 4.61 ± 0.3 g/dL and 0.6 ± 0.6 mg/mL at birth, 5.83 ± 0.73 g/dL and 22.2 ± 9.6 mg/mL at 24 h after colostrum feeding, and 5.78 ± 0.52 g/dL and 16.1 ± 7.3 mg/mL at d 10 of age, respectively. The IgG concentration declined over subsequent days relative to IgG measured at 24 h at a rate of approximately 0.69 mg/mL per day, declining by 27.6 ± 6.2% (mean ± SD) on d 10. The concentration of STP did not decrease over time. Concentrations of IgG at 24 h after colostrum feeding were highly correlated with each of the measures of IgG over the 10-d period (r ≥0.97). These correlations were supported by the Bland-Altman plots of agreement between the 24-h sample and subsequent samples. Compared with the reference value at 24 h, STP concentrations were highly correlated on d 2 and 3 (r ≥0.98), highly correlated but variable from d 4 to 9 (r ≥0.88), and lower at d 10 (r = 0.76). These results indicate that calves may be reliably tested for passive transfer of immunity using IgG or STP concentrations up to 9 d of age.

Effect of delaying colostrum feeding on passive transfer and intestinal bacterial colonization in neonatal male Holstein calves

The objective of this study was to investigate the effect of time of first colostrum feeding on the passive transfer of IgG and on bacterial colonization in the intestine of neonatal dairy calves. Twenty-seven male Holstein calves were randomly assigned to 1 of 3 treatments at birth: calves were fed colostrum at 45 min (0 h, n = 9), 6 h (n = 9), or 12 h after birth (n = 9). Calves were fed pooled, heat-treated colostrum (62 g of IgG/L) at their respective feeding times at 7.5% of birth body weight and fed milk replacer at 2.5% of birth body weight per meal every 6 h thereafter. Blood samples were taken every 3 h using a jugular catheter and were analyzed for determination of serum IgG by radial immunodiffusion. At 51 h after birth, calves were euthanized for collection of tissue and digesta of the distal jejunum, ileum, and colon. Quantitative real-time PCR was used to estimate the prevalence of Bifidobacterium spp., Lactobacillus spp., Fecalibacterium prausnitzii, Clostridium cluster XIVa, and total Escherichia coli. Delaying colostrum feeding by 6 h (35.6 ± 1.88%) and 12 h (35.1 ± 3.15%) decreased the maximum apparent efficiency of absorption of IgG compared with feeding colostrum immediately after birth (51.8 ± 4.18%) and delayed the time to maximum serum IgG concentration (24 h vs. 15 h, respectively). Moreover, 12-h calves tended to have a lower prevalence of Bifidobacterium spp. (0.12 ± 0.017%) and Lactobacillus spp. (0.07 ± 0.019%) associated with the colon mucosa compared with 0-h calves (1.24 ± 0.648% and 0.26 ± 0.075%, respectively). In addition, 6-h (0.26 ± 0.124%) and 12-h (0.49 ± 0.233%) calves had a lower prevalence of total E. coli associated with ileum mucosa compared with 0-h calves (1.20 ± 0.458%). These findings suggest that delaying colostrum feeding within 12 h of life decreases the passive transfer of IgG and may delay the colonization of bacteria in the intestine, possibly leaving the calf vulnerable to infections during the preweaning period.

Transcriptional changes detected in fecal RNA of neonatal dairy calves undergoing a mild diarrhea are associated with inflammatory biomarkers.

