Effects of feeding a corn straw or mixed forage diet on immune function in dairy cows

Abstract Text: It has been demonstrated in previous researches that dietary nutrients affect immune function through their regulations on producing and activating immune factors. This study was conducted to evaluate the effects of feeding a corn straw or mixed forage diet on immunity of lactating cows by analysing compositions of serum immunoglobulins (Igs), cytokines, inflammation factors and plasma lymphocyte subsets. Twenty primiparous, lactating and ruminally fistulated Holstein cows were used in this study. Cows were randomly assigned to high forage diet (HF, forage : concentrate = 60 : 40) with Chinese wildrye, alfalfa hay and corn silage as the forage source or low forage diet (LF, forage : concentrate = 40 : 60) with corn straw as the forage source. This experiment lasted for 2 months, and blood samples were obtained via jugular vein before morning feeding at the last day of the trial period. Plasma lymphocyte subsets were determined by flow cytometry and other indexes were measured with ELISA kits. Data were analyzed using the PROC MIXED procedure of SAS 9.1. The results showed that levels of serum IgA (37.81 and 39.77 ng/mL), secretory IgA (sIgA) (1.55 and 1.59 ng/mL), interleukin-2 (IL-2) (132.55 and 137.96 ng/L), IL-4 (33.53 and 35.22 ng/L), IL-6 (8.27 and 8.53 ng/L), IL-10 (37.65 and 39.47 ng/L), IL-12 (31.57 and 33.66 ng/L), interferon-alpha (IFN-α) (16.71 and 16.94 ng/L), IFN-γ (865.44 and 851.58 ng/L), tumor necrosis factor-alpha (TNF-α) (199.49 and 206.46 ng/L), prostaglandin E₂ (PGE₂) (152.86 and 160.95 ng/L) and plasma CD4⁺ lymphocyte subset (27.88 and 30.54%), CD8⁺ lymphocyte subset (21.02 and 22.25%) and CD4⁺/ CD8⁺ ratio (1.57 and 1.57) were not affected by experimental treatments (P > 0.05), and cows in LF group tended to have higher serum IgE (498.55 and 469.64 ng/mL, P = 0.09), IgM (195.01 and 182.75 ng/mL, P = 0.09) and insulin-like growth factors-1 (IGF-1) (15.14 and 13.78 μg/L, P = 0.06) concentrations than those in HF group, while serum IgG (16.57 and 17.46 μg/mL, P = 0.09) level tended to be higher in HF group (P < 0.10). The results of this study indicated that different dietary systems had no effect on immunity in lactating cows.

Keywords: diet system, dairy cow, immunity