Abstract
This study aimed to evaluate the effects of weaning pace and probiotic supplementation on blood metabolites, and mRNA abundance of inflammation-related genes in Holstein dairy calves. A total of 38 one day old male calves (43.70 ± 4.77 kg BW ± SD), blocked by birth BW, were randomly assigned to a 2 × 2 factorial arrangement of treatments: (1) abrupt weaning without probiotics (AC), (2) abrupt weaning with probiotics (AP), (3) gradual weaning without probiotics (GC), and (4) gradual weaning with probiotics (GP). Abrupt weaning was performed over 3 d (54–57 d) with 3 step-downs of milk replacer (MR) at 1.13 L per feeding. Gradual weaning occurred over 14 d (49–63 d) with 7 step-downs of MR at 0.49 L per feeding. Probiotics (mixture of Liglactobacillus agilis, Lactobacillus delbrueckii, Limosilactobacilli mucosae and Limosilactobacilli reuteri at 1 × 109 cfu each/d) were supplemented with the MR for 7 d, starting 4 d before weaning. Calves had ad-libitum access to fresh water and were fed calf starter and chopped alfalfa one time daily. Blood was collected at 3 and 7 d of age, and a day before starting and a day after weaning. Calves were euthanized 1 d after weaning, and tissue samples were collected for mRNA abundance analysis. Weaning pace, probiotic, and pace × probiotic were included as fixed, and calf was included as random effects in the model. Blood metabolites were analyzed as repeated measures, and sampling day, pace × sampling day, and probiotic × sampling day were also included as additional fixed effects. An effect of weaning pace was observed for plasma TBARS, where calves weaned at an abrupt pace had 23% greater TBARS concentrations. In addition, there was a tendency for greater NEFA concentrations in abruptly weaned calves. However, no effects of weaning pace were detected for plasma glucose, BHB, Haptoglobin. In addition, probiotic supplementation did not affect blood metabolites in the present study. Probiotic supplementation increased mRNA abundance of IL-6 in the rumen and IL-1β in the colon and tended to increase mRNA abundance of IFN-γ and ICAM1 in the rumen, while reducing mRNA abundance of NF-κB in the jejunum. Hepatic mRNA abundance of IL-6 and NF-κB tended to be lower with abrupt weaning. A decreased mRNA abundance of IL-6 in the liver in abruptly weaned calves may indicate downregulation of systemic inflammatory response. Probiotic supplementation increased mRNA abundance of ruminal inflammation-related gene IFN-γ and ICAM 1 in abruptly weaned calves. These results support the hypothesis that probiotics may help prime local mucosal immunity. Furthermore, the greater TBARS concentrations observed in abruptly weaned calves suggest increased lipid peroxidation and oxidative stress compared with gradually weaned calves, which may reflect a greater physiological challenge associated with the abrupt transition during weaning. Overall, these results indicate that physiological responses during weaning were primarily influenced by weaning pace. Probiotic supplementation did not result in consistent effects on systemic metabolism or inflammatory responses under the conditions of this study.