After birth, a newborn calf has to adapt to an extrauterine life characterized by several physiological changes. In particular, maturation of the gastrointestinal tract in a new environment loaded with potential pathogens, which can predispose neonatal calves to develop diarrhea, and is a major cause of morbidity and mortality during the first 4 wks of life. We aimed to investigate the inflammatory adaptations at a transcriptomic level in the gastrointestinal (GI) tract to a mild diarrhea in neonatal dairy calves using RNA isolated from fresh fecal samples. Eight newborn Jersey male calves were used from birth to 5 wks of age and housed in individual pens. After birth, calves received 1.9 L of colostrum from their respective dams. Calves had ad-libitum access to water and starter grain (22% CP) and were fed twice daily a total of 5.6 L pasteurized whole milk. Starter intake, body weight (BW), fecal score, withers height (WH), and rectal temperature (RT) were recorded throughout the experiment. Blood samples were collected weekly for metabolic and inflammatory profiling from wk 0 to wk 5. Fresh fecal samples were collected weekly and immediately flash frozen until RNA was extracted using a Trizol-based method, and subsequently, an RT-qPCR analysis was performed. Orthogonal contrasts were used to evaluate linear or quadratic effects over time. Starter intake, BW, and WH increased over time. Fecal score was greatest (2.6 ± 0.3) during wk 2. The concentrations of IL-6, ceruloplasmin, and haptoglobin had a positive quadratic effect with maximal concentrations during wk 2, which corresponded to the maximal fecal score observed during the same time. The concentration of serum amyloid A decreased over time. The mRNA expression of the proinflammatory related genes TLR4, TNFA, IL8, and IL1B had a positive quadratic effect of time. A time effect was observed for the cell membrane sodium-dependent glucose transporter SLC5A1, for the major carbohydrate facilitated transporter SLC2A2, and water transport function AQP3, where SLC5A1 and AQP3 had a negative quadratic effect over time. Our data support the use of the fecal RNA as a noninvasive tool to investigate intestinal transcriptomic profiling of dairy calves experiencing diarrhea, which would be advantageous for future research including nutritional effects and health conditions.

NMR-Based Plasma Metabolomics at Set Intervals in Newborn Dairy Calves with Severe Sepsis.

The aim of this first study was to reveal the new potential biomarkers by a metabolomics approach in severe septic calves. Sepsis is a common cause of morbidity and mortality in newborn dairy calves. The main challenges with the use of biomarkers of sepsis in domestic animals are their availability, cost, and time required to obtain a result. Metabolomics may offer the potential to identify biomarkers that define calf sepsis in terms of combined clinical, physiological, and pathobiological abnormalities. To our knowledge, this is the first study presenting an NMR- (nuclear magnetic resonance-) based plasma metabolomics at set intervals in neonatal septic calves. Twenty neonatal dairy calves with severe sepsis and ten healthy calves were used. Hematological and biochemical health profiles were gathered in plasma samples at set intervals. Similarly, NMR spectra were acquired. All diseased animals (except one) died after 72 hours. Clinical and laboratory results were in accordance with those of severe septic animals. Multivariate analysis on NMR plasma spectra proved to be an excellent tool for faster identification of calves with severe sepsis from healthy animals. The NMR-based metabolomic profile may contribute to the better understanding of severe sepsis in newborn calves.

Cryptosporidium outbreak in calves on a large dairy farm: Effect of treatment and the association with the inflammatory response and short-term weight gain

Cryptosporidium spp. infections in neonatal dairy calves can cause diarrhoea and, in rare cases, death. The infection is usually self-limiting, but halofuginone lactate (HL) can be used prophylactically. Calves (n=144) in the study were born during a 2-month period on one farm. A total of 901 serum and 767 faecal samples were collected. Based on HL treatment, the calves were divided into 3 groups: I) not treated, II) treated incorrectly (treatment started >48h after birth, or lasted <7days), and III) treated correctly (started <48h after birth, and lasted ≥7days). Over the 3-month observation period, 14.6% (n=21) of the calves died, of which most (67%) had not been treated with HL. Correctly performed treatment of cryptosporidiosis significantly delayed the onset of oocysts shedding (P<0.001) and reduced haptoglobin (HP) and serum amyloid A (SAA) concentrations in the second week of life. HP concentration and HL treatment were negatively associated with weight gain at 3months of age. Cryptosporidium positive faecal samples were significantly (P<0.001) more likely to be diarrhoeic but Giardia or Eimeria positive samples were not. Correct prophylactic treatment with HL delayed the shedding of Cryptosporidium oocysts and improved survival, but was negatively associated with weight gain. Incorrect treatment had a low impact on mortality and resembled no treatment regarding the proportion of calves shedding oocysts. Acute phase response (APR) in the second week of life seemed to be positively associated with shedding high amounts of Cryptosporidium oocysts.

