Several studies and a 2013 meta-analysis have proposed that increased feeding of milk or milk replacer to neonatal calves may improve subsequent milk production. However, data from individual studies are conflicting, and the meta-analysis was unable to assess the influence of calf starter intake. The objective of the current meta-analysis was to review newly published data and evaluate the effects of preweaning diet (including calf starter intake) and growth rate on first-lactation milk, fat, and protein yield. Data from 9 studies representing 21 treatment groups were included in the analysis. We created separate models for each outcome variable using regression methods in SAS (version 9.4, SAS Institute Inc., Cary, NC) to determine the effects of intake and growth rate. We then selected the best-fitting models using Akaike's information criterion. The effect of study explained 98, 85, and 96% of the variance in 305-d milk, fat, and protein yield in first lactation, respectively, indicating that other aspects of management are more important for determining first-lactation production than preweaning intake and growth rate. However, we found a synergistic relationship between preweaning liquid and starter dry matter intake for improving milk, fat, and protein production, and a positive relationship between first-lactation performance and preweaning average daily gain. These data indicate that provision of adequate nutrients from liquid and solid feeds and maintaining average daily gain above 0.5kg/d can enhance the first-lactation performance of heifers when combined with proper postweaning practices.

Historically, radial immunodiffusion (RID) has been the only method that directly measures IgG; however, recent studies have reported IgG concentrations in colostrum, milk, and plasma as measured using an ELISA. To our knowledge no comparison between RID and ELISA methods has been made for bovine colostrum or plasma. The objective of this study was to compare IgG concentrations measured by both methods in samples of bovine colostrum before and after heat treatment and bovine plasma. Concentration of IgG was quantified using a commercially available RID kit and a modified ELISA. Samples of bovine colostrum and plasma were collected from individual animals and colostrum was tested before and after heat treatment at 60°C for 30 min. All samples were tested using both methods. Pearson correlation coefficients were determined for RID and ELISA values from unheated colostrum, heat-treated colostrum, and plasma samples. Mixed models were used to determine the effect of assay on IgG measurement in colostrum and plasma and effect of heat treatment on IgG concentration in colostrum. A weak correlation was found between ELISA and RID results in plasma and unheated colostrum. Concentration of IgG was significantly lower in all sample types when measured by ELISA compared to RID. Thus, direct comparison of ELISA and RID results is not recommended. Colostrum IgG concentration significantly decreased after heat treatment as measured by ELISA, but means were not different when measured by RID. Correlation plots between colostrum values measured before and after heat treatment indicated changes in the colostrum protein matrix due to heat affected RID and ELISA assays differently. This investigation compared RID and ELISA results, but no conclusions could be drawn as to the accuracy of either assay.

Improved IgG absorption in calves fed heat-treated colostrum has been attributed to the reduced bacteria content in colostrum after heat treatment. However, at least one study reported that colostrum bacteria content did not affect IgG absorption. The main objective of the current study was a more conclusive test of the combined effects of colostrum bacteria content and heat treatment on IgG absorption. Comparison of conclusions from plasma IgG as measured by radial immunodiffusion and ELISA and comparison of health scores in the first week of life were secondary and tertiary objectives. Colostrum from individual cows was pooled, divided, either heat treated or unheated, and allowed to incubate for bacterial growth or not. The 4 treatments were unheated, low bacteria; unheated, high bacteria; heat-treated, low bacteria; and heat-treated, high bacteria. Plasma samples were collected from bull calves (n=25-27 per treatment) before and 48h after colostrum feeding for IgG and total protein analysis. Fecal, respiratory, and general health scores were assigned daily for the first 7 d. Plasma IgG, total protein, apparent efficiency of IgG absorption, and frequency of illness were analyzed using the MIXED and FREQ procedures in SAS (SAS Institute Inc., Cary, NC). Plasma IgG values from ELISA were lower than radial immunodiffusion; however, conclusions were similar. Greater colostrum bacteria content reduced total protein, plasma IgG, and efficiency of IgG absorption. Heat treatment tended to improve 48-h plasma IgG as measured by ELISA. Respiratory scores were not affected by colostrum treatment, but calves fed heat-treated, low-bacteria colostrum tended to experience fewer scour days. These results provide conclusive evidence for the benefits of minimizing bacterial contamination in colostrum for feeding calves.

Many common management practices used to raise dairy calves while on milk and during weaning can cause rumen acidosis. Ruminal pH has long been used to identify ruminal acidosis. However, few attempts were undertaken to understand the role of prolonged ruminal acidosis on rumen microbial community or host health in young calves long after weaning. Thus, the molecular changes associated with prolonged rumen acidosis in post weaning young calves are largely unknown. In this study, we induced ruminal acidosis by feeding a highly processed, starch-rich diet to calves starting from one week of age through 16 weeks. Rumen epithelial tissues were collected at necropsy at 17 weeks of age. Transcriptome analyses on the rumen epithelium and meta-transcriptome analysis of rumen epimural microbial communities were carried out. Calves with induced ruminal acidosis showed significantly less weight gain over the course of the experiment, in addition to substantially lower ruminal pH in comparison to the control group. For rumen epithelial transcriptome, a total of 672 genes (fold-change, FC ≥ 1.5; adjusted-p ≤ 0.05) showed significant differential expression in comparison to control. Biological pathways impacted by these differentially expressed genes included cell signaling and morphogenesis, indicating the impact of ruminal acidosis on rumen epithelium development. rRNA read-based microbial classification indicated significant increase in abundance of several genera in calves with induced acidosis. Our study provides insight into host rumen transcriptome changes associated with prolonged acidosis in post weaning calves. Shifts in microbial species abundance are promising for microbial species-based biomarker development and artificial manipulation. Such knowledge provides a foundation for future more precise diagnosis and preventative management of rumen acidosis in dairy calves.

Previous studies with heat-treated colostrum fed to neonatal calves have consistently used average-quality colostrum. Studies have not compared colostrum across a range of immunoglobulin levels. This study was conducted to investigate IgG absorption in neonatal dairy calves using colostrum of various qualities. Colostrum from the Pennsylvania State University dairy was collected over 2 yr and sorted into high, medium, and low quality based on colostrometer measurement. Colostrum within each category was pooled to create 3 unique, uniform batches. Half of each batch was frozen to be fed without heat treatment. The second half of each batch was heat treated at 60°C for 30min. This process was conducted in September 2011, and repeated in June 2012. Colostrum treatments were analyzed for standard plate count, coliforms, noncoliform gram-negative bacteria, and total IgG concentration. Plasma samples were collected from 145 calves 48h after birth and analyzed for IgG1, IgG2, total protein, and hematocrit. Colostrum quality (high, medium, or low), treatment (unheated or heat treated), and their interactions were analyzed as fixed effects, with year included as a random effect. Heat treatment significantly reduced all types of bacteria and IgG concentration. Plasma IgG concentration at 48h increased linearly with the concentration of IgG in the colostrum that was consumed. Heat treatment of colostrum increased plasma IgG concentration by 18.4% and apparent efficiency of absorption by 21.0%. Results of this study suggest that heat treatment of colostrum containing approximately 50 to 100mg IgG/mL increases absorption of IgG from colostrum.