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

Abstract

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.

Keywords: bovine; dairy calves; leukocyte; probiotic; respiratory.

Figure 1

Weight (A) and weight gain (B) over time of dairy calves fed a milk replacer without probiotics (control) or with probiotics (probiotics).

Figure 2

Five-part differential counts of jugular blood samples in EDTA on d 7, 21, 42, and 49 for calves given a milk replacer only (control) or a milk replacer supplemented with probiotics (probiotics).

Figure 3

Total leukocyte counts and percentages of cells that were lymphocytes, neutrophils, monocytes, eosinophils, or basophils at 7, 21, 42, or 49 days of age for calves fed a milk replacer alone (control) or a milk replacer supplemented with probiotics (probiotic).

Figure 4

Lymphocyte phenotypes of calves given a milk replacer or a milk replacer with probiotics on d 7, 21, 42, and 49 of age. Mean fluorescence intensity (MFI; (A)) and percentage of cells expressing CD3, CD4, or CD8 (B).

Figure 5

Mean fluorescence intensity (MFI) and percentage of cells fluorescing for antigen-presenting cells using CD14 (monocytes) and CD205 (dendritic cells) on d 7, 21, 42, and 49. Calves were fed a milk replacer only or a milk replacer with a probiotic supplement. Points with differing letters tend towards significance (p = 0.08).

Figure 6

Mean fluorescence intensity (MFI) and percentage of cells fluorescing (%) for Cd11b (activation and adhesion marker), phagocytosis of opsonized E. coli bioparticles, and resulting oxidative burst on d 7, 21, 42, and 49. Calves were fed a milk replacer only (control) or a milk replacer supplemented with probiotics (probiotics). Points with differing letters are significantly different (p < 0.05).

Figure 7

Expression of TLR 4, TLR 9, and IL-10 in peripheral blood leukocytes as measured using qRT-PCR. The expression of TLR 4 and 9 was not statistically different; however, overall trends for TLR 9 varied over time, as did the expression of IL-10.

Figure 8

Expression of TLR 2, 4, 9 and IL-16, -10, and 17 in lung lavage cells as measured using quantitative (q)RT-PCR. Expression of the TLR 2, 4, and 9 on the surface of leukocytes obtained by lung lavage does not differ, nor does expression of the anti-inflammatory cytokines IL-6, IL-10, nor the pro-inflammatory cytokine IL-17 by these cells.