Short communication: Effect of age at group housing on behavior, cortisol, health, and leukocyte differential counts of neonatal bull dairy calves

To determine the effect of age at grouping on behavior, health, and production of dairy bull calves, 90 Holstein-Friesian bull calves were housed in individual pens until moved to 1 of 3 treatments. Calves were housed in groups of 3 calves at 3 d old (GH3), 7 d old (GH7), or 14 d old (GH14) until 7 wk of age. Ten groups of 3 calves for each treatment were used, with 5 pens/treatment in each of 2 replications (10 pens/treatment, 3 treatments, 3 calves/treatment; 90 calves total). Direct behavioral observations using instantaneous scan sampling every 10 min were conducted twice per week for 7 wk. At the same times, video data were recorded for continuous observations at feeding time to observe the overall activity of group-housed calves. Hip height, heart girth, and health scores were recorded weekly and body weight was recorded at the start and end of the study. Calves in GH3 spent more time playing and but more time cross-sucking and displacing other calves from milk bottles. Calves engaged in social interaction as early as 3 d of age, and social interactions between 3 to 6 wk of age increased markedly. Calves housed in GH14 vocalized more than did calves in GH7 and GH3. No difference was found between treatments in growth performance. Calf fecal, cough, and nasal and ocular discharge scores, differential leukocyte counts, and plasma cortisol concentrations were not affected by age at grouping. However, during the first week of grouping, when calves were moved from individual pens to group pens, some calves were unable to find their milk bottles and required guidance. In conclusion, these data show no adverse effects on health or performance and some benefits on social behavior for early (d 3) grouping of calves.

Relationships between oxidative stress, haematology and iron profile in anaemic and non-anaemic calves

The aim of this study was to investigate the relationships between oxidative stress, haematology and iron profile in neonatal dairy calves. Serum and haemolysate malondialdehyde (MDA), serum total antioxidant capacity,...

Application of phototherapy for the healing of the navels of neonatal dairy calves.

The present work evaluated the effects of LED light irradiation on the healing of the navels of neonatal dairy calves. Fifty-seven neonatal calves were divided into two groups. Animals had their umbilical stumps immersed in 10% iodine tincture for 60s, and this process was repeated every 24h for three consecutive days. The 29 animals in the first group did not receive LED therapy. The 28 animals in the second group received LED light irradiation at 640nm with 300mW power, 46.8J/cm2 energy density, 60s irradiation time, and 0.385cm2 spot size. The animals were irradiated at four points (46.8J/cm2 per point) evenly distributed around the insertion site of the umbilical stump every 24h for three consecutive days. Irradiation with LED light was applied before the umbilical stumps were immersed in the iodine solution. The time after birth at which the umbilical stump fell off of each calf was noted. The umbilical stumps of all animals fell off by the 25th day of age. After the umbilical stump fell off, the healing of the remnant wound was followed up to the 30th day after birth. The area of the wound was measured on the 15th, 20th, and 25th day after birth using digital photographs and computer-assisted area measurements. A two-tailed unpaired t test was applied to analyze the falling off the umbilical stump, whereas a Kruskal-Wallis one-way ANOVA test with a Dunn's multiple comparison test was used for the wound size evolution. GraphPad Prisma 5.0® and GraphPad StatMate 2.00® were used for the statistical analysis. The results revealed that phototherapy hastened the falling off the umbilical stump, accelerated navel healing, and reduced the mortality rate in newborn calves. Therefore, this study introduced a preventive and adjuvant after birth treatment that proved to be effective in reducing the incidences of omphalitis and newborn mortality.

