The neonatal period for dairy calves is crucial for immune, metabolic, and physical development, which opens a window of disease susceptibility. Although the industry has relied on tools such as colostrum and vaccination to support early life immunity, there are several challenges when vaccinating neonatal calves: (1) the inability to mount an effective immune response, (2) interference with maternal antibodies, and (3) oxidative stress (OS). Oxidative stress is characterized as the imbalance of pro-oxidants to antioxidants that results in cellular oxidative damage or dysfunction. Oxidative stress has become a topic of interest in the neonatal period because it negatively affects lymphocyte function, which might affect vaccine response. Widely studied in mature cattle, antioxidant supplementation has the potential to improve reduction-oxidation balance and immune response. Evidence supporting the use of antioxidants such as vitamins and minerals in neonatal calves is far scarcer but necessary to optimize immunity and disease resistance. This review summarizes research on the effect of antioxidant supplementation on calf immunity, health, and productivity and highlights remaining gaps in knowledge. Overall, micronutrient supplementation, including vitamins and minerals, in preweaning and postweaning calves improved immune responses but there is conflicting evidence supporting the subsequent positive effect on calf health and growth performance.

Adding milk replacer powder (MRP) to whole milk during the entire preweaning period can increase growth but raises concern because of low starter feed intake and slumps in ADG at weaning and postweaning. In the current study, effects of adding MRP to pasteurized whole milk (PWM) during d 10 to 41 or d 10 to 59 of age were investigated in comparison with PWM. Calves (24 females and 21 males; 39.8 ± 1.85 kg BW) were randomly allocated to 1 of 3 treatments: (1) conventional protocol, 5 L/d PWM from d 3 to 56, and 2.5 L/d from d 57 to 59 of age (CONV; TS intake = 31.9 kg), (2) short duration of adding MRP to PWM protocol, 5 L/d PWM from d 3 to 9, 5 L/d PWM + MRP (18% TS) from d 10 to 41, 5 L/d PWM from d 42 to 56, and 2.5 L/d PWM from d 57 to 59 (SHD; TS intake = 42.3 kg), (3) long duration of adding MRP to PWM protocol, 5 L/d PWM from d 3-9, 5 L/d PWM + MRP from d 10-56, 2.5 L/d PWM + MRP from d 57-59 (LD; TS intake = 47.7 kg). The osmolality of PWM and PWM + MRP was 278 and 519 mOsm/L, respectively. Calves were weaned on d 60, and the study terminated on d 75. There was a treatment × time interaction for starter intake, where intake was greater for CONV than other treatments from d 14-41 and was greater in CONV than LD during d 42 to 48 and d 56 to 62 of age. Final BW was lower in CONV calves than LD calves. Weaning BW and overall hip height were lower in CONV calves than other treatments. The CONV calves had lower ADG at d 14 to 27 and d 35 to 41, and SHD calves had lower ADG at d 42 to 48 than other treatments. Calves fed CONV treatment had lower ruminal acetate and greater propionate than SHD calves during preweaning. Calves fed LD treatment had lower total VFA and tended to have greater ruminal pH than other treatments. Calves fed CONV had greater neutrophils and neutrophils/lymphocytes ratio and lower lymphocytes than other treatments. Glucose concentration was greater for LD versus other treatments at d 56, and lower for SHD versus other treatments at d 70 of study. Insulin concentration and homeostatic model assessment of insulin resistance index were greater in LD compared with other treatments during preweaning but were not different postweaning. Serum BHB was greater in CONV than other treatments. Albumin was greater for CONV versus other treatments at d 56, however, it was greater in LD-fed calves at d 70 of study. Results indicate that feeding a PWM + MRP to the calves during the entire preweaning period resulted in lower starter feed intake around weaning, but overall starter intake was similar with a greater final BW and fewer health-related issues throughout the study. Shifting a PWM + MRP to the conventional whole milk at d 40 of age decreased the ADG of calves.

The colonization and development of the gut microbiome in dairy calves play a crucial role in their overall health and future productivity. Despite the widely proposed benefits of inulin-related products on the host, there is insufficient information about how supplementing fructo-oligosaccharides (FOS) affects the colonization and development of the gut microbiome in calves. In a randomized intervention trial involving newborn male Holstein dairy calves, we investigated the effect of FOS on the calf hindgut microbiome, short-chain fatty acids (SCFA), growth performance, and the incidence of diarrhea. The daily administration of FOS exhibited a time-dependent increase in the ADG and the concentration of SCFA. Concurrently, FOS delayed the natural decline of Bifidobacterium, promoting the maturation and stabilization of the hindgut microbiome. These findings not only contribute to a theoretical understanding of the judicious application of prebiotics but also hold significant practical implications for the design of early life dietary interventions in the rearing of dairy calves.

