Impact of stressors on immune system parameters in yearling horses and fermentation characteristics and aerobic stability of inoculated corn silages

Abstract

A study was conducted in a Latin rectangle to determine the impact of stressors on immune function in yearling horses. After 51 d of supplementation with either block 1, a molasses block containing 14.30% fat or block 2, a molasses block containing 7.58% fat, horses were subjected to three forms of stress. Blood samples were collected 6 h pre-stress and at h 1, 6, 12, 24, 48, 72, 96, and 168 post stress. Nasopharyngeal flush (NPF) was conducted 6 h pre-stressor and h 12 and 72 post-stressor. Blood was analyzed for fatty acids, various hematological parameters, cytokines, PGE₂, and cortisol. Nasopharyngeal flush samples were analyzed for IgA. Composition of molasses blocks were found to be inconsistent with documented formulation and n-6:n-3 ratios were found to be similar between blocks. Therefore, main effect of hour was evaluated. White blood cells were elevated (P < 0.01) above baseline at subsequent sampling times and platelet count was elevated (P = 0.01) at h 1, 6, 24, 48, and 96 h post-stressor compared to baseline. Lymphocyte concentrations were reduced (P < 0.01) at h 1 compared to baseline but were elevated above baseline by h 6 (P < 0.01). Neutrophil concentrations were elevated (P < 0.01) at h 1 and 6 compared to baseline. Nasal mucosal IgA concentrations had a tendency (P < 0.07) to be greater at h 12 relative to baseline. Serum cortisol dropped to concentrations below baseline (P < 0.01) at h 1 and 6 but increased above baseline by h 12 (P < 0.01). It appears that stressors applied were sufficient to induce mild changes in several of the hematological parameters evaluated but an overall more profound effect may have been displayed if stressors were more profound or prolonged. A second experiment was conducted to evaluate fermentation characteristics and aerobic stability of whole-plant corn silage after inoculation with three different bacterial inoculants. Treatments consisted of Lactobacillus plantarum and Lactobacillus buchneri (LPB), L. plantarum, L. buchneri, and Lactobacillus diolivorans (LPBD), and L. diolivorans (LD). Silages were sampled on d 0, 14, 39, and 90. Propionate was elevated in silages inoculated with LPBD on d 39 and d 90 compared to other treatments (P < 0.03). 1, 2-propanediol was elevated (P < 0.01) in silages inoculated with LPB and LPBD on d 39 and d 90 compared to CON and LD silages. An effect of sampling day (P < 0.05) was detected for DM, aNDF, ADF, ash, starch, pH, total VFA, acetate, propionate, lactate, ethanol, and 1,2-propanediol. When silages sampled on d 14, 39, and 90 were subjected to an aerobic stability test, only treatment differences were detected (P < 0.05) for lactate: acetate and 1-propanol. Sampling day differences were detected (P < 0.05) for pH, total VFA, acetate, propionate, butyrate, lactate:acetate, 1-propanol, and 1, 2-propanediol. Overall, results suggest that epiphytic microflora populations largely dominated the ensiling process as indicated by the relative similarities in silages throughout the trial.