314 Physiological adaptations in the gastrointestinal tract detected by a fecal RNA method and blood inflammatory biomarkers in neonatal dairy calves undergoing a mild diarrhea

314 Physiological adaptations in the gastrointestinal tract detected by a fecal RNA method and blood inflammatory biomarkers in neonatal dairy calves undergoing a mild diarrhea

A Randomized Clinical Trial Evaluating the Effects of Oligosaccharides on Transfer of Passive Immunity in Neonatal Dairy Calves.

BackgroundBacterial contamination of colostrum is common and can decrease IgG absorption in neonatal calves. Strategies that mitigate this situation without complicating colostrum management will benefit dairy calf health and survival.ObjectivesTo evaluate the effects of supplementing colostrum with oligosaccharides (OS) on serum IgG concentration and apparent efficiency of absorption of IgG (AEA%) in calves fed unpasteurized colostrum and characterize these outcomes with respect to colostrum bacterial exposures.AnimalsOne hundred twenty‐three neonatal dairy calves.MethodsRandomized, blinded, controlled clinical trial conducted at a commercial dairy operation. Calves were enrolled at birth in 1 of 4 treatment groups. Data were complete for 123 calves, which were distributed across the treatment groups as follows: mannan‐oligosaccharides (MOS), n = 33; Saccharomyces galacto‐oligosaccharides (SGOS), n = 31; Bifidobacterium galacto‐oligosaccharides (BGOS), n = 28; and lactose control (CON), n = 31. A commercial radial immunodiffusion kit was used to determine colostrum and serum IgG concentrations. Conventional microbiology methods were used to enumerate colostrum bacterial counts.ResultsBacterial counts were not significantly different among treatment groups. Total bacterial plate counts (TPC) were relatively low for the majority of colostrum samples, but TPC had a significant negative effect on serum IgG concentration and AEA% in the lactose‐supplemented control group but not the OS treatment groups.Conclusions and Clinical ImportanceThese results suggest that a complement of OS structures may mitigate adverse effects of bacteria on transfer of passive immunity (TPI).

Prevalence of Escherichia coli adhesion-related genes in neonatal calf diarrhea in Uruguay.

Neonatal calf diarrhea (NCD), one of the most important diseases of neonatal dairy and beef calves in Uruguay, has become relevant in association with intensive systems. This disease generates substantial economic losses every year worldwide as a result of increased morbidity and mortality. Escherichia coli, one of the pathogens associated with NCD, can express several fimbrial and afimbrial adhesins. The objective of this study was to assess the presence of clpG, f5, f17A, f17G(II), and f17G(I) genes that encode three important adhesins expressed in diarrheagenic E. coli: F5, F17 and CS31A, isolated from feces of calves in Uruguay. Feces of 86 (70 diarrheic and 16 healthy) calves, from 15 animal facilities in Uruguay, were collected between 2012 and 2013. Biochemical and molecular identification were performed to finally obtain 298 E. coli isolates. Partial amplification of adhesion-related genes was performed by polymerase chain reaction. The most prevalent gene was f17A (31.2%), followed by f17G(II), clpG, f17G(I) and f5 (25.8%, 17.5%, 3.7% and 0.7%, respectively). All genes were present in diarrheic and healthy animals except f5 and f17G(I); these genes were present only in affected calves, although in low numbers. This is the first report of the presence of F5, F17, and CS31A genes in E. coli strains from NCD cases in Uruguay. Prevalence values of the genes, except f5, were in accordance with regional findings. It is expected that further characterization of locally transmitted strains will contribute to control a problem of regional and international magnitude.

Effect of nucleotides in milk replacers on growth and health of male dairy calves