In commercial dairy production systems, feeding calves once daily could be an alternative to reduce labor expenses. Several studies comparing once-a-day (OAD) versus twice-a-day (TAD) milk feeding systems have not evidenced differences in calf growth, rumen development, blood parameters or health scores, but effect on ruminal microbiota remains to be investigated. The objective of this study was to determine the effects of OAD or TAD on the establishment of the ruminal microbiota and its metabolic activity. Sixteen male calves (45.9 ± 5.7 kg at birth) were involved in the trial from birth to weaning (63 d). After the colostrum phase, 2 feeding programs based on a milk replacer were tested and calves were allocated to these programs on d 5. To study the establishment of the bacterial community, ruminal fluid was obtained from each calf 1 h after the morning meal at 7, 35, and 63 d of age. The ruminal metabolome was evaluated at a 7-d interval from d 1 to d 63. Ruminal microbiota and metabolite profiles were characterized by 16 S rRNA gene sequencing- and by 1H nuclear magnetic resonance spectroscopy, respectively. Our results showed that feeding milk replacer once or TAD did not change the ruminal microbiota and metabolites of dairy calves from birth to weaning. Microbial data showed that diversity and richness increased with age, suggesting a shift from a heterogeneous and less diverse community after birth (d 7) to a more diverse but homogeneous community at 35 and 63 d. These findings suggest that feeding milk OAD can be successfully applied to a calf feeding system without compromising microbial establishment and functions.

Diarrhea and respiratory diseases pose significant challenges in the rearing of pre-weaned calves, motivating the investigation of tools to improve gastrointestinal tract development, health, and overall performance in young calves. Consequently, the primary objective of this study was to assess the effectiveness of an additive incorporated into milk replacer to promote the development and health of the animals. Forty-six dairy calves were randomly assigned into two treatments: control (CON, n = 23; with 15 females and 8 males), and sodium butyrate (SB, n = 23; with 15 females and 8 males). The calves in the SB treatment group were supplemented with 4 g/d of unprotected sodium butyrate (Adimix, Adisseo, China), added to the milk replacer from 4 to 60 days of age. Water and starter were fed ad libitum. The study evaluated several parameters, including feed intake, nutrient digestibility, ruminal pH, ammonia and volatile fatty acids, blood metabolites (glucose, insulin-like growth factor type 1, urea, β-hydroxybutyrate), hemogram, health scores, performance, and feed efficiency. Bull calves were euthanized at 60 days of age for organ comparison, while heifer calves were assessed for carryover effects up to 90 days of age. Data were analyzed independently using linear mixed models using the nlme package in R, and the Artools package for non-parametric categorical outcomes. Although the feed intake and performance variables exhibited differences within weeks, no divergence was observed between treatment groups. Notably, a positive treatment-by-week interaction was identified for starter feed intake (p = 0.02) and total dry matter intake (p = 0.04) during pre-weaning for CON animals. Ruminal parameters, blood metabolites, and hemogram values such as glucose, urea, insulin-like growth factor type 1, mean corpuscular value, lymphocytes, and neutrophils displayed differences within weeks during the pre-weaning stage, but similar results within groups. No differences between supplemented and non-supplemented calves were found across nutrient digestibility, organ development, and histology. Regarding health scores, differences were noted within weeks for fecal and respiratory scores during the pre-weaning stage, and only the respiratory score during the post-weaning stage. Consequently, butyrate supplementation did not elicit improvements or negative effects in the body development or health status of dairy calves.

