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Effect of soy co-products in supplements for growing cattle on hemocytology following a lipopolysaccharide challenge

Midkiff, K., R. Scott, S. Dunkel, R. Cheek, B. Lansdell, B. Littlejohn, J. Powell, D. Galloway, J. Reynolds and E. Kegley

The objective of this study was to determine the effect of including soy co-products (soybean meal and soy oil) in the diet on the hemocytology of cattle after an endotoxin challenge. For the growing phase, crossbred Angus steers (n = 36; initial body weight 289 ± 31 kg) were stratified by body weight and sire and randomly assigned to pastures (n = 9; 0.45 ha mixed grass). Pastures were assigned randomly to 1 of 3 dietary treatments: 1) a control supplement containing no soy co-products (CON); 2) a supplement containing soybean meal (SBM); or 3) a supplement containing soy oil (SBO). All supplements were isonitrogenous and isoenergetic. Cattle were fed supplements (2.45 kg DM/day) for 56 days. At the conclusion of the growing phase, cattle were assigned randomly to 1 of 2 groups for a lipopolysaccharide (LPS) challenge (i.v. infusion of 0.5 µg LPS/kg of body weight). A minimum of 18 hours before sampling, cattle were fitted with jugular vein catheters and placed into stanchions. Blood was collected starting 2 hours before LPS infusion (-2 hr), immediately prior to LPS infusion (0 hr), and at 2, 4, 6, and 8 hr. Statistical analyses were performed using the MIXED procedure of SAS 9.4® as repeated measures with treatment, time, and treatment × time interaction as fixed effects, challenge group as random effect, and calf specified as the subject. Statistical significance was declared at P ≤ 0.05 and tendencies declared at 0.05 < P ≤ 0.1. There were treatment × time interactions for neutrophils (P = 0.003), percentage of neutrophils (P = 0.002), percentage of lymphocytes (P = 0.006), and neutrophil/lymphocyte ratio (NE:LY ratio; P = 0.001). Briefly, neutrophils, percentage of neutrophils, and NE:LY ratio were lower for cattle on CON diets compared to SBM at -2 hr and 0 hr (P < 0.01). Also, the percentage of neutrophils were greater at 8 hr for cattle on SBO diets than SBM diets (P = 0.018). The percentage of lymphocytes were greater for cattle on the CON diets compared to the SBM diets at 0 and -2 hr (P < 0.015). There was a treatment effect for percentage of monocytes (P = 0.035), as the CON diet had greater monocyte percentage compared to the SBM diet, and the SBO diet tended to have greater monocyte percentage compared to SBM diet. There was a time effect for all other hematology variables (P < 0.0001), as leukocytes were typically higher pre-administration of LPS, sharply decreased at 2 and 4 hrs post-administration of LPS and began to increase at 6 and 8 hrs.

Preliminary results indicated that the inclusion of soy co-products in growing cattle diets influenced hemocytology.