Forty-eight male Holstein calves (16 per treatment) were fed milk replacer (MR; 27% CP, 17% fat powder) with 0, 10, and 20% nucleotides (NU). The MR were fed at 0.66 kg of DM daily divided into 2 equal meals fed at 0630 and 1600 h for d 1 to 25, then 0.33 kg of DM in only the a.m. feeding for d 26 to 28. Free-choice starter (20% CP) and water were fed from d 1 to 56. Calves were initially 2 to 3 d of age and 46 ± 0.9 kg. Data were analyzed as a completely randomized design with repeated measurements over time. When NU treatment was P < 0.1, means were analyzed with linear and quadratic polynomial contrasts. Calf ADG and feed efficiency declined linearly (P < 0.05) from 0 to 4 and 0 to 8 wk as NU increased in the MR. Calf ADG and starter intake tended to decline linearly (P < 0.08) from 4 to 8 wk as NU increased in the MR. Abnormal fecal score days decreased linearly (P < 0.05) from 0 to 4 wk as NU increased in the MR; however, medical days among treatments did not differ. Change in hip width and BCS declined linearly (P < 0.05) from 0 to 4 and 0 to 8 wk as NU increased in the MR. Nucleotides at 10 and 20% reduced calf growth and did not improve calf health as measured. Concentrations of ≥10% NU cannot be recommended for MR intended for neonatal dairy calves.

Influence of nonmedicated additives as alternatives to antibiotics on calf growth and health

The objective was to determine whether a milk replacer with a blend of nonmedicated additives would have similar benefits to a milk replacer with added neomycin and oxytetracycline on calf health and growth. Thirty-six bull calves were purchased and fed 1 of 3 treatments through weaning. All treatments used a 20% CP, 20% fat milk replacer with either no additives (CON), a blend of nonmedicated additives (ADD; animal plasma, yeast cell wall extracts, inulin, ascorbic acid, and direct-fed microbials), or neomycin and oxytetracycline (MED; 362.87 g/t of neomycin; 181.44 g/t of oxytetracycline). Six calves from each treatment were slaughtered, and intestinal tissues were collected. Blood samples were obtained weekly and analyzed for glucose, BUN, creatinine, minerals, bicarbonate, albumin, proteins, and anion gap. Proc Mixed in SAS was used with repeated week statement to analyze blood results and repeated calf statement to analyze intestinal results. Hematocrit values and fecal scores were greater for control calves (P 0.15). These results indicate that both nonmedicated and medicated additives may beneficially affect gastrointestinal morphology, reduce scouring, and improve growth characteristics of neonatal dairy calves compared with unsupplemented calves.

Assessment of two measuring devices for estimation of body weight in newborn beef and dairy calves

Calf birth weight is an important factor that can impact cow and calf health as well as performance on beef, dairy, and veal operations. Methods of estimating weight on-farm without the use of a scale have been developed, the most common of which are measuring tapes that determine the circumference around either the fetlock or girth of a calf. Despite the potential utility of these devices, there is a paucity of peer-reviewed research that evaluates their accuracy. Furthermore, many of the previous studies have not used appropriate statistical methodology to assess the agreement between 2 continuous measures. The objective of this study was to evaluate the agreement of commonly-used measuring devices with actual body weight of neonatal beef and dairy calves.

Presence of Selected Methanogens, Fibrolytic Bacteria, and Proteobacteria in the Gastrointestinal Tract of Neonatal Dairy Calves from Birth to 72 Hours.

The microbial communities in the gastrointestinal tract of a young calf are essential for the anatomical and physiological development that permits a transition from milk to solid feed. Selected methanogens, fibrolytic bacteria, and proteobacteria were quantified in the rumen fluid and tissue, abomasum fluid, cecum fluid and tissue, and feces of Holstein bull calves on day 0 (0–20 mins after birth), day 1 (24 ± 1 h after birth), day 2 (48 ± 1 h after birth), and day 3 (72 ± 1 h after birth). Methanogens, fibrolytic bacteria, and Geobacter spp. were found to be already present from birth, indicating that microbial colonization of the gastrointestinal tract occurred before or during delivery. The abundance of methanogens and Geobacter spp. differed between the days tested and between compartments of the digestive tract and feces, but such difference was not observed for fibrolytic bacteria. Our findings suggests that methanogens might have an alternative hydrogen provider such as Geobacter spp. during these early stages of postnatal development. In addition, fibrolytic bacteria were present in the rumen well before the availability of fibrous substrates, suggesting that they might use nutrients other than cellulose and hemicellose.