OBJECTIVE: Bovine respiratory disease (BRD) has serious impacts on dairy production and animal welfare. It is most commonly diagnosed based on clinical respiratory signs (CRS), but in recent years, thoracic ultrasonography (TUS) has emerged as a diagnostic tool with improved sensitivity and specificity. This study aimed to assess the alignment of BRD diagnoses based on a Clinical Respiratory Scoring Chart (CRSC) and weekly TUS findings throughout the progression of BRD of variable severity in preweaned Holstein dairy heifers.
METHODS: A total of 60 calves on two farms were followed from the 2nd week of life through the 11th week of life and assessed on a weekly basis for CRS and lung consolidation via TUS. The alignment of BRD diagnoses based on CRSC scores and TUS findings was evaluated across disease progression (pre-consolidation, onset, chronic, or recovered) and severity (lobular or lobar lung consolidation) using receiver operator curves and area under the curves combined with Cohen\'s kappa (κ), sensitivity, and specificity.
RESULTS: The diagnosis of BRD using CRSC scores ≥5 aligned best with the onset of lobar lung consolidation (>1 cm in width and full thickness). This equated to an acceptable level of discrimination (AUC = 0.76), fair agreement (κ = 0.37), and a sensitivity of 29% and specificity of 99%. Similarly, there was acceptable discrimination (AUC = 0.70) and fair agreement (κ = 0.33) between CRSC ≥5 and the onset of a less severe threshold of disease based on lobular (1-3 cm2 but not full thickness) or lobar consolidation. Discrimination remained acceptable (AUC = 0.71) with fair agreement (κ = 0.28) between CRSC scores ≥2 for nasal discharge and/or cough (spontaneous or induced) and the onset of lobar consolidation. However, sensitivity was <40% across comparisons and outside of the onset of disease there tended to be poor discrimination, slight agreement, and lowered sensitivity between CRS and TUS diagnoses of lobular or lobar consolidation (pre-consolidation, chronic, or recovered). Conversely, specificity was relatively high (≥92%) across comparisons suggesting that CRSC diagnoses indicative of BRD and associated lung consolidation tend to result in few false positive diagnoses and accurate identification of healthy animals.
CONCLUSIONS: Although we found the specificity of clinical signs for diagnosing lung consolidation to be ≥92% across all methods of TUS evaluations, the low levels of sensitivity dictate that clinical assessments lead to many false negative diagnoses. Consequently, depending on clinical signs alone to diagnose BRD within populations of dairy calves will likely result in overlooking a substantial proportion of subclinically affected animals that could inform the success of treatment and prevention protocols and guide management decisions.

The preweaning period for a dairy calf is characterized by high morbidity and mortality rates, leading to financial losses for producers. Identifying strategies to improve the health and welfare of calves while reducing antimicrobial use continues to be crucial to the success of the dairy industry. The objective of this study was to determine the effects of feeding colostrum replacer (CR) to dairy heifer calves beyond d 1 of life on growth, serum IgG, the incidence of diarrhea and bovine respiratory disease (BRD), and the risk of mortality in the preweaning period. At birth, Holstein heifer calves (n = 200; 50/treatment) weighing 40.7 ± 0.35 kg (mean ± SE) were fed 3.2 L of CR (205 g IgG/feeding) at 0 h and 12 h of life. Calves were then randomly assigned to 1 of 4 treatments: 450 g of milk replacer (MR) from d 2 to 14 (control, CON), 380 g of CR + 225 g of MR from d 2 to 3, then 450 g of MR from d 4 to 14 (transition, TRAN), 45 g of CR + 450 g of MR from d 2 to 14 (extended, EXT); or 380 g of CR + 225 g of MR from d 2 to 3, then 45 g of CR + 450 g of MR from d 4 to 14 (transition + extended, TRAN+EXT). Each treatment was reconstituted to 3 L and fed twice daily. All CR treatments were fed using bovine-derived CR containing 27% IgG. From d 15 to 41, all calves were fed 600 g of MR reconstituted to 4 L twice daily. Body weight was recorded at birth and every 7 d until study completion on d 49. Blood samples were taken daily until d 7 to evaluate serum IgG and then every 7 d until d 49. A health assessment was performed daily to evaluate calves for BRD and diarrhea. Data were analyzed using mixed linear regression, mixed logistic regression, and survival analysis models in SAS 9.4. Serum IgG concentrations were not affected by treatment for the study period. The EXT and TRAN+EXT groups had greater average daily gain (ADG) from d 7 to 14 (0.14 kg/d) and the TRAN group had greater ADG from d 14 to 21 (0.11 kg/d), compared with CON. There was no association of treatment with the odds or the duration of a diarrhea bout. However, provision of CR to the TRAN and EXT calves was associated with a reduced hazard of diarrhea compared with CON calves. Furthermore, TRAN and EXT calves have a lower hazard of mortality compared with CON calves, with TRAN and EXT calves had a 2.8- and 3.8-times lower hazard of mortality, respectively. Our findings suggest that the supplementation of CR to dairy calves positively affects ADG, and reduces the hazard of diarrhea and mortality during the preweaning period. Future research should look to further refine the supplementation strategy of CR to calves and explore the mechanism of action.

This study was conducted to investigate the impact of probiotic supplementation using Lactobacillus plantarum DSA 20174 and/or Bacillus toyonensis ATCC 55050 on growth performance, blood parameters, hematological measures, and fecal microbiota in pre-weaning Holstein calves. Thirty-two four-day-old male calves with a similar genetic background, weighing an average of 38.27 ± 0.12 kg, were randomly assigned to four groups. The groups consisted of a control group (CON) without supplementation, a group receiving B. toyonensis (BT) at 3 × 109 cfu/calf/day, a group receiving L. plantarum (LP) at 1 × 1010 cfu/calf/day, and a group receiving a combination of LP and BT (LP + BT) at half the dosage for each. The study found that calves supplemented with LP and LP + BT experienced significant improvements in average daily gain and final body weight compared to the control group. The LP + BT group showed the most positive effects on TDMI, starter intake, and CP intake. RBC counts tended to be higher in the probiotic groups, with the LP + BT group having the highest values. The LP + BT group also had higher total protein, albumin, globulin, and hematocrit concentrations. All probiotic groups showed higher serum IgG concentrations. Probiotic supplementation led to increased total bacterial count and decreased levels of E. coli, salmonella, and clostridium. The LP + BT group had a significant decrease in coliform count, while both LP and LP + BT groups had increased Lactobacillus populations. In conclusion, LP + BT probiotic supplement showed the most beneficial effects on growth, feed efficiency, blood constituents, and modulation of fecal microbiota composition.

In Uruguay, the mortality of dairy calves due to infectious diseases is high. Escherichia coli is a natural inhabitant of the intestinal microbiota, but can cause several infections. The aim of the work was to characterize E. coli isolates from intestinal and extraintestinal origin of dead newborn calves. Using PCR, virulence gene characteristics of pathogenic E. coli were searched. The pathogenic E. coli were molecularly characterized and the phylogroup, serogroup and the Stx subtype were determined. Antibiotic susceptibility was determined using the Kirby-Bauer disk diffusion method and plasmid-mediated quinolone resistance (PMQR) genes with PCR. Finally, clonal relationships were inferred using PFGE. Gene characteristics of the Shiga toxin-producing E. coli (STEC), Enteropathogenic E. coli (EPEC) and Necrotoxigenic E. coli (NTEC) were identified. The prevalence of the iucD, afa8E, f17, papC, stx1, eae and ehxA genes was high and no f5, f41, saa, sfaDE, cdtIV, lt, sta or stx2 were detected. The prevalence of STEC gene stx1 in the dead calves stood out and was higher compared with previous studies conducted in live calves, and STEC LEE+ (Enterohemorrhagic E. coli (EHEC)) isolates with stx1/eae/ehxA genotypes were more frequently identified in the intestinal than in the extraintestinal environment. E. coli isolates were assigned to phylogroups A, B1, D and E, and some belonged to the O111 serogroup. stx1a and stx1c subtypes were determined in STEC. A high prevalence of multi-resistance among STEC and qnrB genes was determined. The PFGE showed a high diversity of pathogenic strains with similar genetic profiles. It can be speculated that EHEC (stx1/eae/ehxA) could play an important role in mortality. The afa8E, f17G1 and papC genes could also have a role in calf mortality. Multidrug resistance defies disease treatment and increases the risk of death, while the potential transmissibility of genes to other species constitutes a threat to public health.

Calf behavior is closely related to its early growth, production performance, and health performance. Continuous behavior recording is the most accurate but also time-consuming method used for monitoring animal behaviors, so the instantaneous sampling method is often adopted to minimize the time required to quantify behavioral observations in animal studies. Moreover, the optimal sampling intervals required to yield accurate information for estimating Holstein dairy calves\' behaviors are still unknown. Our primary objective was to determine the most optimal sampling intervals for monitoring behaviors of Holstein dairy calves during preweaning and weaning periods to improve efficiency while maintaining reliability. The secondary objective was to describe their behavioral patterns. Rumination, lying, standing, and non-nutritive oral behavior (NNOB) data of 18 calves (observation time: 360 h/calf, 6,480 h in total) were continuously recorded for 15 d (3 d at 1, 3, 6, 9, and 12 wk of age). The continuous behavioral data were compared with instantaneous sampling at 5 s, 10 s, 15 s, 30 s,1 min, 3 min, 5 min, 10 min, 15 min, 30 min, and 60 min intervals. Sampling intervals were considered accurate if they met 4 criteria: coefficient of determination ≥0.90 (i.e., strongly related to true values), slope = 1, intercept = 0 (i.e., they did not over- or underestimate true values), and relative error <10%. The most optimal sampling interval was considered the highest sampling interval among the 11 sampling intervals that meet the criteria for accurate monitoring. As expected, the strength of the linear relationship between the continuous recording and instantaneous sampling decreased as the sampling intervals increased. The results varied across the different behaviors, with rumination, lying, standing, and NNOB being reliable at instantaneous recordings of 3 min, 10 min, 10 min, and 1 min for the preweaning period (1, 3, and 6 wk of age) and 10 min, 10 min, 15 min, and 3 min for the postweaning period (9 and 12 wk of age). In terms of behavioral patterns, lying time decreased, whereas rumination, standing, and NNOB time increased with age. After weaning, no significant changes in time spent performing these behaviors. Additionally, the rumination behavioral pattern becomes stable after wk 6 with decreasing after the morning feeding and occurring mainly in the morning. In conclusion, instantaneous sampling is a reliable method for monitoring the behaviors of dairy calves, but the optimal sampling intervals should be selected based on different ages and management conditions.